Loop current order and d-wave superconductivity: some observable consequences

TL;DR

This paper explores the observable effects of loop current order in cuprate superconductors, predicting a remnant Bogoliubov Fermi surface and its experimental signatures, including quantum oscillations under certain conditions.

Contribution

It provides a theoretical analysis of how loop current order influences superconducting properties and proposes experimental signatures to confirm its presence.

Findings

Remnant Bogoliubov Fermi surface exists in the superconducting state due to loop order.

Quantum oscillations are suppressed without field-induced spin stripe order.

Field-induced spin stripe order reconstructs the Fermi surface, enabling quantum oscillations.

Abstract

Loop current order has been reported in the pseudogap regime of a few cuprate systems in polarized neutron scattering experiments. Here we study several observable consequences of such order in the d-wave superconducting state at low T. The symmetries of the loop order removes degeneracy between momenta k and -k. Consequently there is a remnant Bogoliubov Fermi surface in the superconducting state. Bounds on the possible existence of such a Fermi surface may be placed from existing data. Detecting such a Fermi surface will be a very useful confirmation of the existence of loop order in various cuprates. We show through explicit calculations that the Bogoliubov Fermi surface does not display quantum oscillations in a magnetic field consistent with natural expectations. Inclusion of a field induced spin stripe order reconstructs the Bogoliubov Fermi surface to develop pockets which then show quantum oscillations in the superconducting state. Difficulties with interpreting quantum oscillation data in the cuprates along these lines are pointed out.