Normal-state spin gap of Bi-based superconductors

Mao Zhiqiang; Xu Gaojie; Wang Ruiping; Wang Keqing; Tian Mingliang; Zhang Yuheng

doi:10.1103/PhysRevB.55.14581

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Normal-state spin gap of Bi-based superconductors

Mao Zhiqiang, Xu Gaojie, Wang Ruiping, Wang Keqing, Tian Mingliang, Zhang Yuheng

DOI 10.1103/PhysRevB.55.14581 · Physical Review B

T1

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Abstract

The thermoelectric power (TEP) S(T) and resistivity ρ(T) were measured for underdoped and overdoped Bi1.8Pb0.2Sr2Can−1CunO2n+4+δ (n=1,2) samples with different oxygen contents. A specific heat measurement was also conducted for the n=2 system. We found that S(T) exhibited a significant enhancement below a characteristic temperature Tg for these samples, as observed in underdoped samples of YBa2Cu3O7−δ and YBa2Cu4O8. Such an anomaly in S(T) below Tg suggests that an energy gap exists in the normal states of underdoped and overdoped Bi-based superconductors (n=1 or 2). The normal-state gap temperature (Tg) increases with decreasing oxygen content in both n=1 and 2 systems. A downturn behavior in ρ(T) with the opening of a normal-state gap was also observed for some overdoped samples. On the other hand, the experimental data also showed that S(T) had a positive slope at high temperatures for the heavily overdoped samples of the n=1 system, while all the overdoped samples of the n=2 system had a negative slope in S(T) within the whole measured temperature range. This suggests that the Bi2O2 layers are metallic and make a contribution to the TEP in the heavily overdoped region of the n=1 system, but are insulating in the whole overdoped region of the n=2 system. In addition, specific heat measurements for the n=2 system reveal that a decrease in oxygen content results in the occurrence of phase segregation.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
Bi1.8Pb0.2Sr2CuO6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	20	Pressure not reported	onset
Bi1.8Pb0.2Sr2CuO6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	14	Pressure not reported	onset
Bi1.8Pb0.2Sr2CaCu2O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	67	Pressure not reported	midpoint
Bi1.8Pb0.2Sr2CaCu2O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	78	Pressure not reported	midpoint
Bi1.8Pb0.2Sr2CaCu2O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	92	Pressure not reported	midpoint
Bi1.8Pb0.2Sr2CaCu2O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	80	Pressure not reported	midpoint
Bi1.8Pb0.2Sr2CaCu2O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	81	Pressure not reported	midpoint
Bi1.8Pb0.2Sr2CaCu2O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	64	Pressure not reported	unknown
Bi1.8Pb0.2Sr2CaCu2O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	90	Pressure not reported	unknown
Bi1.8Pb0.2Sr2CaCu2O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	60	Pressure not reported	unknown
Bi1.8Pb0.2Sr2CaCu2O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	58	Pressure not reported	unknown
Bi1.8Pb0.2Sr2CaCu2O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	87	Pressure not reported	unknown
YBa2Cu3O7-δ Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown
YBa2Cu4O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown
La2-xSrxCuO4 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown
Tl2Ba2CuO6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown
Bi2Sr2CaCu2O8 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown