Paring instability in the mixed state of ad-wave superconductor

Abstract

We propose that an excitonic gap can be generated along nodal directions by Coulomb interaction in the mixed state of d-wave cuprate superconductors. In a superconductor, the Coulomb interaction usually can not generate any fermion gap since its strength is weakened by superfluidity. It becomes stronger as superfluid density is suppressed by external magnetic field, and is able to generate a gap for initially gapless nodal quasiparticles beyond some critical field Hc. By solving the gap equation, it is found that the nodal gap increases with growing field H, which leads to a suppression of thermal conductivity at zero temperature. This mechanism naturally produces the field-induced thermal metal-insulator transition observed in transport experiments.

INFLUENCE OF A UNIFORM MAGNETIC FIELD ON DYNAMICAL CHIRAL SYMMETRY BREAKING IN QED3

“…There will be a thermal metal-toinsulator transition with growing magnetic field in the limit of m(H) ≫ Γ 0 . These results qualitatively agree with the conclusion given by Jiang et al in [46], where the authors introduced a two-dimensional Coulomb interaction between Dirac fermions to generate an excitonic gap. We note that QED 3 in a uniform magnetic field was studied previously in several papers [47][48][49][50].…”

Coulomb interaction and semimetal–insulator transition in graphene

“…This kind of excitonic instability may also exist in other correlated electron systems than graphene. For instance, it was suggested by one of the authors that such instability can provide a qualitative understanding on the field-induced thermal metal-insulator transition observed in the vortex state of high temperature cuprate superconductor [21].…”