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Helmuth Berger

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Publications associées (311)

Examining Experimental Raman Mode Behavior in Mono- and Bilayer 2H-TaSe2 via Density Functional Theory: Implications for Quantum Information Science

Helmuth Berger

Tantalum diselenide (TaSe2) is a metallic transition metal dichalcogenide whose structure and vibrational behavior strongly depend on temperature and thickness, and this behavior includes the emergence of charge density wave (CDW) states at very low temper ...

2021

One-dimensional composite host-guest structure in BaVS3

Helmuth Berger, László Forró, Gervais Chapuis, Neven Barisic, Alla Arakcheeva, Philip Pattison

A detailed synchrotron X-ray diffraction (XRD) study performed with a single crystal of BaVS3 (barium vanadium trisulfide) in the temperature range between 10 and 295 K is reported. Aside from the known tetragonal–orthorhombic (240 K) and orthorhombic–mono ...

2021

Microwave Spectroscopy of the Low-Temperature Skyrmion State in Cu2OSeO3

Helmuth Berger

In the cubic chiral magnet Cu2OSeO3 a low-temperature skyrmion state (LTS) and a concomitant tilted conical state are observed for magnetic fields parallel to h100i. Here, we report on the dynamic resonances of these novel magnetic states. After promoting ...

AMER PHYSICAL SOC2021

Tunable cooperativity in coupled spin-cavity systems

Helmuth Berger

We experimentally study the tunability of the cooperativity in coupled spin-cavity systems by changing the magnetic state of the spin system via an external control parameter. As a model system, we use the skyrmion host material Cu2OSeO3 coupled to a micro ...

AMER PHYSICAL SOC2021

Confined dipole and exchange spin waves in a bulk chiral magnet with Dzyaloshinskii-Moriya interaction

Helmuth Berger, Dirk Grundler, Ping Che, Jianing Li, Andrea Mucchietto

The Dzyaloshinskii-Moriya interaction (DMI) has an impact on excited spin waves in the chiral magnet Cu2OSeO3 by means of introducing asymmetry in their dispersion relations. The confined eigenmodes of a chiral magnet are hence no longer the conventional s ...

2021

Preferential out-of-plane conduction and quasi-one-dimensional electronic states in layered 1T-TaS2

Helmuth Berger, László Forró, Alla Arakcheeva, Ana Akrap, Luka Ciric, Andrea Pisoni, Edoardo Martino, Philip Johannes Walter Moll, Matthias Carsten Putzke, Konstantin Semeniuk

Layered transition metal dichalcogenides (TMDs) are commonly classified as quasi-two-dimensional materials, meaning that their electronic structure closely resembles that of an individual layer, which results in resistivity anisotropies reaching thousands. ...

2020

Archetypal Soft-Mode-Driven Antipolar Transition in Francisite Cu3Bi(SeO3)(2)O2Cl

Helmuth Berger

Model materials are precious test cases for elementary theories and provide building blocks for the understanding of more complex cases. Here, we describe the lattice dynamics of the structural phase transition in francisite Cu3Bi(SeO3)(2)O2Cl at 115 K and ...

2020

Structural investigation of InSe layered semiconductors

Helmuth Berger, Daniela Pacilè

During the last decade, III-VI layered semiconductors (GaSe, InSe, GaS, etc.) have emerged as potential candidates for various applications, such as FET and optoelectronic devices. The properties of this class of layered materials are strongly dependent on ...

2020

Role of a higher-dimensional interaction in stabilizing charge density waves in quasi-one-dimensional NbSe3 revealed by angle-resolved photoemission spectroscopy

Christophe Berthod, Helmuth Berger

We revisit charge density wave (CDW) behavior in the archetypal quasi-one-dimensional (quasi-1D) material NbSe3 by high-resolution angle-resolved photoemission spectroscopy measurements utilizing a microfocused laser with a photon energy of 6.3 eV. We pres ...

2020

Room-temperature skyrmion phase in bulk Cu2OSeO3 under high pressures

Helmuth Berger

A skyrmion state in a noncentrosymmetric helimagnet displays topologically protected spin textures with profound technological implications for high-density information storage, ultrafast spintronics, and effective microwave devices. Usually, its equilibri ...

National Academy of Sciences2020

Insight into the electronic structure of semiconducting epsilon-GaSe and epsilon-InSe

Helmuth Berger, Marco Grioni, Daniela Pacilè, Alberto Crepaldi

Metal monochalcogenides (MX) have recently been rediscovered as two-dimensional materials with electronic properties highly dependent on the number of layers. Although some intriguing properties appear in the few-layer regime, the carrier mobility of MX co ...

AMER PHYSICAL SOC2020

Structural Phase Transition and Bandgap Control through Mechanical Deformation in Layered Semiconductors 1T-ZrX2 (X = S, Se)

Helmuth Berger, Oleg Yazyev, Ana Akrap, Edoardo Martino, Michele Pizzochero, Kristians Cernevics, Konstantin Semeniuk

Applying elastic deformation can tune a material's physical properties locally and reversibly. Spatially modulated lattice deformation can create a bandgap gradient, favoring photogenerated charge separation and collection in optoelectronic devices. These ...

AMER CHEMICAL SOC2020

Nature of native atomic defects in ZrTe5 and their impact on the low-energy electronic structure

Helmuth Berger, Oleg Yazyev, Ana Akrap, Shengnan Zhang

Over the past decades, investigations of the anomalous low-energy electronic properties of ZrTe5 have reached a wide array of conclusions. An open question is the growth method's impact on the stoichiometry of ZrTe5 samples, especially given the very small ...

AMER PHYSICAL SOC2020

Patterns and driving forces of dimensionality-dependent charge density waves in 2H-type transition metal dichalcogenides

Helmuth Berger, László Forró

Charge density wave (CDW) is a startling quantum phenomenon, distorting a metallic lattice into an insulating state with a periodically modulated charge distribution. Astonishingly, such modulations appear in various patterns even within the same family of ...

Nature Research2020

Giant anomalous Hall effect in quasi-two-dimensional layered antiferromagnet Co1/3NbS2

Helmuth Berger, László Forró, Edoardo Martino

The discovery of the anomalous Hall effect (AHE) in bulk metallic antiferromagnets (AFMs) motivates the search of the same phenomenon in two-dimensional (2D) systems, where a quantized anomalous Hall conductance can, in principle, be observed. Here we pres ...

AMER PHYSICAL SOC2020

Magnetic-field-induced reorientation in the spin-density-wave and the spin-stripe phases of the frustrated spin-1/2 chain compound beta-TeVO4

Helmuth Berger

beta-TeVO4 is a frustrated spin-1/2 zig-zag chain system, where spin-density-wave (SDW), vector-chiral (VC) and an exotic dynamic spin-stripe phase compete at low temperatures. Here we use torque magnetometry to study the anisotropy of these phases in magn ...

2020

Light-Induced Renormalization of the Dirac Quasiparticles in the Nodal-Line Semimetal ZrSiSe

Helmuth Berger, Philippe Bugnon, Marco Grioni, Majed Chergui, Arnaud Magrez, Luca Moreschini, Alberto Crepaldi, Simon Karl Moser, Gianmarco Gatti, Serhii Polishchuk, Michele Puppin

In nodal-line semimetals, linearly dispersing states form Dirac loops in the reciprocal space with a high degree of electron-hole symmetry and a reduced density of states near the Fermi level. The result is reduced electronic screening and enhanced correla ...

2020

Field-induced reorientation of helimagnetic order in Cu2OSeO3 probed by magnetic force microscopy

Helmuth Berger

Cu2OSeO3 is an insulating skyrmion-host material with a magnetoelectric coupling giving rise to an electric polarization with a characteristic dependence on the magnetic-field (H) over right arrow. We report a magnetic force microscopy imaging of the helic ...

AMER PHYSICAL SOC2020

Probing intraband excitations in ZrTe5: A high-pressure infrared and transport study

Helmuth Berger, Ana Akrap, Mathieu François Padlewski, Edoardo Martino, Philip Johannes Walter Moll, Matthias Carsten Putzke

Zirconium pentatetelluride, ZrTe5, shows remarkable sensitivity to hydrostatic pressure. In this work we address the high-pressure transport and optical properties of this compound, on samples grown by flux and chemical vapor transport. The high-pressure r ...

2020

Ferrimagnetic 120 degrees magnetic structure in Cu2OSO4

Helmuth Berger, Arnaud Magrez, Henrik Moodysson Rønnow, Ivica Zivkovic, Virgile Yves Favre, Lin Yang, Romain Sibille, Gregory Scott Tucker, Nicola Casati

We report magnetic properties of a 3d(9) (Cu2+) magnetic insulator Cu2OSO4 measured on both powder and single crystal. The magnetic atoms of this compound form layers whose geometry can be described either as a system of chains coupled through dimers or as ...

AMER PHYSICAL SOC2020

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