Zeeman Coupling and Abnormal Thermal Conductivities in BSCCO Superconductors

TL;DR

This paper derives a microscopic Ginzburg-Landau theory for BSCCO superconductors incorporating Zeeman coupling, explaining abnormal thermal conductivities observed experimentally through a time-reversal-symmetry-breaking pairing state.

Contribution

It introduces a microscopic derivation of Zeeman coupling effects in a superconductor with mixed pairing channels, revealing a novel pairing state that explains experimental thermal conductivity anomalies.

Findings

Zeeman coupling induces a time-reversal-symmetry-breaking pairing state.

The theory coherently explains thermal conductivity anomalies above 5K and below 1K.

Energy considerations clarify the conflicting experimental observations.

Abstract

Using the path-integral formulation we derive microscopically a Ginzburg-Landau free energy with a Zeeman coupling between the magnetic field and the orbital angular momentum of the Cooper pairs in a superconductor with singlet pairing in the $d_{x^{2}-y^{2}}$- and the sub-dominant $d_{xy}$- channels. The Zeeman coupling induces a time-reversal-symmetry-breaking pairing state. Based on careful examinations of the energy gain due to the Zeeman coupling, the energy lost due to the kinetic energy of the excess superfluid, and the Doppler energy shift for quasi-particle excitations, we present a coherent interpretation for the puzzling and conflicting thermal conductivites observed at above 5K (K. Krishana, {\it et al}, Science {\bf 277}, 83(1997)) and at sub-Kelvins (H. Aubin, {\it et al}, Phys. Rev. Lett. {\bf 82}, 624 (1999)).