arXiv subjects

E. Scheer

Publications and source records attributed to E. Scheer.

15 recordsLinked to original sources

arXiv2026

Topography-based navigation in a millikelvin scanning tunneling microscope using binary-encoded position markers

We present a compact millikelvin scanning tunneling microscope (STM) operating at 270mK with topographic navigation to micron-scale targets. Two piezoelectric low-temperature nanopositioners extend the accessible sample area, while a multi-stage copper powder and capillary filter scheme preserves millikelvin energy resolution, verified by BCS spectroscopy on aluminium thin films. A lithographically fabricated binary-encoded gold pattern encodes unique 16-bit coordinates in 4x4 pixels of 200nm$\times$200nm each. We demonstrate absolute positioning across a 350$\times$350$\mathrm{\mu}$m$^2$ area from a single STM scan. Requiring only a single lithography step and no hardware modifications to existing STM setups, the navigation system provides a versatile platform for scanning tunneling spectroscopy of nanoflakes and nanoscale devices.

cond-mat.mes-hall↗

arXiv2026

Benchmarking Current-to-Voltage Amplifiers for Quantum Transport Measurements

Accurate electrical amplification is essential in molecular electronics for measuring conductance through atomic and molecular junctions, where currents often span several orders of magnitude. In this work, we present a systematic design and comparative analysis of four current-to-voltage ($I\text{--}V$) amplifier architectures: single-stage linear, series-linear, logarithmic, and multi-stage cascaded, specifically optimized for break junction (BJ) techniques, including scanning tunneling microscopy (STM-BJ) and mechanically controllable break junctions (MCBJ). Each configuration is evaluated based on sensitivity, noise performance, and dynamic range. Our results characterize the trade-offs between circuit complexity and noise, providing a robust framework and practical guidelines for selecting amplification schemes in quantum transport experiments.

cond-mat.mes-hall↗

arXiv2025

Imaging of Gate-Controlled Suppression of Superconductivity via the Meissner Effect

It was recently discovered that supercurrents flowing through thin superconducting nanowires can be quenched by a gate voltage. This gate control of supercurrents, known as the GCS effect, could enable superconducting transistor logic. Here, we report that the GCS also manifests in a suppression of Meissner screening, establishing the phenomenon as a genuine feature of superconductivity that is not restricted to transport. Using a scanning nitrogen-vacancy magnetometer at sub-Kelvin temperatures, we image the nanoscale spatial region of GCS suppression in micron-size niobium islands. Our observations are compatible with a microscopic hot-spot model of quasiparticle generation and diffusion, and in conflict with other candidate mechanisms such as Joule heating or an electric field effect. Our work introduces an alternative means for studying quasiparticle dynamics in superconducting nanostructures, and showcases the power of local imaging techniques for understanding emergent condensed matter phenomena.

cond-mat.mes-hall↗

arXiv2023

Demonstration of high-impedance superconducting NbRe Dayem bridges

Here we demonstrate superconducting Dayem-bridge weak-links made of different stoichiometric compositions of NbRe. Our devices possess a relatively high critical temperature, normal-state resistance, and kinetic inductance. In particular, the high kinetic inductance makes this material a good alternative to more conventional niobium-based superconductors (e.g., NbN or NbTiN) for the realization of superinductors and high-quality factor resonators, whereas the high normal-state resistance yields a large output voltage in superconducting switches and logic elements realized upon this compound. Moreover, out-of-plane critical magnetic fields exceeding 2 T ensure that possible applications requiring high magnetic fields can also be envisaged. Altogether, these features make this material appealing for a number of applications in the framework of quantum technologies.

cond-mat.supr-con↗

arXiv2022

Calorimetry of a Quantum Phase Slip

In a Josephson junction, which is the central element in superconducting quantum technology, irreversibility arises from abrupt slips of the gauge-invariant quantum phase difference across the contact. A quantum phase slip (QPS) is often visualized as the tunneling of a flux quantum in the transverse direction to the superconducting weak link, which produces dissipation. In this work, we detect the instantaneous heat release caused by a QPS in a Josephson junction using time-resolved electron thermometry on a nanocalorimeter, signaled by an abrupt increase of the local electronic temperature in the weak link and subsequent relaxation back to equilibrium. Beyond providing a cornerstone in experimental quantum thermodynamics in form of observation of heat in an elementary quantum process, this result sets the ground for experimentally addressing the ubiquity of dissipation, including that in superconducting quantum sensors and qubits.

cond-mat.mes-hall↗

arXiv2019

Influence of electron-vibration interactions on electronic current noise of atomic and molecular junctions

We present an ab-initio method to simulate the current noise in the presence of electron-vibration interactions in atomic and molecular junctions at finite temperature. Using a combination of nonequilibrium Keldysh Green's function techniques and density functional theory, we study the elastic and inelastic contributions to electron current and shot noise within a wide range of transmission values in systems exhibiting multiple electronic levels and vibrational modes. Within our model we find the upper threshold, at which the inelastic noise contribution changes sign, at a total transmission between $\tau\approx 0.90$ and $0.95$ for gold contacts. This is higher than predicted by the single-level Holstein model but in agreement with earlier experimental observations. We support our theoretical studies by noise measurements on single-atom gold contacts which confirm previous experiments but make use of a new setup with strongly reduced complexity of electronic circuitry. Furthermore, we identify 1,4-benzenedithiol connected to gold electrodes as a system to observe the lower sign change, which we predict at around $\tau\approx 0.2$. Finally, we discuss the influence of vibrational heating on the current noise.

cond-mat.mes-hall↗

arXiv2016

Electronic Transport in Gadolinium Atomic-Size Contacts

We report on the fabrication, transport measurements, and density functional theory (DFT) calculations of atomic size contacts made out of gadolinium (Gd). Gd is known to have local moments mainly associated with $f$ electrons. These coexist with itinerant $s$ and $d$ bands that account for its metallic character. Here we explore whether and how the local moments influence electronic transport properties at the atomic scale. Using both Scanning Tunneling Microscope (STM) and lithographic Mechanically Controllable Break Junction (MCBJ) techniques under cryogenic conditions, we study the conductance of Gd when only few atoms form the junction between bulk electrodes made out of the very same material. Thousands of measurements shows that Gd has an average lowest conductance, attributed to an atom-size contact, below $\frac{2e^2}{h}$. Our DFT calculations for monostrand chains anticipate that the $f$ bands are fully spin polarized and insulating, and that the conduction may be dominated by $s$, $p$, and $d$ bands. DFT quantum transport calculations quantitatively reproduce the experimental results for zero bias and reveal that, while $s-p$ bands are dominant for transport, $d$ orbitals seem to have a relevant contribution in some cases.

cond-mat.mes-hall↗

arXiv2010

Sub-harmonic resonant excitation of confined acoustic modes at GHz frequencies with a high-repetition-rate femtosecond laser

We propose sub-harmonic resonant optical excitation with femtosecond lasers as a new method for the characterization of phononic and nanomechanical systems in the gigahertz to terahertz frequency range. This method is applied for the investigation of confined acoustic modes in a free-standing semiconductor membrane. By tuning the repetition rate of a femtosecond laser through a sub-harmonic of a mechanical resonance we amplify the mechanical amplitude, directly measure the linewidth with megahertz resolution, infer the lifetime of the coherently excited vibrational states, accurately determine the system's quality factor, and determine the amplitude of the mechanical motion with femtometer resolution.

cond-mat.mes-hall↗

arXiv2007

Influence of chopped laser light onto the electronic transport through atomic-sized contacts

This article reports on the influence of laser irradiation onto the electrical conductance of gold nanocontacts established with the mechanically controllable breakjunction technique (MCB). We concentrate here on the study of reversible conductance changes which can be as high as 200%. We investigate the dependence on the initial conductance of the contacts, the wavelength, the intensity and position of the laser spot with respect to the sample. Under most conditions an enhancement of the conductance is observed. We discuss several physical mechanisms which might contribute to the observed effect including thermal expansion, rectification and photon-assisted transport. We conclude that thermal expansion is not the dominating one.

cond-mat.mes-hall↗

arXiv2005

Structure and conductance histogram of atomic-sized Au contacts

Many experiments have shown that the conductance histograms of metallic atomic-sized contacts exhibit a peak structure, which is characteristic of the corresponding material. The origin of these peaks still remains as an open problem. In order to shed some light on this issue, we present a theoretical analysis of the conductance histograms of Au atomic contacts. We have combined classical molecular dynamics simulations of the breaking of nanocontacts with conductance calculations based on a tight-binding model. This combination gives us access to crucial information such as contact geometries, forces, minimum cross-section, total conductance and transmission coefficients of the individual conduction channels. The ensemble of our results suggests that the low temperature Au conductance histograms are a consequence of a subtle interplay between mechanical and electrical properties of these nanocontacts. At variance with other suggestions in the literature, our results indicate that the peaks in the Au conductance histograms are not a simple consequence of conductance quantization or the existence of exceptionally stable radii. We show that the main peak in the histogram close to one quantum of conductance is due to the formation of single-atom contacts and chains of gold atoms. Moreover, we present a detailed comparison with experimental results on Au atomic contacts where the individual channel transmissions have been determined.

cond-mat.mes-hall↗

arXiv2004

Electrical transport properties of stable single-atom contacts of zinc

We report low-temperature measurements of the electrical transport properties of few-atom contacts of the superconducting metal zinc, arranged with lithographically fabricated mechanically controllable breakjunctions (MCB). The conductance histogram shows several narrow peaks, not regularly observed for multivalent metals. The first peak - corresponding to the single-atom contact - is located slightly below one conductance quantum and is split into two subpeaks, possibly indicating two preferred configurations of the single-atom contact. The current-voltage characteristics in the superconducting state show nonlinearities due to multiple Andreev reflections (MAR). In addition we find nonlinearities in the current-voltage characteristics that we attribute to electronic-interaction effects due to the granular structure of the film. Some of these latter findings are in qualitative agreement with a prediction by Avishai et al. A. Avishai, A. Golub, A. D. Zaikin, Europhys. Lett. {\bf 54}, 640.

cond-mat.mes-hall↗

arXiv2004

Conduction Channels of One-Atom Zinc Contacts

We have determined the transmission coefficients of atomic-sized Zn contacts using a new type of breakjunction which contains a whisker as a central bridge. We find that in the last conductance plateau the transport is unexpectedly dominated by a well-transmitting single conduction channel. We explain the experimental findings with the help of a tight-binding model which shows that in an one-atom Zn contact the current proceeds through the 4s and 4p orbitals of the central atom.

cond-mat.mes-hall↗

arXiv2000

Generalized conductance sum rule in atomic break junctions

When an atomic-size break junction is mechanically stretched, the total conductance of the contact remains approximately constant over a wide range of elongations, although at the same time the transmissions of the individual channels (valence orbitals of the junction atom) undergo strong variations. We propose a microscopic explanation of this phenomenon, based on Coulomb correlation effects between electrons in valence orbitals of the junction atom. The resulting approximate conductance quantization is closely related to the Friedel sum rule.

cond-mat.mes-hall↗

arXiv2000

Conductance oscillations in mesoscopic rings: microscopic versus macroscopic picture

The phase of Aharonov-Bohm oscillations in mesoscopic metal rings in the presence of a magnetic field can be modulated by application of a DC-bias current I_DC. We address the question of how a variation of I_DC and hence of the microscopic phases of the electronic wave functions results in the macroscopic phase of the conductance oscillations. Whereas the first one can be varied continuously the latter has to be quantized for a ring in two-wire configuration by virtue of the Onsager symmetry relations. We observe a correlation between a phase flip by +/- pi and the amplitude of the oscillations.

cond-mat.mes-hall↗

arXiv2000

Conduction channels of superconducting quantum point contacts

Atomic quantum point contacts accommodate a small number of conduction channels. Their number N and transmission coefficients {T_n} can be determined by analyzing the subgap structure due to multiple Andreev reflections in the current-voltage (IV) characteristics in the superconducting state. With the help of mechanically controllable break-junctions we have produced Al contacts consisting of a small number of atoms. In the smallest stable contacts, usually three channels contribute to the transport. We show here that the channel ensemble {T_n} of few atom contacts remains unchanged up to temperatures and magnetic fields approaching the critical temperature and the critical field, respectively, giving experimental evidence for the prediction that the conduction channels are the same in the normal and in the superconducting state.

cond-mat.supr-con↗