109 Search Results

Josephson diodes are of interest for nonlinear superconducting circuit elements, which have many applications such as in solid-state qubit readout and coupling. Many different mechanisms can give rise to Josephson diode effects (JDEs). In this work, we investigate JDEs generated by the self-field of the supercurrent in the junction. To this end, we experimentally investigate JDEs in the supercurrent quantum interference patterns of planar hybrid Josephson junctions, composed of a cadmium arsenide thin film interfaced with a conventional superconductor. A model that includes the supercurrent self-field accurately describes the experimental observations. We show that self-field-induced JDEs are generally expected inmore » planar junctions in perpendicular magnetic fields, even in cases of symmetric and uniform junctions, as long as they exhibit sufficiently large critical currents. Here, we discuss the tunability of self-field-induced JDEs via the supercurrent density and other parameters.« less

We investigate the effects of Hund’s coupling on the resonant X-ray absorption spectra of the recently discovered family of layered nickelate superconductors. We contrast two scenarios depending on the relative strength of the ratio of the effective Hund’s coupling (J_H) to the crystal fields (∆) in these systems. We carry out the cluster and DFT+DMFT simulations of the RIXS signal at the Ni L-edge for different values of Hund’s coupling. We find the latter dominates for the parent compound while the former becomes important for sufficiently large doping. Our results are consistent with the observations of a softening of amore » RIXS peak as a function of doping by Rossi et al., only when the Hund coupling is sizeable. To interpret the results, we separate the theoretical RIXS signal into spin conserving and non-spin conserving channels and conclude that the infinite layer nickelates are in a regime where ∆ and J compete effectively and suggest further experimental tests of the theory.« less

The compound SrNi_2⁢P₂ is unique among the ThCr₂⁢Si₂ class since it exhibits a temperature-induced transition upon cooling from an uncollapsed tetragonal (ucT) state to a one-third-collapsed orthorhombic (tcO) state where one out of every three P-rows bond across the Sr layers. This compound is also known for exhibiting bulk superconductivity below 1.4 K at ambient pressure. Here, in this paper, we report on the effects of Rh substitution in Sr⁢(Ni_1-x⁢Rh_x)₂⁢P₂ on the structural and superconducting properties. We studied the variation of the nearest P-P distances as a function of the Rh fraction at room temperature, as well as its temperaturemore » dependence for selected compositions. We find that increasing the Rh fraction leads to a decrease in the transition temperature between the ucT and tcO states, until a full suppression of the tcO state for x ≥ 0.166. The superconducting transition first remains nearly insensitive to the Rh fraction, and then it increases to 2.3 K after the tcO state is fully suppressed. These results are summarized in a phase diagram, built upon the characterization by energy dispersive x-ray spectroscopy, x-ray diffraction, resistance, magnetization, and specific heat measurements done on crystalline samples with varying Rh content. The relationship between band structure, crystal structure, and superconductivity is discussed based on previously reported band structure calculations on SrRh₂⁢P₂. Moreover, the effect of Rh fraction on the stress-induced structural transitions is also addressed by means of strain-stress studies done by uniaxial compression of single-crystalline micropillars of Sr⁢(Ni_1-x⁢Rh_x)₂⁢P₂.« less

Here, the simplified scaling of the orbital upper critical field, H_c2⁡(T), for an isotropic s-wave superconductor is introduced. To facilitate the analysis of the experimental data, we suggest a simple but accurate approximation of the Helfand-Werthamer upper critical field in the entire temperature range valid for any transport scattering rate: H_c⁢2⁡/⁢H_c⁢⁢2⁡(0) ≈ (1 -t²)/(1 + 0.42t^1.47).

In this article, London, λ_L(T), and Campbell, λ_C(T), penetration depths were measured in single crystals of a topological superconductor candidate AuSn₄. At low temperatures, λ_L(T) is exponentially attenuated and, if fitted with the power law, λ(T) ~ Tⁿ, gives exponents n > 4, indistinguishable from the isotropic single s- wave gap Bardeen-Cooper-Schrieffer (BCS) asymptotic. The superfluid density fits perfectly in the entire temperature range to the BCS theory. The superconducting transition temperature, T_c = 2.40 ± 0.05 K, does not change after 2.5 MeV electron irradiation, indicating the validity of the Anderson theorem for isotropic s- wave superconductors. Campbell penetrationmore » depth before and after electron irradiation shows no hysteresis between the zero-field cooling (ZFC) and field cooling (FC) protocols, consistent with the parabolic pinning potential. Interestingly, the critical current density estimated from the original Campbell theory decreases after irradiation, implying that a more sophisticated theory involving collective effects is needed to describe vortex pinning in this system. In general, our thermodynamic measurements strongly suggest that the bulk response of the AuSn₄ crystals is fully consistent with the isotropic s- wave weak-coupling BCS superconductivity.« less

Superconducting transition-edge sensors (TES) have emerged as fascinating devices to detect broadband electromagnetic radiation with low thermal noise. The advent of metallic transition metal dichalcogenides, such as NbSe₂, has also created an impetus to understand their low-temperature properties, including superconductivity. Interestingly, NbSe₂-based sensor within the TES framework remains unexplored. In this work, direct-probed superconducting NbSe₂ absorbers led to a proof-of-concept demonstration for the transduction of incoming light to heat, where a thermodynamic superconducting phase transition in NbSe₂ was evident to switch it to the normal-state, when biased below its superconducting transition temperature. A wavelength-dependent response of its optical absorption propertiesmore » was observed, based on the incident optical excitation source used. Furthermore, extensive optical characterization studies were conducted using Raman spectroscopy, where the in-plane and out-of-plane thermal conductivity was empirically determined. Our results open new possibilities for the use of NbSe₂ in superconducting radiation detectors, including in a TES framework« less

${\mathrm{FeTe}}_{0.55}{\mathrm{Se}}_{0.45}$ (FTS) occupies a special spot in modern condensed matter physics at the intersections of electron correlation, topology, and unconventional superconductivity. The bulk electronic structure of FTS is predicted to be topologically nontrivial due to the band inversion between the $d_{xz}$ and $p_z$ bands along $\mathrm{\Gamma }\text{−}Z$ . However, there remain debates in both the authenticity of the Dirac surface states (DSSs) and the experimental deviationsmore » of band structure from the theoretical band inversion picture. Here we resolve these debates through a comprehensive angle-resolved photoemission spectroscopy investigation. We first observe a persistent DSS independent of $k_z$ . Then, by comparing FTS with FeSe, which has no band inversion along $\mathrm{\Gamma }\text{−}Z$ , we identify the spectral weight fingerprint of both the presence of the $p_z$ band and the inversion between the $d_{xz}$ and $p_z$ bands. Furthermore, we propose a renormalization scheme for the band structure under the framework of a tight-binding model preserving crystal symmetry. Our results highlight the significant influence of correlation on modifying the band structure and make a strong case for the existence of topological band structure in this unconventional superconductor. Published by the American Physical Society 2024« less

Detecting electronic hot spots is important for understanding the heat dissipation and thermal management of electronic and semiconductor devices. Optical thermoreflective imaging is being used to perform precise temporal and spatial imaging of heat on wires and semiconductor materials. We apply quantum squeezed light to perform thermoreflective imaging on micro-wires, surpassing the shot-noise limit of classical approaches. We obtain a far-field temperature sensing accuracy of 42 mK after 50 ms of averaging and show that a 256×256 pixel image can be constructed with such sensitivity in 10 min. We can further obtain single-shot temperature sensing of 1.6 K after only 10  μs ofmore » averaging, enabling a dynamical study of heat dissipation. Not only do the quantum images provide accurate spatiotemporal information about heat distribution but also the measure of quantum correlation provides additional information, inaccessible by classical techniques, which can lead to a better understanding of the dynamics. We apply the technique to both aluminum and niobium microwires and discuss the applications of the technique in studying electron dynamics at low temperatures.« less

Considering the growing interest in magnetic materials for unconventional computing, data storage, and sensor applications, there is active research not only on material synthesis but also characterisation of their properties. In addition to structural and integral magnetic characterisations, imaging of magnetisation patterns, current distributions and magnetic fields at nano- and microscale is of major importance to understand the material responses and qualify them for specific applications. In this roadmap, we aim to cover a broad portfolio of techniques to perform nano- and microscale magnetic imaging using superconducting quantum interference devices, spin centre and Hall effect magnetometries, scanning probe microscopies, x-ray-more » and electron-based methods as well as magnetooptics and nanoscale magnetic resonance imaging. The roadmap is aimed as a single access point of information for experts in the field as well as the young generation of students outlining prospects of the development of magnetic imaging technologies for the upcoming decade with a focus on physics, materials science, and chemistry of planar, three-dimensional and geometrically curved objects of different material classes including two-dimensional materials, complex oxides, semi-metals, multiferroics, skyrmions, antiferromagnets, frustrated magnets, magnetic molecules/nanoparticles, ionic conductors, superconductors, spintronic and spinorbitronic materials.« less

Ultraprecise mechanical sensors offer an exciting avenue for testing new physics. While many of these sensors are tailored to detect inertial forces, magnetically levitated (Maglev) systems are particularly interesting, in that they are also sensitive to electromagnetic forces. In this work, we propose the use of magnetically levitated superconductors to detect dark-photon and axion dark matter through their couplings to electromagnetism. Several existing laboratory experiments search for these dark-matter candidates at high frequencies, but few are sensitive to frequencies below 1 kHz (corresponding to dark-matter masses $m_{\mathrm{DM}}\lesssim {10}^{-12}more »$ eV ). As a mechanical resonator, magnetically levitated superconductors are sensitive to lower frequencies, and so can probe parameter space currently unexplored by laboratory experiments. Dark-photon and axion dark matter can source an oscillating magnetic field that drives the motion of a magnetically levitated superconductor. This motion is resonantly enhanced when the dark matter Compton frequency matches the levitated superconductor’s trapping frequency. We outline the necessary modifications to make magnetically levitated superconductors sensitive to dark matter, including specifications for both broadband and resonant schemes. We show that in the $\mathrm{Hz}\lesssim f_{\mathrm{DM}}\lesssim \mathrm{kHz}$ frequency range our technique can achieve the leading sensitivity among laboratory probes of both dark-photon and axion dark matter. Published by the American Physical Society 2024« less