Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEmergence of a ferromagnetic insulating state in LaMnO$_3$/SrTiO$_3$ heterostructures: The role of strong electronic correlations and strain
125
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Inspired by the experimental findings of an exotic ferromagnetic insulating state in LaMnO$_3$/SrTiO$_3$ heterostructures, we calculate the electronic and magnetic state of LaMnO$_3$/SrTiO$_3$ superlattices with comparable thicknesses employing ab-initio dynamical mean-field theory. Projecting on the low-energy subspace of Mn $3d$ and Ti $3d$ states, and solving a multi-impurity problem, our approach emphasizes on local correlations at Mn and Ti sites. We find that a ferromagnetic insulating state emerges due to intrinsic effects of strong correlations in the system, in agreement with experimental studies. We also predict that, due to electronic correlations, the emerging 2D electron gas is located at the LMO side of the interface. This is in contrast to DFT results that locate the electron gas on the STO side. We estimate the transition temperature for the paramagnetic to ferromagnetic phase transition, which may be verified experimentally. Importantly, we also clarify that the epitaxial strain is a key ingredient for the emergence of the exotic ferromagnetic insulating state. This becomes clear from calculations on a strained LaMnO$_3$ system, also showing ferromagnetism which is not seen in the unstrained bulk material.
rate research
Read More
We have performed ab initio calculations within the LDA+U method in the multilayered system (LaMnO$_3$)$_{2n}$ / (SrMnO$_3$)$_n$. Our results suggest a charge-ordered state that alternates Mn$^{3+}$ and Mn$^{4+}$ cations in a checkerboard in-plane pattern is developed at the interfacial layer, leading to a gap opening. Such an interfacial charge-ordered situation would be the energetically favored reconstruction between LaMnO$_3$ and SrMnO$_3$. This helps understanding the insulating behavior observed experimentally in these multilayers at intermediate values of $n$, whose origin is known to be due to some interfacial mechanism.
This review provides a summary of the rich physics expressed within SrTiO$_3$-based heterostructures and nanostructures. The intended audience is researchers who are working in the field of oxides, but also those with different backgrounds (e.g., semiconductor nanostructures). After reviewing the relevant properties of SrTiO$_3$ itself, we will then discuss the basics of SrTiO$_3$-based heterostructures, how they can be grown, and how devices are typically fabricated. Next, we will cover the physics of these heterostructures, including their phase diagram and coupling between the various degrees of freedom. Finally, we will review the rich landscape of quantum transport phenomena, as well as the devices that elicit them.
Motivated by the puzzling report of the observation of a ferromagnetic insulating state in LaMnO$_3$/SrTiO$_3$ heterostructures, we calculate the electronic and magnetic state of LaMnO$_3$, coherently matched to a SrTiO$_3$ square substrate within a strained-bulk geometry. We employ three different density functional theory based computational approaches: (a) density functional theory (DFT) supplemented with Hubbard U (DFT+U), (b) DFT + dynamical mean field theory (DMFT), and (c) a hybrid functional treatment of the exchange-correlation functional. While the first two approaches include local correlations and exchange at Mn sites, treated in a static and dynamic manner, respectively, the last one takes into account the effect of non-local exchange at all sites. We find in all three approaches that the compressive strain induced by the square substrate of SrTiO$_3$ turns LaMnO$_3$ from an antiferromagnet with sizable orbital polarization to a ferromagnet with suppressed Jahn-Teller distortion in agreement with experiment. However, while both DFT+U and DFT+DMFT provide a metallic solution, only the hybrid calculations result in an insulating solution, as observed in experiment. This insulating behavior is found to originate from an electronic charge disproportionation. Our conclusions remain valid when we investigate LaMnO$_3$/SrTiO$_3$ within the experimental set-up of a superlattice geometry using DFT+U and hybrid calculations.
We report a detailed analysis of magneto-transport properties of top- and back-gated LaAlO$_3$/SrTiO$_3$ heterostructures. Efficient modulation in magneto-resistance, carrier density, and mobility of the two-dimensional electron liquid present at the interface is achieved by sweeping top and back gate voltages. Analyzing those changes with respect to the carrier density tuning, we observe that the back gate strongly modifies the electron mobility while the top gate mainly varies the carrier density. The evolution of the spin-orbit interaction is also followed as a function of top and back gating.
Artificially fabricated 3$d$/5$d$ superlattices (SLs) involve both strong electron correlation and spin-orbit coupling in one material by means of interfacial 3$d$-5$d$ coupling, whose mechanism remains mostly unexplored. In this work we investigated the mechanism of interfacial coupling in LaMnO$_3$/SrIrO$_3$ SLs by several spectroscopic approaches. Hard x-ray absorption, magnetic circular dichroism and photoemission spectra evidence the systematic change of the Ir ferromagnetism and the electronic structure with the change of the SL repetition period. First-principles calculations further reveal the mechanism of the SL-period dependence of the interfacial electronic structure and the local properties of the Ir moments, confirming that the formation of Ir-Mn molecular orbital is responsible for the interfacial coupling effects. The SL-period dependence of the ratio between spin and orbital components of the Ir magnetic moments can be attributed to the realignment of electron spin during the formation of the interfacial molecular orbital. Our results clarify the nature of interfacial coupling in this prototypical 3$d$/5$d$ SL system and the conclusion will shed light on the study of other strongly correlated and spin-orbit coupled oxide hetero-interfaces.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
