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Superconductivity in La2CuO4 under pressure: two step superconducting transition and decrease in Tc with pressure
Journal of Magnetism and Magnetic Materials 104-107 (1992) 515-516 North-Holland
Superconductivity in La2CuO 4 under pressure" two step superconducting transition and decrease in Tc with pressure M. Kurisu
", S. M a t s u d a
b,
T. Suzuki
b and T. Fujita b
" Faculty of Engineering, lwate Unicersity, Morioka 020, Japan h Faculty of Science, Hiroshima Unit'ersity, Hiroshima 7.70, Japan We have observed anomalous pressure dependences of the resistance and the superconducting transition temperature T,. in La2CuO 4 to 17 kbar. With pressure, T~ first decreases, then takes a minimum at 3 kbar and finally increases at a rate of 0.5 K/kbar. Some likely origins are briefly discussed for a two-step superconducting transition and negative/positive dT~/dP. R a t h e r divergent e x p e r i m e n t a l results have b e e n given on the pressure d e p e n d e n c e of superconductivity in L a 2 C u O 4 [1-5]. A n increase of Tc with applied pressure is generally agreed, but the m a g n i t u d e of the pressure derivative of T~, d T J d P , is b e t w e e n 0.23 and 1 K / k b a r . In this paper, we report the effects of pressure on T~ in polycrystalline samples by the electrical resistance m e a s u r e m e n t . In particular, a two-step superconductive resistive transition and a shift of T~ with pressure to lower t e m p e r a t u r e s are p r e s e n t e d a n d some likely origins are briefly discussed. T h e polycrystalline L a 2 C u O 4 sample was p r e p a r e d by a solid state reaction. A stoichiometric mixture of L a z O 3 and C u O (99.99% purity) powders was g r o u n d in an agate mortar, fired in an almina crucible at 900 o C for 28 h and slowly cooled to room t e m p e r a t u r e in air. A f t e r t h r e e times grindings and h e a t - t r e a t m e n t procedures, the mixture was cold-pressed into a pellet, fired at 1 0 5 0 ° C for 15 h, at l l 0 0 ° C for 24 h and then slowly cooled in the furnace. T h e two r e c t a n g u l a r sampies (no. 1 and no. 2) of 1 x 1 × 3 m m 3 were cut from the same pellet• T h e electrical resistance was m e a s u r e d by the fourp r o b e m e t h o d in which b o t h voltage a n d c u r r e n t wires were a t t a c h e d by using ultrasonic solder• T h e sample was m o u n t e d inside the teflon cell of a self-clamp piston cylinder high-pressure device. As a hydrostatic pressure m e d i u m a 1 : 1 mixture of isoamyl alcohol and n - p e n t a n e was used. A Au + 0.07 a t % F e / c h r o m c l t h e r m o c o u p l e was a t t a c h e d inherently to the cylinder to m o n i t o r the t e m p e r a t u r e • Fig. 1 shows the t e m p e r a t u r e d e p e n d e n c e of the resistance R for LaECUO 4 no. 1 and no. 2 at various pressures a n d low t e m p e r a t u r e s . A n interesting result for P = 1 bar is that s u p e r c o n d u c t i n g state is achieved t h r o u g h a two-step transition: (a) the first resistance m a x i m u m at 47 K, (b) the second gradual increase in R below 42 K and (c) final large drop. A C m a g n e t i c susceptibility m e a s u r e m e n t shows only a very obscure sign of d i a m a g n e t i s m below ~ 40 K implying filamentary s u p e r c o n d u c t i v e n a t u r e of the sample. W h e n the
pressure is applied, the two-step transition b e c o m e s a single m a x i m u m in the R ( T ) curve. O f f u r t h e r interest in our samples u n d e r pressure is the unusual pressure d e p e n d e n c e of the superconducting transition t e m p e r a t u r e Tc, as shown in fig. 2. O n e can discern two pressure ranges. Below ~ 3 kbar, a clear shift of Tc to lower t e m p e r a t u r e s with pressure can be seen. T h e reduction in Tc with the applied pressure is the first observation for L a 2 C u O 4 and d o p e d system (La I .~Mx)2CuO 4 ( M = S r and Ba). l
i
3.1 k b a r ~ :'..-T~.. • ..-
5-I
...
k bor.~:"
"-::..
6.9 k bor,~." ;"-"~.~:,. 9.1k bar ~ .~i"'-'):;. 1 bar-
:" :" i.r'"-~'".i~?".'. .. -.-
,.,
..
::;' ":
La2Cu 0 4 #1,2
'" :":
"~-.:12.0kbar
; :16.9kbar
•...
.2
.
.. ::;..
v
"% '..~
:; i"/"~""i~ ""'
!'(if
c" 3
....:...
.. -.~.....::~
,. -
•
.
.. ;.;:. 1 : .~ .. : ; :
J
:7S:
/ oW , , , . ~ 20
/,: ' -. 30
40
50
Temperature ( K )
Fig. 1. Temperature dependence of resistance R of La2CuO 4 samples no. l and no. 2 at various pressures and low tempera -
0312-8853/92/$05.00 ¢7 1992 - Elsevier Science Publishers B.V. All rights reserved
tures.
516
M. Kurisu et al. / Superconductivity in La 2CuO 4 under pressure
46
'La2C u~n4
42 E 4O
~v38 36
o,P onset ~ . midpoint
34
0
'
1'0
Pressure
' (k be, r)
2JO
Fig. 2. Pressure dependence of superconducting transition temperature T~,, onset (circle) and midpoint (triangle), of La2CuO 4 samples no. 1 (open symbols) and no. 2 (solid symbols).
Above ~ 5 kbar, a rapid and linear increase in T~ is found. T h e pressure derivatives of T~ are + 0 . 4 0 K / k b a r for the onset and + 0 . 5 0 K / k b a r for the midpoint T c, showing a narrowing of the superconductive resistive transition. It is also worthy of note that the decrease in T~ for low pressures is reversible against p r e s s u r e / t e m p e r a t u r e cycling. We a c c u m u l a t e d the data for samples no. 1 and no. 2 on the pressure-releasing run and pressure-reincreasing run as well. T h e results are quitc reproducible. T h e T~ e n h a n c e m e n t by pressure is c o m p a r e d with those of previous works; A linear increase in T~ at a rate of + 0 . 2 6 K / k b a r [1], + 1 K / k b a r [2], + 0.5 K / k b a r [3], + 0.23 K / k b a r [5] and a quadratic increase with pressure [4]. The sign reversal with pressure of d T j d P a r o u n d 3 kbar seems to be intimately associated with r e m a r k a b l e change in the shape of the R ( T ) curve to a single peak near Tc. O n e possible picture for the negative and positive d e p e n d e n c e of T~ on pressure is a strong pressure d e p e n d e n c e , such as a competing one, of superconductivities of multi-phases with different T~. An extrapolation of the onset T~. data above 3 kbar to P = 0 yields T c of 38 K. We suppose that this low-T~ of 38 K is masked by high-T~ of 42 K and 47 K at P = 0. C o m p e t i t i o n between favored and unfavored supercon-
ductivities with pressure (one increasing low-T~, and the o t h e r decreasing high-Tc) would give rise to the minim u m in T~. at low pressure which is observed. A twostep transition at P = 0 may be also well explained in this scheme. Two o t h e r possibilities seem to exist for explanation to a two-step transition. O n e is intra- and inter-grain s u p e r c o n d u c t i n g transitions. As the temperature is lowered, the intra-grain s u p e r c o n d u c t i n g transition takes place before the inter-grain transition does. It is, however, difficult to explain the T~.(P) unless we assume complex pressure d e p e n d e n c e s of these terms. T h e o h t c r is a lattice instability at T = 36 K [6] which may be closely related with the superconductivity in the sample. But, we c a n n o t speculate which part of the resistive anomalies c o r r e s p o n d s to 7~. In summary,, we havc observed for the first time the decrease in T,, with the applied pressure for L a 2 C u O 4. After a m i n i m u m in T~, at 3 kbar a rapid increase in 77. follows. A two-step superconductive resistive transition is also an interesting aspect in L a 2 C u O 4.
References [1] J. Beille, R. Cabanel, C. Chaillout, B. Chevalier, G. Dcmazeau, F. Deslandes, J. Etourneau, P. Lejay, ('. Michel, J. Provost, B. Raveau, A. Sulpice, J.L. Tholencc and R. Tournier, C.R. Acad. Se. Paris 304 II (1987) 1097. [2] P.M. Grant, S.S.P. Parkin, V.Y. Lee, E.M. Engler, M.L. Ramirez. J.E. Vazquez, G. Lim and R.D. ,lacowitz. Phys. Rev. Lett. 58 (1987) 2482. [3] J. Beille, B. Chevalier, G. Demazeau, F. Deslandes, J. Etourneau, O. Laborde, C. Michel, P. Lejay, J. Prow)st. B. Raveau, A. Sulpice, J.L. Tholence and R. Tournier, Physica B 146 (1987) 307. /4] M.C. Aronson, S-W. Cheong, F.H. Garzon, J.D. Thompson and Z. Fisk, Phys. Rev. B 39 (1989) 11445. [5] J. Beille, G. Demazeau, H. Dupendant, J. Etourneau, P. Lejay A. Sulpice and R. Tournier, Physica C 157 (1989) 446. [6] M. Lang, F. Steglich, R. Schefzyk, T. Lechner, H. Spillc, H. Rietschel, W. Goldacker and B. Renker, Europhys. Lett. 4 (1987) 1145.
Superconductivity in La2CuO 4 under pressure" two step superconducting transition and decrease in Tc with pressure M. Kurisu
", S. M a t s u d a
b,
T. Suzuki
b and T. Fujita b
" Faculty of Engineering, lwate Unicersity, Morioka 020, Japan h Faculty of Science, Hiroshima Unit'ersity, Hiroshima 7.70, Japan We have observed anomalous pressure dependences of the resistance and the superconducting transition temperature T,. in La2CuO 4 to 17 kbar. With pressure, T~ first decreases, then takes a minimum at 3 kbar and finally increases at a rate of 0.5 K/kbar. Some likely origins are briefly discussed for a two-step superconducting transition and negative/positive dT~/dP. R a t h e r divergent e x p e r i m e n t a l results have b e e n given on the pressure d e p e n d e n c e of superconductivity in L a 2 C u O 4 [1-5]. A n increase of Tc with applied pressure is generally agreed, but the m a g n i t u d e of the pressure derivative of T~, d T J d P , is b e t w e e n 0.23 and 1 K / k b a r . In this paper, we report the effects of pressure on T~ in polycrystalline samples by the electrical resistance m e a s u r e m e n t . In particular, a two-step superconductive resistive transition and a shift of T~ with pressure to lower t e m p e r a t u r e s are p r e s e n t e d a n d some likely origins are briefly discussed. T h e polycrystalline L a 2 C u O 4 sample was p r e p a r e d by a solid state reaction. A stoichiometric mixture of L a z O 3 and C u O (99.99% purity) powders was g r o u n d in an agate mortar, fired in an almina crucible at 900 o C for 28 h and slowly cooled to room t e m p e r a t u r e in air. A f t e r t h r e e times grindings and h e a t - t r e a t m e n t procedures, the mixture was cold-pressed into a pellet, fired at 1 0 5 0 ° C for 15 h, at l l 0 0 ° C for 24 h and then slowly cooled in the furnace. T h e two r e c t a n g u l a r sampies (no. 1 and no. 2) of 1 x 1 × 3 m m 3 were cut from the same pellet• T h e electrical resistance was m e a s u r e d by the fourp r o b e m e t h o d in which b o t h voltage a n d c u r r e n t wires were a t t a c h e d by using ultrasonic solder• T h e sample was m o u n t e d inside the teflon cell of a self-clamp piston cylinder high-pressure device. As a hydrostatic pressure m e d i u m a 1 : 1 mixture of isoamyl alcohol and n - p e n t a n e was used. A Au + 0.07 a t % F e / c h r o m c l t h e r m o c o u p l e was a t t a c h e d inherently to the cylinder to m o n i t o r the t e m p e r a t u r e • Fig. 1 shows the t e m p e r a t u r e d e p e n d e n c e of the resistance R for LaECUO 4 no. 1 and no. 2 at various pressures a n d low t e m p e r a t u r e s . A n interesting result for P = 1 bar is that s u p e r c o n d u c t i n g state is achieved t h r o u g h a two-step transition: (a) the first resistance m a x i m u m at 47 K, (b) the second gradual increase in R below 42 K and (c) final large drop. A C m a g n e t i c susceptibility m e a s u r e m e n t shows only a very obscure sign of d i a m a g n e t i s m below ~ 40 K implying filamentary s u p e r c o n d u c t i v e n a t u r e of the sample. W h e n the
pressure is applied, the two-step transition b e c o m e s a single m a x i m u m in the R ( T ) curve. O f f u r t h e r interest in our samples u n d e r pressure is the unusual pressure d e p e n d e n c e of the superconducting transition t e m p e r a t u r e Tc, as shown in fig. 2. O n e can discern two pressure ranges. Below ~ 3 kbar, a clear shift of Tc to lower t e m p e r a t u r e s with pressure can be seen. T h e reduction in Tc with the applied pressure is the first observation for L a 2 C u O 4 and d o p e d system (La I .~Mx)2CuO 4 ( M = S r and Ba). l
i
3.1 k b a r ~ :'..-T~.. • ..-
5-I
...
k bor.~:"
"-::..
6.9 k bor,~." ;"-"~.~:,. 9.1k bar ~ .~i"'-'):;. 1 bar-
:" :" i.r'"-~'".i~?".'. .. -.-
,.,
..
::;' ":
La2Cu 0 4 #1,2
'" :":
"~-.:12.0kbar
; :16.9kbar
•...
.2
.
.. ::;..
v
"% '..~
:; i"/"~""i~ ""'
!'(if
c" 3
....:...
.. -.~.....::~
,. -
•
.
.. ;.;:. 1 : .~ .. : ; :
J
:7S:
/ oW , , , . ~ 20
/,: ' -. 30
40
50
Temperature ( K )
Fig. 1. Temperature dependence of resistance R of La2CuO 4 samples no. l and no. 2 at various pressures and low tempera -
0312-8853/92/$05.00 ¢7 1992 - Elsevier Science Publishers B.V. All rights reserved
tures.
516
M. Kurisu et al. / Superconductivity in La 2CuO 4 under pressure
46
'La2C u~n4
42 E 4O
~v38 36
o,P onset ~ . midpoint
34
0
'
1'0
Pressure
' (k be, r)
2JO
Fig. 2. Pressure dependence of superconducting transition temperature T~,, onset (circle) and midpoint (triangle), of La2CuO 4 samples no. 1 (open symbols) and no. 2 (solid symbols).
Above ~ 5 kbar, a rapid and linear increase in T~ is found. T h e pressure derivatives of T~ are + 0 . 4 0 K / k b a r for the onset and + 0 . 5 0 K / k b a r for the midpoint T c, showing a narrowing of the superconductive resistive transition. It is also worthy of note that the decrease in T~ for low pressures is reversible against p r e s s u r e / t e m p e r a t u r e cycling. We a c c u m u l a t e d the data for samples no. 1 and no. 2 on the pressure-releasing run and pressure-reincreasing run as well. T h e results are quitc reproducible. T h e T~ e n h a n c e m e n t by pressure is c o m p a r e d with those of previous works; A linear increase in T~ at a rate of + 0 . 2 6 K / k b a r [1], + 1 K / k b a r [2], + 0.5 K / k b a r [3], + 0.23 K / k b a r [5] and a quadratic increase with pressure [4]. The sign reversal with pressure of d T j d P a r o u n d 3 kbar seems to be intimately associated with r e m a r k a b l e change in the shape of the R ( T ) curve to a single peak near Tc. O n e possible picture for the negative and positive d e p e n d e n c e of T~ on pressure is a strong pressure d e p e n d e n c e , such as a competing one, of superconductivities of multi-phases with different T~. An extrapolation of the onset T~. data above 3 kbar to P = 0 yields T c of 38 K. We suppose that this low-T~ of 38 K is masked by high-T~ of 42 K and 47 K at P = 0. C o m p e t i t i o n between favored and unfavored supercon-
ductivities with pressure (one increasing low-T~, and the o t h e r decreasing high-Tc) would give rise to the minim u m in T~. at low pressure which is observed. A twostep transition at P = 0 may be also well explained in this scheme. Two o t h e r possibilities seem to exist for explanation to a two-step transition. O n e is intra- and inter-grain s u p e r c o n d u c t i n g transitions. As the temperature is lowered, the intra-grain s u p e r c o n d u c t i n g transition takes place before the inter-grain transition does. It is, however, difficult to explain the T~.(P) unless we assume complex pressure d e p e n d e n c e s of these terms. T h e o h t c r is a lattice instability at T = 36 K [6] which may be closely related with the superconductivity in the sample. But, we c a n n o t speculate which part of the resistive anomalies c o r r e s p o n d s to 7~. In summary,, we havc observed for the first time the decrease in T,, with the applied pressure for L a 2 C u O 4. After a m i n i m u m in T~, at 3 kbar a rapid increase in 77. follows. A two-step superconductive resistive transition is also an interesting aspect in L a 2 C u O 4.
References [1] J. Beille, R. Cabanel, C. Chaillout, B. Chevalier, G. Dcmazeau, F. Deslandes, J. Etourneau, P. Lejay, ('. Michel, J. Provost, B. Raveau, A. Sulpice, J.L. Tholencc and R. Tournier, C.R. Acad. Se. Paris 304 II (1987) 1097. [2] P.M. Grant, S.S.P. Parkin, V.Y. Lee, E.M. Engler, M.L. Ramirez. J.E. Vazquez, G. Lim and R.D. ,lacowitz. Phys. Rev. Lett. 58 (1987) 2482. [3] J. Beille, B. Chevalier, G. Demazeau, F. Deslandes, J. Etourneau, O. Laborde, C. Michel, P. Lejay, J. Prow)st. B. Raveau, A. Sulpice, J.L. Tholence and R. Tournier, Physica B 146 (1987) 307. /4] M.C. Aronson, S-W. Cheong, F.H. Garzon, J.D. Thompson and Z. Fisk, Phys. Rev. B 39 (1989) 11445. [5] J. Beille, G. Demazeau, H. Dupendant, J. Etourneau, P. Lejay A. Sulpice and R. Tournier, Physica C 157 (1989) 446. [6] M. Lang, F. Steglich, R. Schefzyk, T. Lechner, H. Spillc, H. Rietschel, W. Goldacker and B. Renker, Europhys. Lett. 4 (1987) 1145.