MARVEL Junior Seminar — May 2020

Zoom meeting link:

https://epfl.zoom.us/j/93881551248
Password: 3417

The MARVEL Junior Seminars aim to intensify interactions between the MARVEL Junior scientists belonging to different research groups.

Each seminar consists of two presentations of 25 minutes each, allowing to present on a scientific question in depth, followed by time for discussion. The discussion is facilitated and timed by the chair.

MARVEL Junior Seminar Organizing Committee — Giuliana Materzanini, Stefano Falletta, Olga Syzgantseva, Maria Fumanal, Markus Stricker, Kristians Cernevics, Max Veit and Patrick Mayor

Talk 1 —  Metal-insulator transitions in complex oxide heterostructures

Sophie Beck, Claude Ederer

Materials Theory laboratory, ETHZ

We study the interplay between several control mechanisms on the emerging functionalities of complex oxide thin films and heterostructures composed of different early transition metal oxides, including correlated metals, Mott insulators and band insulators, using a combination of density functional theory (DFT) and dynamical mean field theory (DMFT).
We discuss several examples where factors, such as e.g. lattice missmatch-induced epitaxial strain, dimensional confinement and substrate effects lead to modifications of structural as well as electronic properties, resulting in metal-insulator transitions. We further investigate interface reconstruction mechanisms such as charge transfer phenomena and their length scales in multilayer structures. We show how these effects can give rise to phenomena such as metallic interfaces in multilayers of two Mott insulators, LaVO₃ and LaTiO₃, or a metal-insulator transition in the correlated metal CaVO₃, for which we find that both tensile strain and a reduced film thickness can lead to a strong quasiparticle renormalization. We draw a conceptual comparison of different types of polar heterostructures and give an overview on interface effects in early transition metal oxides.

Talk 2 —  Anisotropic magnetic interactions from many-body wavefunction calculations

Ravi Yadav, Oleg Yazyev

Chair of Computational Condensed Matter Physics (C3MP), EPFL

The prospect of realizing quantum spin-liquid (QSL) ground states in layered honeycomb materials with strong spin-orbit interactions has triggered intense research activity in the condensed matter community [1,2]. Of particular interest is the Kitaev Hamiltonian on the honeycomb lattice [3].  We use many body quantum chemical methods to derive nearest-neighbor (NN) magnetic exchange coupling for honeycomb systems. In this talk I will discuss, the approach to obtain and map our ab initio data onto a generalized effective spin Hamiltonian. I will also show results obtained for a newly synthesized honeycomb system YbCl₃ [4], a first rare-earth honeycomb complex, where we find that Kitaev interactions on NN bonds are four times larger than the isotropic Heisenberg interactions. However, the presence of relatively strong second and third neighbor coupling yields a long range magnetic order also reported in the experiments.   
_{[1] A. Banerjee et al., Nature materials 15, 733 (2016).
[2] A. Kitaev, Annals of Physics 321, 2 (2006).  
[3] J. Chaloupka, G. Jackeli, and G. Khaliullin, Phys. Rev. Lett. 105, 027204 (2010).
[4] G. Sala et al., Physical Review B 100, 180406 (2019).}

Check the list of the next MARVEL Junior Seminars here.