Internal friction study of carriers in high-Tc superconductors

Physiea C 185-189 (1991) 1373-1374 North-Holland

INTERNAL FRICTION STUDY OF CARRIERS IN HIGH-Tc SUPERCONDUCTORS

L i n h a i Sun, Yening Wang and Zhen Yu National Laboratory of Solid State Microstructures, The P e o p l e ' s R e p u b l i c o f C h i n a

Nanjing University,

N a n j i n g 210008,

Internal friction in the KHz range of Bi(Pb}SrCaCuO shows an obvious hysteretic plateau (~-x} above Tc that drops linearly with temperature below Tc. The ~ - x of YBaCuO decreases with decreasing oxygen content. The results imply the existence of distortion clouds around the carriers, caused by the inelastic electron-phonon interaction.

I.

INTRODUCTION In

metallic

superconductors

the ultrasonic

attenuation drops sharply below Tc and generally obeys This

the

formula

derived

attenuation,

damping,

is

being

BCS theory*.

called the electronic

attributed

scattering.

from

to

electron-phonon

In YBaCuO, the ultrasonic attenua-

tion 2-s and even the KHz range z,6

internal

friction

in the

decrease

related

high-Tc superconductivity,

energy

to

the

used to gaps s.

was

supposed

However,

friction

in

YBazCu30x

attenuation

and

(Q'*) peaks

below Tc

is due

superconductivity

or

there

( =

) or

around Tc.

needs to be clarified whether the drop of Q-* just

to be

calculate the superconducting

always exist the obvious internal

It

a and

to the transition to

only

it

is

the

low

temperature side of a peak. Recently,

Saint-Paul

et al. 7

ultrasonic

attenuations

Bi2SrzCaCuzOs

single

cant

peaks

decreases

To measure we s e l e c t e d

around as

a

be too small

Tc,

below

which

the a

linear functioh of temperature

that the to

in

crystals show no signifi-

instead of on exponential pointed out

found that the measured

be

one.

Almond et al. 8

electronic damping should detected

for

the high-Tc

the internal the

method

b a r s w i t h a low s t r a i n could minimize dependent

peaks

For

the

free-free

resonant

such

as

of any amplitudeinduced

by

phase-

(mainly

2223 phase)

polycrystalline sample (B1) with Tc at 108 K, the basic and triple

frequency fr

were 1.3 and

3.9 kHz, respectively~ the internal friction Q-l and the relative variations of Young's

modulus

AY/Y (Y~fr z) as well as the electric resistance R are shown in fig.

I.

peaks

around

are

visible

It

plateau of the internal

shows

Tc,

indeeed no

but an obvious

friction Qp-1

above Tc

for both resonant ~odes after subtraction of the internal friction

peak

The

Qp-1

background

independent, Such a

showing

plateau Qp-1

of temperature below

located is a

around

nearIy

hysteretic

220 K.

frequency character.

drops as a linear function Tc

with

a

turning point

iocated just at Tc. In

order

to

investigate

responsible for the the internal

internal

oxygen

method

reported

content

mechanism

friction plateau,

x

(determined

by

a

elsewhere 9) were measured also

in the Id4z range (fig. Z}.

0921-4534/91/$03.50 © 1991 - Elsevier Science Pub ,shers B.V. All fights reserved.

the

friction of YBazCu3Ox samples with

various

to he explored.

background,

a m p l i t u d e ( 1 × 1 0 - s ) , which

Bi(Pb)SrCaCuO

be reconfirmed,

its origin needs

of

the influence

oxides near Tc, thus the above phenomenon should and moreover,

friction

transitions z .

often diminish exponentially below

Tc too, thus its

was even

2. EXPERIMENTAL METHODS AND RESULTS

For

the sample with

L. Sun et aL / Study of carriers in hiEh-Tc superconductors

1374

20

.z.

q

]

' Im

f

~

. ti"

q tram

x 10

m

• :4

-eL

....... .

7 '

I00

T(K)

200

:

m

it

I00

300

Im

200

300

T(K)

FIGURE 1 Q-z and AY/Y of Bi(Pb)SrCaCuO vs. T measured 1.3 KHz (m) and 3.9 KHz (A)

at

FIGURE 2 Q-* vs T of YBa2CuaOx with: x=6.95 (m); x=6.75 ( e ) ; x=6.5 ( 4 ) . The i n s e t shows t h e background v a l u e s Qp-, a t 150 K ( l ) and 300 K ( e ) v s x, f = 2 . 7 KHz

oxygen content x=6.9 (Tc=90 K, fr=2.7 kHz) t h e r e

distortions

been verified

by p h o t o - i n d u c e d

exist

absorption measurements of the

c o p p e r o x i d e s 12,

indeed

two

turning point below Tc

peaks

becomes obscure

could still

values at

60 and

peaks, the obvious

be seen

150 K.

nearly

thus the

but the decrease

and

by comparing the

mass o f t h e c a r r i e r .

After subtracting the

of A

implies that

inelastic

T>Tc

is also

interactions

that

of

f o r m a t i o n o f Cooper p a i r s .

With

reduction

the

be

seen

more

t h e dynamic e f f e c t i v e rapid decrease

to

perhaps play

a

o f Qp-1

electron-phonon

main

role

in the

of the

clearly in

REFERENCES 1. J.Bardeen, L.N. Cooper and J.R. Schrieffer,

of fig. 2 in which Qp-1 values at two Phys. Rev. B 108 (1957) 1175.

temperatures, 150 and 300 K, are chosen. The

b e l o w Tc

enhancement

for

x, the background Qp-1 decreases

gradually, which can

the

Qp-1

Bi(Pb)SrCaCuO samples. oxygen content

Tc,

equal

background

and

the inset

zround

has

hysteretic

friction

appearing

commonly

attributed

background in

of

the internal

crystalline

to

solids

dislocations t0

or

is

2. Y.N. Wang et al., J. Phys. C 20 (1987) L665. 3. M.-F. Xu et al., Phys. Rev. B 37 (1988) 3675.

to

coherent boundaries in the ferroelastic phase 11.

4. Z.J. Sun et al., Phys. Rev. B 42 (1990) 2569.

However the densities of the dislocations in the

5. Y.S. He e t a l . ,

high-Tc oxides

and twins in BSCCO are too small

to cause such a large result for

Qp-l.

YBazCu3Ox, the

with x may be speculated diminished

carrier

In

view

be

density.

caused The

6. G . C a n n e l l i e t a l . ,

Phys. C 21 (1988) L783. Phys.Rev.B 36 (1987) 8907.

of the

decrease of the Qp-1 to

J.

by the

hysteretic

7. M . S a i n t - P a u l e t a l . , 8. D.P. Almond, J . 9. L.H. Sun e t a l . ,

P h y s i c a C 166 (1990) 405

P h y s . C 21 (1988) L l 1 3 7 . Phys. Rev. B 38 (1988) 5114.

background Qp-1 may still be ascribed to similar inelastic

interactions

distortions and structural

the lattice,

distortions

carriers, just like with carriers.

between

the

exist,

structural

if such localized induced

polarons,

by the

lO.G.Gremaud, J. de Phys. 48 (1987) C8-15. II.Y.N. Wang et al, J. de Phy~, 42 (1981) C5-10; Z.J. Yang et al.~ Acta Metall. Sinica 18 (1982) 21.

but movable

In fact, the existence of such

12.Y.H. Kim eL a l . ,

Phys. Rev. B 38 (1988) 6478.