Shubnikov-de Haas Oscillations in New Organic Conductors (ET)8[ Hg4Cl12(C6H5Cl)2] and (ET)8[ Hg4Cl12(C6H5Br)2]

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Shubnikov-de Haas Oscillations in New Organic Conductors (ET)8[ Hg4Cl12(C6H5Cl)2] and (ET)8[

Hg4Cl12(C6H5Br)2]

R. Lyubovskii, S. Pesotskii, A. Gilevski, R. Lyubovskaya

To cite this version:

R. Lyubovskii, S. Pesotskii, A. Gilevski, R. Lyubovskaya. Shubnikov-de Haas Oscillations in New Or-

ganic Conductors (ET)8[ Hg4Cl12(C6H5Cl)2] and (ET)8[ Hg4Cl12(C6H5Br)2]. Journal de Physique

I, EDP Sciences, 1996, 6 (12), pp.1809-1818. �10.1051/jp1:1996189�. �jpa-00247282�

J.

Phys.

I France 6

(1996)

1809-1818 DECEMBER1996, PAGE 1809

Shubnikov-de Haas Oscillations in New Organic Conductors

(ET)8[Hg4C1i2(C6H5Cl)2j ^and (ET)8[Hg4C1i2(C6H5Br)2j

R-B-

Lyubovskii

(~~~~*), S-I- Pesotskii

(~,~),

^{A. Gilevski}

(~) and

R-N-

Lyubovskaya (~)

(~) ^{Institute of Chemical}

Physics

at

Chernogolovka RAS, Chernogolovka,

Moscow region, 142432 Russia

(~) International Laboratory of

High Magnetic

Fields and Low Temperatures, 53-529 Wroclaw, Poland

(Received

5

April

1996,

accepted

ii

June1996)

/

PACS.74.70.Kn,

Organic superconductors

PACS.72.15.Gd

Galvanomagnetic

and other magnetotransport effects

Abstract. Trie results of trie

investigations

of Shubnikov-de Haas oscillations in trie quasi- two-dimensional

organic complexes (ET)s [Hg4C1i2 [C6HSX)2],

^{where X} = Cl, Br in trie

magnetic

fields _up to 40 T

were reported. These results allow

one to obtain _some information about Fermi surface in trie mentioned

complexes.

Shubnikov-de Haas oscillations in trie

compound

with X

= Cl

correspond

at least to two different

cyhndrical

sheets of Fermi surface with trie cross-section in

(bc)-plane

of13% and 20% Brillouin _zone cross-section. Shubnikov-de Haas oscillations _m trie complex ^{»ith X} = Br

correspond

to _one

cy.hndrical

sheet ~vith trie _cross- section in

(bc)-plane

of13% of Brillouin _zone cross-section. Trie

experimental

results for trie

complex

~vith X

= Br _more agree with the theoretical calculations of Fermi surface than for trie

complex

~vith X

= Cl

Introduction

In trie fate 80ies the

family

of

quasi-tn<-dimeiisional

organic

superconductors

based _on bis-

(ethylenedithio)tetrathiafulvalene ^(ET)

~N.as filled _up

by

two new

superconductors

with

poly-

merized halomercurate orrions,

namely (ET)4Hg2_78C18

^and

(ET)4Hg2 898r8

with

Tc

= 1.8 K

and 4.3 h.

respectively il, ii.

Trie work n~ith trie _anions of this type seemed to be _promising due to trie unusual

properties

of trie

superconductors.

In

particular,

a record value of trie

derivative of trie _Upper critical field

dHc2/dT

m~ 10

T/K along

trie

conducting

sheets

regis-

tered in

(ET)4Hg2 sgBr8

at a

relatively

low critical

temperature,

^{leads to} a record _excess of

a

paramagnetic

^{bruit in} organic

superconductors

_[3].

^Besides,

an unusual

growth

of critical

temperature

^n>ith an externat _pressure noncharacteristic of normal

superconductors

was ob- served in this

compound

at a pressure up to 3-5 kbar [4]. ^{Trie electron structure} of these

compounds

_was of

importance,

however its detailed

investigation

^with

using

a

magnetic

field

was restricted

by

_an internai random

potential

inherent in these

compounds,

^{which results in}

trie value _{~dT «} 1 in trie total _range of

really existing

fields. Such _a

potential

is _a result of that

(*)

^Author for

correspondence le-mail: rustem©icp.ac.ru)

©

Les

Éditions

_{de Physique} 1996

Hg

atoms form their _own sublattice in

(ET)4Hg2

_78C18 and

(ET)4Hg2.898r8 single crystals

which is incommensurate with trie lattice of trie basic matrix

[5].

Therefore it is

quite

rea-

sonable to

synthesize

trie conductors with halomercurate _{aurons without a random}

potential.

This

opportunity

_was realized in trie

synthesis

of _a

family

of isostructural

organic

conductors

(ET)8(Hg4C1i2(C6H5Cl)21 II), (ET)8(Hg4C1i2(C6H5Br)2] (II), (ET)8(Hg4Br12(C6H5Cl)21 (III)

and

(ET)8(Hg4Br12(C6H5Br)2] (IV)

_[6]. Trie

crystal

lattices _are

regular

in these salts ~N.hich

are metals at room temperatures

I?i.

^{However III} and IV become dielectrics below 90 K and 160

K, respectively.

Il is characterized

by

_a weak

growth

of trie resistance below 10 K and

only

I

keeps

_a metallic behaviour down to 1.4 Ii [8].

Trie

magnetoresistance

of trie salt I denoted below _as

(Cl, Cl)

and that of trie salt II, denoted below _as

(Cl, Br)

_was studied in this work. We

reported

earlier about trie observation of

Shubnikov-de Haas

(SdH)

oscillations in these

complexes _[9, loi.

Trie present work exhibits

more detailed

investigations

of SdH oscillations and first of all trie detailed

comparative analysis

of SdH oscillations _in trie

compounds (Cl, Cl)

and

(Cl, Br)

and their Fermi surfaces

(FS).

Experimental

The

objects

under

study

_were trie

samples

of

(ET)8(Hg4Ch2(C6H5Cl)21 single crystals

which appear as

irregular parallelepipeds

with I.o _x I.o _x o-1

mm3

characteristic _sizes. Trie total

X-ray analysis

of this

compound

made at _room

temperature

is described in

[îj. (Cl, Cl) single crystals

bave _a

layered

_structure

analogous

with that of trie other ET-based conductors. ET

loyers

_are located in

(bc) plane.

All ET molecules _are

parallel

to each other _in trie

layer

that

is characteristic of

p-type packing.

ET

layers

alternate

along

a* direction and _are

separated by polymerized [Hg4C1i2(C6H5Cl)~~]

anions. Trie unit cell is triclinic with Z

= 1 and contains 8 ET molecules _per cell.

(Cl, Br) complex

_is isostructural _to

(Cl, Cl)

_one. Trie

conductivity

of both salts _in

(bc) plane,

_{i e.} in trie

plane

of ET

loyers

constitutes _s

= 10

S/cm

and that

between trie

loyers,

1.e.

along

a* direction, is 3-4 orders lower. Trie

temperature dependence

of trie resistance for

(Cl, Cl) complex

is metal-like without any

peculiarities

within 1.4-300 K at trie

measuring

current I j

(bc).

At trie _same direction of trie _{current a} weak

growth

of trie

resistance _was observed below 10 K in

(Cl, Br) complex

_[8].

Magnetoresistance

measurements _were carried _ont

by

_{using a} standard

four-probe technique

at _an

alternating

current of 330 Hz. Both _a

longitudinal

resistance at I j

(bc)

and _a transverse

one at I j a* _were measured. For

measuring

_a

magnetoresistance

a

magnetic

field _up to 15 T

was

generated by

_a

superconducting

solenoid and that _up

to_40

T _was

generated by

_a

pulse

solenoid.

Only

_in trie _case of _a

superconducting

solenoid _one could _{rotate a}

sample

_varying its

orientation in _a

magnetic

^field. SdH oscillations of trie resistance found in these measurements were

analyzed by using

_a standard method of fast Fourier transform

(FFT).

Results

Figure

1 shows trie field

dependence

of

magnetoresistance

for

(Cl, Cl) single crystals

at field direction

perpendicular

to

(bc) plane

and _{at current} direction

along

this

plane.

SdH oscillations

are observed _{even at} î-8 T and appear as almost _an ideal sinusoid with 250 T

frequency.

FFT

of this _curve

(see

insert A in

Fig. 1)

confirms this fact

demonstrating

_{a very} weak contribution

of trie second harmonic. However _at trie _same field and _current directions trie contribution of SdH oscillations with

higher frequencies

_grows

quickly

_in trie fields

higher

than 15 T

(pulse

fields _{up to} 40

T) (see

insert B in

Fig. 1).

Trie _presence of SdH oscillations with other

frequencies

_{can be also observed in trie fields}

up to 15 T but in trie conditions distinct from those

presented

in

Figure

1.

Figure

2

displays

SdH

N°12 OSCILLATIONS IN NEW ORGANIC ET-SALTS 1811

6.5

6.0

5.5

B

£

_{5.0 T}

JZ

O

ç/

_4,5

A

~

4.0

t

(

3.5

~

3.0

1o i

,

T

Fig.

l. Shubnikov-de Haas oscillations _m trie

single crystal

of

(ET)8[Hg4C1i2(C6H5Cl)2]1

H

jj a*,

trie current I is

parallel

to trie bc

plane

and T

= 1.45 K. Insert A:

amplitude

of fast Fourier transform for the oscillations

presented

in

Figure

1. Insert B: Shubnikov-de Haas oscillations in _a

puise field;

H

jj a*, the current is

parallel

to the bc

plane

and T

= 1.45 K.

oscillations at current direction I

jj a* and at ç2 = 25°

,

where _ç2 is trie

angle

between trie field direction and trie direction a*

(~

= o at H

jj

a*).

FFT

represented

in trie insert to

Figure

2 indicates that trie _curve shown in trie

Figure

is a

superposition

of SdH oscillations of at least rive

frequencies.

Figure

3 shows SdH oscillations in

(Cl, Br) single crystal

at trie direction of trie measuring current I ^j a* and at H ^j a*. These oscillations

together

^with their Fourier

spectrum (see

trie insert to

Fig. 3)

_are similar to those observed for

(Cl, Cl) samples

at trie _same field direction.

Moreover,

trie

frequency

of SdH oscillations

(F

= 235

T)

_in

(Cl, Br)

is close to that of trie oscillations found in

(Cl, Cl)

at H

jj a* and I j

(bc). However,

in contrast to

(Cl, Cl)

FFT

yields only

one

frequency

of SdH oscillations in

(Cl, Br) crystals

at ail orientations of _a

magnetic

field

(trie

contributions of trie other

frequencies

or

higher

^harmonics are rather

small).

Trie

angular dependence

of SdH

frequency

was studied

quite

^{in detail} in a wide range of trie

angles

_{ç2 =} +70°. Trie results of trie measurements are shown _in

Figure

4 in

polar

coordinates for

(Cl, Cl) samples

and in

Figure

3

(see

insert

B)

for

(Cl, Br)

_ones. Trie

following peculiarities

of these measurements should be noted:

1)

^SdH oscillations are characterized in

(Cl, Br) by

trie

only frequency,

whose

angular dependency

appears as a

straight

line

perpendicular

to

a*;

2)

in

(Cl,

Cl SdH oscillations _are characterized

by

six

frequencies

^whose

angular dependence

are also _{more or} less

correctly

described

by straight

^hnes

perpendicular

to

a*; 3)

at H ^j a*

trie values of these

frequencies

constitute

Fi

" 150

T, F2

" 250

T, F3

" 400

T, F4

" 500

T,

0.2

O.1

~

O.O

(

_-0.1

~

d e

~'

(

fÎÎ

-0.2 ~

Î

S

-0.3

H,

-0.4

O.lO 0. 0.12 0.13

/H, /T

Fig.

2. Shubnikov-de Haas oscillations in the

single crystal

of

(ET)8[Hg4C1i2(C6H5Cl)2]

after _a subtraction of the

regular

_part where _~J

=

25°,

trie current is I

jj a* and T

= 1.45 K. Insert:

amplitude of trie fast Fourier transform for the oscillations presented in

Figure

2.

F5

" 650 T and

F6

" 910 T,

respectively (this

is trie result of trie

interpolation

of trie hnear

dependencies

_in

Fig.

4 _on trie field direction H ^j a*

); 4)

trie contribution of oscillations of each

frequency

to trie

resulting

oscillation _curve

essentially depends

_{on ç2} and current direction in

(Cl, Cl).

At I j

(bc)

trie oscillations with

F2 frequency

dominate

significantly

at almost all

angles

ç2. Trie contribution of SdH oscillations with other

frequencies

_is not

large,

_moreover trie oscillations with

Fi

and

F6 frequencies

_were not observed at any

angle

_ç2. At I ^j a* SdH oscillations with

F2 frequency

dominate _as well. However for most ç2

values, especially

if

they

are not close to ç2 =

o°,

trie contribution of oscillations with other

frequencies

_is

significant

and _even

compatible

with that of trie _main

frequency F2 (see

trie insert in

Fig. 2).

Trie fact that under certain conditions trie contribution of SdH oscillations _in

(Cl. Cl)

is made

only by

trie _main

frequency F2,

enables trie evaluation of

cyclotron

_mass of trie _carriers

associated with trie oscillations of this

frequency.

Trie insert in

Figure

5 shows trie temperature

dependence

of

logarithm

of trie reduced

amplitude

of SdH oscillations at I ^j

(bc)

and _ç2

= o°.

Trie

dependence

_is well

approximated by

_a

straight

hne within trie

experimental

_error. Thus

one can use a standard

relationship

for trie evaluation of _a

cyclotron

_mass:

In(À/T)

= const

2~~ckBm*(T TD)lehH Il)

where A is _an oscillation

amplitude,

m* is _a

cyclotron

_{mass, TD} is

Dingle temperature.

Trie evaluation

yields

m*

= 1.35 mû

N°12 OSCILLATIONS IN NEW ORGANIC ET-SALTS 1813

11

~ B

Î

1

HJn.

0f

A

E

W

OE E

<

t~

H,T

4 14 16

H, T

Fig.

3. Shubnikov-de Haas oscillations _in trie

single

crystal

(ET)8[Hg4C1i2(C6H5Br)2]

with trie

field orientation H

ii a* and temperature T

= 1.45 K. Insert A: FFT for trie oscillations

displayed

in the

figure,

msert B:

angular dependence

of the frequency of Shubnikov-de Haas oscillations in

polar

coordinates.

The insert in

Figure

6 shows that trie

application

of trie

relationship Il)

to SdH oscillations in

(Cl, Br) complex

is

quite

correct. Trie evaluation of _a

cyclotron

_mass in this

compound yields

m*

= 1.25 _mû which is close to trie

analogous

_{one in}

(Cl, Cl).

Figures

5 and 6 exhibit trie

angular dependences

of trie

amplitudes

of SdH oscillations of trie main

frequency F2

in

(Cl, Cl)

at I

jj

(bc)

and those of trie

frequency

^F in

(Cl, Br)

at I

jj

a*, respectively.

Trie

amplitudes

of oscillations bave _a maximum in both

compounds

which does trot coincide with trie direction H ^j a*. Trie

amplitude

becomes almost

equal

to _zero in each

compound

at ç2 > +60°. Besides trie intermediate _minima ii which trie

amplitude

_is close to

zero, are

quite

^of

importance.

^{These minima} appear ^at trie

angles

_{ç2 =} +28° for

(Cl, Cl)

and

at ç2 = +35° for

[Cl, Br).

Discussion

The

analysis

of

X-ray

data I?i enabled _one to calculate _{a zone} structure of

(Cl, Cl)

salt

[11].

Its unit cell contains 8 donor ET

molecules,

therefore trie interaction between 8

highest

oc-

cupied

molecular orbitals

(HOMO)

results in trie formation of 8 energy zones.

According

to a stoichiometric formula each ET molecule bas 1.5 electron in trie unit cell and therefore 12 electrons _are to be

populated

at 8 energy levels. Trie system under

study

_may be either _a two-dimensional semiconductor _or a two-dimensional metal

depending

on trie

degree

of trie

Hia* j

§

+

5°° T 250

T

Hla*

Fig.

4.

Anglular dependence

of trie

frequencies

of Shubnikov-de Haas oscillations in

(ET)8 [Hg4C1i2(C6H5Cl)2]

_m

polar

coordinates.

overlapping

_or trie

availability

of trie energy gap between trie 6th _zone and trie 7th _one. Trie calculations [11] showed that there is _a small

overlapping

between these _zones which defines their

partial occupation by

electrons and

consequently

a metallic behaviour of

conductivity

of this salt down to helium

temperatures.

Trie calculated Fermi surface

(FS)

_was found _{to consist} of two

cylinders

whose _{axes are}

parallel

to a*. Trie cross-section of these

cylinders

in bc

plane

is shown _in

Figure

7. Trie calculations

yielded

trie

rigorously equal

values for trie _areas of trie sections for these

cylinders

which constitute

13%

of trie _area of _a

corresponding

section of trie first Brillouin _zone. However _trie

cylinder

A is associated with electrons _as carriers and trie

cylinder

B is associated with holes. It is stated in

[11]

^{that these closed FS}

appeared

_{as a} result of trie

hybridization

of two hidden one-dimensional FS. One could

expect

quantum oscillations

only

with trie

frequency

of about 250 T _at H j a* from FS of such _a

shape (not considering

trie

possible

contribution of trie harmonics and

magnetic

breakdown

orbits).

These calculations _are

qualitatively

and

quantitatively

in

agreement

with trie

experimental

data _on SdH oscillations in

(Cl, Br).

Trie

angular dependence

of trie

frequency

of SdH oscil- lations

apparently

enables trie

imagination

of FS in this

compound

_{as one}

cylinder (or

several

cylinders

with

equal

_areas of

cross-sections)

with trie _axis directed

along

trie direction a*. At H ^j a* trie

frequency

of SdH oscillations is 235 T that is close to trie calculated value.

A

significantly

_more

_comphcated

case is for

(Cl, Cl) compound

for which trie calculation of FS

was made

il ii.

Trie

study

of SdH oscillations at various field and

measuring

current orientations revealed trie existence of oscillations with _six different

frequencies.

All these

frequencies

bave trie

dependences

_on trie

angle corresponding

to trie

cylindrical

sheets of FS

(see Fig. 4).

However

only

_{a part} of them

corresponds

to

really existing

closed orbits. It

obviously

follows from trie

fact that trie _sum of all

frequencies

is _more than trie

frequency corresponding

to

loo%

of trie first Brillouin _zone. One _{can see} that all

frequencies

_{are a} hnear combination of two

frequencies Fi

and

F21 F3

"

Fi

+

F2, F4

"

2F2, F5

"

Fi

+

2F2

and

F6

"

Fi

₊

3F2. Figure

4 demonstrates

that trie

frequency Fi

_is observed in _a very narrow range of trie

angles,

at trie _same time

N°12 OSCILLATIONS IN NEW ORGANIC ET-SALTS 1815

200

f~

ÎÎ

il, K

o -ioo

~tJo

Fig.

5.

Angular dependence

of the

amplitude

of Shubnikov-de Haas oscillations at the fundamental frequency F2 _m

JET)8[Hg4C1i2(C6H5Cl)2]

single

crystal

when current is

parallel

to the bc

plane

and T

= 1.45 K. Insert: temperature

dependence

of the reduced

amplitude

of Shubnikov-de Haas

oscillations at the basic

frequency

F2.

trie

frequency F3

_appears at FFT

significantly

_more

frequently.

Therefore _we suppose that trie

frequencies F2

and

F3 correspond

to trie real closed orbits. Trie

frequency F4

is most

probably

trie second harmonic of

F2.

Trie other

frequencies

are

probably

_so called combined

frequencies: Fi

=

F3 F~, F5

₌

F3

+

F~, F6

₌

F3

₊

2F2,

which can arise for

example

due to _a

magnetic

interaction

[12].

^{It also cannot be excluded that trie}

frequency F5

is associated

with the

magnetic

^{breakdown orbit. Thus SdH} oscillations show trie existence of at least two different

cylindrical

^{FS sheets in trie}

^complex (Cl, Cl)

^{which have the} cross-section _in bc

plane equal

to

13%

_and

20%

of trie first Brillouin _zone cross-section and

correspond

to trie

frequencies F2

and

F3.

However _{a more} detailed

investigation

will be

enough

to confirm this fact.

Trie

following problem

is not also

quite

clear: how many

cylindric

sheets of FS which possess trie

equal

_areas of

cross-sections,

_are

responsible

for trie oscillations with trie main

frequency F2

in

(Cl, Cl)

and for trie oscillations with trie

frequency

^{F in}

(Cl, Br). According

to trie theoretical calculations of FS for

(Cl, Cl) _[11]

_{one can} expect ^{that two}

Fermi-cylinders

with trie

equal

_areas of cross-sections _{in every}

compound contril~ute

_{to trie} oscillations with these

frequencies.

In this _case trie

relationship (1)

for trie

temperature dependence

of trie

amplitude

of SdH oscillations _is valid

only providing

that both in

(Cl, Cl)

^and

(Cl, Br) Fermi-cylinders

~&.ith

equal

_areas are associated with the _carriers which bave

equal cyclotron

_masses. It is _seen from the inserts _in

Figures

5 and 6 that the

relationship (1)

^holds

quite

well for both

complexes.

Therefore the conclusion _may be drawn that either the contribution to SdH oscillations with

80

/~

é

~

60

Jà à

~

K

m a lJ1

o

ù20

E

-i

angle _(~£J°)

Fig.

6.

Angular dependence

of the

amplitude

of Shubnikov-de Haas oscillations _m

(ET)8 [Hg4C1i2(C6H5Br)2]

at the T ₌ 1.45 K. Insert: temperature

dependence

of the reduced

amplitude

of the oscillations with the field orientation H

jj a*.

/~S/~fi~~

z

a

~~li~/S~~

Fig.

î. The cross-section of Fermi surface _m the bc plane _m

(ET)8[Hg4C1i2(C6H5Cl)2]

at _room

temperature

Ill].

N°12 OSCILLATIONS IN NEW ORGANIC ET-SALTS 1817

the

frequency F2

in

(Cl, Cl)

and the

frequency

F in

(Cl, Br)

is made

by only

_one

corresponding Fermi-cyhnder

_in each

complex,

_or such _a contribution is realized

by

several

cylinders

which

are characterized

by equal

areas of cross-sections and

equal cyclotron

masses of the carriers.

This is confirmed

by

trie

angular dependences

of trie

amplitudes

of SdH oscillations with trie

frequency F2

in

(Cl, Cl)

and trie

frequency

F in

(Cl, Br) represented

in

Figures

^{5 and}

6, respectively.

Both

dependences

_are

quite

similar

qualitatively. They

both _are characterized

by

incoincidence of trie _maximum of trie

amplitude

with trie direction of trie field H

jj a*.

This incoincidence is associated

probably

with _a low

symmetry

^of

crystal

lattice of trie

samples

studied. Both

dependences

demonstrate trie intermediate minima of trie

amplitude

which trie most

probably

arise because of _a

spin splitting

of Landau levels.

Keeping

this

splitting

in mind _{one can} introduce a

lowering multiplier

in trie expression for trie

amplitude

of SdH oscillations [12]

cos(~gpm* /2mo)

where _p is harmonic's number and _g is

g-factor.

It is reduced to zero

providing

that

gpm* /mo

# 2n + 1

where _{n is an}

integer. Considering

that _a

cyclotron

_mass

depends

_{on ç2 as} trie _area

enveloped by

trie

corresponding orbit,

1.e.

m*(ç2)

₌

m*(o)/

_cosç2 and

taking

into account

m*(o)

=

1.35mo

obtained earlier for

(Cl, Cl)

and

m*(o)

=

1.25mo

^for

(Cl, Br),

_one obtains that at g = 2 trie

amplitudes

of trie first harmonics of SdH oscillations with

F2

and F

frequencies

vanish at

n = 1 and _ç2

= +28° and _{ç2 =} +34°

respectively,

that agrees well with trie

experimental

results obtained for both

complexes (see Figs.

5 and

6).

It is obvious that trie

superposition

of SdH oscillations with

equal frequencies

but different

cyclotron

_masses ^could

hardly

enable _one to observe such _very well resolved

pictures

^of

"spin

zeros" which _were found in

(Cl, Cl)

and

(Cl, Br).

Conclusion

The

study

of trie behaviour of SdH oscillations _in trie isostructural

organic

conductors

ETB [Hg4Ch2(C6H5Cl)21

^and

ETB(Hg4C1i2(C6H5Br)21 ^permitted

one to obtain trie

preliminary

vi- sualization _on FS in these

compounds.

In

ETB(Hg4C1i2(C6H5Br)21

it consists of _{one or} several

cylindrical

sheets with trie _axes directed

along

a* and trie

equal

_areas of cross-sections constitut- mg

approximately

13To of trie _area of trie

corresponding

cross-section of trie first Brillouin _zone in

(bc) plane.

In

ETB(Hg4Ch2(C6H5

Cl)2] ^{FS trie most}

probably

contains at least two

cylindri-

cal sheets with different _areas of cross-sections

constituting approximately ^13%

and

20%

of trie

area of trie cross-section of trie first Brillouin zone in

(bc) plane.

For

ETB(Hg4Cl12 (C6H5Br)21

trie data obtained _are in _a

qualitative

and

quantitative agreement

^{with trie} theoretical calcu- lations of FS whereas trie results obtained for

ETB(Hg4Ch2(C6H5Cl)21

are

only partially

_in

agreement

^{with these} calculations.

Acknowledgments

The authors express their

gratitude

to V.I. Nizhankovskii for bis

help

_in trie

experiment,

to A.E. Kovalev and M.V. Kartsovnik for trie

help

in trie treatment of trie

experimental

data and fruitful

discussion,

to Ya.

Klyamut

and E-B-

Yagubskii

^for trie

support

^of this work. Trie work

is

supported by

trie Russian Foundation of Fundamental

Investigations (93-02-2384),

^INTAS

(93-2400)

and TSF

(JB 3100).

References

iii Lyubovskaya R-N-, Lyubovskii R-B-,

Shibaeva

R-P-,

Aldoshina

M.Z., Goldenberg L.M.,

Khidekel'Mi. and

Shul'pyakov Yu.F.,

JETA Lett. 42

(1985)

468.

[2]

Lyubovskaya R.N., Zhylaeva E.I., Zvarykina A.V.,

Laukhin

V.N., Lyubovskii

R-B- and Pesotskii

S-I-,

JETA Lett. 45

(1987)

530.

[3]

Lyubovskaya R-N-, Lyubovskii R-B-,

Makova M.K. and Pesotskii

S-I-,

JETA Lett. 51

(1990)

361.

[4]

Lyubovskaya R-N-, Lyubovskii R-B-,

Makova M.K. and Pesotskii

S-I-,

Proc. III

Europ.

Conf. _on Low Dimen. Cond. and

Supercon. (Zagreb, Sept. 3-8, 1989)

Fizika

(Yugosiama)

21

(1989)

_7; Schirber

J-E-, Overmayer Dl.,

Venturini

El., Wang H-H-,

Carlson

K-D-,

Kwok

W.K.,Kleinjan

S. and Williams

J-M-, Physica

C161

(1989)

412.

[5j

Lyubovskaya R-N-, Zhylaeva E-I-,

Pesotskii

S-I-, Lyubovskii R-B-,

Atovmian

L.O., Dy-

achenko O-A- and Takhirov

T.G-,

JETA Lett. 46

(1987)

188.

(6j

Lyubovskaya R.N.,

Afanas'eva

T-V-, Dyachenko O.A-,

Gritsenko

V.V., Lyubovskii

R-B- and Makova

M.K.,

Izv. Akad. Nauk SSSR _ser. Khim.

(1990)

2872.

(7j

Dyachenko O.A.,

Gritsenko

V.V., Mkoyan Sh.G.,

Shilov G-V- and Atovmian L.O.

Izv.Akad. Nauk SSSR _ser. Khim.

(1991)

2062.

[8]

Lyubovskaya

R.N.,

Dyachenko

O.A. and

LyubovskiiR. B., Synth.

Met. 55

(1993)

2899.

(9]

Lyubovskii R-B-,

Pesotskii

S-I-,

Gilevskii A. and

Lyubovskaya R.N.,

JETA 80

(1995)

946.

[loi Lyubovskii R-B-,

Pesotskii S-I- and

Lyubovskaya R-N-,

JETA Lett. 62

(1995)

37.

[Il]

Veiros L.F. and Canadell

E.,

J.

Phys.

I France 4

(1994)

939.

(12] Shoenberg D., Magnetic

Oscillations _in Metals

(Cambridge University Press, Cambrige,

1984).