Proton NMR spectra of hydrogen-doped superconductor YBa2Cu3O6.94Hx

Phys|ca C 185-189 (1991) 1133-1134 North-Holland

PROTON N ~ SPECTRAOF HYDROGEN-DOPEDSUPERCONDUCTORYBa2Cu306.94Hx H, NIKI, H. KYANa, T, SHINO~ARAb, S, TOMIYOSHIb, M. OMORIb, T. KAJITANIb, T, SATOband R, IGEI Department of Physics, Division of General Education, University of the Ryukyus, Nishihara, Okinawa 903-01, Japan aDepartment of Physics, College of Science, University of the Ryukyus, Nishihara, Okinawa 903-01, apan I n s t i t u t e for Materials Research, Tohoku University, Sendal 980, Japan

~

Proton NMR spectra have been measured in powdered samples of YBa2Cu30694H0.20 (YBHO,2) and YBa2Cu306,g4Ho,s3 (YBHO,S3) from 60 K to 300 K using FT NMR. Above Tc, the'FT NMR spectrum has a single resonance peak, Below Tc, i t begins to s p l i t into double peaks, The separation of the peaks increases with decreasing temperature, reaching about lO Oe at 70 K in YBHO.2 and about 50e at 60 K in YBHO.53, The separation of YBHO.53 is smaller than that of YBHO,2, This difference is caused by that of the penetration depth of the magnetic f i e l d in each superconducting state. The properties of YBazCu307_6Hx are dependent upon the

concentration of the

atoms. 1 carry

doped hydrogen

S i n c e the spin of IH is I/2,

out

proton NMR without

any complexity

coming from the quadrupole effect. proton

we can

Therefore,

NMR is one of the most powerful experi-

measured between 60 and 300 K.

The spectra

for

YBHO.2 and YBHO.53 at several temperatures are shown in Fig. I. are obtained widths

are

YBHO.53 at

The spectra with a single peak

in the normal state. 2.5

The line

Oe in YBHO.2 and 1.5 Oe in

lO0 K and are very

sharp in

both

mental methods for microscopic investigation of

samples at 300 K.

the effect of doped hydrogen atoms.2-5

shifts by about 50 ppm in YBHO.2 and about 20 ppm in YBHO.53 to higher frequency from that of

An NMR study5 indicated

that

proton

NMR

The resonance line at 300 K

spectra and i t s temperature dependence gave the

the

important information of the distribution of

the normal state are consistent with the

magnetic f i e l d

ous results. 2,4

in

the

superconducting state

caused by the magnetic vortices and the penetration that

depth in YBa2Cu307-6 (YBCO) system, and measurementsof i t s concentration depen-

reference sample of water,

the

tion

the

further are

Therefore,

investigations of proton

NMR spectra

carried

out

for

powdered samples of

YBa2Cu306.94Ho.20 (YBHO.2) with onset Tc of 92 K and YBa2Cu306.94Ho.53 (YBHO.53) with onset Tc of 90 K by using Fourier Transform (FT) NMR. NMR spectra

are obtained by using FT NMR in

which a phase-coherent pulsed

spectrometer

is

employed with a resonance frequency of about

33

MHz (the resonance f i e l d of about 7700 Oe). NMR spectra of IH in

YBHO.2and YBHO.53 are

0921-4534/91/$03.50 © 1991 - Elsevier Science Publishers B.V.

previ-

I t should be noticed that

peaks from the peak in the normal state

shown in Fig. 2.

detail,

in

spectra are s p l i t into two peaks below Tc, The temperature dependenceof deviation of

dence were necessary to understand the d i s t r i b u of magnetic f i e l d in

The signals

Below Tc, the

peaks increases with

separation

is of

decreasing tempera-

ture, reaching about I 0 0 e at 70 K in YBHO.2 and about 50e at 60 K in YBHO.53. The shifts of both resonance peaks are associated with the superconductivity. The separation of ¥BH0.53 is smaller than that of YBHO.2. This difference results the

from that of the penetration depth of

magnetic field

in

each supercor,Jucting

state. This s p l i t implies emergence of two d i s t i n c t environments for the hydrogen atoms: one is

All rigtlts reserved.

in

I 134

H, Mild et aL / Proton NMR specvz=

(a)

j~X=0.2

.J

Jl, l\

(b)

A~

~, Q08 "~ Q06 ~. 0.04

X:0,53

',~ O92

,,,-"/At

I

o!

"u-.

:C-0,02

--,,.-tttL

,~-OJ}4

~-1106' n

.....

.-

3289~5 3309EB 32895.5 33095.5 FREQUENCY(kHz) FREQUENCY{WHz) Figure I Proton NMR spectra in YBa2Cu306,94Hx at several temperatures, (a) x = 0,20, (b) x = 0,53, the superconducting region outside core, while the other is in the The conventional

o X=0.2 " X=0.53

the

vortex

vortex core,

Meissner shielding

currents

-0,08

,,

7'0

I

90

('t"

,

"300

T(K) Figure 2 Temperature dependence of the peak-shift A~/~ of spectra of IH in YBa2Cu306,~4Hx (x = 0:20~nd 0,53). v i~ the resonance frequency a~ ~uu ~ in normal state and A~ is the deviation of the peak-frequency from v in both samples, The positive value of A~/~ corresponds to the higher magnetic f i e l d .

induce the additional field to make the magnetic field lower in the former region, and higher

in

that

in the conventional

type-If

tors, resulting in symmetrical double-peaks,

the latter vortex core, In the conventional type-If

superconductors

such as Nb and V metals with

the

triangular

This work is Grant-in-Aid

partly

supported by the

for Science Research on Priority

lattice of vortices, majority of the resonance nuclei sense the low~r fields caused by Meissner shielding currents, 6 Therefore, lower-side peak

Areas from the Ministry of

- : the resonance line appears intensively compared with higher-side one, resulting in asymmetry of the resonance line, However, the spectra with double peaks are almost symmetrical as shown in Fig, I, The amounts of hydrogen atoms in the lower fields are almost equal to those in the higher fields in YBHO.2 and YBHO.53, YBCOconsists of two Cu layers, According to NMR studies, 2,3 hydrogen atoms are trapped in the v i c i n i t y of C,J(!) site. The essential point is that Cu(2) layers are strongly superconductive compared with Cu(1) ones and vortices prefer to pass through Cu(1) layers rather than Cu(2) one~ The majority of protons exist in the vortex region and sense higher fields. Therefore, the higher side of the double peaks appears rather strongly than

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