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Helmuth Berger

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Publications associées (298)

Page 3 sur 15

Triplons, magnons, and spinons in a single quantum spin system: SeCuO3

Helmuth Berger, Henrik Moodysson Rønnow, Ivica Zivkovic, Bruce Normand, Luc Testa

Quantum magnets display a wide variety of collective excitations, including spin waves (magnons), coherent singlet-triplet excitations (triplons), and pairs of fractional spins (spinons). These modes differ radically in nature and properties, and in all co ...

AMER PHYSICAL SOC2021

Strong decoupling between magnetic subsystems in the low-dimensional spin-1/2 antiferromagnet SeCuO3

The search for and understanding of low-dimensional magnetic materials is essential for both fundamental and technological purposes. Here we propose a combined experimental and theoretical investigation of such a system, namely the monoclinic phase of SeCu ...

2019

Analysis of the low-frequency spectrum of the cubic noncentrosymmetric ferrimagnet Cu2OSeO3

The IR reflectance spectra of the cubic noncentrosymmetric ferrimagnet Cu2OSeO3 (T-C approximate to 60 K) were investigated in the temperature range 10-80 K. Detailed analysis of the symmetry and composition of vibrational modes was conducted on the basis ...

2012

Magnetic and resonance properties of the two-dimensional S=1 compound Ni-5(TeO3)(4)Cl-2 with frustrated geometry

The magnetic and magnetoresonance properties of a new single-crystal compound Ni-5(TeO3)(4)Cl-2 are studied. Measurements of the magnetization and magnetic susceptibility of the crystal in a wide temperature range (5-300 K) make it possible to conclude tha ...

2008

Ferrimagnetism of the magnetoelectric compound Cu2OSeO3 probed by Se-77 NMR

Helmuth Berger, Jean-Philippe Ansermet, Frédéric Mila

We present a thorough Se-77 nuclear-magnetic-resonance (NMR) study of a single crystal of the magnetoelectric compound Cu2OSeO3. The temperature dependence of the local electronic moments extracted from the NMR data is fully consistent with a magnetic phas ...

2010

Excitation energy map of high-energy dispersion anomalies in cuprates

The anomalous high-energy dispersion of the conductance band in the high-T-c superconductor Bi(Pb)(2)Sr2CaCu2O8+delta (Pb-Bi2212) has been extensively mapped by angle-resolved photoemission spectroscopy as a function of excitation energy in the range from ...

2008

Soft-mode dynamics and sublattice polarization in an archetypal antiferroelectric

Terahertz and far-infrared techniques are combined with complementary Raman and inelastic neutron scattering results to probe the low-energy phonon dynamics of archetypal antiferroelectric candidate - francisite (Cu3Bi(SeO3)(2)O2Cl). The combined results c ...

IEEE2022

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

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

Differential-thermal analysis around and below the critical temperature T-c of various low-T-c superconductors: A comparative study

We present specific-heat data on the type-II superconductors V3Si, LuNi2B2C and NbSe2 which were acquired with a low-temperature thermal analysis (DTA) technique. We compare our data with available literature data on these superconductors. In the first par ...

2008

Magnetoelectric effects in single crystals of the cubic ferrimagnetic helimagnet Cu2OSeO3

Helmuth Berger, Jean-Philippe Ansermet

We present magnetodielectric measurements in single crystals of the cubic spin-1/2 compound Cu2OSeO3. A magnetic-field-induced electric polarization (P) and a finite magnetocapacitance (MC) is observed at the onset of the magnetically ordered state (T-c = ...

2012

Low-temperature magnetic and thermal properties of the frustrated two-dimensional S=1 compound Ni-5(TeO3)(4)Cl-2

The temperature and magnetic field dependent magnetization of the two-dimensional quantum spin system Ni-5(TeO3)(4)Cl-2 has been investigated using single crystals in temperature range 1.8-100 K and in magnetic fields up to 14 T. The magnetization below th ...

2011

Microscopic evidence for strong periodic lattice distortion in two-dimensional charge-density wave systems

Helmuth Berger, Ji Dai

In quasi-two-dimensional electron systems of layered transition metal dichalcogenides (TMDs) there is still controversy about the nature of the transitions to charge-density wave (CDW) phases, i.e., whether they are described by a Peierls-type mechanism or ...

Amer Physical Soc2014

Observation of charge-transfer-driven antiferroelectricity in 3d-pyrochlore multiferroic Cu2OCl2

Very recently, multiferroic behavior close to the boiling temperature of liquid nitrogen was reported in oxohalide-based Cu2OCl2. In this study, we have established yet another novel mechanism for the origin of charge ordering in multiferroic Cu2OCl2. The ...

ELSEVIER SCIENCE BV2019

Magnetic structure of the S=1Ni(5)(TeO3)(4)Br-2 layered system governed by magnetic anisotropy

Magnetization, neutron diffraction, and antiferromagnetic resonance measurements were employed to investigate the magnetic ground state of Ni-5(TeO3)(4)Br-2 single crystal. Despite the layered topology of the Ni2+ sites, typical for frustrated antiferromag ...

2007

Raman study of the Verwey transition in magnetite at high-pressure and low-temperature: Effect of Al doping

We employed Raman spectroscopy to investigate how the hydrostatic pressure affects the temperature of the Verwey transition in pure (Fe3O4) and Al-doped (Fe2.8Al0.2O4) magnetite. In both samples, pressure suppresses the transition. The Al-doped sample disp ...

Amer Inst Physics2012

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

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

Anomalous frequency and intensity scaling of collective and local modes in a coupled-spin tetrahedral system Cu2Te2O5Cl2

We report on the magnetic excitation spectrum of the coupled-spin tetrahedral system Cu2Te2O5Cl2 using Raman scattering on single crystals. The transition to an ordered state at T-N(Cl)=18.2 K evidenced from thermodynamic data leads to the evolution of dis ...

2009

Charge transfer enhanced magnetic correlations in type-II multiferroic Co3TeO6

Magnetic structure of the Co ions in monoclinic Co3TeO6 in the antiferroelectric state at 16 K has been determined by neutron powder together with single-crystal diffractions. The indices of the magnetic reflections that appear at the incommensurate positi ...

2021

Photoemission as a probe of coexisting and conflicting periodicities in low-dimensional solids

Helmuth Berger, Marco Grioni, Luca Perfetti

When two different periodic potentials are present at the same time in a solid, the electron wavefunctions must conform to the resulting overall periodicity. It is the case of the broken-symmetry phases which are often observed in low-dimensional systems. ...

Institute of Physics (IoP) and Deutsche Physikalische Gesellschaft2005

Field-dependent dielectric and magnetic properties in multiferroic CdCr2S4

Based on the results of field-dependent dielectric and magnetic measurements, we observe several interesting behaviors and phase transitions in this geometrically frustrated spinel system CdCr2S4. (1) A glassy dipolar state occurs near T-C similar to 85 K, ...

2009