Collective Modes in the Loop Ordered Phase of Cuprates

TL;DR

This paper demonstrates that the collective modes observed in under-doped Cuprates are a direct result of the loop-current order, predicts a third mode, and aligns theoretical parameters with experimental observations.

Contribution

It establishes a link between collective modes and loop-current order in Cuprates and predicts a new excitation branch.

Findings

Two collective mode branches are explained by loop-current order.

Predicted a third collective mode for experimental detection.

Ground state moments are oriented in a cone at an angle to the c-axis.

Abstract

We show that the two branches of collective modes discovered recently in under-doped Cuprates with huge spectral weight are a necessary consequence of the loop-current state. Such a state has been shown in earlier experiments to be consistent with the symmetry of the order parameter competing with superconductivity in four families of Cuprates. We also predict a third branch of excitations and suggest techniques to discover it. Using parameters to fit the observed modes, we show that the direction of the effective moments in the ground state lies in a cone at an angle to the c-axis as observed in experiments.