Mixed-symmetry superconductivity and the energy gap

Abstract

The symmetry of the superconducting order parameter, or simply the ``gap'', provides certain constraints on the actual mechanism that gives rise to pairing and ultimately to superconductivity. In this work we show how superconducting phases with mixed singlet-triplet symmetries can arise below $T_c$ for a generic tight-binding model. We first examine the 1D case to better illustrate the prevalence of symmetry-breaking transitions below $T_c$, and then the more realistic 2D case. In both cases we illustrate the implication for spectroscopic investigations of the energy gap by calculating the density of states for different temperatures below $T_c$. We find that the structure of the density of states near $T_c$ can vary dramatically from its form near $T=0$. A complete picture of the superconducting symmetry can only be attained if measurements are made over the entire temperature range.

arXiv comment15 pages, 17 figures. We wish to acknowledge the memory of Jan Zaanen with this manuscript. His animated discussion of a multitude of topics at conferences and accompanying meals will always be remembered. His enthusiasm for discovery and for "new ways of thinking about things'' remain an inspiration for those who knew him. v2: published version

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