Publications by Helmuth Berger

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Doping Bi2Sr2Ca1Cu2O8+y with Co causes a superconductor-insulator transition. We study correlations between changes in the electrical resistivity rho(ab)(T) and the electronic bandstructure using identical single crystalline samples. For undoped samples the resistivity is linear in temperature and has a vanishing residual resistivity. In angle resolved photoemission these samples show dispersing band-like states. Co-doping decreases Te and causes and increase in the residual resistivity. Above a threshold C

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 ...

We use a combination of experimental techniques to demonstrate a general occurrence of spin-orbit interaction (SOI) in graphene on transition metal dichalcogenide (TMD) substrates. Our measurements indicate that SOI is ultrastrong and extremely robust, des ...

Due to imperfect surfaces of most cuprate samples, almost all photoemission studies in the past decade were performed on Bi2Sr2CaCu2O8+x, even though a large fraction of other studies and electronic applications was reported for YBa2Cu3O7-delta (YBCO) family of superconducting compounds. In order to systematically study the gap parameter and the Fermi surface variation in high symmetry directions of YBCO and related oxide films we have constructed a new facility at the Wisconsin Synchrotron Radiation Center

We present high resolution (Delta E=120 meV) resonant inelastic x-ray scattering data measured at the Ni L-3 edge (2p(3/2)-> 3d) on the paradigmatic antiferromagnetic oxide NiO. Spectra reveal clear signatures of magnetic excitations at similar to 95 and s ...

Elementary excitations in condensed matter capture the complex many-body dynamics of interacting basic entities in a simple quasiparticle picture. In magnetic systems the most established quasiparticles are magnons, collective excitations that reside in or ...

In Ti-intercalated self-doped 1T-TiSe2 crystals, the charge density wave (CDW) superstructure induces two nonequivalent sites for Ti dopants. Recently, it has been shown that increasing Ti doping dramatically influences the CDW by breaking it into phase-sh ...

The manipulation of the electronic properties of solids by light is an exciting goal, which requires knowledge of the electronic structure with energy, momentum and temporal resolution. Time- and angle-resolved photoemission spectroscopy (tr-ARPES) is the ...

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 ...

We observe a giant spin-orbit splitting in the bulk and surface states of the noncentrosymmetric semiconductor BiTeI. We show that the Fermi level can be placed in the valence or in the conduction band by controlling the surface termination. In both cases, ...

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 ...

The ab-plane optical properties of the high-temperature superconductor Bi2Sr2CaCu2O8 are anisotropic in both the normal and the superconducting state. Consistent with the orthorhombic structure, the principal axes lie along the a and b crystallographic axes, nearly 45 degrees from the Cu-O bond direction. In the normal state, analysis of the temperature-dependent optical conductivity suggests a:scattering rate for the free carriers that shows ab anisotropy in both magnitude and temperature dependence. In;th

We investigate by means of high resolution angular resolved photoemission spectroscopy the classical one-dimensional organic conductor TTF-TCNQ and the inorganic one-dimensional conductor (TaSe4)(2)I. We measure dispersive features (1D bands) in accordance with band structure calculations. We observe typical bulk specific properties like the band periodicities (i.e. the Fermi wavevector) and the CDW-gap, which are in agreement with other experimental techniques. Peculiar for one-dimensional systems, we do n

The quest for investigating the non-equilibrium dynamics of the band structure of strongly-correlated materials over their entire Brillouin zone is a primary objective. However, the actual ultrafast UV light sources are not suitable for addressing several ...

High-resolution angle-resolved photoemission spectroscopy data reveal evidence of a crossover from one-dimensional (1D) to three-dimensional (3D) behavior in the prototypical charge density wave (CDW) material NbSe3. In the low-temperature 3D regime, gaps ...

As carriers are introduced into the cuprates (by doping the insulating "parent" compounds) spectral weight appears in the optical spectrum at photon energies below the charge-transfer gap. This spectral weight increases as the doping level increases. Magnetic penetration depth measurements have shown a good correlation between superfluid density and superconducting transition temperature in the underdoped-to-optimally-doped part of the phase diagram. Optical measurements allow independent determination of t

This paper is devoted to investigation of luminescence and some electric properties of C-60 single crystal and their connection with X-traps model. Luminescence properties for C-60 single crystal, the temperature dependence of the luminescence spectra and decay kinetics were measured for wide range of excitation energies. At low temperatures the emission spectra with well resolved structure were detected. Opposite to the case of C-60 films, the single crystal shape of the luminescence spectra also change wi

Long known for its peculiar resistivity, showing a thus far unexplained anomalous peak as a function of temperature, ZrTe5 has recently received rising attention in a somewhat different context. While both theoretical and experimental results seem to point ...

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 ...

We have studied the influence of Co and Ni doping on the electronic band structure and the transport properties of high-temperature superconductors. The doping has dramatic effects on both the normal and the superconducting state. Upon doping the residual resistivity increases strongly. For sufficiently high Co concentration the temperature dependence rho(T) turns from a simple linear dependence to one displaying a minimum around T-min = 190 K. This minimum is followed by an upturn (d rho/dT

Helmuth Berger

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Localization Effects in Transition-Metal Doped Bi2sr2cacu2o8+Y High-Temperature Superconductors

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

Origin and Magnitude of 'Designer' Spin-Orbit Interaction in Graphene on Semiconducting Transition Metal Dichalcogenides

Electronic properties of layered oxides: Pulsed laser deposition of YBCO films for in-situ studies by photoemission spectroscopy

Observation of Two Nondispersive Magnetic Excitations in NiO by Resonant Inelastic Soft-X-Ray Scattering

Elementary excitation in the spin-stripe phase in quantum chains

Local resilience of the 1T-TiSe2 charge density wave to Ti self-doping

Time-resolved ARPES at LACUS: Band Structure and Ultrafast Electron Dynamics of Solids

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

Giant Ambipolar Rashba Effect in the Semiconductor BiTeI

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

Anisotropy in the ab-plane optical properties of Bi2Sr2CaCu2O8 single-domain crystals

Photoemission study of organic and inorganic CDW-systems

Advancing non-equilibrium ARPES experiments by a 9.3 eV coherent ultrafast photon source

Dimensional Crossover in a Charge Density Wave Material Probed by Angle-Resolved Photoemission Spectroscopy

Superfluid and normal-fluid density in the cuprate superconductors

X-trap influence on luminescence and electric properties of C-60 single crystal

Nature and topology of the low-energy states in ZrTe5

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

Localization effects in Co- and Ni-doped Bi2Sr2CaCu2O8+gamma