Tunable site- and orbital-selective Mott transition and quantum confinement effects in La$_{0.5}$Ca$_{0.5}$MnO$_3$ nanoclusters

TL;DR

This study uses dynamical mean-field theory to explore how size and external gating influence charge, orbital, and electronic phase transitions in La$_{0.5}$Ca$_{0.5}$MnO$_3$ nanoclusters, revealing tunable Mott transitions and quantum confinement effects.

Contribution

It demonstrates how nanostructuring and gate voltage can control Mott transitions and electronic properties in La$_{0.5}$Ca$_{0.5}$MnO$_3$ nanoclusters, highlighting potential device applications.

Findings

Size reduction induces insulator-to-metal transition in nanoclusters.

Further size reduction causes reentrant insulating behavior due to quantum confinement.

Gate voltage triggers site- and orbital-selective Mott transition.

Abstract

We present a dynamical mean-field theory (DMFT) study of the charge and orbital correlations in finite-size La$_{0.5}$Ca$_{0.5}$MnO$_3$ (LCMO) nanoclusters. Upon nanostructuring LCMO to clusters of 3 nm diameter, the size reduction induces an insulator-to-metal transition in the high-temperature paramagnetic phase. This is ascribed to the reduction in charge disproportionation between Mn sites with different nominal valence [Das et al., Phys. Rev. Lett. 107, 197202 (2011)]. Here we show that upon further reducing the system size to a few-atom nanoclusters, quantum confinement effects come into play. These lead to the opposite effect: the nanocluster turns insulating again and the charge disproportionation between Mn sites, as well as the orbital polarization, are enhanced. Electron doping by means of external gate voltage on few-atom nanoclusters is found to trigger a site- and orbital-selective Mott transition. Our results suggest that LCMO nanoclusters could be employed for the realization of technological devices, exploiting the proximity to the Mott transition and its control by size and gate voltage.