Dependence of the superconducting transition temperature on the type and number of CuO2 layers in Tl2Ba2Can−1CunO2n+4−y

Xiaojia Chen; Changde Gong

doi:10.1103/PhysRevB.59.4513

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Dependence of the superconducting transition temperature on the type and number of CuO2 layers in Tl2Ba2Can−1CunO2n+4−y

Xiaojia Chen, Changde Gong

DOI 10.1103/PhysRevB.59.4513 · Physical Review B

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Abstract

The CuO2 layer dependence of the superconducting transition temperature Tc at ambient pressure on the intrinsic transition temperature Tc(i) of the type-I CuO2 plane in which the copper atom has fivefold pyramid coordination of oxygen and the fourfold square coordinated type-II plane is studied in terms of the generalized Lawrence-Doniach theory. Calculations show that the increase of Tc with the number of CuO2 layers benefits from the difference of the intrinsic Tc(i) of the two types of CuO2 layers and that interlayer coupling between the neighboring CuO2 layers can enhance Tc for the multilayer cuprates. The upper limit of Tc is predicted to be 146 K for the bilayer thallium-based series. We present an extended pressure-induced charge transfer model for layered cuprate superconductors, assuming that the charge distribution among the crystallographically inequivalent CuO2 layers is nonhomogeneous, which enables us to investigate the pressure effect on the intrinsic Tc(i). The intrinsic Tc(i) of the two types of CuO2 layers is predicted to behave with pressure in a paraboliclike manner. For the optimally doped single, double, and triple CuO2 sheets compounds, the saturation values of Tc(I) of the type-I CuO2 plane of 91.1, 119.6, and 133.9 K are obtained when P=2.3, 2.9, and 6.0 GPa, respectively. For the underdoped Tl-2234 compound with Tc=113 K, the calculated Tc(I) of 118.5 K is obtained at P=6.0 GPa. Under the application of pressure, the intrinsic Tc(II) of the type-II CuO2 plane in Tl-2234 increases strongly compared with a modest increase of Tc(II) in Tl-2223, possibly resulting from its underdoped nature. We suggest that at low pressure the Tc is the intrinsic Tc(i) of the type-I CuO2 plane, and at relatively high pressures the intrinsic effect of the type-II plane dominates. Our theoretical results are in agreement with experiments.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
Tl2Ba2CuO6-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	90	Pressure not reported	unknown
Tl2Ba2CaCu2O8-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	118	Pressure not reported	unknown
Tl2Ba2Ca2Cu3O10-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	128.5	Pressure not reported	unknown
Tl2Ba2Ca3Cu4O12-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	116	Pressure not reported	unknown
Tl2Ba2Ca3Cu4O12-y Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	113	Pressure not reported	unknown