Physical Properties of Some ET-Based Organic Metals
and Superconductors with Mercury Containing Anions
R. Lyubovskii, R. Lyubovskaya, O. Dyachenko
To cite this version:
R. Lyubovskii, R. Lyubovskaya, O. Dyachenko. Physical Properties of Some ET-Based Organic
Metals and Superconductors with Mercury Containing Anions. Journal de Physique I, EDP
Sciences, 1996, 6 (12), pp.1609-1630. <10.1051/jp1:1996178>. <jpa-00247269>
HAL Id: jpa-00247269
https://hal.archives-ouvertes.fr/jpa-00247269
Submitted on 1 Jan 1996
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publics ou privés.
J.
Phys.
I
France
(1996)
6
DECEMBERI996,
1609-1630
Pl~ysical Properties of Some
ET.Based
Organic Metals
Superconductors witl~ Mercury Containing Anions
Lyubovskii (*),
R.B.
Institute
(Received
Physics RAS,
Chemical
of
April 1996,
6
Lyubovskaya
R.~.
accepted
ii
PACS.72.15.Gd
Galvanomagnetic
PACS.74.70.Kn
Organic
Because
Abstract.
ordination,
dation
of ET
orrions
of
described
(X
and
for
three
8uperconductivity
reported for the
MD
and
Russia
142432
1996)
June
other
effects
magnetotransport
superconductors
capability of forming the
atoms
electrolytes with Hg containing
mercury
of the
(bis(ethylenedithio)tetrathiafulvalene)
different
F, Br, I for
=
of
application
the
Chernogolovka,
1609
Dyachenko
O.A.
and
PAGE
results
in
the
compounds
anions
formation
with
various
co-
electrochemical
in
of ET
salts
oxi-
with
the
composition.
The properties of organic
metals and
superconductors are briefly
familles:
Cl, Br, 1) 2) (ET)2(Hg(SCN)3-nXn]
1) ET4Hg3-àX8 ((à < 0.3, X
Cl for n
Cl, Br). The
1, 2), 3) (ET)8(Hg4X12(C6HSY)] (X, Y
1; X
=
n
=
of
first
=
=
=
(ET)2(Hg(SCN)C12]
time.
The
under
coexistence
of
pressure
about
9
kbar
incommensurate
two
with
Tonset
sublattices
"
the
in
2
K
8alts
is
of
(ET)4Hg3-sX8 family
probably grues use to their
unusual
physical properties such as an abnormally high anisotropy of conductivity together with its growth with
drop, a
temperature
of the
critical
field,
positive
magnetic
Hc2,
and
exceeding
of
Clogston
curvature
upper
an
paramagnetic limit, the invalidity of Korringa law for the
dependence of spin-lattice
temperature
relaxation
Tc with
transition
rate, the growth of the
temperature of a superconducting
pressure,
dTc /dp > 0, and a serres of other peculiarities.
Shubnikov-de
oscillations
observed
for
Haas
were
(ET
salts
of
(Hg4X12(C6HSY)2]
family.
The
possible
of
Fermi
surface
discussed
types
)8
some
are
for
these
softs.
Introduction
Shchegolev I.F. predetermmated in
linear conducting chains" iii (1972)
his
generahzing
further
work
intensive
"Electrical
development
and
of the
magnetic
science
properties of
field
connected
discovery of the first orgamc
orgamc
been
reported [3-5j.
than 70 organic
superconductors
have
superconductor (1979) [2j more
associated
first of all
superconductors are
The problem of the design of orgamc
metals
and
the choice of
suitable
donor
with
acceptor (capable to oxidizing or reducing an
organic
or
state) and the choice of a corresponding
responsible for the processes of
ion-radical
counterion
formmg the conducting orgamc crystal's part.
of donor (D) moleelectrochemical
oxidation
obtained by
radical
salts
Most
cation
now
are
solvents (S). The electrolytes (E) used for these
cules m different polar orgamc
purposes
serve
with
the
(*)
Author
@
Les
search
for
Éditions
and
study of
correspondence
de
Physique
je-mail:
1996
conductors.
[email protected])
Since
the
JOURNAL
1610
as
of
source
a
(A)
anions
for
radical
PHYSIQUE
DE
salts
cation
N°12
be
to
obtained
(D. )+(D°)[A~j
fi
D + E + S
have
I
stable and labile.
During the reaction
electrolytes employed can be divided into two groups:
electrolytes (traditional electrolytes for electrochemistry, for example, with
anions of stable
Labile
electrolytes con change during the
BFj, CIO), Reoj, PFj etc. anions) remain.
A
different
As rule they are
metal-containing
anions.
anions.
reaction
giving rise to new
successful
considerably depends on the understanding of
synthesis of new organic conductors
of the
their
with organic conducting layers.
the origin of
mechanism
and
connection
anions
The problem of the design of metal containing anions is a problem of
coordination
chemistry.
transformations
Equilibrium
and
solvents play an
important role m the process of synthesis.
The last years
investigations showed that the most promising metals are soft metals such as
Cu, Hg and Au because of their
coordinational
multiplicity. Most
ET-based
organic supercon-
All
the
ductors
obtained
are
Cu-containing
with
[3-6j.
anions
possibility for creating
mercury
conincluding polymeric ones.
The
chemical
oxidation of ET which depends on a supporting electrolyte,
solvent and
reaction
different
(Tab. I).
conditions
yields some
of ET salts with
containing
groups
mercury
aurons
It should be noted
that the labile
Cl, Br, I and SCN) dissociate in a
anion (HgX3)~ IX
different
of
solution
and
combinations
dissociation
products provide many different
anions.
The composition and the
of organic
conductors
with
halomercurates
obtained
in
structure
the
electrocrystallization
strongly dependent of a solvent, composition and
concentration
are
of a supporting electrolyte,
temperature and current density.
The
choice of a solvent is of a particular
determmes
the
dissociation
since it
importance
and complex
formation.
Various
halomercurate
anions
may exist in solution, hence a number
of radical
salts
formed.
cation
The growth of the least
soluble
and the
highly
most
may be
conducting crystals has a decisive role for the electrocrystallization at the anode.
ET salts
shown in Table I consist of the families of
isostructural
compounds that permits the
comparison of their properties depending on small changes introduced in the amon part of the
chemistry of
The
taining
with
anions
salts
mercury
provides
also
coordinations
various
and
wide
a
structures
=
molecule.
investigations
Our
(Hg3Xs)~~
However
ation.
m
where
solution
a
from
of
that
A
low.
should
It
that
It
be
interesting
compounds
also
with
can
found
anion
obtained
are
(HgX3)~
with
and
its
needed
for
HgI2
and
the
electrolyte
in
unstable
is
large excess of HgX2 is
the solubility of HgC12
a
that
mentioned
former
the
that
coexist
anion
dissoci-
concentration
dissociation
a
differs
strongly
HgBr2.
of the
family
(ET)4Hg3-ôX8
of
with I differs
salt
comparable unit
strongly. The former
differ
most
which
dissociation
was
tural, despite
also
the
and I
Br
of the
because
stoichiometric
structure
Cl,
=
rather
is
[î].
inhibition
showed
X
from
cell
is
the
lengths
where
X
structures
and
the
while
the
and
Cl
with
space
same
semiconductor
a
Cl, Br
=
ones
I
and
which
two
are
The
isostruc-
physical
Their
group.
latter
synthesized.
was
Br
salts
properties
superconduc-
are
tors.
It
was
axis
a
second
and
shown
by X-ray analysis
[8,9].
one
The
Hg-Br ones in
depending
defined
from
first
of
consists
another
the
that
penetrating
mcommensurate
two
lattice
Hg
is
atoms.
on
each
periodicities
specific
of
crystal
structures
different
with
of the
salts
two
anion
location
are
trot
of
Hg
mcommensurate
constant
atom.
but
The
sublattices
with
along
periodicity
composed of ET molecules and
Therefore Hg-Cl bond lengths in
bromomercurate
a
the
lattices
Cl
a
vary
Cl and Br
the
or
Br
atoms
chloromercurate
from
contain
crystallographic
one
unit
the
and
anion
cell
to
stoichiometry of these salts
~-(ET)4Hg2 7sC18 [10]
are
PROPERTIES
N°12
Table
I.
Main
of
gro~tps
OF
ET
SOME
based
ET-SALTS
radical
with
saits
cation
~
ANIONS
Hg contaimng
1611
anions.
IET)41Hg3"1X8)
E=(HjX3) +HgX2
E=(HgX3)
m=1,2,3,4
MERCURY
WITH
S=TCE,THF
X=Cl, Br, I
S=TCE,THF
n=1,2
X=Cl, Br, I
+
E
+
s
iET~~iHgiscN)3~nxJ
IET)~iHz4xi~ic~Hs~o~
E=Hg(SCN)2+RSCN+MX
E=(HjX3)
S=C6HSY
X,Y=Cl,Br
and
The
S=TCE
X=Cl
R=Bu4N, Me4N
(n=1,2), F, Br, I (n=1)
~-(ET)4Hg2.898r8 [9]. (ET)4Hg2.7s-ôC18 was the first sait with K-ET type
pecuharities resulted in some interesting physical properties.
structural
structure
iii].
~-(ET)4Hg2.78C18
conductivity of ~-(ET)4Hg2 7sCls crystals measured in ab conducting
The
room-temperature
direction
measured along c*
is a factor of
plane, ranges from 5 to 30 S/cm. The conductivity
10~
dependence
The
salt
high.
of
this
is
the
temperature
smaller,
5)
amsotropy
(3
1. e.
very
x
There
low
metalhc
down
and
for
both
directions
is
temperatures.
to
of conductivity is the
same
from 4 to 20 K for different crystals
diversity m the
temperatures
is some
resistance
at the
demonstrates
Figure
reaching a minimum.
sometimes
begms to
and the
resistance
mcrease
that
It
applied
is
and
ambient
of
dependence
resistivity
the
at
seen
temperature
pressures.
However at 12 kbar the
higher under applied pressure than at ambient one.
In
with
1.8 K iii]
superconducting
transition
changed
by
sharp
T~
is
resistance
a
of
changes
the
dependence
kbar)
(about
the
resistance
29
higher
temperature
range
pressure
a
Fig. 1) [12]. This
5.4 K (see msert
abruptly
decreases
qualitatively and the
resistance
at
high pressure.
under
transition
with
phase
associated
probably
superconducting
transition
a
is
compared
with
peculiarities
The
investigation of magnetic properties also showed
as
some
observed
AH of ESR
linewidth
temat
The peak-to-peak
those of other
room
~-type salts.
linewidth
anisotropy
falls into 80 -100 Oe range [13]. The
orientations
perature for all crystal
characteristic
of
formula
orientations
caused by different crystal
agrees well with the empirical
the
is
resistance
increase
all
types
ET
based
=
softs:
AH
AHn, is the
where
AH
maximal
is
rather
value
[4].
value
The
is
~lHm
the
between
higher
large hnewidth
Hg lattice
incommensurate
perature
and
value
average
=
than
is
the
+
(0.2)~lHm
known
associated
sigmficant
as
and
minimal
well.
one
mainly
maximal
the
for
other
with
a
hnewidths
salts
but
the
at
tem~-type
room
strong spin-orbital coupling
JOURNAL
1612
PHYSIQUE
DE
I
N°12
~°~
~~~4@
~O°
OO
~OD
°
D
é~
~°~
J~
O
~~
~p
°0~6
ùf
éD
Î
O~
.
,~
a
a~~~
~
a
.
aô~
~
~
a
.
.~ô
o~
O
,
O
O
O
°
O
~p
°
'
~O
a
~
aô
~A~
a
Î~~~É /~ôô~~Î
ôôô
&/
0fO~4
.
ôo
;
à
à
O
ô
t
O
.'
o
a*
a
a
ho.*
0~2
"
cor
T,
Fig.
1.
(o)
12
kbar
Re818tance
kbar, (à
29
temperature
vs.
kbar.
The
in8ert
for ET4Hg2 78C181 (ZL) i bar, (D)
pre88ures
superconducting
(.) and
transitions
at 12
different
at
8hows
the
9
29
kbar,
(.
pressures.
Figure 2 shows the
dependence of the
temperature
hnewidth
AH for a
random
oriented
single crystal [13]. AH is constant for T > 80 K whereas it decreases
rive
than
times
more
nearly linearly with temperature m 4 K < T < 80 K range. This temperature
behaviour of
AH
differs strongly from that for the other ~-type salts for which the most
distinct
feature
is that the
peak-to-peak
linewidth
increases
with the
decrease [4]. The starting
temperature
point of AH decrease
correlates
with the
of paramagnetic
maximum
susceptibility (see insert
Fig. 2) and the anomaly of the electric conductivity iii].
m
The static
paramagnetic
susceptibility is well described in terms of Bonner-Fisher
model [14]
with the exchange integral1
6.4 x10~~ eV and the
The spm susceptibility
0.î.
parameter i
calculated
from ESR signal behaves precisely as the static
the whole
temperature
one
m
range
behaviour
magnetic
[13j. The unusual
arises
probably from a strong spin-orbital coupling
caused by the
and
cation
interaction.
More
additional
researches
for (ET)4Hg2.78C18
amon
obviously needed for elucidating its magnetic and superconducting properties, the pressure
are
dependence and the structural
More mteresting and
aspects.
intricate
properties are observed
for the other
member of the family, namely (ET)4Hg3-ôBrs.
=
(ET)4iig2
Like
be
the
898r8
previous
mentioned
mateIy
r~
ù-1
salt
that
À sI1orter
with
the
Cl
this
repeating
tI1an
in
cl
one
contains
distance
contaimng
two
between
sait
tI1at
mcommensurate
Hg
atoms
results
m
m
a
sublattices.
Hg sublattice
Iarger mercury
It
is
should
approxiin
content
PROPERTIES
N°12
OF
ET-SALTS
SOME
WITH
°°~"°
°°'°
~~J>°°°°~°
MERCURY
ANIONS
1613
°~°°
~O
O
/
~
E
£
O
O
O
O
J
~
~
E
o
O
O
w
m
~
i
Fig.
a
dependence
Temperature
susceptibility
paramagnetic
2.
static
of
a
T,
linewidth
of
us.
ESR
for
temperature
for ET4Hg2 78C18 single crystal.
ET4Hg2.78C18.
dependences of the
the compound.
Figure 3 shows the
temperature
allel, pjj, and perpendicular, pi, to the conducting ab plane. It is
metallic
a
behaviour
with
decrease
temperature
the
pi
increases
resistance
that
seen
with
the
The
measured
while
pjj
temperature
insert:
par-
has
de-
[15j. Such a behaviour of pi is unusual for organic metals for
crease
pi(T) debehave just the
Such
dependences of pjj and pi
which
the
temperature
same.
pendence for (ET)4Hg2.s9Brs implies that the crystals are quite good or the salt has a high
pi/pjj shown m the insert in Figure 3, is
two-dimensionality. The amsotropy of the
resistance
decrease
with the
approximately equal to 5000 at room
increases
temperature
temperature,
it
Below 5 K both pjj and pi vamsh at
and has a
3.5 K. The midpoint
maximum
in 10 K range.
for a superconductivity is Tc
investigations of various crystals of this
4.3 K. The
resistance
family showed the diversity of a superconductivity with somewhat lower Tc. This implies that
of
made in
conclusion
other
superconducting phases could exist. The same
process
was
some
by high magnetic fields [15j.
study of destroying the superconducting
transition
down
to
10
20
K
r~
r~
Upper
critical
down
temperature
fields
critical
One
can
clearly of
For
for
directions
two
Hj~H)(
in
» Hj(,
quasi-two-dimensional
that
see
a
the
magnetic fields, Hc2(T)
Figure
to 1.5 K [16j.
temperature
field
H(( (T)
this
interval
there
gives
is
way
the
ab
1.e.
the
magnetic fields up to 15 T and the
dependence of the upper
direction.
plane of a crystal and for a perpendicular
amsotropy of the crystal fields m (ET)4Hg2 s9Brs is
were
4
studied
shows
the
at
temperature
nature.
dependences of both longitudinal critical field Hj~ (T) and the
transverse
interval with a positive
4.3 K. At lower
temperatures
curvature
near
probably
interval in Hc2 (T)
This positive
curvature
to a hnear
is
curves.
an
JOURNAL
1614
PHYSIQUE
DE
I
N°12
2~O
.5
o
ce
'1
oo
~
n~
o.5
O.o
T,
Fig. 3.
Temperature
perpendicular (ZL) to the
of
the
of this
resistance
dependence
conducting
of
resistance
the
plane.
ab
The
ET4Hg2 89Br
for
insert:
temperature
measured
dependence
parallel (D) and
anisotropy
of the
sait.
of a phase with higher Tc [15j. The
correspond to a
mechanism
common
for the
destruction
of a superconductivity
the main
volume of the crystal.
The extrapolam
tions of these
intervals
approximately coincide and yield a transition
to the
temperature
axis
for the main
K
volume of a
3.3
superconductor.
The slopes of the linear
temperature Tc
mtervals
dHj~ /dT
110 koe/K and dH(( /dT
Using these
derivatives
and
5 koe/Il.
are
the
relations of Ginzburg-Landau theory for the model of an anisotropic
structure
of
result
a
break
a
mtervals
linear
of weak
H]~(T)
in
links
volume
between
H(((T)
and
elements
apparently
curves
=
r~
r~
7rÎ'loi
~~~~°~
which 4lo is flux
m
parallel
perpendicular
and
not
The
enough
reason
layers
is
(4lo
ab
to
2.07
"
plane,
is
for
that
condition
necessary
a
a
(((i(o)
10~~ Oe cm~), (jj (o) and fi (O)
we
estimated
(jj(o)
for
the
realization
r~
170
between
are
À and
the
correlation
(i(o)
layers.
lengths
À.
The
However
this
r~
8
superconductor.
junction between the
two-dimensional
of
Josephson
il?]
d is the
Therefore
27rii
length fi (o) is roughly half a distance
considering (ET)4Hg2.898r8 complex as a
r
where
x
"
correlation
transverse
is
quantum
~~~~°~
~~~
distance
between
(ET)4Hg2.s9Br8
two-dimensional
is
amsotropy.
a
the
very
=
(16/7r)[(1(o)/dj~
<
1
layers. In the sample studied this
three-dimensional
highly anisotropic
yields r
1.
superconductor with
relation
r~
PROPERTIES
N°12
OF
ET-SALTS
SOME
MERCURY
WITH
ANIONS
1615
'
,
,
,
,
,
[
QJ
© IOC
j
ci
18~4#T~
T,
Fig.
and
4.
H[1 ID
Below
Temperature dependence of the upper
critical
magnetic
perpendicular to ab plane for ET4Hg2.898r8.
2.5
K
the
Hj~(T)
deviate
while
Hj~(T)
an
for
absolute
On
the
Hj~(o)
=
observed
we
hmit
in
orbital
superconductor
and
is
+~
+~
170
negative
koe
which
of
with
ones
the
we
formula
~Î2(°)
j~
Hc2(o)
found
we
a
of the
an
curvature.
is
nearly
estimated
for
a
the
dirty
H(j (x) parallel
and
H(](T)
fields
critical
Hp(o)
interaction,
weak
H$2 ID
and
abnormally positive
curvature,
An extrapolation of Hj~(T) to
three
times larger than Clogston
significantly smaller than the
Considering Hj~(o)
250 koe.
paramagnetic
accordance
in
Hj~(T)
standard
a
dependence
temperature
For
approximation
the
other
hand Hj~(o)
o.î(dHj~/dT)Tc
fect of both
the
linearity.
a
yields Hj~(o)
zero
paramagnetic
of
curves
from
fields
18.4
=
diamagnetic
as
a
result
paramagnetic
effect
of
the
limit
Tc
at
60
T
combined
Hp(o)
K.
+~
for
=
o,
efthis
superconductor [18j
~)~~~ ~)(jjl/2
effect.
We found
absence
of a paramagnetic
in the
larger than the usual Clogston paramagnetic limit. There
possibilities for understanding a great value of a paramagnetic limit. It may be
various
are
with a triplet
associated
pairing of electrons, with a large spin-orbit scattering or with a strong
that
likely mterpretation for an upper
electron
most
pairing in (ET)4Hg2.s9Br8. We
suppose
large
which
results
critical field above a paramagnetic
hmit is a strong
electron
a
m
pairing
electron-phonon couphng constant
[16].
>
Some other
peculiarities are
characteristic
of this salt in a magnetic field, namely a spinlattice
relaxation
magnetic fields in T < 170 K range
time Ti of hydrogen Hi nuclei m
various
where
Hp(o)
+~
310
is
koe
an
upper
which
critical
is rive
times
field
JOURNAL
1616
PHYSIQUE
DE
I
N°12
oO
0~8
/s
~
Î~Î
0~6
CQ
É
',
/5O.4
~
lÎl
M
~
0~2
P, kbar
cor
T(K)
Fig.
5.
1
pressures:
diagram
where
for
Temperature
dependence of
(Dl 1bar, (ZL) 7 kbar, (x)
ET4Hg2 898r8.
dominant
the
relaxation
the
re818tance
23
kbar, (+)
mechamsm
is
the
tivity electrons [19]. Ordinary metals and organic
T) m this temperature
dependence (Tp~
range
ET4Hg2 898r8 8ingle
for
30
(*)
kbar,
of
interaction
kbar.
34
nuclei
crystals
at
different
pha8e
The
in8ert:
T
p
spins
with
the
conduc-
Korringa temperature
a
and the
relaxation
of
is independent
rate
field.
(ET)4Hg2.s9Br8
magnetic
For
the
dependence
of
Tp~
nonlinear,
furis
temperature
a
thermore
there is a rapid
increase of Tp~ with H and
within
the
studied
range of magnetic
fields (7
21 koe) the dependence Tp~ (H) can be approximated by hnear
functions at
various
relaxation
unusual for
temperatures
[19]. This field dependence of a spin-lattice
rate is quite
metals
and organic
conductors
and
be explained by
cross-relaxation
quadrupolar Br
can
ma
conductors
exhibit
+~
nuclei
It
[20].
was
shown
above
that
the
effect of the
applied
for the
pressure
first
member
of the
studied
family, namely (ET)4Hg2.78C18 exhibits the typical decrease of Tc with the pressure
mcrease,
dTc /dp < o. This effect was
observed for most
superconductors [4]. However the study
orgamc
of superconducting
(ET)4Hg2.898r8 under the applied pressure
transition
demonstrated
m
an
unusual
behaviour
for the organic superconductors, namely dTc/dp > o [21, 22]
Figure 5 shows the temperature
dependence of the
for (ET)4Hg2 898r8 single
resistance
crystal at different
With the application of a hydrostatic
pressures
up to 34 kbar.
pressure
Tc begins to
reaching the
equal to
(5 + 2) kbar.
This
maximum
6.8 K at
mcrease
with
conclusion
that the
superconductivity is
Tc
unambiguous
permits
pressure
mcrease
an
+~
associated
the
surface
with
or
the
in
the
intrinsic
bulk
properties
of the
crystal
of the
phase
specimen.
rather
With
+~
than
the
with
further
the
elemental
application
of
mercury
at
pressure
Tc
PROPERTIES
N°12
OF
SOME
ET-SALTS
MERCURY
WITH
ANIONS
1617
3eo
~°~
2~5
go~8
2~O
'
Q
o
n~
oeo~4
'1~5
~
o~o
ltl
T,K
i eo
ces
o~o
i
Fig.
for
crystals
remains
[22j
m
under
low
almost
that
pressure
constant
the
phase but this
decrease
is Dot
superconductivity
transition
and
to
dTMi/dp
an
+~
yet
(r~
from
the
300
bar).
and
then
of Tc
10
K/kbar
at
begins
a
[23j.
batch.
The
pressure
It is
the
rate
about
further
of this
(30-34)
three
different
msert:
the
the
studies.
pressure
transition
kbar.
crystals at ambient
pressure
dependences for the same
same
slowly above
mdicates
structural
the
with
of
The
decrease
to
pressure
by
and
state
same
with
confirmed
disappeared
msulating
R(T)/R(290 K)
re818tivity
electrical
Relative
6.
~-(d8-ET)4(HgBr2Hg2Br6]
T,K
10
kbar.
changes
in
In
kbar
21-25
increase
the
rapidly
Insert
in the
It
the
suggested
was
structure
range
pressure
salt
increases
Figure
of
underwent
with
5
the
the
the
pressure
shows T
p
phase diagram for studied
salt.
clearly seen that the
electrical
magnetic and
pressure,
research
properties of the salts of this family are so unusual and comphcated that much more
needed to fully explain its
nonstandard
structural
superconducting
properties.
aspects and
is
We
obtained
quite unexpected results m attempt to mvestigate an isotopic effect for (ET)4
Hg2.898r8 [24j. An isotope effect is used for elucidating the mechamsm of superconducting
electron
couphng in
conventional
superconductors.
The magnitude of the shift in Tc in isotopic
substitution
is predicted for the
electron-phonon
mechamsm
by BCS theory. The study of the
isotope effect in ET based
contradictory results which
superconductors led to some
orgamc
be interpreted in
of BCS theory [25,26]. We tried to synthesize a
deuterated
cannot
terms
of the
analog of (ET)4Hg2.898r8 but all the attempts
unsuccessful.
Small
variations
were
electrolyte composition resulted in the synthesis of ~-(d8-ET)4Hg3Brs. However this sait was
ambient
Figure 6 shows trie temperature dependences ofà
net a superconductor at
pressure.
different
relative
resistivity of three
crystals of this salt at ambient
None of these
pressure.
crystals is seen to undergo a superconducting
and a large diversity m their
behaviour
transition
JOURNAL
1618
After
observed.
is
applying
superconducting
a
them
some
Tc
Tona~t
different.
are
of
them
the
low
very
a
(see
transition
equal
are
transition
insert
is
not
PHYSIQUE
DE
I
N°12
pressure (+~ o.3 kbar) to the
the
in Fig. 6), however
2.o
to
K,
complete,
K
3.o
for
crystals all of them undergo
Tonset for all of
different
crystals. For
and 4.5 K for
of them the midpoint
corresponds to
one
temperatures
3.9 K [24]
=
of this salt with
structural
features
those of the
It is interesting to
the
orgamc
compare
corresponds to ~-type
superconductor ~-(ET)4Hg2.898r8 [24, 27]. The cation layer structure
and Br atoms
distributed
similarly in anion layers. However the locations of
in both
cases
are
distributed
strongly
differ
the
In (ET)4Hg2 898r8
anions.
atoms
atoms
mercury
are
mercury
m
channel
and form an
independent
sublattice
whose period is
bromine
incommensurate
in a
with a cation
sublattice
period [27]. Hg atoms form a regular hnear chain in bromine chanof
nels with the
distances
between
the
Hg-Hg atoms equal to 3.8î7 À. The
structure
nearest
(d8-ET)4Hg3Br8 is solved in the frame of one lattice [24]. The inorganic anion layer consists of
three-atomic
quasi-linear HgBr2 molecules and dimeric anions Hg2Br6. Hg atoms form a linear
them
channels
of Hg-Hg dimers
with the
distances
inside
chain in the
bromine
which
consists
with the
distances
Hg
equal to 3.68 À and Hg atom located
between
the
dimers
to the
nearest
from the dimers equal to 3.81 À.
atoms
the
deuteration
and very small changes in
Thus the analysis of these two salts shows that
even
considerable
and properties of (ET)4Hg3-ôX8
the electrolyte
result in
changes m the
structure
for I in the
of crystal growth a new salt was
obtained
salts.
When Br was
substituted
process
drastically differed from those of the salts with Cl
whose physical properties and the
structure
and
Br.
(ET)4Hg3I8
In
contrast
to
(ET)4Hg3-ôX8 IX
sublattices,
mensurate
the
la [28] The
space
group
types alternating along a
the
stacks
but
axis.
those
Cl, Br)
of
layer
cation
12
within
=
structure
There
ones
are
which
in
the
(ET)4Hg3I8
was
located
ab
is
are
shortened
no
between
in
the
in
S
S
of
terms
plane and
neigbouring
composed of
cell is
unit
solved
one
of the
consists
between
contacts
stacks
forming
incom-
two
lattice
with
the
of two
molecules
stacks
ET
two-dimensional
a
plane. The amon layer of (ET)4Hg3I8 consists of Hg and I atoms.
Iodine
atoms
form slightly
distorted 14
tetrahedra
stretched
along a axis and Hg atom is located inside each
tetrahedron
with positional population of o-àThe
dependence of the
for (ET)4Hg3I8 single crystal
measured
along
temperature
resistance
b axis, is presented in Figure î.
semiconductor-dielectric
phase
that a
transition
It is seen
salt at T
At this
the
by
in the
260 K.
resistivity sharply
temperature
occurs
mcreases
orders of magnitude.
The
the
and
1-1.5
is Ei
soc K above
transition
activation
energy
E2
5500 K below it. This is the first type phase
with the hysteresis of
7 K.
transition
The
hysteresis of the similar type was
sait at studying the
observed
in this
temperature
dependence of the reflectivity spectra at 900 cm~~ and 3200 cm~~ frequencies [29] (see the
in Fig. 7). However
the study of unpolarized
msert
spectra of reflectivity from the conducting
ab plane
recorded in 300
and at T
soc cm~~
230 K, showed
temperature
range at
room
net
in
ab
=
"
"
+~
=
that
they practically do
net
differ
from
each
reflectivity band in the
molecular
vibration
for example m (ET)8[Hg4Br12(C6H5Br)2] [30].
of
structural
transition
appear)
does
not
was
drawn
when
was
studied
[28]
is
not
and is due
the
practically concemed
to the changes m
temperature
behaviour
of
range
This
with
is
at
low
temperatures
may
be
ET
no
longitudinal
amon
and
a
The
transverse
same
splitting
takes
assuming
"face-to-face"
layer.
or
it
as
explained by
layer (the
iodomercurate
a
sharpening
There
another.
that
place
the
overlappmg
conclusion
conductivity
N°12
PROPERTIES
OF
ET-SALTS
SOME
MERCURY
WITH
1619
j
i~l
O
ANIONS
i~
0~7
ùi
'20
~~50
260
270
280
T, K
~
~/
ùi
T,
Fig. 7.
reflectivity
resistivity vs.
temperature
ET4Hg3I8 at 900 cm~~ (a) and
Relative
for
for
3200
K
ET4Hg3I8.
cm~~ (b).
The
insert:
temperature
dependence
of
The
first type phase
observed
during the study of the
transition
temperature
same
was
dependence of thermopower [28j (see Fig. 8). The thermopower is independent of temperature
(S(300 K)
down to
+55 mcv/K) and at lowering the
at high
temperatures
temperature
T
followed by a hysteresis cycle of
260 K it has a break
8 K. Right after the
transition
the
thermopower vanishes and then sharply increases
with a negative sign with the
temperature
decrease.
The
independence of thermopower together with its value imply that
temperature
there is spm
contributes
thermopower as it is
characteristic
of
entropy which mamly
to the
TCNQ salts [31j with a strong Coulomb repulsion at one site. The thermopower below phase
T~~ and is described by the formula applicable for
changes as
semiconductors
transition
=
=
+~
+~
~
~
kT
e
Here
of the
the
activation
activation
energy
of the
energy
corresponds to Ea
conductivity below
=
~
6000
the
K.
This
transition
value
correlates
well
with
The insert in Figure 8 shows the
dependence of a static paramagnetic
temperature
bility, xp, of (ET)4Hg3I8 [28] At high temperatures (T > 50 K) the xp behaviour is
by Curie-_Weiss law with Curie
approximately corresponding to a localized
constant
per
two
ET
molecules.
compound according
in xp
corresponds to
electrons
are
localized
Such
which
to
the
on
a
the
behaviour
average
thermopower
ET
molecules
corresponds
to
the
stoichiometric
susceptidescribed
electron
formula
of
charge is +o.5. The fact that Curie law is
(at high temperatures) which suggests
behaviour
ET
because
of
a
strong
that
temperature.
Coulomb
repulsion.
At
the
the
valid
that
phase
JOURNAL
1620
PHYSIQUE
DE
N°12
I
ioo
ç
~Îj
W
[
W
éJ
T, K
T, K
Fig.
paramagnetic
8tatic
temperature
transition
of
behaviour
described
is
dependence of the thermopower
susceptibility for ET4Hg3I8.
along
Temperature
8.
(T
K)
260
+~
~
Xp
(where
2J
the
mside
connected
behaviour
xp
conductivity, thermopower
by the formula
55
=
pair.
by
"
~2~ ~2
kT
K) typical
According
for the
shortened
intermolecular
system of
X-ray
to
and
not
is
b
axis
peculiar
very
reflectivity.
The
low
(-)
+
exp
data
contacts
at
a
insert:
compared
with
a
the
behaviour
of xp
exchange
energy
temperature
kT
paired
isolated
structural
as
The
-i
~ j
(3
ET4Hg3I8.
for
Here I is the
sites.
molecules
ET
high
coupled
are
while
temperatures,
pairs
in
the
inter-
neigbouring
thought to be
weaker. In terms of magnetic properties
these pairs
are
interconnected
two-dimensional
contaimng one electron per every site and
into a
network in ab plane. In the phase
this
network is assumed
altemation
transition
to undergo an
that
these
coupled into pairs more or less isolated from one another.
states
so
are
Figure 9 exhibits the
dependence of conductivity for (ET)4Hg3I8 single crystemperature
different
tals under
hydrostatic
It is seen
that the first type phase
pressures
up to 26 kbar.
pairs
are
isolated
transition
lowest
the
interconnected
sites
characteristic
pressure.
temperature
mcrease.
This
of this
However
salt
of this
transition
transition
is
dependence of the
resistance
characterized
by dTc/dp >
at
ambient
pressure,
semiconductor-dielectric
a
at
o
being
shifted
suppressed
not
the
and
even
the
to
at
is
absent
transition
26
low
kbar
the
in
is
realized
temperature
pressure.
obtained
curve
at
every
with the
range
The study
of
a
higher than 293 K showed that this
temperatures
rapidly shifted to
transition
the first type phase
is
at
the
pressure.
pressure
pressure
salt is
a
high
PROPERTIES
N°12
OF
ET-SALTS
SOME
WITH
ANIONS
MERCURY
1621
o
$
6kbar
to
8kbar
°~
12kbar
16kbar
22kbar
T, K
Fig.
dependence
Temperature
9.
of
relative
a
re818tivity
for
ET4Hg3I8
at
different
pre88ure8.
growth (in low pressure range) with a very high derivative
temperature
pressure
range with the
state.
approximately equal to 60 K/kbar. The insert in Figure 10 shows T
p plot for this
It is
temperature.
Figure 10 depicts basic dependence of the resistance for ET4Hg3I8 at room
between
with
the
transitions
kbar
three
phase
in
10
that
there
states
range
pressure
are
seen
It is obvious
II-III phases at
5
6 kbar.
between
I-II phases in
1 kbar
range and those
shifted to a high
between
I-II phases is rapidly
(see the msert in Fig. 10) that the interface
+~
+~
temperature
range
and
the
attains
(ET)2[Hg(SCN)3-nXn]
maximum
in
1.5
4
kbar
pressure
range.
Family
of ET in
electrochemical
oxidation
presented in Table I allow the conclusion that the
halide
and
thiocyanate
other
and
mercurate-thiocyanates
of
complex
comsome
presence
of new
metals of (ET)2 [Hg(SCN)~-3
formation
results in the
crown-ethers
pounds with
orgamc
Cl in
attempts to
1, 2) [32, 33]. The
F. Br and I in
1) and X
X~j family where X
successful.
As for the salts
analysis
for
suitable
X-ray
F
not
crystals
with
X
the
were
grow
Cl, Br and I all of them have ~-type packing of ET molecules in a catiomc layer.
with X
I.
3.59 À) in the salts except X
inside ET dimers (3.53
shortened S
S
There
contacts
are
(3.40 3.53 À). The
S
contacts
neighbouring dimers are also connected by shortened S
The
the
discriminates
arrangement of its
structural
peculiarity which
I has a specific
sait with X
mdependent
part of the unit
layers from those of the other salts of this family. An
catiomc
data
The
the
=
=
=
=
=
=
=
=
cell
A
of
and
cation
(ET)2(Hg(SCN)21]
B
contains
belong to the
consists only of
different
which
layer
[Hg(SCN)2Ij
A
and
the
radical
second
anion
cation
one
and
two
ET
radical
layers [34] It is shown
only of B. Both
consists
labeled
cations
that
one
layers
as
radical
have
the
JOURNAL
1622
DE
PHYSIQUE
I
N°12
2~5
2~O
j
las
~'
'
Î
Él
o
ces
o~o
i
kbar
p,
Fig. 10.
pha8es are
distances
S
interaction
A
the
with
bidentate
anion
chains
with
sheets
two
and
the
but
B
of
the
bridged
T
insert:
different
a
has 8
amon
character
resistivity
of
The
pressure.
on
packing
~-type
same
S
dependence
Pre88ure
seen
ones.
p
at
temperature
room
phase diagram
number
of S
Besides
these
S
two
of
phase
shortened
layers
ET4Hg3I8.
for
I-II
A has 6
contacts:
have
Three
different
transition.
different
shortened
characters
of the
sheet.
of SCN
ligand
compounds
SCN
results
with
connected
groups
formation
the
m
[Hg(SCN)2X]~ (X
by
shortened
of
a
Cl, Br
secondary
=
polymerized
I)
anion,
thus
polymeric
intermolecular
Hg
N
and
form
contacts
~scN,
/f~'
',
'Ncs
The
synthesis of these salts
which
synthesized
was
fragment
SCN
/
x
at
scN,
/f8,
40 °C
out
the
20
at
/
',.
/f8,,
'Ncs
x
Ncs
carried
was
scN,
anion
°C.
forms
/
x
As for
a
the
polymeric
group
/~~~'
Î /~~~'
ci
ÎÎ /~~~'
Îg
~i
~i
/
salt
chain
with
[Hg(SCN)C12]
bridged
one
with
N°12
PROPERTIES
OF
SOME
ET-SALTS
WITH
ANIONS
MERCURY
1623
eo
oe8
(0~6
'
1
ÉO~4
O.2
O.O
T,
Fig.
(O).
pressure
organic
family.
The
salt
any
X-ray
crystals
data
the
for
onset
lies
down
thin
very
are
crystals.
these
within
=
7 S
without
/cm
(n
=
i)
ambient
at
isostructural
and
range for all
increase of
shape.
well-cut
a
Three
I
loo-fold
the
(Hg(SCN)CI2]
superconducting
the
F, Br,
1.5
with
4.5 K
of ET2
2 K of
near
ET2(Hg(SCN)3-nXn] (X
metal
as
resistivity
relative
a
conductivity
behaves
The
temperature.
of
of
shows
insert
temperature
room
containing
The
8uperconductor
first
obtain
dependence
Temperature
ii.
kbar
9
K
salts
We
(two
(ZL) and
transition
X
=
CI
salts.
in
The
conductivity
did
salts
not
with
for
=
fluorine
at
manage
Cl
the
1, 2))
and
this
to
one
Br)
metals at
but undergo the
dielectric
with
transition
temperature
to a
state
are
room
decrease.
The
conductivity of (ET)2 [Hg(SCN)C12] increases 11 times with the
temperature
decrease
down to Tmax
increases
4 times
35 K and that of (ET)2[Hg(SCN)2 CII
temperature
transform
dielectric
with the
decrease
down to Tmax
50 K. Both salts
temperature
to a
state
with
the
=
=
at
temperatures
or
bridged
two
former
of
salt
below Tmax, The
groups
allows
a
ET2[Hg(SCN)2Br]
the
m
only
mcreases
of
1.4
a
between
interesting
It is
anion.
stabilization
difference
metallic
times
to
state
the
these
that
the
at
lower
temperature
salts
two
anion
with
is the
a
less
presence
symmetry
The
temperatures.
Tmax
130 K and
=
of
one
in
the
conductivity
sharply
then
decreases.
the
dependence of conductivity for (ET)2[Hg(SCN)C12]. It was found
We studied
pressure
(see Fig. Il) that the dielectric state below 35 K is rapidly suppressed and the salt transforms
with the onset
2 K in 9-12 kbar
temperature
state
to a superconducting
near
pressure
range (see
insert in Fig. Il). As it is usual for orgamc superconductors [35,36] dTc/dp < 0 for this sait and
Unfortunately we had
superconducting drop rapidly disappears with the pressure
increase.
a
no
possibility
to
lower
the
experimental
temperature
below
1.7 K in
the
pressure
apparatus.
JOURNAL
1624
conductivity
The
down
this
of
140 K
to
then
=
salt [34] showed it
ESR signal lies in 9.5-11
the
other
known
fall
to
into
G
family
of this
softs
lie
G
60-loo
between
interaction
quasi-one-dimensional
of
Table
demonstrates
I
Such
X, Y
that
=
solvent
a
shortened
a
TTF-TCNQ
as
Cl,
Br
used
in
salt
radical
the
softs
are
with
the
layers
cation
chains
signal
of ESR
and
very
a
characteristic
is
(TMTTF)2Cl04
[38] and
of
linewidths
~-type
associated
is
inside
contacts
linewidth
narrow
conductors
orgamc
(ET)8[Hg4X12(C6HSY)2],
with
bands
chains.
of this
X-ray analysis [34] the
to
the
of all
hnewidths
linewidth
narrow
According
while
directions
60-90
[4]. A
range
the
magnetic field
G [37]. The
ail
range at
within
peculiarities of its crystal
structure.
quasi-one-dimensional
consist of
weak
N°12
I
K-(ET)2[Hg(SCN)21] (the last salt of this family) is nearly constant
ESR study of
decreases
in a factor of 6 to T
5 K.
it gradually
linewidth
other
~-type ET based salts. The
to differ strongly from the
of
and
PHYSIQUE
DE
[39]
Family
electrochemical
an
of
oxidation
ET
of
is
great
together with the
tetrachloroethylene for benzene
derivatives
importance.
isostructural
application of HgXj containing electrolyte results in the formation of a new type
compounds with the anion which includes a sÀvent molecule, namely (ET )8 [Hg4X12 (CG HSY)2]
ix, Y
Cl, Br).
isostructural
salts with the cation
X-ray analysis of these four compounds showed them to be
compounds [40]. Figure 12 shows
and anion layers altemating along a axis hke most ET based
of (ET)8 [Hg4X12 (C6HSY)2] along b axis. The anion
consists of four HgX[
the crystal
structure
another
through
short
molecules
of
C6HSY
bound
and
the
solvent
to
contacts.
two
one
groups
(b
c)
of
direction.
parallel
stacks
along
described
series
The cation layer can be
+
runmng
as a
inequivalent ET molecules form B-A-C-D
along the stack and every
Four symmetric
sequence
S
S
through inversion
Shortened
intermolecular
stack is related to its adjacent
centers.
ones
smaller than 3.85 À are
observed for both inter- and
intrastack
The values
interactions.
contacts
The
of
substitution
=
of S
S
The
The
salt
down
with
with
X
=
K
160
to
and
densification
For
of the
with
X
interactions
of ET
calculations
for the
values,
showed
the
=
role
salt
X
Cl, Y
the
different
of
Cl
=
the
layers and fall
of
of
energies
[41]. They
o.04
into
electron
Y
of
compound
reduced by
the
shghtly (1.5 times)
is
S
stabilization
contacts
S
of
a
14
to
different
molecular
Tight-binding band
range.
with X = Cl, Y = Cl based
hole
Fermi
surfaces
that
is
metalhc
donor-donor
of the salt
and
contacts
properties
transport
m
highest occupied
of the
of Br
substitution
shortened
the
m
13.
metal
is
Br
=
of
resistance
Br
=
correspond
eV
o.3
structure
closed
group
sequence
shortened
Cl,
=
Br
the
decreases
resistance
consequent
formation
a
Its
X
a
S
interaction
room-temperature
existence
as
types S
Il.
minimal
a
Thus
the
in
are
characteristic
Br, Y
=
a
salts
1.3
with
has
transition.
calculated
were
these
The
the
with
in
K is
90
compound
packing
to
compound
temperature
of the
these
down
below
compounds results
of conducting layers and
metallic
conductivity.
study of optical properties of
compounds as compared with
with
a
The
metal-insulator
a
(HOMO-HOMO)
orbitals
as
transition
the
ET
of
metal
isostructural
defining
salt
of
denser
a
decrease
the
decreasing from
bond length in
conducting layer.
shown in Figure
compound
of the
with
resistivities
K.
1.3
at
this
At
has
and
these
the
Cl.
resistance
for Cl in
state.
behaves
metal-insulator
=
The
=
Cl
in
relatike
of
lower
times
A
Br, Y
=
Cl, Y
associated
results
This
dependences
loo
K.
10
times.
lower
X
being
to
for Cl.
substitution
composition
the
salts.
temperature
linearly
5-7
Br
at
anion
strongly depend on
This is evidently
distances
containing
Cl
to
structure
on
these
agreement
m
2D
peculiarities
electron-vibrational
bands
crystal
structure
of the
softs of these
the
other
in
conducting
1100-1300
due
to
which
family showed
ET
salts is the
cm~~
range.
the
electron
This
that
the
absence
may
transfer
be
specific feature
of
associated
between
of
characteristic
a
ET
with
the
molecules
N°12
PROPERTIES
OF
SOME
ET-SALTS
MERCURY,ANIONS
WITH
1625
"
"
c
~
~
~
~~
j
~
~
'
'
Fig.
is
Cry8tal
12.
broken
of
8tructure
(ET)8(Hg4X12(C6HSY)2] along
through
realized
the
side
sulfur
vibrations
from the
symmetric
totally symmetric modes to this
magnetoresistance
The
of
down
to
found
[43, 44]. Figure
1.5
K
was
process
two
investigated.
14
shows
which
atom
in
its
electron-vibrational
The
shortened
contacts
are
by
of
in
static
For
both
SdH
leads
tum
to
and
interaction
the
to
of
exclusion
the
inclusion
totally
of
non-
[42]
salts
(ET)8[Hg4Ch2(C6H5Br)2] III)
and
b ax18.
line8.
this
family, namely (ET)8[Hg4Ch2(C6H5Cl)2] (1)
magnetic
salts
oscillations
fields
for I
observed
15
to
up
Shubnikov-de
Haas
at
a
T
and
(SdH)
measuring
the
temperature
oscillations
current
were
parallel
perpendicular to the conducting bc plane) and the angle çJ between
a*). It is seen that the
of a magnetic field and a* equal to 25° (yJ
o at H
the
direction
ii
transform
Fast
Fourier
of SdH
oscillations
superposition of different frequencies.
is
a
curve
oscillations
this
R(1/H)
(see
shows
that
SdH
(FFT) of the curve
the
in Fig.
14)
insert
at
of
frequencies.
The
detailed
investigation
different
field
correspond at least to six
direction
il
proportional
all
of
be
of
frequencies
showed
them
dependence
these
the angular
to
to
cosçJ.
the
combination
conclusion
that all of them
The analysis of these frequencies permits the
are
of two
fundamental
F2 and F3 frequencies equal to 250 T and 400 T, respectively, at Hjja*.
surface as two
of these frequencies enables the specification of Fermi
dependence
The angular
of
these
cylinders
cross-sectional
in the bc
parallel
The
the
a*.
cylinders with
to
areas
axes
first
20%
of
the
Brillomn
13%
of
and
the
cross-section
correspond
plane
to
zone.
Figure 15 shows the angular dependence of magnetoresistance of (ET)8[Hg4Ch2(C6H5Cl)2]
observed
smgle crystal at a current parallel to a* A very high anisotropy of magnetoresistance
to
a*
(a*-the
direction
=
JOURNAL
1626
PHYSIQUE
DE
N°12
I
~2
~O
oe8
O
lÎl
'0~6
~
~
0.4
0~2
cor
T,
Fig.
13.
X
Y
=
A
noteworthy.
is
this
mum
do
not
insert
this
with
both
SdH
of the
the
15.
the
X,
salts
Y
ix
Cl, Br.
=
Br.
are
=
magnetoresistance.
angles
confirming
of the
numbers
=
equal to 3 at the absolute minithe angular dependence of magespecially prominent at çJ
55°,
40
The
magnetic field thus
of angular
oscillations
while
Y
=
Besides
which
of
part
X
approximately
maximum.
oscillations
Figure
Cl, (ZL)
=
is
absolute
classical
in
arrows
minima
Fig. 15),
in
the
with
of the
Rio)] /R(o)
90 at
ETB(Hg4X12(C6HSY)2]
for
Y
=
[R(14T)
reaches
oscillations
vary
numbers
=
While
marked
are
=
exhibits
angular
ones
X
ratio
netoresistance
and
resistivity vs.
temperature
Cl, Y
Br, (D) X
Br,
relative
Cl, (O)
=
their
follow
of
maxima
law
corresponding
these
to
origin.
Shubnikov
the
of the
minima
corresponding
çJn
almost
The
latter
oscillations
At çJ >
the
o
a* tan çJn (see the
oscillations
poorly satisfy
n
+~
relation.
type of angular
Such
periodic
tan çJ,
m
corrugated
oscillations
of
associated
are
planes
with
classical
a
the
motion
part of
magnetoresistance
electrons
of
m
open
whose
orbits
minima
are
belong
which
to
quasi-one-dimensional
electron
system. Such an infrom angular
terpretation of the electron
motion
oscillations
of the
classical part of magnetorecontradicts
the electron
sistance
motion in closed orbits belonging to Fermi cylinder corrugated
along its axis which was predicted by band
calculations
for (ET)8 [Hg4CIi2 (CùH5Cl)2] [41] and
the results of SdH
oscillations.
This problem is to be solved in the future.
As for
that
only
direction
(F(o)
same
=
SdH
one
235
two
characteristic
found
oscillations
frequency
[44]. The
section
obtained
least
Fermi
is
in
present
in
of
(ET)8[Hg4C1i2(C6H5)Br)2] fast
these
oscillations
for all angles
dependence of SdH
oscillations
T) relation and corresponds
area) of Fermi surface with
demonstrate
that
cylindrical
sheets
this
of
salt
Fermi
on
çJ
is
well
described
Fourier
between
by F(çJ)
single cyhndrical sheet (or several
the
directed along a*. On one
axes
differs from its
isostructural
analog with
to
surface
a
with
different
cross-section
transform
areas
shows
and
a*
=
F(o) /
sheets
hand
Cl in
were
field
the
with
the
çJ
cos
the
results
which
at
observed.
PROPERTIES
N°12
SOME
OF
ET-SALTS
WITH
ANIONS
MERCURY
1627
5e5
sec
E
4~5
~
©
lÎ~
4~O
3e5
3~o
12
H, T
Fig.
Shubnikov-de-Haa8
14.
(çJ is the
angle
between
units)
for
arbitrary
On
the
other
It is
clear
the
hand
surface
Fermi
m
that
o8cillation8
conducting
presented
oscillations
these
results
in
are
salt [41]
additional
research
surface
for
properties of three
families
of ET
obtained
ETB(Hg4Ch2(C6H5Cl)2]
a
The
Figure
in
good
fast
insert:
8alt
T
at
1-S K
=
and çJ
=
(the amplitude
transform
Fourier
25°
is in
14.
agreement
with
trie
theoretical
calculations
of
this
Fermi
mental
for
plane).
bc
is
these
needed
to
softs
two
fully explain
and
trie
contradiction
theoretical
experi-
between
calculations
of it.
Conclusion
The
organic
based
metals
and
superconductors
with
halomer-
(ET)4Hg2.78C18 and (ET)4Hg2.898r8 formed by two mutaare
aurons
12 kbar
lattices, are superconductors with Tc
1.8 K at p
bly penetrating
mcommensurate
characterized
by trie apCl containing salt is
respectively.
and Tc
4.3 K at p
1 bar,
Trie
29 kbar.
of a new
superconducting phase with Tc
5.3 K at p
existence
pearance
briefly
curate
discussed.
=
=
=
=
of
=
=
incommensurate
sublattices
gave
exceeding of
Hc2, the growth
rise
to
a
serres
of
limit,
unusual
properties
for
(ET)4Hg2.898r8,
of the
critical
curvature
upper
a positive
a
as
dTc/dp
and
other.
of Tc with the
decrease,
o
magnetic field
>
some
pressure
formation
resulted in the
this salt for the study of an isotope effect
The
deuterate
attempt to
of a new
phase of (ET)4[HgBr2Hg2Br6] composition which undergoes a supercommensurate
characterized
by three
0.3 kbar. (ET)4Hg3I8 is
conducting
transition
3.9 K under p
at Tc
Trie cooling of this salt results m the first
phases depending on pressure at room
temperature.
with a
transition
260 K which is shifted
type the phase
at T
to a high
temperature
range
high derivative dT/dp
application.
60 K /kbar at
pressure
such
the
paramagnetic
5-fold
=
=
=
=
JOURNAL
1628
PHYSIQUE
DE
I
N°12
t
-iso
po
Angular
Fig. là.
parallel
a*
to
shown
It is
ducting
T
dependence
the
insert:
dependence
and
ax18
for the
of
first
that
time
"
minima
minima
on
salt
the
2 K at p
9
+~
(lJg4C1i2 (C6H5Cl)2] at H
oscillations
angle
marked
are
tanget of the anile corresponding
of ETB
resistance
The
K.
number
a
with Tonset
state
of the
1.45
=
a
(ET)2 [Hg(SCN)C12]
is
the
14 T,
=
by
of
to
transformed
current
arrows.
The
çJn.
to
a
supercon-
kbar.
Shubnikov-de
oscillations
Haas
observed for two
isostructural
salts (ET)8 [Hg4 Ch2 (C6H5
were
(FFT)
transform
Cl)2] and (ET)8[Hg4Ch2(C6H5Br)2]. It was shown that the fast Fourier
analysis for the former salt enables the assumption of the
of Fermi
surface as two
existence
cylinders with the axes parallel to a*, whose
cross-sections
in bc plane
correspond to 13%
and 20% of the
of the first
cross-section
Brillomn
The analysis of FFT for the other
zone.
salt
results
the
conclusion
the
of the only cylindrical
existence
Fermi
surface
with the
m
on
equal to 13% that is in a good agreement with the theoretical
cross-section
calculations
for
this
salt
The
[41]
results
every
studies
described
in this
family but at
clearly needed for
are
demonstrate
paper
studied
in
the
time
same
gammg
insight
it
into
a
quite
should
these
number
be
noted
unusual
of
physical properties
unusual
that
classes
additional
considerable
of
compounds.
Acknowledgments
The
and
authors
A.V.
Rozenberg
express
Afanas'eva
their
who
sincere
gratitude
synthesized
all
Zhilyaeva, M.Z. Aldoshina,
compounds studied, to R.P.
k-type packing of ET molecules
to
E.I.
the
L.M.
Shibaeva
Goldenberg
and
L.P.
crystals, to
S.V.
Konovahkhin
of many of these compounds.
and V.V.
Gritsenko
who studied the
structure
Pesotskii, M.K. Makova, E-I- Yudanova
and M.G. Kaplunov
participated in the study
to S.I.
of physical properties of these compounds.
The thorough investigation
would be impossible
without a creative activity of all these
This work was supported by Russian
Foundation
persons.
of
who
Fundamental
were
the
first
Investigations
to
determme
94-03-o9950a
and
18957.
in
the
N°12
PROPERTIES
OF
SOME
ET-SALTS
MERCURY
WITH
ANIONS
1629
References
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D.,
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[2j
Stat~ts
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[Il] Lyubovskaya R.N., Lyubovskii R.B., Shibaeva R.P., Aldoshina M.Z., Goldenberg L.M.,
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Pesotskii
S.I., Pis'ma v Zh. Eksp. Teor. Fiz. (in Russian) 45 (1987) 416. This paper
which firstly reported on the synthesis and the
properties of a new
superconducorgamc
edited
and
by
the
tor ET4Hg2.898r8,
hand
of
Prof.
I.F.
Shchegolev.
rewritten
He
was
considered
this work to be interesting. During the study he took a hvely
in
the
mterest
work.
to
it
for
J.C.
was
the
papers.
and
However
several
[16]
(1988)
49
Bonner
refused
he
to
hundreds
of
That's
works
interest
constant
the
R.N.,
kind
be
one
of the
Probably
considerable.
not
Lyubovskaya
(1990)
Fisher
but
to
of
the
man
Lyubovskii
sev
authors
that
eral
is
since
Prof.
of
thousands
work, the
he
why
useful
he
I.F.
works
discussion
assumed
that
Shchegolev
express
and
contribution
his
had
no
more
than
gratitude
a deep
the help in writing the
him
was.
R.B.,
Makova
M.K.
and
Pesotskii
S.I.,
JETA
Lett.
51
361.
A.N. and
Buzdin
Bulaevskii L.N., Usp. Fiz. Na~tk (in Russian) 144 (1984) 415; Sov. Phys.
Usp. 27 (1984) 830.
Saint-James
D., Sarma G. and Thomas E.I., Type II superconductivity (Pergamon, New
[18j
York, 1969).
Merzhanov
V.A-, Lyubovskaya R.N. and Lyubovskii R.B.,
[19] Skripov A.V., Stepanov A.P.,
[17]
JETA
j20]
Lett.
49
(1989)
265.
Skripov A.V., Stepanov A.P., Heinmaa
M.Z., Physica C172 (1990) 340
J.,
Vainrub
A., Lyubovskaya
R.N.
and
Aldoshina
JOURNAL
1630
[21]
DE
PHYSIQUE
N°12
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