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Transport properties in superconducting oxides Bi2−xPbxCa2Sr2Cu3Oy system
PhysicaC 162-164 (1989) 1197-1198 North-Holland
TRANSPORT PROPERTIES
IN SUPERCONDUCTING
OXIDES Bi2_xPbxCa2Sr2CU3Oy
SYSTEM
Qirui ZHANG 1,2, Jiansheng XIA I, Zhenhui HE I, Minghu FANG I, Shunxi WANG 1 and Zuyao CHEN 3 I. D e p a r t m e n t of P h y s i c s a n d 3. D e p a r t m e n t Technology of China, Hefei, Anhui, P.R. China
of A p p l i e d
2. Department of Physics,
Hangzhou, P.R. China
Zhejiang University,
Chemistry,
University
of Science
and
Transport properties of Bi2_xPbxCa2Sr2Cu30y (x=0, 0.2, 0.4 and 0.6) were investigated by means of measuring Hall coefficient between Tc up £o 300K. The experimental results show that the carrier density n H is linearly T-dependent, e.g. the formula nx(T)=n o (l+aT) is well satlsified in normal state, n H decreases intensely with increasing Pb content, and does not vary with the magnetic fields. The results are compared with a recent theoretical calculation.
Samples were prepared by the conventional ceramic powder technique as reported by Chen et al I . The s a m p l e s w e r e cut into p l a t e l e t s 12x3x0.7 mm 3. The Hall voltages were m e a s u r e d by a standard four-probe method in the magnetic f i e l d up to 5 Tesla. The m e a s u r i n g current density is about 2 Acm -2 . i. Carrier density n H =i/eP~ For all samples (x = 0, 0.2, 0.4 and 0.6), the Hall coefficient R H is positive from Tc up to 300K. It is f o u n d that Hall number n x is linearly T-dependent in normal state, the f o r m u l a nH(T) = no(l+aT) is well satisfied, where n o and a are two different constant listed in table I for each sample. Fig.l shows the temperature d e p e n d e n c e of n x for x=0 a n d 0.4. This result is in agreement with the t w o - b a n d model with an exterior carrier source proposed
3.9
°
I
3.5
~/'--
• x=0,4
1.5
!
,
1.3
0
%
• 250K 150K
o
o 0.5
012
I
I
0.6
Pb CONTENT
FIGURE 2 Hall number n H as a function of the lead content in the samples for fixed temperature.
Table I the related parameters x
no(1021cm-3)
a(K -I)
Tx*ITo*
0
1.95
0.0034
1
0.2
0.82
0.0056
0.51
0.4
0.41
0.0109
0.24
0.6
0.38
0.0120
0.16
1.1 "-~ t-
~3.1 2.7
0.9 I00
150
200
250
300
T, K
FIGURE 1 Temperature dependence of carrier concentration density, circal for x=0 and dot for x=0.4.
0921 --4534/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland)
by Xing et al 2 recently. In their model, Hall number of the t w o - d i m e n s i o n a l C u - O p l a n e s is given by n x = n o (0) (1+T/T*) (I) and T* = cIN~ l(me+m h ) (2) where N I represents for density of the localized states; d for c - a x i s ; m e a n d m h a r e the effective mass of electroDs and holes. From (2)
1198
Q. Zhang et al. /
Superconducting oxides Bi 2_ ~.PbxCa;Sr2Cu~Oysystem
and assumption m e = m h, N 1 declines sharply with increase of Pb content in the sample as shown in Table I. This is q u i t e r e a s o n a b l e if we interpret N 1 as the contribution of the oxygen vacancies. The partial substitution of Pb 4÷ for Bi 3+ leads to a decrease of vacancies in oxygen deficient material. In addition, we can get dnH/dT a or I/N 1 from (i), this is also fitted to the experimental data as listed in Table I. 2. Relation between hE(T) and lead content n H decreases quickly at small x and slowly at large x. This p h e n o m e n o n can be e x p l a i n e d in terms of the substitution of Pb 4÷ for Bi 3÷. If the oxygen vacancies are fixed in two samples a n d the h o l e s are c o n t r i b u t e d by o x y g e n vacancies, then the P b - d o p e d sample contains fewer h o l e s r e l a t i v e l y . Therefore, this substitution leads to the hole carrier density decreasing with increasing Pb content. To some extent, this is s i m i l a r to the case of ReBa2Cu3OT_y 3, where the density of holes is qualitatively controlled by chemical doping with oxygen. In addition, the l o c a l i z e d energy
3.Hall coefficient R s Hall voltages V~ vs. applied magnetic fields for the samples (x=0 and 0.4) is reproduced in Figure 3. It shows that V H is proportional to the magnetic field and the curves possibly pass through the origin. This means that the Hall coefficient R ~ o r the carrier concentration nH in magnetic field up to 5T is field-independent for temperature above Tc. In addition, according to the semi-classical single band model, in the Bicuprate the f i e l d - i n d e p e n d e n c e of K H implies that the Fermi Surface may be a c o m p l e t e l y closed one and there is no asymmetric magnetic s c a t t e r i n g mechanism, which was p r o p o s e d to explain the e x t r a o r d i n a r y Hall e f f e c t in YBa2Cu307_y superconductors by Fiory et al. 4 REFERENCE i. J. Chen, Z.Y. Chen et al., SOlid State Comm. Vol. 68, (1988) 327. 2. D.Y. Xing and C.S. Ting, Phys. Rev. Vol. 38, No.7, (1988) 5134. 3. N.P. Ong, Z.Z. Wang et al., Phys. Rev. B35, (1987) 8807. 4. A.T. Fiory and G.S. Grader, To appear in Physical Review B, Brief Reports (1988).
o ×=0.4
/o
• x=0
/o.~O
•,•.5 > 0 0
I
2 3 4 5 M A G N E T I C FIELD, fe~a
6
FIGURE 3 Hall v o l t a g e V H as a function of the a p p l i e d magnetic field for fixed temperature.
levels t r a n s f e r to carrier bands in terms of Xing's model as described above. The decrease in the density of localized state induced by Pb doping leads to a d e c r e a s e of the h o l e concentration.
TRANSPORT PROPERTIES
IN SUPERCONDUCTING
OXIDES Bi2_xPbxCa2Sr2CU3Oy
SYSTEM
Qirui ZHANG 1,2, Jiansheng XIA I, Zhenhui HE I, Minghu FANG I, Shunxi WANG 1 and Zuyao CHEN 3 I. D e p a r t m e n t of P h y s i c s a n d 3. D e p a r t m e n t Technology of China, Hefei, Anhui, P.R. China
of A p p l i e d
2. Department of Physics,
Hangzhou, P.R. China
Zhejiang University,
Chemistry,
University
of Science
and
Transport properties of Bi2_xPbxCa2Sr2Cu30y (x=0, 0.2, 0.4 and 0.6) were investigated by means of measuring Hall coefficient between Tc up £o 300K. The experimental results show that the carrier density n H is linearly T-dependent, e.g. the formula nx(T)=n o (l+aT) is well satlsified in normal state, n H decreases intensely with increasing Pb content, and does not vary with the magnetic fields. The results are compared with a recent theoretical calculation.
Samples were prepared by the conventional ceramic powder technique as reported by Chen et al I . The s a m p l e s w e r e cut into p l a t e l e t s 12x3x0.7 mm 3. The Hall voltages were m e a s u r e d by a standard four-probe method in the magnetic f i e l d up to 5 Tesla. The m e a s u r i n g current density is about 2 Acm -2 . i. Carrier density n H =i/eP~ For all samples (x = 0, 0.2, 0.4 and 0.6), the Hall coefficient R H is positive from Tc up to 300K. It is f o u n d that Hall number n x is linearly T-dependent in normal state, the f o r m u l a nH(T) = no(l+aT) is well satisfied, where n o and a are two different constant listed in table I for each sample. Fig.l shows the temperature d e p e n d e n c e of n x for x=0 a n d 0.4. This result is in agreement with the t w o - b a n d model with an exterior carrier source proposed
3.9
°
I
3.5
~/'--
• x=0,4
1.5
!
,
1.3
0
%
• 250K 150K
o
o 0.5
012
I
I
0.6
Pb CONTENT
FIGURE 2 Hall number n H as a function of the lead content in the samples for fixed temperature.
Table I the related parameters x
no(1021cm-3)
a(K -I)
Tx*ITo*
0
1.95
0.0034
1
0.2
0.82
0.0056
0.51
0.4
0.41
0.0109
0.24
0.6
0.38
0.0120
0.16
1.1 "-~ t-
~3.1 2.7
0.9 I00
150
200
250
300
T, K
FIGURE 1 Temperature dependence of carrier concentration density, circal for x=0 and dot for x=0.4.
0921 --4534/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland)
by Xing et al 2 recently. In their model, Hall number of the t w o - d i m e n s i o n a l C u - O p l a n e s is given by n x = n o (0) (1+T/T*) (I) and T* = cIN~ l(me+m h ) (2) where N I represents for density of the localized states; d for c - a x i s ; m e a n d m h a r e the effective mass of electroDs and holes. From (2)
1198
Q. Zhang et al. /
Superconducting oxides Bi 2_ ~.PbxCa;Sr2Cu~Oysystem
and assumption m e = m h, N 1 declines sharply with increase of Pb content in the sample as shown in Table I. This is q u i t e r e a s o n a b l e if we interpret N 1 as the contribution of the oxygen vacancies. The partial substitution of Pb 4÷ for Bi 3+ leads to a decrease of vacancies in oxygen deficient material. In addition, we can get dnH/dT a or I/N 1 from (i), this is also fitted to the experimental data as listed in Table I. 2. Relation between hE(T) and lead content n H decreases quickly at small x and slowly at large x. This p h e n o m e n o n can be e x p l a i n e d in terms of the substitution of Pb 4÷ for Bi 3÷. If the oxygen vacancies are fixed in two samples a n d the h o l e s are c o n t r i b u t e d by o x y g e n vacancies, then the P b - d o p e d sample contains fewer h o l e s r e l a t i v e l y . Therefore, this substitution leads to the hole carrier density decreasing with increasing Pb content. To some extent, this is s i m i l a r to the case of ReBa2Cu3OT_y 3, where the density of holes is qualitatively controlled by chemical doping with oxygen. In addition, the l o c a l i z e d energy
3.Hall coefficient R s Hall voltages V~ vs. applied magnetic fields for the samples (x=0 and 0.4) is reproduced in Figure 3. It shows that V H is proportional to the magnetic field and the curves possibly pass through the origin. This means that the Hall coefficient R ~ o r the carrier concentration nH in magnetic field up to 5T is field-independent for temperature above Tc. In addition, according to the semi-classical single band model, in the Bicuprate the f i e l d - i n d e p e n d e n c e of K H implies that the Fermi Surface may be a c o m p l e t e l y closed one and there is no asymmetric magnetic s c a t t e r i n g mechanism, which was p r o p o s e d to explain the e x t r a o r d i n a r y Hall e f f e c t in YBa2Cu307_y superconductors by Fiory et al. 4 REFERENCE i. J. Chen, Z.Y. Chen et al., SOlid State Comm. Vol. 68, (1988) 327. 2. D.Y. Xing and C.S. Ting, Phys. Rev. Vol. 38, No.7, (1988) 5134. 3. N.P. Ong, Z.Z. Wang et al., Phys. Rev. B35, (1987) 8807. 4. A.T. Fiory and G.S. Grader, To appear in Physical Review B, Brief Reports (1988).
o ×=0.4
/o
• x=0
/o.~O
•,•.5 > 0 0
I
2 3 4 5 M A G N E T I C FIELD, fe~a
6
FIGURE 3 Hall v o l t a g e V H as a function of the a p p l i e d magnetic field for fixed temperature.
levels t r a n s f e r to carrier bands in terms of Xing's model as described above. The decrease in the density of localized state induced by Pb doping leads to a d e c r e a s e of the h o l e concentration.