Violation of Onsager Reciprocity in Underdoped Cuprates ?

TL;DR

This paper presents evidence that the Onsager Reciprocity principle is violated in underdoped cuprates, likely due to a loop-current phase that exhibits magneto-electric symmetry, challenging fundamental assumptions in condensed matter physics.

Contribution

It provides experimental evidence of Onsager reciprocity violation in underdoped cuprates and links this to the presence of a loop-current phase with magneto-electric properties.

Findings

Violation of Onsager reciprocity observed in underdoped YBa2Cu3O6+x.

The violation correlates with the loop-current phase.

Temperature dependence of the violation supports the loop-current hypothesis.

Abstract

One of the canons of condensed matter physics is the Onsager Reciprocity principle in systems in which the Hamiltonian commutes with the time-reversal operator. Recent results of measurements of the Nernst coefficient in underdoped YBa_2Cu_30_{6+x}, together with the measurements of the anisotropy of conductivity and the inferred anisotropy of the thermopower, imply that this principle is violated. The probable violation and its temperature dependence are shown to be consistent with the Loop-current phase which has been directly observed in other experiments. The violation is related directly to the magneto-electric symmetry of such a phase in which an applied electric field generates an effective magnetic field at right angle to it and to the order parameter vector, and vice versa.