arXiv subjects

W. Winkler

Publications and source records attributed to W. Winkler.

5 recordsLinked to original sources

arXiv2020

Electronic structure of InAs and InSb surfaces: density functional theory and angle-resolved photoemission spectroscopy

The electronic structure of surfaces plays a key role in the properties of quantum devices. However, surfaces are also the most challenging to simulate and engineer. Here, we study the electronic structure of InAs(001), InAs(111), and InSb(110) surfaces using a combination of density functional theory (DFT) and angle-resolved photoemission spectroscopy (ARPES). We were able to perform large-scale first principles simulations and capture effects of different surface reconstructions by using DFT calculations with a machine-learned Hubbard U correction [npj Comput. Mater. 6, 180 (2020)]. To facilitate direct comparison with ARPES results, we implemented a "bulk unfolding" scheme by projecting the calculated band structure of a supercell surface slab model onto the bulk primitive cell. For all three surfaces, we find a good agreement between DFT calculations and ARPES. For InAs(001), the simulations clarify the effect of the surface reconstruction. Different reconstructions are found to produce distinctive surface states. For InAs(111) and InSb(110), the simulations help elucidate the effect of oxidation. Owing to larger charge transfer from As to O than from Sb to O, oxidation of InAs(111) leads to significant band bending and produces an electron pocket, whereas oxidation of InSb(110) does not. Our combined theoretical and experimental results may inform the design of quantum devices based on InAs and InSb semiconductors, e.g., topological qubits utilizing the Majorana zero modes.

cond-mat.mtrl-sci↗

arXiv2010

Interpretation of the Dispersion of the Electron States of High-$T_{c}$ Cuprate Superconductors Based on the Theory of Topological Resonance

The unusual dispersion of electron states in antinodal direction for $n_{h}\simeq\frac{1}{8}$ holes/copper is explained. In photoelectron excitations, transformations of the $\mathbf{k}$ space as a consequence of symmetry breaking proves to be an exceptional phenomenon distinctly reflected by the experiments. Paired photoelectron emissions are predicted that enable a new energetic upward shift termed as \emph{pair shake-up effect} which explains the experimentally observed sharp transition between non-dispersive and dispersive behaviour. The disappearance of antinodal states for $\mathbf{k}_{||}ε[0,\pm π/2]$ is explained.

cond-mat.supr-con↗

arXiv2007

Photon pressure induced test mass deformation in gravitational-wave detectors

A widely used assumption within the gravitational-wave community has so far been that a test mass acts like a rigid body for frequencies in the detection band, i.e. for frequencies far below the first internal resonance. In this article we demonstrate that localized forces, applied for example by a photon pressure actuator, can result in a non-negligible elastic deformation of the test masses. For a photon pressure actuator setup used in the gravitational wave detector GEO600 we measured that this effect modifies the standard response function by 10% at 1 kHz and about 100% at 2.5 kHz.

gr-qc↗

arXiv2003

Intrinsically coupled stripes within the CuO2 planes of high-Tc materials

Analysis of the electronic state of the CuO2 planes of high-Tc materials has been performed with special regard to the influence of the Coulomb interactions separated after moments. Different symmetry breaking effects were revealed. A commensurate charge and bonding fluctuation state (CBF) with the period (2a,2b) is established which exists collinearly with the antiferromagnetic spin state. The CBF state and the antiferromagnetic spin state are result of the same electronic renormalizations. The existence of localized topological hole states under hole doping is established. As a consequence of this local symmetry is broken. A quadrupolar-polarization induced attractive hole-hole interaction can exist between such topological hole states. This interaction creates an ordered topological hole structure which leads to a global symmetry breaking. The ordered topological hole structure (b-holes) can be characterized as parallel one-dimensional electronic states (stripes) along particular ..Cu-O-Cu.. bonding directions being intrinsically coupled to each other. The b-hole state exists undisturbed for hole concentrations n in the range of 0.125 <= n <= 0.25 holes/copper. In addition to b-holes, holes which are not intrinsically bonded exist (f-holes) for hole concentrations of n > 0.125 holes/copper. The inevitable consequence is an electronic two fluid behaviour (b-holes, f-holes) within the range of 0.125 < n <= 0.25 holes/copper. A comparison with experimental results is given with particular respect to mySR, neutron scattering (1/8 problem), Hall-effect anomalies and scanning tunneling microscopy (STM).

cond-mat.supr-con↗

arXiv2000

Demonstration of detuned dual recycling at the Garching 30m laser interferometer

Dual recycling is an advanced optical technique to enhance the signal-to-noise ratio of laser interferometric gravitational wave detectors in a limited bandwidth. To optimise the center of this band with respect to Fourier frequencies of expected gravitational wave signals detuned dual recycling has to be implemented. We demonstrated detuned dual recycling on a fully suspended 30m prototype interferometer. A control scheme that allows to tune the detector to different frequencies will be outlined. Good agreement between the experimental results and numerical simulations has been achieved.

gr-qc↗