Alexandra J. Howzen | Searcharxiv

arXiv2026

Transport spin polarization in RuO$_2$ films

Altermagnets host spin-split electronic bands without net magnetization, enabling spin-polarized transport in the absence of conventional ferromagnetism. RuO$_2$ has been proposed as a candidate altermagnet, yet experimental reports remain conflicting, particularly between bulk-sensitive probes and thin-film measurements. Here we investigate the electronic transport properties of epitaxial RuO$_2$ thin films using anomalous Hall effect measurements and point-contact Andreev reflection spectroscopy. We observe transport spin polarization and a strongly orientation-dependent anomalous Hall response, while magnetometry reveals no detectable net magnetization. The anomalous Hall effect appears only in ultrathin (110)-oriented films, consistent with symmetry-driven N\'eel-vector physics, and the measured transport spin polarization is systematically higher for (110)-oriented films than for (001)-oriented films, consistent with the crystallographic anisotropy of the spin-split bands. These results are consistent with altermagnetic behavior in RuO$_2$, with the experimentally accessible signatures confined to near-surface regions. They also establish superconducting transport spectroscopy as a metrology for identifying and characterizing altermagnet candidates.

cond-mat.mes-hall↗

arXiv2025

Upper critical fields in normal metal-superconductor-normal metal trilayers

The role of spin orbit interaction in superconducting proximity effect is an area of intense research effort. Recent theoretical and experimental works investigate the possible role of spin-orbit interaction in generating spin-triplet pair correlations. In this work, we present an experimental survey of thin normal metal-superconductor-normal metal trilayers with Nb superconductor and Al, Ti, Cu, Pt, Ta, and Au normal metals, along with single layers of Nb as reference. We aim to probe the role of spin-orbit interaction and resistivity on the normal metal proximity effect through measurements of the upper critical field. We find that the upper critical fields of the trilayers are lower than that of a single layer Nb reference sample, and that the trilayers with higher resistivity metals, Ti, Pt, and Ta, behave as 2-dimensional superconductors. At low applied in-plane magnetic fields and temperatures close to the zero field transition temperature, we find a possible deviation from 2-dimensional to 3-dimensional behavior in the Ti and Pt trilayers. We also find that compared to single layer Nb films, all of our trilayers show a greater suppression of critical temperature during rotation from an in-plane to an out-of-plane applied magnetic field, with the greatest suppression observed in trilayers with Au or Al. This suppression of the critical temperature under field rotation might appear analogous to the colossal spin valve effect that can be achieved in systems with ferromagnetic materials; however, in our trilayers, only conventional orbital screening contributions to the suppression are present and the additional suppression is not present in the absence of applied magnetic field.

cond-mat.supr-con↗