Orbital order driven quantum criticality

TL;DR

This paper demonstrates that simple orbital models exhibit exact quantum critical points, suggesting orbital order degradation can induce quantum criticality in transition metal compounds, and predicts novel orbital phenomena.

Contribution

It reveals exact quantum critical behavior in orbital models and introduces the concept of orbital spin glass and orbital Larmor precession under pressure.

Findings

Exact quantum critical points in orbital models on diluted lattices

Existence of orbital spin glass in non-uniform orbital coupling systems

Prediction of orbital Larmor precession under uniaxial pressure

Abstract

Charge, spin, and orbital degrees of freedom underlie the physics of transition metal compounds. Much work has revealed quantum critical points associated with spin and charge degrees of freedom in many of these systems. Here we illustrate that the simplest models that embody the orbital degrees of freedom - the two- and three-dimensional quantum orbital compass models - exhibit an exact quantum critical behavior on diluted square and cubic lattices (with a doping fraction of 1/4 and 1/2 respectively). This raises the possibility of quantum critical points triggered by the degradation of orbital order upon doping (or applying pressure to) such transition metal systems. We prove the existence of an orbital spin glass in several related systems in which the orbital couplings are made non-uniform. Moreover, a new orbital Larmor precession (i.e., a periodic change in the orbital state) is predicted when uniaxial pressure is applied.