Hydrostatic pressure effect on Tc and resistance anomaly in normal state of κ-(BEDT-TTF)2CuN(CN)2Br

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Hydrostatic pressure effect on Tc and resistance anomaly in normal state of κ-(BEDT-TTF)2CuN(CN)2Br

Yu. Sushko, V. Bondarenko, R. Petrosov, N. Kushch, E. Yagubskii

To cite this version:

Yu. Sushko, V. Bondarenko, R. Petrosov, N. Kushch, E. Yagubskii. Hydrostatic pressure effect on

Tc and resistance anomaly in normal state of κ-(BEDT-TTF)2CuN(CN)2Br. Journal de Physique I,

EDP Sciences, 1991, 1 (10), pp.1375-1379. �10.1051/jp1:1991209�. �jpa-00246421�

J

Phys.

Ifrmce 1

(1991)

1375-1379 ~K3OBRE1991, PAGE 1375

classification

PhysicsAbs1racts

74.70K 72.15

Short Communication

Hydrostatic _pressure effect

_on

Tc and resistance anomaly in

normal state of ~-(BEDT-TTF)2CuN(CN)2Br

Yu.V

Sushko(~ ),

VJi~

Bondarenko(~ ),

^R.A~

Petrosov(~),

^N.D.

Kushch(2)

and ELB.

Yagubskii(2)

('

_{Institute of}

Semiconductors,

Ukrainian

Academy

of

Sciences,

Kiev

252650, Ukraine,

U-S-S-R-

(2)

^Institute of chemical

Physics, Academy

of Sciences of the

USSR, chernogolovka,

14243~

U.S.S.R~

(Received

21

Mqy1991,

^revbed19 Jane 1991,

accepted 31Ja~y1991)

Abstract. Tile pressure ^effect on the

temperature dependence

of the

resistivity

and supercon-

ducting

transition temperature ^for

organic superconductor x-(BEDT-TlF)~cuN(cN)~Br

is studied.

Pronounced anomalies of normal state

(resistidty

maximum _near 80 K and inflection of

R(T)

curve at

~-

50

K)

are found

strongly suppressed

under pressure and

disappearing

at P > SW bar. Simulta-

neously,

a linear and monotonic decrease of Tc in the pressure range up ^{to 750 bar is observed.}

Recently,

the

discovery

of _{a new} ambient

pressure organic superconductor, K-(BEDT-TTF)~

CUN(CN)~Br,

with

Tc

= 11.5

lQ

_was

reported ill.

Besides the

high Tc

value this

compound

ex-

hibits _a

puzzling

normal state

anomaly

a

pronounced resistivily

maximum around W K

[1, 2].

The _same

type anomaly

has been

previously

^{found also in another}

high-Tc organic _supercon- ductor, K-IBEDT-TTF)~Cu(NCS)~ [3],

^{and has attracted much attention in view of its}

possible

relation _to the

highest

for

organic superconductors

^{value of}

Tc.

The extreme

sensitivity

to the

pressure

^{of both}

Tc

and the resistance maximum

height

_was established. In

particular,

^Shirber

et al.

[4], using

a low field ESR

technique,

found that

Tc

decreases

monotonously

with _a rate of 3

K/kbar;

Murata et al.

reported

on the same

pressure dependence

of

n

and also found that

the

resistivily hump disappears

at P _> 3 kbar. An

attempt

^{of Parker} et al. [6] ^to

study

simulta-

neously

the pressure influence _on both

Tc

and the normal state

resistivity anomaly

at moderate pressures

yielded

_an

intriguing

result:

n

remains

nearly

constant in _a pressure range ^P < 3 kbar where the above mentioned

resistivily hump

_occurs, and

steeply

falls at

higher _pressure,

when the

hump

is

suppressed.

However,

_a

liquid-medium

_pressure

technique

of [6] is

inadequate

for

temperature dependence

measurements at moderate

pressures owing

to

strong

^and non-monotonous

temperature

^variation of the

pressure

^{at P} < 3-4 kbar

(See,

for

example

Refs.

[7, 8]).

In order to

investigate

the

relationship

between the normal state

anomaly

mentioned above and the

superconductivity

in the

(BEDT-TTF)~CUN(CN)~Br

we have carried out the simultane-

1376 JOURNAL DE PHYSIQUE I N°10

ous

pressure

measurements of both the

superconducting

transition

temperature

^{and normal} state

resbtivity by

_means of _an

"Unipress"

helium

gas pressure technique,

free from

disadvantage

of the method in

[fl.

Single crystals

of

K-(BEDT-TTF)~CUN(CN)~Br

have been obtained

by

the electrochemical oxidation of BEDT-TTF

(2 mmolA)

in

I, 1,

2 triclorethane under _{constant current} conditions

vith a current of 0.50

PA

A mixture of

I8~crown-6-ether,

CuBr and

NaN(CN)~ (5

mmol/l

each)

has been used as an

electrolyte.

^{Pressure values have been} measured

by

means of _a

manganin gauge placed

at the

entry

^of a

capillary coupling

^the

gas compressor

^{and the}

pressure

^{vessel. The}

temperature

has been measured with _a

germanium

thermometer attached _to the

pressure

^vessel

at the

sample

level.

The reshtance _vs.

temperature ^behavior, R(T),

at different

pressures

^is illustrated in

figure

I.

The

pronounced

resistance maximum _near 65-80 K h

rapidly suppressed

with the

increasing

_pres-

sure and

dhappears

ⁱⁿ

pressure

range ^{435 bar} < P _< 750 bar.

Simultaneously,

the

superconduct- ing

transition is found to shift to lower

temperatures.

^Another

resistivily anomaly,

_an inflection

on the

R(T)

curve near 50

lQ

is also

strongly pressure dependent

as it is seen from

figure

_2~ where

the

temperature dependence

of the

derivative, dR/dT,

is shown for different pressures.

2.~~

' '

'BE~~"~~) ~~~~~'2~'

'

~ ,-××=25c bG<

~

°

'j'~'~~ -~"~~~ _~~

,

i

^~

~~~

~

~yy©*.O"

~

O"~

Q

~'

'

i

~~~~~~"'i _~~'~~'~~~~

l",

,-

5

°°-~~

~

ill ^<~i, ii~iiii11

^?~

Iii

# j

j h

~ C

~fl

~~~

~÷~~~~

/

O

~ "

Q

g

<

"

'

+ _"

~ ~C j

~

,

~ '_

0

~~

~"'

°'°°.

°°

E

~

~~'l'~

^~~~~

_~

'))~'~~£

~ ~~ ~

~~~ ~ ~'~

Fig.

1. -

bmperatureendence

of

resistance

pressures:

a) general

_view;

b)

part.

The _pressuredependence

of Tc h

_shown in figure 3.

It

_is

seen

that, decreases

^with

pressure

very rapidly.Moreover,

we

^note

the

^{notonous Tc}

vs. P

pendence

(dTc/dP

=-2.8

K/kbar) in the whole _{pressureinterval}

up

to 740

the resistivily and

the

nflection

point

^are resent or not.

In figure 4 the

onductivity

vs. pressure

behavior is shownfor ^two different

temperatures.

We did

not _find any preciable both

at

252lQ well

N° lo PRESSURE EFFECT ON _K

(BEDT TTF)2cuN(cN)2Br

1377

1.6

~~~

~~

0.8

~~

*~

*~ _l~

o-Q

1.6 2

~%

~ 0.8

~,*

7J

/* ~§_

~

_0.0

3~ ^~.6 ~

.~ ~

l.6 ^~

O.8

J+#~~

O-o

TEMPERATURE

Fig.

Z

lbmperature dependence

of the temperature derivative of

K-(BEDT-TTF)~cu[N(cN)~Br

resis- tance,

dR/dT (Ohm/K),

at different pressures: 1) ²⁵⁰

bar, 2)

340

bar, 3)

⁵⁶⁰ bar,

4)

750 bar.

a

~' a

~ n

~ O

n

o-o soo o coo.o

PRESSURE

(bar)

Fig.

3. Pressure

dependence

of

superconducting

transition temperature.

In

conclusion,

the simultaneous measurements of the

superconducting

^transition

temperature

and the normal _state

resbtivily

_vs.

temperature

^{variation at different}

pressures

^{have been carried}

out

by using

the

helium-gas _pressure technique.

The monotonous

drop

^of

Tc

with the rate of -2.8

K/kbar

has been found under

pressures up

^{to 740 bar. It has been}

shown,

that both normal state

reshtivily anomalies,

the

hump

on the

R(T)

curve near 65-80 K and the inflection

point

near

50

lQ

are also

strongly suppressed, disappearing

at P _> 560 bar.

However,

no

changes

ⁱⁿ the

slope

of

Tc

_{vs. pressure}

dependence

have been found.

Hence,

it is

possible

to conclude that there are no sufficient evidences of the role of normal state anomalies noted _on

superconducting

transition

temperature

^value.

1378 JOURNAL DE PHYSIQUE I N° lo

(B£DT-TTF~ ^CUN(CN)₂^Br 2,0

~

_K

> '.5

~ ~~~

~

©

~ O Z

° _'.O

©

a Lu t~4

~ o.5

~i

tt Q z

o.o

PRESSURE

Fig.

4. Pressure

dependence

of

K-(BEDT-TTF)~culN(cN)~]Br conductiwty

at temperatures ^{252 and} 122 K.

Acknowledgements.

The authors thank I.F

Schegolev

for

stimulating

discussions and critical

reading

of the manu-

script.

This work is

supported by

the Scientific Council _on the U.S.S.R. State

Program "High-Tc Superconductivity".

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N° lo PRESSURE EFFECT ON _K

(BEDT TTF)2cuN(cN)2Br

¹³⁷⁹

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