Doping a Mott insulator with orbital degrees of freedom

TL;DR

This paper investigates how hole doping affects one-dimensional Mott insulators with orbital degrees of freedom, revealing phase transitions, phase separation, and potential superconductivity using exact and numerical methods.

Contribution

It introduces a generalized t-J model for orbital degrees of freedom, applies Bethe ansatz and DMRG techniques, and explores realistic models for cubic titanates.

Findings

Transition from antiferromagnetic to ferromagnetic spin phases

Strong phase separation tendency at high Hund's coupling

Possible instability towards triplet superconductivity

Abstract

We study the effects of hole doping on one-dimensional Mott insulators with orbital degrees of freedom. We describe the system in terms of a generalized t-J model. At a specific point in parameter space the model becomes integrable in analogy to the one-band supersymmetric t-J model. We use the Bethe ansatz to derive a set of nonlinear integral equations which allow us to study the thermodynamics exactly. Moving away from this special point in parameter space we use the density-matrix renormalization group applied to transfer matrices to study the evolution of various phases of the undoped system with doping and temperature. Finally, we study a one-dimensional version of a realistic model for cubic titanates which includes the anisotropy of the orbital sector due to Hund's coupling. We find a transition from a phase with antiferromagnetically correlated spins to a phase where the spins are fully ferromagnetically polarized, a strong tendency towards phase separation at large Hund's coupling, as well as the possibility of an instability towards triplet superconductivity.