Understanding the negative compressibility in a 2D electron gas: Application to LaAlO₃/SrTiO₃

We investigate the effects of a two-band coupling on the negative compressibility for the two-dimensional electron gas. Using a homogeneous 2D electron model and a two-band description of the electron interactions, we examine the dependence of critical carrier density, dielectric constant, and effective mass on the negative compressibility of the 2D electron gas and compare results to the at the complex oxide interface of LaAlO₃/SrTiO₃. From our calculations, we show that the presence of interband coupling will produce a dramatic decrease in the polarizability and the critical carrier density of the 2DEG. Furthermore, we find that the ratio of the effective masses of the bands has a distinct and dramatic effect on the negative compressibility.