Superconductor-to-metal transition in overdoped La2−xSrxCuO4

Abstract

The low-temperature transition from superconductor to metal of overdoped La2−xSrxCuO4 has been monitored by measurements of resistivity versus temperature as a function of pressure over the compositional range 0.15≤x≤0.30. Polycrystalline samples were annealed under oxygen for periods up to 1 month to obtain homogeneous, stoichiometric samples. The pressure dependence of the critical temperature is dTc/dP>0 in the orthorhombic phase found for x≤0.22; it vanishes in the tetragonal phase occurring with x>0.22. Pressure favors the tetragonal phase, lowering the orthorhombic-tetragonal transition temperature Tt and shifting the transitional composition xt to xt<0.20 above 10 kbar. This shift is shown to be due to an unusually large compressibility of the Cu-O bonds in the CuO2 sheets. The persistence of Tc into the tetragonal phase with x>xt is not due to orthorhombic-phase fluctuations, as has been speculated. Whereas the superconductive transition temperature Tc decreases with increasing x, an elastic transition at Td≊37 K persists over the entire compositional range, including the metallic phase at x=0.30. Careful measurements of resistance and Seebeck coefficient across Td reveal a Td≥Tc; but superconductive-pair fluctuations may occur below a Tf>Td where Tc≊Td, which is consistent with a transition from two- to three-dimensional metallic conduction. The data also suggest that the superconductor-metal transition is not smooth.

Source-reported materials — not catalogue approval

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