Publications by Helmuth Berger

Spin-Reorientation-Driven Linear Magnetoelectric Effect in Topological Antiferromagnet Cu3TeO6

The search for new materials for energy -efficient electronic devices has gained unprecedented importance. Among the various classes of magnetic materials driving this search are antiferromagnets, magnetoelectrics, and systems with topological spin excitat ...

Amer Physical Soc2024

Peculiarities of electron transport and resistive switching in point contacts on TiSe2, TiSeS, and CuxTiSe2

Helmuth Berger

Compound TiSe2 has received much attention among the transition metal chalcogenides because of its thrilling physical properties concerning atypical resistivity behavior, the emergence of charge density wave (CDW) state, induced superconductivity, etc. Her ...

2023

Origin of Subgap States in Normal-Insulator-Superconductor van der Waals Heterostructures

Helmuth Berger, László Forró

Superconductivity in van der Waals materials, such as NbSe2 and TaS2, is fundamentally novel due to the effects of dimensionality, crystal symmetries, and strong spin-orbit coupling. In this work, we perform tunnel spectroscopy on NbSe2 by utilizing MoS2 o ...

AMER CHEMICAL SOC2023

Coherent description of the magnetic properties of SeCuO3 versus temperature and magnetic field

Helmuth Berger

We report a combined theoretical and experimental investigation devoted to getting deeper insights into the exotic magnetic properties of the low-dimensional SeCuO3 system, for which the two inequivalent Cu(1) and Cu(2) sites show different quantum dynamic ...

AMER PHYSICAL SOC2023

Electronic transport and magnetism in the alternating stack of metallic and highly frustrated magnetic layers in Co(1/3)NbS(2)

Helmuth Berger, László Forró, Julian Piatek, Henrik Moodysson Rønnow, Ivica Zivkovic, Jacim Jacimovic, Nikolay Tsyrulin

Transition-metal dichalcogenides (TMDs) are layered compounds that support many electronic phases, including various charge density waves, superconducting, and Mott insulating states. Their intercalation with magnetic ions introduces magnetic sublayers, wh ...

AMER PHYSICAL SOC2023

Second-harmonic generation in atomically thin 1T-TiSe2 and its possible origin from charge density wave transitions

Helmuth Berger, László Forró

Optical second-harmonic generation (SHG) can only occur in noncentrosymmetric crystals in the leading electric-dipole approximation. Transition metal dichalcogenides with the 1T octahedral coordination is centrosymmetric, hence precluding SHG. Here we repo ...

AMER PHYSICAL SOC2022

Soft-mode dynamics and sublattice polarization in an archetypal antiferroelectric

Helmuth Berger

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

Influence of Dimensionality on the Charge Density Wave Phase of 2H-TaSe2

Helmuth Berger

Metallic transition metal dichalcogenides like tantalum diselenide (TaSe2) exhibit exciting behaviors at low temperatures, including the emergence of charge density wave (CDW) states. In this work, density functional theory (DFT) is used to catalog influen ...

WILEY-V C H VERLAG GMBH2022

van der Waals pi Josephson Junctions

Helmuth Berger, László Forró

Proximity-induced superconductivity in a ferromagnet can induce Cooper pairs with a finite center-of-mass momentum and stabilize Josephson junctions (JJs) with pi phase difference in superconductor-ferromagnet-superconductor heterostructures. The emergence ...

AMER CHEMICAL SOC2022

Axial-Bonding-Driven Dimensionality Effect on the Charge-Density Wave in NbSe2

Helmuth Berger, László Forró

2H-NbSe2 is a prototypical charge-density-wave (CDW) system, exhibiting such a symmetry-breaking quantum ground state in its bulk and down to a single-atomic-layer limit. However, how this state depends on dimensionality and what governs the dimensionality ...

AMER CHEMICAL SOC2022

Optically induced changes in the band structure of the Weyl charge-density-wave compound (TaSe4)(2)I

Helmuth Berger, Marco Grioni, Majed Chergui, Oleg Yazyev, Alberto Crepaldi, Daniel Gosalbez Martinez, Michele Puppin

Collective modes are responsible for the emergence of novel quantum phases in topological materials. In the quasi-one dimensional (1D) Weyl semimetal (TaSe4)(2)I < i , a charge density wave (CDW) opens band gaps at the Weyl points, thus turning the system ...

2022

Role of intercalated cobalt in the electronic structure of Co1/3NbS2

Helmuth Berger, László Forró

Co1/3NbS2 is the magnetic intercalate of 2H-NbS2 where electronic itinerant and magnetic properties strongly influence each other throughout the phase diagram. Here we report the angle-resolved photoelectron spectroscopy (ARPES) study in Co1/3NbS2. In agre ...

AMER PHYSICAL SOC2022

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

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

Origin of large magnetoresistance in the topological nonsymmorphic semimetal TaSe3

Jean-Philippe Ansermet, Helmuth Berger, Oleg Yazyev, Alberto Crepaldi, Gabriel Albert Autes, Gianmarco Gatti, Daniel Gosalbez Martinez, Quansheng Wu, Michele Puppin, Shengnan Zhang

TaSe3 is a layered van der Waals semimetal with several inverted band gaps throughout the entire Brillouin zone and nontrivial Z(2) topological indices, which place it at the boundary between a strong and a weak topological phase. Our transport experiments ...

2021

Charge transfer enhanced magnetic correlations in type-II multiferroic Co3TeO6

Helmuth Berger

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

Order-disorder type of Peierls instability in BaVS3

Helmuth Berger

Lattice dynamics of low-dimensional BaVS3 is reported across the metal-insulator Peierls transition occurring at T-P = 69 K using a combination of the thermal diffuse scattering of x rays, inelastic x-ray scattering, and density-functional theory calculati ...

AMER PHYSICAL SOC2021

Hidden bulk and surface effects in the spin polarization of the nodal-line semimetal ZrSiTe

Helmuth Berger, Marco Grioni, Arnaud Magrez, Oleg Yazyev, Alberto Crepaldi, Mauro Fanciulli, Gianmarco Gatti, Daniel Gosalbez Martinez, Silvan Dino Marcos Roth

Local inversion symmetry breaking in centrosymmetric materials can lead to large spin polarization of the electronic band structure in separate sectors of the unit cell. Here, the authors reveal such hidden spin polarisation in ZrSiTe using spin and angle ...

NATURE RESEARCH2021

Control of a polar order via magnetic field in a vector-chiral magnet

Helmuth Berger

Vector-chiral (VC) antiferromagnetism is a spiral-like ordering of spins which may allow ferroelectricity to occur due to loss of space inversion symmetry. In this Letter we report direct experimental observation of ferroelectricity in the VC phase of beta ...

AMER PHYSICAL SOC2021

Two-fold symmetric superconductivity in few-layer NbSe2

Helmuth Berger, László Forró, Xi Zhang

The strong Ising spin-orbit coupling in certain two-dimensional transition metal dichalcogenides can profoundly affect the superconducting state in few-layer samples. For example, in NbSe2, this effect combines with the reduced dimensionality to stabilize ...

NATURE RESEARCH2021

Unidirectional Kondo scattering in layered NbS2

Helmuth Berger, László Forró, Oleg Yazyev, Christoph Koch, Edoardo Martino, Quansheng Wu, Shengnan Zhang, Philip Johannes Walter Moll, Matthias Carsten Putzke, Konstantin Semeniuk

Crystalline defects can modify quantum interactions in solids, causing unintuitive, even favourable, properties such as quantum Hall effect or superconducting vortex pinning. Here we present another example of this notion-an unexpected unidirectional Kondo ...

NATURE PORTFOLIO2021