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

摘要

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