Ariando Ariando

Breakdown of selection rules and emergence of optical activity in Raman spectroscopy typically signal symmetry-breaking events essential for understanding novel phases of solids. Here, we apply our recently developed rotational anisotropy Raman spectroscopy technique to single-crystal ruthenium dioxide—a compound of recent interest as a candidate workhorse material for altermagnetism yet whose magnetic ground state remains under intense debate. Our data reveal a salient breakdown of selection rules for zone-center phonons, accompanied by clear splitting in the angle-dependent polarimetry plots for the two opposite helicity-nonconserving circularly polarized scattering channels. These observations provide definitive evidence of a previously overlooked symmetry-breaking event, involving either spatial or time-reversal symmetry. In either scenario, the underlying mechanism is likely a bulk hidden order parameter, potentially involving multipole moments of Ruthenium(IV) set by the local crystal field environment. Our work demonstrates how subtle symmetry-breaking events can manifest through lattice dynamics and calls for renewed experimental and theoretical efforts to map the phase diagram of ruthenium dioxide as a system poised near quantum phase transition boundaries.

The recent discovery of high-temperature superconductivity in hole-doped SmNiO ₂ , exhibiting the record-high transition temperature T _c among infinite-layer (IL) nickelates, has opened a new avenue for exploring design principles of superconductivity. Experimentally determining the electronic structure and magnetic interactions in this new system is crucial to elucidating the mechanism behind the enhanced superconductivity. Here, we report a Ni L -edge resonant inelastic x-ray scattering (RIXS) study of superconducting Sm-based IL nickelate thin films Sm _{1− x − y} Eu _x Ca _y NiO ₂ (SECNO). Dispersive paramagnonic excitations are observed in both optimally and overdoped SECNO samples, supporting a spin-fluctuation-mediated pairing scenario. However, despite the two-fold enhancement of T _c in the Sm-based nickelates compared to their Pr-based counterparts, the effective exchange coupling strength is reduced by approximately 20%. This behavior contrasts with hole-doped cuprates, where magnetic interactions correlate positively with T _c , highlighting essential differences in their superconducting mechanisms.

Proton implantation induced modulation of quantum transport in LAO/STO heterostructures.

The SrTiO3-based conducting heterointerfaces, when laterally confined by nanopatterning or defined using a conductive atomic force microscope, exhibit superior electronic properties compared to their macroscopic two-dimensional counterparts. This enhancement is attributed to the modulation of nanoscale transport properties by the polarity of SrTiO3 domain walls. However, the impact of polar domain walls on macroscopic electronic behavior remains poorly explored. In this study, we observe two distinct resistance anomalies at approximately 80 and 40 K, characteristic temperatures of SrTiO3 domain wall polarity, by measuring the macroscopic electrical transport properties of the (La0.3Sr0.7)(Al0.65Ta0.35)O3/SrTiO3 conducting heterointerface. As the carrier density decreases with decreasing gating voltage, these anomalies become more pronounced, with a metal-insulator-metal transition occurring near 40 K at a carrier density threshold of approximately 1 × 1012 cm−2. Our findings provide valuable insights into the role of polar domain walls in shaping the electronic characteristics of SrTiO3-based heterostructures and highlight the potential for manipulating macroscopic electronic behavior through domain wall engineering.

Magnetic fields typically suppress superconductivity through Pauli and orbital limiting effects. However, there are rare instances of magnetic-field-induced superconductivity, as seen in Chevrel phase compounds [1], organic conductors [2], uranium-based heavy-fermion systems [3, 4], and moire graphene [5], though these materials possess inherently low superconducting transition temperatures (Tc). Here, we demonstrate high field-stabilized superconductivity in a class of materials with a significantly higher Tc (up to 40 K): the infinite-layer nickelates [6]. Both low-field and high-field superconducting states can be plausibly explained by a compensation mechanism akin to the Jaccarino-Peter effect. These findings demonstrate the possibility of achieving substantially enhanced upper critical fields in high-temperature superconductors.