Resonant dependences of Raman scattering in Y1Ba2Cu3O7−x at different oxygen content

Physica C 185-189 (1991) 1025-1026 North-Holland

RESONANT DEPENDENCES OF RAMAN SCATTERING IN YIBa2 Cu307_ x

O.V.MISOCHKO

AT DIFFERENT OXYGEN CONTENT

, E.YA.SHERMAN +, V.B. TIMOFEEV,

Institute of Solid State Physics, Acad.Sci., 142432 Chernogolovka, Moscow Physical Technical Institute, Dolgoprudny, USSR.

~oscow district,

USSR.

The analysis of resonant properties of Raman scattering revealed "he scattering mechanism. It was suggested to apply resonant Raman scattering for detecting superconducting gap. The technique allow to obtain information on A(k) dependence of superconducting gap.

The

studies

Raman

of

resonant

scattering

by

properties

the

A

g

of

the

phonons

in

YBazCU307_ x (x ~ O.I} have shown that the resonant and

profiles

(RP) o[ zz-polarization

5OOcm "I phonons

practically

contains

1,2

overlap

initial ^ elements ~ y

matrix

small,

since their overlap is of the ~-type. scattering

zz-polarization

for

the

proceeds

mainly

two-band

her characteristic

terms of the electron-phonon

tence of two maxima 4'5. mine

how

the

two

In this study we exa-

maxima

appeared

in

RP

and

discuss what kind of information can be extracted from comparing

tensor shift

RP or normal and supercon-

contribution

to

the

P~

the

by diagonal

interaction 4. The the

polarizability

P ~LX depends most essentially and has

in

after

scheme and is determined

resonance

are

500cm -I phonon

This peculiarity has been elucidated in 3. Anotfeature of RP is the exis-

and

states.

The

The

between

final

for 435

coincide

o-type

on the 04

form:

dA i'.~1 /:' ~Jif (k)-

~' - l / r

)

{1}

ducting states under condition that Raman scatHere

tering mechanism has been determined.

coi~,.{k)

-:,t f i ~ ! ] RP f o r

the

difference

<<~i i ~ i t i , ~ i

in

, i,

the

energies

states,

co -

polarizations

are

obtained

shown

for diffe-

in Fig.l,2.

All

light

experimental

data

are

dependence

of

corrected

the

for

quantum

i/z (Q~<
energy.

An

imaginary

frequency

takes into account of finite width

intermediate

state.

Integration

in

Eq.(1)

fre-

occurs along a part of the Brillouin zone quency

the

light

penetration satisfying

depth. It should be noted that RP for these two crystals lained

the

for YBazCu307_ ~ crystals with oxygen

content x -=0.1 and x~ 0.8 rent

is

~,.

are completely

different.

by the alteration

It is exp-

of electronic

system

the condition

OPz z (~)/OO should E~(kF)-EI(kF) and liege

the

have ~ ~

Ef(k)~EF.

Therefore,

singularities

at

Ef(A~-n}-Ei(k=~).

first maximum

(BZ)

,~

We be-

of RP is related

to

after oxygen chain removal. the first singu]aritv, To

describe proposed in 3

RP we

proceed

from

As an

initial

state

the

model [or

ponsible is chosen cienc%

o h , an odd

of

combination

04-p z orbita]s.

The

{( L ~

Denoting

matrix

element

~,

contributed

mainly

and the second is res-

by

A

the

a

sharp

increase

in

~aman

effi-

i n the ~-~nerqv_ r e , w e

,:.. 5e% ~',¢.~,~d!na "~

iff(k}

the

fi(i)-co!

_

[,:)t

.

resonauc¢

.

a':

the Fermi surface {FS) and at the band top (~'r) transitions dy2_z2,

from the initial state to the Cul-

d3z2_r2

orbitals

, is large,

since

in zz polarization we g e t :

it i [/( ~aF A ) 2

AvH Foundation research fellow. The address: ~alther-geiSner Institut f~r peraturforschung, 8046 Garching, FRG

092t-4534f91/$03.50 ©

1991

present Tieftem-

Elsevier Science Publishers B V .

zz

A,I ~ights

(

,.)

<~ t %

rc::cp,,.:J.

~"

[

~tA 3

<

-',':-

j' z~:

~

~A >> l

"C& <<

i

1026

Misochko et aL / Raman scattering bz Y1Ba2Cu307...:at different oxygen content

O. E

2.4

47S

crn-'

475

1.8

era-'

Q

o

1.2

500

20

/m-'

10

0.6 ~

/

t~,~¢;3~--~"

-- . . . . . .

. . . . . .

0.0 12-

0

----

~2~

~,

9"

6"

4

,5" 0

142

2.0

e m '-~

1.5

~4 ~

o ~,~-'

I 5

er,~-'

146;

c r,~-'

1.0 racm~-~-

-rm-

~D

1.0

0.5

o.q

2.2

2.6 energE,

Photon

0.0

5.0

0.4-

eV

Fig.l. Resonant profiles of Raman scattering taken at room temperature for (xx+yy) -polarization of YBa Cu 0 (- - - x--=O.l, - - ~-~0,8). 2 3 7-x

0.2

0"01

Here

~F

is

effective

the

Fermi

carriers

velocity

mass.

The

and

-

m

resonance

~

the

2.6

2.2 on

Phot

6

3.0

energy,

eV

in the Fig.2. The same as Fig. I for zz-po]arization.

second case

should

to the first

be more

case)

strong

(as compared

due to a higher

We have thus explained

degree of

maxima

in the denominator. Analyzing conside~

Iab

[or

the

500cm -~

phonon

we

with

the

case

when

electric

vector

is

second

only

along the chains. an qh-even the

energy

earlier. under

As an initial

combination close

The

of

to

final

Ei

the

state

consideration

of

state we choose

04-p z orbitals

is I

adopted

with

by

us

the

same

as

. The

main

contri-

that

ZZ

bution between

to

I

here

YY the orbitals

described

by

comes

from

the

o[ 04 and

the n-type

the t r a n s i t i o n s

proceed between

~"~,,~ r e f e r r i n g

to

by

eik,

factors

the

BZ e d g e .

FS

fyy(c~)

a

and

M z are

the

functions

Y~'

....

~

the

"-~t turns

this

the

case

for

/zzCOS 4 (k r / 2 )

matrix

~ m/& a t

For

the resonance

r A ~1 and

I

yy

at

orbitals

of

~ mr a t

to

the

comparing

range

where

dominate,

detect

is

at

dif[erent

of

and In

profiles

states

the this

~or

in the energy

the

Fermi

in

principle,

to

superconducting

gap,

possible,

opening

the

top.

resonant

transitions

it

surface, band

of two

associated

polarizations

on s u p e r c o n d u c t i n g

we

gap

surface

may o b t a i n

a~isotropy.

1, O.V. M i . s o c h k o , ~ i z , [ v l e l a 31 ( 1 9 8 9 ) 280 /Soviet P h y~s. . o o l j d Sta~.e 31 ( t 9 8 9 ) 1998/

~. . . . " zero

at

~es~mance

at

to

taken

the

that

Fermi

is

Since

(My M z )~ , here M v

elements

the

the existence maximum

normal and superconducting

information

are

first

to

with

case carefully

, which

~

,~ ~ c o s ( k / 2 ) y

one

Studying

element.

The

transition

transitions

on

5T we get

r & <~1.

"

He~;'en

~-. i ,

i,n {;S,} ~.,.', }.

O.V.Misochkc

~.£ ~i et !i.i~;~,~'~ ,

i.;.

al,, <

in: ,~i.,

~,~shba

5pr~nqor SV 1 9 9 0 , ;~

a[.,

wave

of Ol and 04 and of 04 and {Zui, ~es-

pectively. I

In

~

Ol

matrix

in RP.

4.

O.V.

N~9ochk,x~

Z h . [ ] x p . ~ ' e ~ l . ~ : i ::.

a~ixJ [ . ' { a .

'::;9 (i

9~;

~]hernia~'~,

117

Series p.}2,1 Physics