Phase separation and long-wavelength charge instabilities in spin-orbit coupled systems

¹ Institut für Physik, BTU Cottbus-Senftenberg - PBox 101344, 03013 Cottbus, Germany
² Dipartimento di Fisica Università di Roma Sapienza - Piazzale Aldo Moro 5, I-00185 Roma, Italy
³ ISC-CNR and Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, Unità di Roma Sapienza Roma, Italy

Received: 16 July 2014
Accepted: 18 December 2014

Abstract

We investigate a two-dimensional electron model with Rashba spin-orbit interaction where the coupling constant $g=g(n)$ depends on the electronic density. It is shown that this dependence may drive the system unstable towards a long-wavelength charge density wave (CDW) where the associated second-order instability occurs in close vicinity to global phase separation. For very low electron densities the CDW instability is nesting-induced and the modulation follows the Fermi momentum k_F. At higher density the instability criterion becomes independent of k_F and the system may become unstable in a broad momentum range. Finally, upon filling the upper spin-orbit split band, finite momentum instabilities disappear in favor of phase separation alone. We discuss our results with regard to the inhomogeneous phases observed at the LaAlO₃/SrTiO₃ or LaTiO₃/SrTiO₃ interfaces.