Quantum oscillations of the specific heat in d-wave superconductors with loop current order

Abstract

We report numerical results of quantum oscillations of the specific heat in the vortex state of a dx2−y2-wave superconductor in the presence of loop current order [C. M. Varma, Phys. Rev. B 55, 14554 (1997); Phys. Rev. Lett. 83, 3538 (1999)], which gives rise to the Fermi pockets coexisting with nodal dx2−y2-wave superconductivity. Within a lattice tight-binding model, we find that in an intermediate temperature range, the oscillations seem to approximately follow the Onsager relation with an effective charge comparable to the electric charge. However, the quasiparticle spectrum does not resemble the Landau levels. In order to understand the origin of the oscillations, we also perform the Franz-Tesanovic transformation in the presence of the loop order and find that in addition to scalar and the Berry potentials [M. Franz and Z. Tešanović, Phys. Rev. Lett. 84, 554 (2000)], one component of the gauge invariant superfluid velocity couples to the low-lying Dirac particles as a component of a vector potential. The magnetic field associated with this vector potential vanishes on average but is highly nonuniform in the magnetic unit cell. We attribute the quantum oscillations to this field. We also compare the results with the model without the loop order but with the Zeeman-like coupling, which also induces the Fermi pockets in the superconducting state.

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