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Helmuth Berger

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Related publications (311)

Unexpected observation of splitting of skyrmion phase in Zn doped Cu2OSeO3

Helmuth Berger

Polycrystalline (Cu1-xZnx)(2)OSeO3 (0

Nature Publishing Group2015

Universal helimagnon and skyrmion excitations in metallic, semiconducting and insulating chiral magnets

Helmuth Berger, Dirk Grundler

Nearly seven decades of research on microwave excitations of magnetic materials have led to a wide range of applications in electronics(1-4). The recent discovery of topological spin solitons in chiral magnets, so-called skyrmions(5-9), promises high-frequ ...

Nature Publishing Group2015

Bulk and surface band structure of the new family of semiconductors BiTeX (X=I, Br, Cl)

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

We present an overview of the new family of semiconductors BiTeX (X = I, Br, Cl) from the perspective of angle resolved photoemission spectroscopy. The strong band bending occurring at the surface potentially endows them with a large flexibility, as they a ...

Elsevier2015

Torque magnetometry study of magnetically ordered state and spin reorientation in the quasi-one-dimensional S=1/2 Heisenberg antiferromagnet CuSb2O6

Helmuth Berger

The antiferromagnetically ordered state of the monoclinic quasi-one-dimensional S = 1/2 Heisenberg antiferromagnet CuSb2O6 was studied combining torque magnetometry with a phenomenological approach to magnetic anisotropy. This system is known to have a num ...

Amer Physical Soc2015

Enhanced low-temperature thermoelectrical properties of BiTeCl grown by topotactic method

Helmuth Berger, Philippe Bugnon, László Forró, Richard Gaal, Arnaud Magrez, Ana Akrap, Jacim Jacimovic, Xavier François Mettan, Sergiy Katrych, Andrea Pisoni

We developed a topotactic strategy to grow BiTeCl single crystals. Structural characterization by means of X-ray diffraction was performed, and the high crystallinity of the material was proven. Measurements of the thermoelectrical coefficients electrical ...

Pergamon-Elsevier Science Ltd2014

Enhanced quasiparticle dynamics of quantum well states: The giant Rashba system BiTeI and topological insulators

Helmuth Berger

In the giant Rashba semiconductor BiTeI, electronic surface scattering with Lorentzian linewidth is observed that shows a strong dependence on surface-termination and surface-potential shifts. A comparison with the topological insulator Bi2Se3 evidences th ...

American Physical Society2014

Establishing the Fundamental Magnetic Interactions in the Chiral Skyrmionic Mott Insulator Cu2OSeO3 by Terahertz Electron Spin Resonance

Jean-Philippe Ansermet, Helmuth Berger

The recent discovery of Skyrmions in Cu2OSeO3 has established a new platform to create and manipulate Skyrmionic spin textures. We use high-field electron spin resonance with a terahertz free-electron laser and pulsed magnetic fields up to 64 T to probe an ...

Amer Physical Soc2014

Anisotropic softening of magnetic excitations along the nodal direction in superconducting cuprates

Helmuth Berger, Marco Grioni, Bastien Dalla Piazza, Henrik Moodysson Rønnow, Marco Guarise, Thorsten Schmitt

The high-T-c cuprate superconductors are close to antiferromagnetic order. Recent measurements of magnetic excitations have reported an intriguing similarity to the spin wavesmagnons- of the antiferromagnetic insulating parent compounds, suggesting that ma ...

Nature Publishing Group2014

Doping Nature of Native Defects in 1T-TiSe2

Helmuth Berger, Philipp Aebi

The transition-metal dichalcogenide 1T-TiSe2 is a quasi-two-dimensional layered material with a charge density wave (CDW) transition temperature of T-CDW approximate to 200 K. Self-doping effects for crystals grown at different temperatures introduce struc ...

Amer Physical Soc2014

Magnetic, structural, and electronic properties of the multiferroic compound FeTe2O5Br with geometrical frustration

Helmuth Berger

We report electron spin resonance (ESR), Raman scattering, and interband absorption measurements of the multiferroic FeTe2O5Br with two successive magnetic transitions at T-N1 = 11.0 K and T-N2 = 10.5 K. ESR measurements show all characteristics of a low-d ...

Iop Publishing Ltd2014

Mono- and Bilayer WS2 Light-Emitting Transistors

Helmuth Berger

We have realized ambipolar ionic liquid gated field-effect transistors based on WS2 mono- and bilayers, and investigated their opto-electronic response. A thorough characterization of the transport properties demonstrates the high quality of these devices ...

Amer Chemical Soc2014

Spin dynamics and magnetoelectric properties of the coupled-spin tetrahedral compound Cu2Te2O5Cl2

Helmuth Berger

We report on the spin dynamics and discovery of magnetoelectricity in the coupled-spin tetrahedral compound Cu2Te2O5Cl2. Te-125 NMR measurements show an anomalous resonance frequency shift and a signal wipe-out phenomenon around the Neel temperature T-N = ...

Amer Physical Soc2014

Atomic and electronic structure of a Rashba p-n junction at the BiTeI surface

Helmuth Berger, Philippe Bugnon, Marco Grioni, Oleg Yazyev, Gabriel Albert Autes, Cédric Tournier-Colletta

The non-centro-symmetric semiconductor BiTeI exhibits two distinct surface terminations that support spin-split Rashba surface states. Their ambipolarity can be exploited for creating spin-polarized p-n junctions at the boundaries between domains with diff ...

American Physical Society2014

High-energy collective electronic excitations in layered transition-metal dichalcogenides

Helmuth Berger

We characterize experimentally and theoretically the collective electronic excitations in two prototypical layered transition-metal dichalcogenides, NbSe2 and Cu0.2NbS2. The energy- and momentum-dependent dynamical structure factor was measured by inelasti ...

Amer Physical Soc2014

Momentum and photon energy dependence of the circular dichroic photoemission in the bulk Rashba semiconductors BiTeX (X = I, Br, Cl)

Helmuth Berger, Philippe Bugnon, Marco Grioni, Arnaud Magrez, Oleg Yazyev, Luca Moreschini, Alberto Crepaldi, Gabriel Albert Autes, Cédric Tournier-Colletta, Jens Christian Johannsen

Bulk Rashba systems BiTeX (X = I, Br, Cl) are emerging as important candidates for developing spintronics devices because of the coexistence of spin-split bulk and surface states, along with the ambipolar character of the surface charge carriers. The need ...

American Physical Society2014

Exploration of the helimagnetic and skyrmion lattice phase diagram in Cu2OSeO3 using magnetoelectric susceptibility

Helmuth Berger, Arnaud Magrez, Krunoslav Prsa, Henrik Moodysson Rønnow, Ivica Zivkovic, Arash Alahgholipour Omrani, Jonathan White

Using superconducting quantum interference device magnetometry techniques, we have studied the change in magnetization versus applied ac electric field, i.e. the magnetoelectric (ME) susceptibility dM/dE, in the chiral-lattice ME insulator Cu2OSeO3. Measur ...

Amer Physical Soc2014

Thermal diffusivity measurements of templated nanocomposite using infrared thermography

Helmuth Berger, Philippe Bugnon, Arnaud Magrez, Manish Sharma

Electrodeposited bismuth telluride (Bi2Te3) nanowires using anodic alumina (AAO) templates show anisotropic thermal properties in a direction parallel and perpendicular to the nanowire/nanochannel axis. The present study reports thermal diffusivity measure ...

Elsevier Science Bv2014

Optical properties of BiTeBr and BiTeCl

Helmuth Berger, Philippe Bugnon, Arnaud Magrez, Ana Akrap, Dirk Van der Marel

We present a comparative study of the optical properties-reflectance, transmission, and optical conductivity- and Raman spectra of two layered bismuth-tellurohalides BiTeBr and BiTeCl at 300 and 5 K, for light polarized in the a-b planes. Despite different ...

Amer Physical Soc2014

An innovative Yb-based ultrafast deep ultraviolet source for time-resolved photoemission experiments

Helmuth Berger, Arnaud Magrez

Time- and angle-resolved photoemission spectroscopy is a powerful technique to study ultrafast electronic dynamics in solids. Here, an innovative optical setup based on a 100-kHz Yb laser source is presented. Exploiting non-collinear optical parametric amp ...

Amer Inst Physics2014

Unusual Shubnikov-de Haas oscillations in BiTeCl

Helmuth Berger, Philippe Bugnon, Arnaud Magrez

We report measurements of Shubnikov-de Haas oscillations in single crystals of BiTeCl at magnetic fields up to 31 T and at temperatures as low as 0.4 K. Two oscillation frequencies were resolved at the lowest temperatures, F-1 = 65 +/- 4 T and F-2 = 156 +/ ...

Amer Physical Soc2014

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