arXiv subjects

A. Schmid

Publications and source records attributed to A. Schmid.

8 recordsLinked to original sources

arXiv2026

Sign-resolved nanoscale readout and control of hidden antiferromagnetic spin order

Antiferromagnetic memories promise ultrafast, stray-field-free information storage. Yet perfect magnetic compensation conceals the information carrier itself: the sign of the N\'eel vector distinguishing two time-reversed states. Moreover, in future dense memories, the local polarity of N\'eel domains would need to be read out on the nanoscale. We make this hidden polarity visible in a fully-compensated, high-N\'eel-temperature, PT-symmetric antiferromagnet by driving interband electric-dipole transitions by mid-infrared near-fields confined at a scanning probe. The excitation generates a N\'eel-order-dependent quantum-metric photocurrent, a Hall-like signal reversing with N\'eel order, which we term the optical nonlinear anomalous Hall effect. This optically induced electrical readout maps opposite N\'eel polarities with sub-100-nm resolution at room temperature and, combined with spin-orbit-torque writing, reveals N\'eel-texture polarization and reversible domain-wall motion, establishing electrical-write/optoelectronic-read antiferromagnetic functionality.

cond-mat.mtrl-sci↗

arXiv2013

Investigation on the energy and mass composition of cosmic rays using LOPES radio data

The sensitivity to the mass composition as well as the reconstruction of the energy of the primary particle are explored here by leveraging the features of the radio lateral distribution function. For the purpose of this analysis, a set of events measured with the LOPES experiment is reproduced with the latest CoREAS radio simulation code. Based on simulation predictions, a method which exploits the slope of the radio lateral distribution function is developed (Slope Method) and directly applied on measurements. As a result, the possibility to reconstruct both the energy and the depth of the shower maximum of the cosmic ray air shower using radio data and achieving relatively small uncertainties is presented.

astro-ph.HE↗

arXiv2013

Vectorial Radio Interferometry with LOPES 3D

One successful detection technique for high-energy cosmic rays is based on the radio signal emitted by the charged particles in an air shower. The LOPES experiment at Karlsruhe Institute of Technology, Germany, has made major contributions to the evolution of this technique. LOPES was reconfigured several times to improve and further develop the radio detection technique. In the latest setup LOPES consisted of 10 tripole antennas. With this, LOPES 3D was the first cosmic ray experiment measuring all three vectorial field components at once and thereby gaining the full information about the electric field vector. We present an analysis based on the data taken with special focus on the benefits of a direct measurement of the vertical polarization component. We demonstrate that by measuring all polarization components the detection and reconstruction efficiency is increased and noisy single channel data can be reconstructed by utilising the information from the other two channels of one antenna station.

astro-ph.IM↗

arXiv2013

Reconstructing energy and Xmax of cosmic ray air showers using the radio lateral distribution measured with LOPES

The LOPES experiment, a digital radio interferometer located at KIT (Karlsruhe Institute of Technology), obtained remarkable results for the detection of radio emission from extensive air showers at MHz frequencies. Features of the radio lateral distribution function (LDF) measured by LOPES are explored in this work for a precise reconstruction of two fundamental air shower parameters: the primary energy and the shower Xmax. The method presented here has been developed on (REAS3-)simulations, and is applied to LOPES measurements. Despite the high human-made noise at the LOPES site, it is possible to reconstruct both the energy and Xmax for individual events. On the one hand, the energy resolution is promising and comparable to the one of the co-located KASCADE-Grande experiment. On the other hand, Xmax values are reconstructed with the LOPES measurements with a resolution of 90 g/cm2 . A precision on Xmax better than 30 g/cm2 is predicted and achievable in a region with a lower human-made noise level.

astro-ph.IM↗

arXiv2013

Mass sensitivity in the radio lateral distribution function

Measuring the mass composition of ultra-high energy cosmic rays is one of the main tasks in the cosmic rays field. Here we are exploring the composition signature in the coherent electromagnetic emission from extensive air showers, detected in the MHz frequency range. One of the experiments that successfully detects radio events in the frequency band of 40-80 MHz is the LOPES experiment at KIT. It is a digital interferometric antenna array and has the important advantage of taking data in coincidence with the particle detector array KASCADE-Grande. A possible method to look at the composition signature in the radio data, predicted by simulations, concerns the radio lateral distribution function, since its slope is strongly correlated with Xmax. Recent comparison between REAS3 simulations and LOPES data showed a significantly improved agreement in the lateral distribution function and for this reason an analysis on a possible LOPES mass signature through the slope method is promising. Trying to reproduce a realistic case, proton and iron showers are simulated with REAS3 using the LOPES selection information as input parameters. The obtained radio lateral distribution slope is analyzed in detail. The lateral slope method to look at the composition signature in the radio data is shown here and a possible signature of mass composition in the LOPES data is discussed.

astro-ph.IM↗

arXiv1995

Resonances in the current-voltage characteristics of a dissipative Josephson junction

The I-V characteristics of a Josephson junction shunted by an Ohmic resistor shows sharp peaks when levels in neighbouring wells are crossing. We consider the shape and size of these peaks using a double-well model where the wells are given in parabolic approximation. The friction of arbitrary strength is included by the help of a bath of infinitely many degrees of freedom.

cond-mat↗

arXiv1995

Vortex dynamics in disordered type-II superconductors

A field theoretical method is developed which permits us to study the dynamics of vortices in disordered environments. In particular, we obtain a self-consistent system of equations for disorder averaged quantities. Making use of a Hartree-type approximation, we calculate the current-voltage (I-V) characteristics in the flux flow regime. In order to probe incipient melting of the vortex lattice we propose an experiment where interference steps in the I-V characteristics are observed, which arise when a small ac field is superimposed on the constant voltage.

cond-mat↗

arXiv1995

Mesoscopic Systems With Fixed Number of Electrons

In this paper, we study the physics of mesoscopic systems with noninteracting, but fixed number of electrons. From a technical point of view, this means a discussion of the differences between the canonical and the grand canonical ensemble (fixed versus fluctuating number of particles). Such a discussion is not trivial since the grand canonical ensemble is the most convenient basis for the statistics of identical particles and one has to spend labour in order to retrieve the canonical ensemble. Specifically, we are considering ensembles of mesoscopic systems with disorder, either by atomic defects or by fluctuations in their geometric definitions and we discuss various forms of disorder averages.

cond-mat↗