Quantum Materials Modelling

News and Highlights


GW for perovskites

'Converged GW quasiparticle energies for transition metal oxide perovskites' published in Phys. Rev. Materials

PhD Defensio: Zeynep Ergonenc

Congratulation Zeynep!

Surface Labyrinth on KTaO3

When a crystal is broken along certain directions the atoms reorganize in amazing ways: Polarity compensation mechanisms on the perovskite surface KTaO3(001).
Our combined experimental (TU Wien, Group Diebold) and theoretical (QMM group) work published in Science.

M. Setvin et al., Science 359, 572 (2018).

Topological MIT in Ag2BiO3

Tunable metal-insulator transition, Rashba effect and Weyl Fermions in the relativistic charge-ordered ferroelectric oxide Ag2BiO3.

J. He et al., Nature Communication 9, 492 (2018) (2018).

Surface geometry by DFT & X-ray standing wave

Probing the geometry of copper and silver adatoms on magnetite: quantitative experiment versus theory.

M. Meier et al., Nanoscale 10, 2226 (2018).

Erasmus student: Jana Martincova

From: Palacky University Olomouc (Group Petr Lazar)"

Talk by Claude Ederer, ETH Zurich

Monday 20/11/2017: "DFT+DMFT studies of metal-insulator transitions in complex 3d transition metal oxides"

Hidden magnetic order in SrVO4

By combining relativistic density functional theory with an extended spin-1/2 compass-Heisenberg model, we find an antiferromagnetic single-stripe ground state with highly competing exchange interactions, involving a non-negligible interlayer coupling, which places the system at the crossover between the XY-model and Heisenberg-model regimes. Most strikingly, we find a strong two-site “spin-compass” exchange anisotropy which is relieved by the orthorhombic distortion induced by the spin stripe order. Based on these results, we discuss the origin of the hidden-order phase and the possible formation of a spin liquid at low temperatures.
B. Kim et al., Phys. Rev. B 96, 180405(R).

Self-consistent hybrids for oxides

Self-consistent scPBE0: evaluation of the mixing parameter alpha by means of an iterative calculation of the static dielectric constant using the perturbation expansion after discretization (PEAD) method. Assesed for a materials dataset composed formed by 30 compounds covering a wide range of band gaps and dielectric properties, and includes materials with a wide spectrum of applications such as thermoelectrics, photocatalysis, photovoltaics, transparent conducting oxides, and refractory materials.
J. He & C. Franchini, J. Phys.: Condens. Matter 29, 454004 (2017).

Visting PhD: Meisam Farzalipour Tabriz

From: University of Shanghai, China (Group Wei Ren)

Surface reconstruction: polarons

When a crystal is cleaved, a new surface forms that interrupts the regular distribution of ions within the material. The breaking of surface bonds and the alteration of interatomic forces increase the surface stress and reduce the stability of the fresh surface. To overcome this instability, the majority of surfaces undergo a spontaneous geometrical reconstruction, which is generally associated with charge transfer between surface atoms. Unraveling the mechanism responsible for such reconstructions is essential to understanding properties of surfaces, and it helps optimize materials performance in applications such as microelectronics and fuel cells. By combining calculations and experiments, we have found an alternative and radically different mechanism for surface reconstructions based on charge trapping
Reticcioli et al., Phys Rev. X 7, 031053 (2017).
Highlighted in Nature Review Materials

Superconductivity: relativistic spins

A new framework for analysing the role of magnetic interactions on the unconventional superconductivity in strontium ruthenate. Strontium ruthenate is an unconventional superconductor that used to be touted a potential three-dimensional analogue of Helium-3, as it was thought to have the same type of chiral p-wave pairing. It is now widely accepted that this is not the case, but many questions remain over the exact nature of the pairing, particularly regarding the role of magnetic interactions. This work presents a framework that can incorporate the leading isotropic and anisotropic magnetic interactions in a different but complimentary way to the widely used Hubbard-model, providing an alternative way of exploring the superconducting pairing symmetry.
Kim et al., npj Quantum Materials 2, 37 (2017).

New PhD student: Thomas Hahn

Welcome Thomas. On Nov. 1 Thomas will start his PhD in the framework of the project POLOX: polaron in oxides

3D Weyl Semimetal

By combining bulk sensitive soft-x-ray angular-resolved photoemission spectroscopy and first-principles calculations we explored the bulk electron states of WTe2, a candidate type-II Weyl semimetal featuring a large nonsaturating magnetoresistance. Despite the layered geometry suggesting a two-dimensional electronic structure, we directly observe a three-dimensional electronic dispersion. We report a band dispersion in the reciprocal direction perpendicular to the layers, implying that electrons can also travel coherently when crossing from one layer to the other. The measured Fermi surface is characterized by two well-separated electron and hole pockets at either side of the Γ point, differently from previous more surface sensitive angle-resolved photoemission spectroscopy experiments that additionally found a pronounced quasiparticle weight at the zone center. Moreover, we observe a significant sensitivity of the bulk electronic structure of WTe2 around the Fermi level to electronic correlations and renormalizations due to self-energy effects, previously neglected in first-principles descriptions.
D. Di Sante et al., Phys. Rev. Lett. 119, 026403 (2017).

Master Thesis: Thomas Hahn

Oct. 9 2017. Thomas Hahn has defended his master thesis: Congratulations!

Diagrammatic Quantum Monte Carlo for the Fröhlich Polaron

Visting PhD: Meisam Farzalipour Tabriz

From: University of Bremen, Germany (Group Thomas Frauenheim & Peter Deak)

Visiting PhD: Shujaat Khan

From: Hazara University Mansehra, Pakistan (Group Bin Amin)