Anomalous thermodynamic properties of the electron accumulation layer in SrTiO3

Abstract

Due to the nonlinear dielectric response within SrTiO$_{3}$ (STO), an accumulation layer created by positive charges at the surface of the STO sample ($x=0$) has an electron density profile $n(x)$ that slowly decays as $1/x^{12/7}$. Here we show that the long tail of $n(x)$ causes the magnetization and the specific heat of the accumulation layer to diverge at large $x$. We explore the truncation of the tail by the finite sample width $W$, the transition from the nonlinear to linear dielectric response with dielectric constant $\kappa$, and the use of a back gate with a negative voltage $-|V|$. We find that both the magnetization and specific heat are anomalously large and obey nontrivial power law dependences on $W$, $\kappa$, or $|V|$. We conclude with a discussion of how the capacitance as a function of the back gate voltage may be used to study the shape of the $n(x)$ tail in thin samples.