arXane › Physics › Condensed Matter
Wednesday, 4 November 2026: 4 new papers, 1 cross-list and 9 replacements in Superconductivity (cond-mat.supr-con), in arXiv's order, with full abstracts. The same papers as arXiv's own listing, set as a newspaper; every title links to arXiv.
Monolayer FeSe grown on SrTiO$_3$ (001) exemplifies interface-enhanced superconductivity, exhibiting a transition temperature nearly ten times that of bulk FeSe. Yet, its tunneling spectra lack clearly identifiable superconducting coherence peaks, preventing an unambiguous determination of the gap magnitude. Here, we use ultralow-temperature scanning tunneling spectroscopy as a function of temperature, tip-sample separation, and lateral position to disentangle tunneling contributions by statistical analysis. Decay rates extracted by regression of tip-height-dependent spectroscopy reveal three energy regimes: Andreev-reflection-dominated tunneling below 6 meV, mixed Andreev and quasiparticle tunneling between 6 and 13 meV, and predominantly quasiparticle tunneling above 13 meV. Spatially resolved spectroscopy and correlation analysis further reveal that the tunneling conductance is predominantly localized near defects below 6 meV but becomes spatially extended at higher energies. Together, these results constrain the superconducting gap to lie between 6 and 13 meV. Our findings establish statistical analysis of spectroscopy as a powerful approach to constraining superconducting gap structures when complex spectral features prevent the unambiguous identification of coherence peaks.
The predominantly $d_{x^2-y^2}$-wave pairing symmetry of cuprate superconductors is well established, yet its microscopic manifestation in local Cooper-pair tunneling remains less explored. Here, we investigate Bi$_{1.2}$Pb$_{0.8}$Sr$_2$CaCu$_2$O$_{8+\delta}$, using Josephson scanning tunneling spectroscopy with a conventional $s$-wave superconducting Pb tip. We observe a zero-bias conductance enhancement whose approximately quadratic dependence on junction conductance is consistent with phase-diffusive Josephson tunneling. Atomic-resolution conductance maps and site-resolved spectra reveal a pronounced intra-unit-cell modulation, with enhanced Josephson response near oxygen sites and strong suppression near copper sites and along diagonal directions. Microscopic calculations incorporating the bilayer electronic structure and realistic Wannier-based tunneling matrix elements reproduce the observed spatial pattern through interference between pairing contributions of opposite signs. Our results reveal how the sign-changing $d$-wave superconducting order parameter manifests itself in atomic-scale Josephson tunneling, providing complementary evidence for unconventional pairing symmetry in cuprates.
Nonreciprocal charge transport, where current flows preferentially in one direction, has become a key topic across quantum materials. This review covers some recent progress in bulk crystals, artificial heterostructures, van der Waals systems, high-temperature superconductors, and magnetic materials. The review discusses both intrinsic origins, such as band-structure effects, and extrinsic ones, including vortex motion, device geometry, and heating artifacts. A central focus is the superconducting diode effect due to its application potential, which shows different critical currents for opposite directions. The review also examines how symmetry breaking, spin-orbit coupling, and magnetic order contribute to the observed responses. However, there remain challenges when many exciting findings lack a unified picture, and the field continues to debate the relative importance of various mechanisms. The review highlights key open questions and suggests future directions, including better experimental standards and device integration. This review aims to give a balanced view of what is known, what is uncertain, and where the field might go next.
In this work, we have presented S-I-S Josephson junctions with $\rm\alpha$-Ta electrodes and a ${\rm TaO}_x$ barrier. We grew base and top ${\alpha}$-Ta electrodes using seed layer engineering, showing both Nb and ${\rm TaN}_x$ are viable seed layer choices, and particularly emphasize that at room temperature a re-seed layer is required to nucleate $\rm\alpha$-Ta for the top electrode. However, we note that the choice of seed layer can have subtle implications on the electrical tunneling behavior of the junctions. We used room-temperature probing of variable junction areas, combined with Ambegaokar-Baratoff physics, to characterize the wafer scale critical current densities. For 0.4 $\mu$m$^2$ junctions, we found junction spreads as low as 2.0% across the 20 x 20 mm chip relevant for device performance. The entire process was carried out using standard industry foundry processing using 150 mm wafer tooling, which is an important step towards proving that Ta-based junctions can be implemented at scale. We have successfully fabricated and tested junctions with $\rm\alpha$-Ta electrodes and a ${\rm TaO}_x$ insulating tunnel barrier, demonstrating that this is a material platform which merits further investigation and studies for potential application in classical and quantum superconducting technologies.
We show that a microscopic model of twisted MoTe$_2$ with screened Coulomb interactions produces topological superconductivity. Using the density matrix renormalization group (DMRG) on infinite cylinders, we find that the narrow Chern band of twisted MoTe$_2$ has Cooper pair correlations that strengthen with cylinder circumference, consistent with two dimensional superconductivity. The superconductor has chiral $f$-wave pairing around the valley center, and its topology produces chiral Majorana edge modes and non-Abelian vortex cores. At zero displacement field, the superconductor spans fillings $-0.78\lesssim\nu\lesssim-0.72$, close to the experimental range, and extends in a dome to finite displacement field. We then predict how its stiffness evolves with the filling and the tunable displacement field. The interplay with screening length is also examined. Nearby, we find a fractional Chern insulator, a topological charge density wave, a metal, and a charge-ordered state. The last is a candidate for the reentrant integer Hall regime in experiments. These results establish a route from repulsive interactions in microscopic models of moir\'e materials to chiral topological uperconductors with chiral Majorana edge modes.