Optical Properties of (SrMnO3)n/(LaMnO3)2n superlattices: an insulator-to-metal transition observed in the absence of disorder

TL;DR

This study investigates the optical conductivity of (SrMnO3)n/(LaMnO3)2n superlattices, revealing an insulator-to-metal transition driven by temperature and polaronic effects, occurring without chemical disorder, and indicating a novel electronic state.

Contribution

First observation of an insulator-to-metal transition in manganite superlattices driven by temperature, without chemical doping-induced disorder, highlighting a new electronic phase.

Findings

IMT occurs for n ≤ 3 with temperature dependence

MIR band softening correlates with IMT

Large-period superlattices remain insulating regardless of temperature

Abstract

We measure the optical conductivity of (SrMnO3)n/(LaMnO3)2n superlattices (SL) for n=1,3,5, and 8 and 10 < T < 400 K. Data show a T-dependent insulator to metal transition (IMT) for n \leq 3, driven by the softening of a polaronic mid-infrared band. At n = 5 that softening is incomplete, while at the largest-period n=8 compound the MIR band is independent of T and the SL remains insulating. One can thus first observe the IMT in a manganite system in the absence of the disorder due to chemical doping. Unsuccessful reconstruction of the SL optical properties from those of the original bulk materials suggests that (SrMnO3)n/(LaMnO3)2n heterostructures give rise to a novel electronic state.