arXiv subjects

Theodore I. Weinberger

Publications and source records attributed to Theodore I. Weinberger.

7 recordsLinked to original sources

arXiv2026

Coherence-driven origin of metamagnetism in anisotropic heavy-fermion systems

A number of heavy-fermion materials exhibit magnetic field-induced metamagnetism: on applying a field along the magnetic hard axis, the magnetization first rises gradually, then jumps abruptly once a critical field is reached. Despite decades of phenomenological modeling, the microscopic origin of the pronounced magnetic anisotropy underlying this behavior has remained unresolved. The same is true of a related, long-standing puzzle: an anomalous maximum in the hard-axis susceptibility versus temperature. Both are complicated in $5f$ compounds by the dual localized-itinerant character of the relevant electrons. Here we develop an analytic $c$--$f$ theory of magnetic anisotropy in heavy-fermion metamagnets, identifying the mixed susceptibility $χ_{\rm cf}(T,h,p)$ as a single thermodynamic observable that unifies the anisotropic response across temperature, field, and pressure. We test this theory against primary and literature data for the heavy-fermion superconductor UTe$_2$, finding excellent quantitative agreement in the temperature, field, and pressure evolution of its magnetic anisotropy -- including a Kondo-coherence origin for the anomalous hard-axis susceptibility maximum, which we show is directly connected to the metamagnetic transition itself. Our results establish a general, microscopic, coherence-driven framework for anisotropic metamagnetism, applicable across the broad class of heavy-fermion compounds that display this phenomenology.

cond-mat.str-el↗

arXiv2026

3D bulk-resolved $g$-wave altermagnetic order parameter in CrSb

Electronic phases of matter, such as magnetism and superconductivity, are defined and distinguished by their order parameters quantifying the spontaneous symmetry breaking underlying each phase. Simple cases include the uniform magnetisation of ferromagnets and isotropic gap function of conventional superconductors. Unconventional superconductors often have a nodal gap function, where the gap changes sign at nodes on the Fermi surface. This concept of unconventional/nodal order parameter symmetry has recently been extended to numerous magnetic systems, including altermagnets, in which up- and down-spin species are non-degenerate around the Fermi surface. Here we demonstrate that magnetic quantum oscillation measurements can provide a high resolution, bulk-sensitive, 3D mapping of the order parameter in an unconventional magnet. By rotating a magnetic field through high- and low-symmetry directions of the CrSb Brillouin zone, we show that this material's altermagnetic band structure leads to a reduction of symmetry for each spin-split Fermi sheet away from nodal orientations. In momentum space, the exchange splitting between up and down spins follows the profile of the $\mathcal{Y}_{4}^{-3}=zy(3x^2-y^2)$ real spherical harmonic - analogous to a $g$-orbital of the hydrogen atom. While notoriously difficult to resolve in unconventional superconductors, our work demonstrates that the order parameter symmetry of unconventional magnets can be precisely mapped via quantum-oscillatory quasiparticle spectroscopy, establishing CrSb as a prototypical $g$-wave metallic altermagnet.

cond-mat.mtrl-sci↗

arXiv2026

Metamagnetism in UTe2: the roles of itinerancy and localization

The metamagnetic transition in UTe$_2$ plays a key role in stabilizing two enigmatic field-induced superconducting phases. One of these phases (SC2) is truncated by the transition, lying directly below it, while the other (SC3) sits predominantly above it and appears to be stabilized because of it. While numerous pulsed field studies have examined this transition, comparatively few steady field experiments have investigated it. Here we report a suite of measurements of metamgnetism in UTe$_2$, at ambient pressure by torque magnetometry and extraction magnetometry techniques, and of the magnetoconductance under pressure. Our steady field measurements resolve a complex sub-structure within the transition, with separate features that possess different temperature evolutions, pointing to distinct contributions from itinerant and localized moments. The itinerant contribution might relate to a possible spin-density wave state. We theoretically model the evolution of Kondo and RKKY interactions and propose that the SC2 state is stabilized under pressure due to the collapse of magnetic anisotropy, leading to an enhancement of longitudinal spin fluctuations along the hard $b$ axis, which are pair-forming in the $p$-wave channel.

cond-mat.str-el↗

arXiv2026

Electrically-controllable superconducting memory effect in UTe2

If a computer could be assembled from superconducting components, the energy efficiency would far surpass that of conventional electronics. Historic research efforts towards this goal yielded pivotal breakthroughs in the development and discovery of scanning tunnelling microscopy and high temperature superconductivity. Although recent strides have been taken in advancing superconducting diode and switching technologies, harnessing read/writeable memory functionality in superconducting platforms has remained challenging. Here we show that bulk single crystal specimens of the triplet superconductor candidate uranium ditelluride (UTe$_2$) possess such properties. Upon applying a magnetic field to access an intermediate regime straddling two distinct superconducting phases, we find that direct current pulses can push the material in and out of a metastable state possessing an enhanced critical current $J_c$. This switching is controllable by the strength and duration of the stimuli, with the system `remembering' whether it is in the high or low $J_c$ state for extended periods. We interpret this to be due to competition between two distinct vortex species, which can be perturbatively pushed into a non-equilibrium high-disorder configuration with stronger pinning forces and thus higher $J_c$. Rather than requiring proximate magnetic or semiconducting interfaces, this memory functionality appears to be an intrinsic property of UTe$_2$ rooted in the superconducting order itself. Our findings underscore the rich complexity of quantum vortex matter, and demonstrate the viability of engineering a new class of superconducting memory elements with ultralow-power switching.

cond-mat.supr-con↗

arXiv2026

Direct Observation of the Spillover of High Magnetic Field-induced SC3 Superconductivity Outside the Spin-Polarized State in UTe2

In our recent study of the high magnetic field phase landscape of UTe$_2$ [Phys. Rev. X 15, 021019 (2025)] we found indirect evidence that the SC3 superconducting phase spills out beyond the first-order phase boundary of the spin-polarized state. This prior study was limited to a maximal field strength of 41.5 T, and mapped the $b-ac$ rotation plane. Here we measure a high quality sample with residual resistivity ratio RRR = 605 under rotations in the $b-c$ plane up to 45 T. This extended field range helps to unambiguously demonstrate the spillover of SC3 outside the polarized paramagnetic state. This is identified by the observation of zero resistance at low temperatures, for magnetic field strengths lower than the metamagnetic transition field resolved at higher temperatures. This observation is consistent with the scenario that electronic pairing of the SC3 phase is mediated by quantum critical fluctuations.

cond-mat.supr-con↗

arXiv2025

The Fermi surface of RuO2 measured by quantum oscillations

The metallic oxide RuO$_2$ has emerged as a promising altermagnet candidate, owing to reports of this material hosting antiferromagnetic ordering accompanied by a spin-split electronic band structure characteristic of time-reversal symmetry-breaking. However, recent studies have robustly questioned this scenario. Here we map the Fermi surface of pristine single-crystalline RuO$_2$. By measuring magnetic quantum oscillations of a bulk thermodynamic property, our study resolves the electronic structure present in the bulk of RuO$_2$. Several Fermi sheets are discerned, with a range of effective quasiparticle masses up to five times that of the bare electron mass. We compare our measurements with the predictions for altermagnetic and nonmagnetic Fermi surfaces deduced from density functional theory calculations. The quantum oscillatory frequency spectra correspond very poorly to the profile expected for the case of altermagnetism; by contrast, they correspond well to the nonmagnetic scenario. Our findings place significant constraints on the bulk magnetic properties of RuO$_2$, and strongly suggest that this material is a paramagnet.

cond-mat.mtrl-sci↗

arXiv2022

Superconductivity beyond the Pauli limit in high-pressure CeSb2

We report the discovery of superconductivity at a pressure-induced magnetic quantum critical point in the Kondo-lattice system CeSb2, sustained up to magnetic fields that exceed the conventional Pauli limit eight-fold. Like CeRh2As2, CeSb2 is locally non-centrosymmetric around the Ce-site, but the evolution of critical fields and normal state properties as CeSb2 is tuned through the quantum critical point motivates a fundamentally different explanation for its resilience to applied field.

cond-mat.str-el↗