FisMat2017 - Submission - View

Abstract's title: Size control of charge-orbital order and site-selective Mottness in nanoscopic La-doped Manganites
Submitting author: Angelo Valli
Affiliation: Scuola Internazionale Superiore di Studi Avanzati (SISSA)
Affiliation Address: Via Bonomea, 265, 34136 Trieste
Country: Italy
Oral presentation/Poster (Author's request): Poster
Other authors and affiliations: Hena Das (UC Berkeley), Giorgio Sangiovanni (Uni Wuerzburg), Karsten Held (TU Wien), and Tanusri Saha-Dasgupta (Bose National Center for Basic Science)
Abstract
The half-doped La0.5Ca0.5MnO3 (LCMO) manganite exhibits both charge- and orbital-order (CO) below T_CO=155K accompanied to a structural change from orthorhombic to monoclinic. The insulating CO state can be destabilized by various means, including doping, pressure, and electromagnetic fields.
Highly debated experimental evidence suggest that the destabilization of the CO can also be achieved by size reduction. 
In order to clarify this scenario, we perform calculations within the framework of ab-initio density functional theory in combination with dynamical mean-field theory (DFT+DMFT) which are able to deal with bulk and nano-manganites on the same footing.
We establish that the DFT+DMFT interplay between the structural changes that follow upon size reduction and the electronic correlations leads to the weakening of the CO and trigger an insulating-to-metal transition. 
We also show that the effects of nanostructuring are very different from those of hydrostatic pressure (at the same % of volume reduction) and that nano LCMO is much closer to the Mott state than bulk LCMO under pressure. 
Further reducing the LCMO size to a few nm, quantum confinement effects come into play and lead to the opposite effect, enhancing charge and orbital order. Moreover, electron doping by means of an external gate voltage is found to trigger a site- and orbital-selective Mott transition. 
Our results suggest that LCMO nano-clusters could be employed for the realization of technological devices, exploiting the proximity to the Mott transition and its control achieved by size-engineering and electrostatic doping.
 
References:
T. Sarkar et al., Phys. Rev. B 77, 235112 (2008).
T. Sarkar et al., Appl. Phys. Lett. 92, 123104 (2008).
H. Das, G. Sangiovanni, A. Valli, K. Held, and T. Saha-Dasgupta, Phys. Rev. Lett 107, 197202 (2011).
A. Valli, H. Das, G. Sangiovanni, T. Saha-Dasgupta, and K. Held, Phys. Rev. B 92, 115143 (2015).