The layered transition metal dichalcogenides which show an inherent tendency towards charge density wave order are traditionally considered to realize rather two-dimensional electronic systems. However, recent theoretical and experimental results suggest t ...

2018

Dirac nodal lines and flat-band surface state in the functional oxide RuO2

Helmuth Berger, Philippe Bugnon, Arnaud Magrez, Simon Karl Moser

The efficiency and stability of RuO2 in electrocatalysis has made this material a subject of intense fundamental and industrial interest. The surface functionality is rooted in its electronic and magnetic properties, determined by a complex interplay of la ...

AMER PHYSICAL SOC2018

Observation of two independent skyrmion phases in a chiral magnetic material

Helmuth Berger

Magnetic materials can host skyrmions, which are topologically non-trivial spin textures. In chiral magnets with cubic lattice symmetry, all previously observed skyrmion phases require thermal fluctuations to become thermodynamically stable in bulk materia ...

2018

Coexisting spinons and magnons in the frustrated zigzag spin-1/2 chain compound beta-TeVO4

Helmuth Berger

We investigate magnetic excitations in the frustrated zigzag spin-1/2 chain compound beta-TeVO4 by inelastic neutron scattering. In the magnetically ordered ground state, the excitation spectrum exhibits coexisting magnon dispersion, characteristic of long ...

AMER PHYSICAL SOC2018

Semiconducting van der Waals Interfaces as Artificial Semiconductors

Helmuth Berger, Evgeniy Ponomarev

Recent technical progress demonstrates the possibility of stacking together virtually any combination of atomically thin crystals of van der Waals bonded compounds to form new types of heterostructures and interfaces. As a result, there is the need to unde ...

2018

Thermodynamic evidence of a second skyrmion lattice phase and tilted conical phase in Cu2OSeO3

Helmuth Berger

Precision measurements of the magnetization and ac susceptibility of Cu2OSeO3 are reported for magnetic fields along different crystallographic directions, focusing on the border between the conical and the field-polarized state for a magnetic field along ...

2018

Strongly bound excitons in anatase TiO2 single crystals and nanoparticles

Helmuth Berger, Marco Grioni, Majed Chergui, Arnaud Magrez, Gerald Auböck, Simon Karl Moser, Edoardo Baldini

Anatase TiO2 is among the most studied materials for light-energy conversion applications, but the nature of its fundamental charge excitations is still unknown. Yet it is crucial to establish whether light absorption creates uncorrelated electron-hole pai ...

Nature Publishing Group2017

Linearly polarized GHz magnetization dynamics of spin helix modes in the ferrimagnetic insulator Cu_2OSeO_3

Helmuth Berger, Dirk Grundler

Linear dichroism — the polarization dependent absorption of electromagnetic waves— is routinely exploited in applications as diverse as structure determination of DNA or polarization filters in optical technologies. Here filamentary absorbers with a large ...

Nature Research2017

BiTeCl and BiTeBr: A comparative high-pressure optical study

Helmuth Berger, Philippe Bugnon, Arnaud Magrez, Oleg Yazyev, Ana Akrap, Gabriel Albert Autes

We here report a detailed high-pressure infrared transmission study of BiTeCl and BiTeBr. We follow the evolution of two band transitions: the optical excitation beta between two Rashba-split conduction bands, and the absorption. across the band gap. In th ...

Amer Physical Soc2017

Anisotropic pressure effects on the Kagome Cu3Bi(SeO3)(2)O2Cl metamagnet

Helmuth Berger

The anisotropic spin-flip-induced multiferroic property of the Kagome single-crystal Cu3Bi(SeO3)(2)O2Cl was recently investigated. The doping effects on the structural and magnetic properties of Cu3Bi(Se1-xTexO3)(2)O2Cl (0

Iop Publishing Ltd2017

Pressure-induced superconductivity in the giant Rashba system BiTeI

Helmuth Berger

At ambient pressure, BiTeI exhibits a giant Rashba splitting of the bulk electronic bands. At low pressures, BiTeI undergoes a transition from trivial insulator to topological insulator. At still higher pressures, two structural transitions are known to oc ...

Iop Publishing Ltd2017

Dimensional Crossover in a Charge Density Wave Material Probed by Angle-Resolved Photoemission Spectroscopy

Christophe Berthod, Helmuth Berger, Matthias Wolf

High-resolution angle-resolved photoemission spectroscopy data reveal evidence of a crossover from one-dimensional (1D) to three-dimensional (3D) behavior in the prototypical charge density wave (CDW) material NbSe3. In the low-temperature 3D regime, gaps ...

Amer Physical Soc2017

Unscreened plasmon dispersion of 2H transition metal dichalcogenides

Helmuth Berger

The plasmon dispersion in 2H transition metal dichalcogenides has been reported to be negative, which is a strong renormalization with respect to the expectations for a homogeneous electron gas. This has been interpreted to be either due to the interaction ...

Amer Physical Soc2017

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