Excitonic magnet in external field: complex order parameter and spin currents

TL;DR

This paper explores the behavior of spin-triplet exciton condensates in a two-orbital Hubbard model under external magnetic fields, revealing complex order parameters and spin currents that challenge existing theorems.

Contribution

It introduces a DMFT approach with complex hybridization functions to study excitonic condensates under magnetic fields, highlighting exceptions to the Bloch theorem.

Findings

Triplet order parameter tends to align perpendicular to the magnetic field.

In certain solutions, the Bloch theorem does not hold, allowing for spontaneous spin currents.

Doped and stoichiometric systems show distinct excitonic behaviors.

Abstract

We investigate spin-triplet exciton condensation in the two-orbital Hubbard model close to half filling by means of dynamical mean-field theory. Employing an impurity solver that handles complex off-diagonal hybridization functions, we study the behavior of excitonic condensate in stoichiometric and doped systems subject to external magnetic field. We find a general tendency of the triplet order parameter to lay perpendicular with the applied field and identify exceptions from this rule. For solutions exhibiting k-odd spin textures, we discuss the Bloch theorem which, in the absence of spin-orbit coupling, forbids the appearance of spontaneous net spin current. We demonstrate that the Bloch theorem is not obeyed by the dynamical mean-field theory.