Hall effect studies of Bi2Sr2CuOx crystals

Hall effect studies of Bi2Sr2CuOx crystals

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Physica C 235-240 (1994) 1387-1388 North.Holland

I-Iall Effect C r y s t a l s



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X. H. Hou, J. W. Li, J. L. Zhang, S. Q. Guo, B. Yin, J. W. Xiong, C. Dong, and Z. X. Zhao National L a b o r a t o r y for S u p e r c o n d u c t i v i t y , I n s t i t u t e of P h y s i c s , Chinese Academy of S c i e n c e s , Beijing, P.O.Box 603, ] 00080, China We h a v e i n v e s t i g a t e d t h e t e m p e r a t u r e d e p e n d e n c i e s of the i n - p l a n e r e s i s t i v i t y a n d t h e Hall c o e f f i c i e n t in BL2Sr2CuO c r y s t a l s a c r o s s the m e t a l - i n s u l a t o r (MI) t r a n s i t i o n , i n the i n s u l a t o r crysta~ at low t e m p e r a t u r e (32 K
I. I n t r o d u c t i o n

Since the d i s c o v e r y of s u p e r c o n d u c t i v i t y in c u p r a t e s m a n y efforts have been made to understand the normal-state p r o p e r t i e s of t h e cuprates. The central concern is w h e t h e r the c o n v e n t i o n a l F e r m i - l i q u i d t h e o r y is valid for the cuprates. It is recognized that the normal-state p r o p e r t i e s a r e anomalous in m a n y r e s p e c t s . Since Bi2Sr2CuOx (Bi2201 hereafter) has lowest critical t e m p e r a t u r e s a m o n g the c u p r a t e s , it is b e s t c a n d i d a t e to s t u d y the normal-state properties of the c u p r a t e s . We will show t h a t Bi2201 has very interesting transport p r o p e r t i e s a t low t e m p e r a t u r e . 2. E x p e r i m e n t a l S i n g l e - c r y s t a l s were g r o w n from a CuO-rich mel~ as d e s c r i b e d in detail e l s e w h e r e . A s - g r o w n cry~ta!~w e r e s u p e r c o n d u c t i n g with T c u p to

7,5 K. A f o u r - t e r m i n a l method was used for resistivity measurements. The Hall c o e f f i c i e n t s w e r e m e a s u r e d b y a dc method a n d the magnetic field was o r i e n t e d p a r a l l e l to t h e c axis. T h e m e a s u r e m e n t s were c a r r i e d o u t with 5 m A d c in a fixed magnetic field of 5 T, We f i n d t h a t a metali n s u l a t o r (MI) t r a n s i t i o n could be i n t r o d u c e d by a n n e a l i n g the c r y s t a l s in Ar a t m o s p h e r e o r vacuum f o r h o u r s ai, 550-650 °C. 3, R e s u l t s and D i s c u s s i o n s The i n - p l a n e r e s i s t i v i t y of Bi2201 c r y s t a l s b e f o r e a n d a f t e r ~FLxi~tiJit~ .... "-~ is s h o w n in Fig. 1 a s a f u n c t i o n of t e m p e r a t u r e . Before a n n e a l i n g the c r y s t a l shows a metallic c o n d u c t i o n a n d a t y p i c a l T - l i n e a r r e s i s t i v i t y is o b s e r v e d , This r e s u l t is c o n s i s t e n t with the earlier report . The l i n e a r i t y of r e s i s t i v i t y maintained e v e n down to o n e v t w e n t i e t h of t h e Debye t e m p e r a t u r e z. It is d i f h c u l t to

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X.H. Hou et al./Physica C 235-240 (1994) 1387-1388

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Fig. 1 T e m p e r a t u r e d e p e n d e n c e P a b O f Bi2201 c r y s t a l s .

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understand this result by the conventional Fermi-liquid theory. The reason for this remarkable ! i n e a r i t y r e m a i n s to be c l a r i f i e d in t h e f u t u r e . A f t e r a n n e a l i n g in Ar a t m o s p h e r e o r v a c u u m for h o u r s a i n s u l a t i n g b e h a v i o r is o b s e r v e d , T h e i n s u l a t i n g b e h a v i o r of t h e p - T c u r v e follows the e q u a t i o n , P=P0 e x p ( T 0 / T ) n. The value of the exponent n determines the nature of the c o n d u c t i o n m e c h a n i s m . We f i n d t h a t the electrical conduction can be d e s c r i b e d well w i t h n = l / 3 b e t w e e n 32 and 115 K, Thus we believe that the 3.6 ~- .....| ....! .... I 3.3 3.0 ,'""""'-. u

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c o n d u c t i o n is d o m i n a t e d b y t h e t w o dimensional (2D) variable-rangeh o p p i r t ~ V R H ) . A p l o t of Ln p vs T " is s h o w n in F i g u r e ~. F i g u r e ~, s h o w s t h e t e m p e r a t u r e d e p e n d e n c e s of t h e Hall c o e f f i c i e n t of t h e Bi2201 b e f o r e and after annealing as a function of t e m p e r a t u r e . It can be seen t h a t t h e Hall c o e f f i c i e n t is t e m p e r a t u r e d e p e n d e n t for both c a s e s . For the a s - g r o w n c r y s t a l we c a n c l e a r l y see t h a t t h e r e is a b r o a d maximum a t a b o u t 90 K. This r e s u l t is a l s ~ c o n s i s t e n t with a n e a r l i e r r e p o r t . H o w e v e r , we find t h a t t h e b r o a d maximum d i s a p p e a r e d in R h - T c u r v e a f t e r a n n e a l i n g . The s i m i l a r r e s u l t s were also observed in other c u p r a t e s . T h u s we s u g g e s t t h a t a b r o a d maximum o r a p e a k a t low t ~ m p e r a t u r e is a common f e a t u r e of all t h e c u p r a t e s u p e r c o n d u c t o r s .

Fig. 3 Logarithm of the low temp%rgt~ure r e s i s t i v i t y a s a f u n c t i o n

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I. X. H. Hou, et al., to a p p e a r in P h y s . R e v . B 50, (1994). 2. S. M a r t i n et al., P h y s . Rev. B 41, (1990) 846. 3. A. P. M a c k e n z i e et al., P h y s . Rev. B 45, (1992) 527.