DQMP Forum - Length Scales of Interfacial Coupling between Metal and Insulator Phases in Oxides - Multiloop Functional Renormalization Group Approach to Frustrated Quantum Magnets

16.02.2021 13:00 – 14:30

Length Scales of Interfacial Coupling between Metal and Insulator Phases in Oxides
Claribel Domínguez (group of Prof. Triscone)

Understanding the mechanisms that control the metal to insulator transition (MIT) in correlated electron systems is one of the major challenges in condensed matter physics. Moreover, remarkably little is known about the characteristic lengths scale over which a metallic or insulating region can be established and the physics that sets this length scale. In this work, we use experimental and theoretical methods to design and study superlattices of two distinct rare earth nickelate oxides SmNiO3 and NdNiO3 that in bulk form show a MIT at two very different temperatures (400 K and 200 K, respectively). We find that, depending on the superlattice periodicity, these new complex oxide superlattices display different MIT behavior than that of the bulk materials. We show that the length scale of the metal-insulator transition in the superlattices is set not by the length scale of the propagation of structural motifs across the two materials, which ab-initio calculations and STEM analysis suggest is minimal, but rather by the balance between the energy cost of the boundary between a metal and an insulator and the energy gain of the bulk phases [1].
1. Dom´ınguez, C., Georgescu, A.B., Mundet, B. et al. Nat. Mater.19, 1182 (2020)

Multiloop Functional Renormalization Group Approach to Frustrated Quantum Magnets
Julian Thoenniss (group of prof. Abanin)

The intriguing low-energy properties of frustrated magnets continue to attract considerable experimental and theoretical interest in the condensed-matter community. From a theoretical perspective, the computation of phase diagrams and spin correlation functions for models of frustratedquantum magnets in 3D is very challenging as most standard analytical approaches are restricted to semi-classical large-S limits and numericaltechniques are typically either limited to small system sizes or low dimensionalities. One method that can circumvent these limitations is the Multiloop Functional Renormalization Group (mfRG) which has originally been developedfor strongly correlated electron systems and is based on the self-consistent parquet equations. We show how this framework can be extended to quantum spin systems where it allows for a simple evaluation of spin correlationfunctions. We present benchmark results from an application to the Heisenberg model on the Kagome lattice.

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