Home

Person

Helmuth Berger

This person is no longer with EPFL

About
Privacy
Disclaimer

Graph Chatbot

Related publications (311)

Strongly enhanced charge-density-wave order in monolayer NbSe2

Helmuth Berger, László Forró

Two-dimensional materials possess very different properties from their bulk counterparts. While changes in single-particle electronic properties have been investigated extensively(1-3), modifications in the many-body collective phenomena in the exact two-d ...

Nature Publishing Group2015

Role of sulfur in BaVS3 probed by S K-edge absorption spectroscopy

Helmuth Berger, László Forró

We show that the quasi-1D behavior of BaVS3 can be understood analyzing the X-ray absorption near edge spectra at the sulfur K edge. Linear dichroism experiments, analyzed with the help of ab initio calculations, reveal two strong and polarization dependen ...

Elsevier Science Bv2015

The Role of Transport Agents in MoS2 Single Crystals

Helmuth Berger, László Forró, Arnaud Magrez, Bálint Náfrádi, Arnaud Walter, Jacim Jacimovic, Andrea Pisoni

We report resistivity, thermoelectric power, and thermal conductivity of MoS2 single crystals prepared by the chemical vapor transport (CVT) method using I-2, Br-2, and TeCl4 as transport agents. The material presents low-lying donor and acceptor levels, w ...

Amer Chemical Soc2015

High pressure phase transition in FeTe2O5Cl

Helmuth Berger

Raman and optical absorption spectra of FeTe2O5Cl at pressures (P) up to 5.9 GPa were measured in order to identify the point of pressure-induced structural phase transition and to compare the vibrational and optical properties of FeTe2O5Cl to those of FeT ...

Wiley-V C H Verlag Gmbh2015

Electron-Phonon Coupling in the Bulk of Anatase TiO2 Measured by Resonant Inelastic X-Ray Spectroscopy

Helmuth Berger, Philippe Bugnon, Marco Grioni, Arnaud Magrez, Simon Karl Moser, Sara Fatale

We investigate the polaronic ground state of anatase TiO2 by bulk-sensitive resonant inelastic x-ray spectroscopy (RIXS) at the Ti L-3 edge. We find that the formation of the polaron cloud involves a single 95 meV phonon along the c axis, in addition to th ...

Amer Physical Soc2015

Electrostatically Induced Superconductivity at the Surface of WS2

Helmuth Berger

We investigate transport through ionic liquid gated field effect transistors (FETs) based on exfoliated crystals of semiconducting WS2. Upon electron accumulation, at surface densities close to, or just larger than, 10(14) cm(2), transport exhibits metalli ...

Amer Chemical Soc2015

Ultrafast Optical Control of the Electronic Properties of ZrTe5

Helmuth Berger, Philippe Bugnon, Marco Grioni, Arnaud Magrez, Alberto Crepaldi

We report on the temperature dependence of the ZrTe5 electronic properties, studied at equilibrium and out of equilibrium, by means of time and angle resolved photoelectron spectroscopy. Our results unveil the dependence of the electronic band structure ac ...

Amer Physical Soc2015

Manifestation of a Second Dirac Surface State and Bulk Bands in THz Radiation from Topological Insulators

Helmuth Berger, Hua Chen

Topological insulators (TIs) are interesting quantum matters that have a narrow bandgap for bulk and a Dirac-cone-like conducting surface state (SS). The recent discovered second Dirac surface state (SS) and bulk bands (BBs) located similar to 1.5 eV above ...

Nature Publishing Group2015

Magnetoelectric effects in the skyrmion host material Cu2OSeO3

Helmuth Berger

Insulating helimagnetic Cu2OSeO3 shows sizeable magnetoelectric effects in its skyrmion phase. Using magnetization measurements, magneto-current analysis and dielectric spectroscopy, we provide a thorough investigation of magnetoelectric coupling, polariza ...

Nature Publishing Group2015

Heat capacity properties of quasi-one-dimensional magnet beta-TeVO4

Helmuth Berger

We studied the temperature dependence of heat capacity C-P(T) of a quasi-one-dimensional magnetic system beta-TeVO4, in a zero magnetic field and a temperature region of 0.1 K

Amer Inst Physics2015

A study of the magnetic properties of a quasi-one-dimensional magnet beta-TeVO4 in the frame of the J(1)-J(2) model

Helmuth Berger

Magnetic properties of single crystal beta-TeVO4 with a zigzag chain of magnetic centers (V4+ ions, S = 1/2) are analyzed in the framework of the J(1)-J(2) model. The best agreement with experimental data is obtained for the J(1)-J(2) model with parameters ...

Amer Inst Physics2015

Engineering the topological surface states in the (Sb2)m−Sb2Te3(m=0–3) superlattice serie

Helmuth Berger, Philippe Bugnon, Marco Grioni, Arnaud Magrez, Oleg Yazyev, Alberto Crepaldi, Simon Karl Moser, Gabriel Albert Autes, Jens Christian Johannsen

We investigate the evolution of both the occupied and unoccupied electronic structure in representative compounds of the infinitely adaptive superlattice series (Sb2)m−Sb2Te3 (m=0–3) by means of angle-resolved photoemission spectroscopy and time-delayed tw ...

Amer Physical Soc2015

Spin-stripe phase in a frustrated zigzag spin-1/2 chain

Helmuth Berger

Motifs of periodic modulations are encountered in a variety of natural systems, where at least two rival states are present. In strongly correlated electron systems, such behaviour has typically been associated with competition between short-and long-range ...

Nature Publishing Group2015

Strong interface-induced spin-orbit interaction in graphene on WS2

Helmuth Berger, Zhe Wang, Hua Chen

Interfacial interactions allow the electronic properties of graphene to be modified, as recently demonstrated by the appearance of satellite Dirac cones in graphene on hexagonal boron nitride substrates. Ongoing research strives to explore interfacial inte ...

Nature Publishing Group2015

Three-dimensional momentum-resolved electronic structure of 1T-TiSe2: A combined soft-x-ray photoemission and density functional theory study

Helmuth Berger, Philipp Aebi, Elia Razzoli, Thorsten Schmitt

1T-TiSe2 is a quasi-two-dimensional transition metal dichalcogenide, which exhibits a charge density wave transition at a critical temperature of similar to 200 K as well as low-temperature superconductivity induced by pressure or intercalation. The electr ...

Amer Physical Soc2015

Features of the magnetic properties of quasi-one-dimensional beta-TeVO4 magnets at low temperatures

Helmuth Berger

The effect of a magnetic field on the magnetic susceptibility chi(T) and the temperature of the three magnetic phase transitions in single-crystal beta-TeVO4 is studied at low temperatures. The H-T phase diagram is obtained for H parallel to b and H perpen ...

Amer Inst Physics2015

Orbital textures and charge density waves in transition metal dichalcogenides

Helmuth Berger

Low-dimensional electron systems, as realized in layered materials, often tend to spontaneously break the symmetry of the underlying nuclear lattice by forming so-called density waves(1); a state of matter that at present attracts enormous attention(2-6). ...

Nature Publishing Group2015

Momentum-Resolved Spin Dynamics of Bulk and Surface Excited States in the Topological Insulator Bi2Se3

Helmuth Berger, Philippe Bugnon, Marco Grioni, Alberto Crepaldi

The prospect of optically inducing and controlling a spin-polarized current in spintronic devices has generated wide interest in the out-of-equilibrium electronic and spin structure of topological insulators. In this Letter we show that only measuring the ...

Amer Physical Soc2015

Scanning tunneling microscopy of the charge density wave in 1T-TiSe2 in the presence of single atom defects

Helmuth Berger, Philipp Aebi

We present a detailed low-temperature scanning tunneling microscopy (STM) study of the commensurate charge density wave (CDW) in 1T-TiSe2 in the presence of single atom defects. We find no significant modification of the CDW lattice in single crystals with ...

Amer Physical Soc2015

Physical pressure and chemical expansion effects on the skyrmion phase in Cu2OSeO3

Helmuth Berger

The effects of external (hydrostatic) compression and internal (chemical) expansion on the skyrmion phase have been investigated in Cu2OSeO3 single crystal and Cu2OSe1-xTexO3 (0

Iop Publishing Ltd2015

Page 7 of 16