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Anomalous superconducting state gap size versus Tc behavior in underdoped Bi_2Sr_2Ca_1-xDy_xCu_2O_8+d

J. M. Harris·Z. -X. Shen·P. J. White·D. S. Marshall·M. C. Schabel·J. N. Eckstein·I. Bozovic
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Abstract

We report angle-resolved photoemission spectroscopy measurements of the excitation gap in underdoped superconducting thin films of Bi_2Sr_2Ca_{1-x}Dy_xCu_2O_{8+d}. As Tc is reduced by a factor of 2 by underdoping, the superconducting state gap Δdoes not fall proportionally, but instead stays constant or increases slightly, in violation of the BCS mean-field theory result. The different doping dependences of Δand kT_c indicate that they represent different energy scales. The measurements also show that Δis highly anisotropic and consistent with a d_{x^2-y^2} order parameter, as in previous studies of samples with higher dopings. However, in these underdoped samples, the anisotropic gap persists well above T_c. The existence of a normal state gap is related to the failure of Δto scale with T_c in theoretical models that predict pairing without phase coherence above T_c.

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J. M. Harris, Z. -X. Shen, P. J. White, D. S. Marshall, M. C. Schabel, J. N. Eckstein, I. Bozovic. 1996-11-01. Anomalous superconducting state gap size versus Tc behavior in underdoped Bi_2Sr_2Ca_1-xDy_xCu_2O_8+d. https://doi.org/10.1103/physrevb.54.r15665

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