Nowotny chimney ladder crystals combine features of ordered crystals and amorphous solids, making them attractive thermoelectric materials because of their intrinsically low thermal conductivity. We investigate the intermetallic compound Ru2Sn3 and show that, despite its crystalline order, its heat capacity exhibits a boson-peak-like glassy anomaly at 8-14 K. Combining experiments with first-principles calculations and molecular dynamics simulations, we trace this behavior to low-energy optical phonons emerging from the chimney ladder structure. These modes strongly couple to acoustic phonons, producing hybridization and avoided crossings that reshape the vibrational spectrum and cause the hybridized acoustic branches to contribute directly to the anomaly. Thermoelectric measurements reveal additional glass-like signatures linked to these excitations, while the electrical resistivity displays an extended linear temperature dependence and an anomalously large quadratic contribution at low temperatures. A simple theoretical model based on electron scattering by overdamped phonons qualitatively accounts for these observations.

We investigate quantum oscillation measurements in the Dirac nodal-line semimetal TaNiTe_5 which exhibit a strongly enhanced amplitude in the magnetoresistance. We show that mechanical properties of the measurement setup in combination with de Haas - van Alphen oscillations in the magnetic torque can cause this enhancement in the measured resistance, without involvement of any topological properties in this material. To support the empirical data, a numerical model is provided, showing good agreement.

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.

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.

NbTe4undergoes multiple charge density wave transitions that have attracted great interest in this material for decades. Previous work has shown that the crystal obtains the space groupP4/ncc(130) at temperatures below 50 K which allows for the existence of eightfold degenerate double Dirac points in the band structure. We provide insights into the electronic structure of this material through density functional theory calculations, and a rotation study of de Haas-van Alphen oscillations in the magnetic torque. We find that NbTe4exhibits magnetic breakdown orbits between electron and hole pockets.

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 magnetization of ferromagnets1,2 and the isotropic gap function of conventional superconductors3. Unconventional superconductors4 often have a nodal gap function, in which the gap changes sign at nodes on the Fermi surface. This concept of unconventional or nodal order parameter symmetry has recently been extended to numerous magnetic systems5-8, including altermagnets9-13, in which up- and down-spin species have non-degenerate Fermi surfaces. Here we demonstrate that magnetic quantum oscillation14 measurements can provide a high-resolution, bulk-sensitive, three-dimensional (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 the altermagnetic band structure of this material 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 Y 4 - 3 = y z ( 3 x 2 - y 2 ) real spherical harmonic-analogous to a g-orbital of the hydrogen atom. Although notoriously difficult to resolve in unconventional superconductors, our work demonstrates that the order parameter symmetry of unconventional magnets can be precisely mapped by quantum oscillatory quasiparticle spectroscopy, establishing CrSb as a prototypical g-wave metallic altermagnet.

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.

Below a critical temperature T c , superconductors transport electrical charge without dissipative energy losses. The application of a magnetic field B generally acts to suppress T c , up to some critical field strength at which T c → 0 K. Here, we investigate magnetic field–induced superconductivity in high-quality specimens of the triplet superconductor candidate UTe 2 in pulsed magnetic fields up to B = 70 T. Strikingly, we find that this material has a higher T c when B > 40 T ( T c ≈ 2.4 K) than it does for B = 0 T ( T c = 2.1 K). This observation points to a fundamentally distinct mechanism for the formation of superconductivity at high B in UTe 2 compared to the case of B = 0 T.

Quantum critical phenomena are widely studied across various materials families, from high-temperature superconductors to magnetic insulators. They occur when a thermodynamic phase transition is suppressed to zero temperature as a function of some tuning parameter such as pressure or magnetic field. This generally yields a point of instability—a so-called quantum critical point—at which the phase transition is driven exclusively by quantum fluctuations. Here, we show that the heavy fermion metamagnet UTe_{2} possesses a quantum phase transition at extreme magnetic field strengths of over 70 T. Rather than terminating at one singular point, we find that the phase boundary is sensitive to magnetic field components in each of the three Cartesian axes of magnetic field space. This results in the transition surface being bounded by a continuous ring of quantum critical points, the locus of which forms an extended line of quantum criticality—a novel form of quantum critical phase boundary. Within this quantum critical line sits a magnetic field-induced superconducting state in a toroidal shape, which persists to fields over 70 T. We model our data by a phenomenological free energy expansion and show how a quantum critical line—rather than a more conventional singular point of instability—anchors the remarkable high magnetic field phase landscape of UTe_{2}.

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 5 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 an itinerant electron paramagnet.

The phase diagram of the heavy fermion compound UTe_{2} contains multiple superconducting phases, several of which show characteristics of odd-parity pairing. We have investigated the pressure dependence of the superconducting transition in high-quality crystals of UTe_{2} by tracking its signature in the magnetic susceptibility χ(T). A single, sharp superconducting transition is observed at low pressures <0.3 GPa. At higher pressure, a second feature emerges in χ(T), which is located at the lower-temperature superconducting phase boundary previously identified in specific heat measurements. This second transition anomaly in χ(T) can be attributed to a step change in the London penetration depth, providing direct evidence for a change in the superconducting order parameter of UTe_{2}. Thermodynamic constraints suggest that the low temperature, high pressure superconducting state is distinct from zero pressure superconductivity as well as from the high pressure, high temperature superconducting state, raising the possibility of multicomponent superconductivity in high pressure UTe_{2}.

We report a quantum oscillation study in the Dirac nodal-line semimetal candidate TaPtTe5. The Fermi surface is probed via magnetic torque measurements with the magnetic field applied in the crystallographic a-b and b-c planes. The experimentally determined de Haas-van Alphen frequencies are consistent with results from band-structure calculations. This study serves as an extension to the scarce quantum oscillation data on TaPtTe5 currently present in the literature.

The heavy fermion metamagnet uranium ditelluride possesses two distinct magnetic field--induced superconducting states. One of these superconductive phases resides at magnetic fields immediately below a first-order metamagnetic transition to a field--polarized paramagnetic state at a field strength $H_m$, while the other exists predominantly above $H_m$. However, little is known about the microscopic properties of this polarized paramagnetic state. Here we report pulsed magnetic field measurements tracking the evolution of $H_m$ for polar and azimuthal inclinations in the vicinity of the crystallographic $b-a$ plane. We uncover a region of the phase diagram at high fields $>$ 50 T with a ripple-like non-monotonic dependence of $H_m$ on the orientation of field. Within this ripple in the metamagnetic transition surface, $H_m$ exhibits an anomalous temperature dependence. Our results point towards the presence of complex magnetic interactions and possible magnetic sub-phases at high magnetic fields in UTe$_2$, which may have important implications for the manifestation of exotic field-induced superconductivity.

The phase landscape of UTe2 features a remarkable diversity of superconducting phases under applied pressure and magnetic field. Recent quantum oscillation studies at ambient pressure have revealed the quasi-2D Fermi surface of this material. However, the pressure–dependence of the Fermi surface remains an open question. Here we track the evolution of the UTe2 Fermi surface as a function of pressure up to 19.5 kbar by measuring quantum interference oscillations. We find that in sufficient magnetic field to suppress both superconductivity at low pressures and incommensurate antiferromagnetism at higher pressures, the quasi-2D Fermi surface found at ambient pressure smoothly connects to that at 19.5 kbar, with no signs of a reconstruction over this pressure interval. We observe a smooth increase in oscillatory frequency with increasing pressure, indicating that the warping of the cylindrical Fermi sheets continuously increases with pressure. By computing a tight-binding model, we show that this enhanced warping indicates increased f-orbital contribution at the Fermi level – up to and beyond the critical pressure at which superconductivity is truncated. These findings highlight the value of high-pressure quantum interference measurements as a sensitive probe of the electronic structure in heavy fermion materials. The discovery of superconductivity in the heavy fermion compound UTe2, a potential topological and triplet-paired superconductor, has generated significant interest in condensed matter physics with particular interest in the nature of the Fermi surface. Here, the authors employed a contactless conductivity technique to investigate the quantum interference oscillations of compressed UTe2 up to 19.5 kbar, aiming to examine key features of its Fermi surface.

We report a detailed investigation of the Fermi surface in the layered Dirac semimetal TaNiTe 5 . We probed the magnetization, magnetic torque, and magnetoresistance in high-quality single crystals. Pronounced Shubnikov–de Haas and de Haas–van Alphen oscillations are observed in magnetic fields above 3 T and at temperatures of up to 22 K . Multiple fundamental frequencies and light effective quasiparticle masses are obtained by fast Fourier transformation (FFT) and Lifshitz-Kosevich formula fits. The high resolution of the low-temperature FFT spectra allows us to investigate individual peaks in detail for the magnetic fields applied along all three crystallographic axes and the planes in between. Our investigation can confirm the density functional theory calculated band structure and its corresponding Fermi surface.

Commercial adiabatic demagnetisation refrigerators still employ the same hydrated salts that were first introduced over 85 years ago. The inherent limitations of these insulating magnetocalorics - poor thermal conductivity at sub-Kelvin temperatures, low entropy density, corrosiveness - can be overcome by a new generation of rare-earth based metallic magnetocalorics. Here, we present the metallic magnetocaloric YbNi1.6 Sn as an attractive alternative to conventional refrigerants. YbNi1.6Sn retains high entropy into the 100 mK regime and avoids the noble metal constituents of alternative refrigerants. Demagnetisation tests demonstrate that YbNi1.6Sn enables economical and durable alternatives to traditional cooling devices for temperatures reaching below 120 mK. We find that the magnetocaloric properties of this material are facilitated by unusually small Kondo and RKKY interactions, which position YbNi1.6Sn in the extreme local moment limit on the generalised Kondo lattice phase diagram.

The field of hydride superconductivity has recently been mired in a controversy that might divert attention from the question of central importance: do hydrides support genuine superconductivity or not? We examine some key papers from the field, and conclude that hydride superconductivity is real.

The unconventional superconductor UTe 2 exhibits numerous signatures of spin-triplet superconductivity—a rare state of matter which could enable quantum computation protected against decoherence. UTe 2 possesses a complex phase landscape comprising two magnetic field-induced superconducting phases, a metamagnetic transition to a field-polarized state, along with pair- and charge-density wave orders. However, contradictory reports between studies performed on UTe 2 specimens of varying quality have severely impeded theoretical efforts to understand the microscopic origins of the exotic superconductivity. Here, we report a comprehensive suite of high magnetic field measurements on a generation of pristine quality UTe 2 crystals. Our experiments reveal a significantly revised high magnetic field superconducting phase diagram in the ultraclean limit, showing a pronounced sensitivity of field-induced superconductivity to the presence of crystalline disorder. We employ a Ginzburg–Landau model that excellently captures this acute dependence on sample quality. Our results suggest that in close proximity to a field–induced metamagnetic transition the enhanced role of magnetic fluctuations—that are strongly suppressed by disorder—is likely responsible for tuning UTe 2 between two distinct spin-triplet superconducting phases.

UTe 2 is a spin -triplet superconductor candidate for which high quality samples with long mean free paths have recently become available, enabling quantum oscillation measurements to probe its Fermi surface and effective carrier masses. It has recently been reported that UTe 2 possesses a 3D Fermi surface component [Phys. Rev. Lett. 131 , 036501 (2023)]. The distinction between 2D and 3D Fermi surface sections in triplet superconductors can have important implications regarding the topological properties of the superconductivity. Here we report the observation of oscillatory components in the magnetoconductance of UTe 2 at high magnetic fields. We find that these oscillations are well described by quantum interference between quasiparticles traversing semiclassical trajectories spanning magnetic breakdown networks. Our observations are consistent with a quasi -2D model of this material 's Fermi surface based on prior dHvA-effect measurements. Our results strongly indicate that UTe 2 -which exhibits a multitude of complex physical phenomena -possesses a remarkably simple Fermi surface consisting exclusively of two quasi -2D cylindrical sections.

The heavy fermion paramagnet UTe$_2$ exhibits numerous characteristics of spin-triplet superconductivity. Efforts to understand the microscopic details of this exotic superconductivity have been impeded by uncertainty regarding the underlying electronic structure. Here we directly probe the Fermi surface of UTe$_2$ by measuring magnetic quantum oscillations in pristine quality crystals. We find an angular profile of quantum oscillatory frequency and amplitude that is characteristic of a quasi-2D Fermi surface, which we find is well described by two cylindrical Fermi sheets of electron- and hole-type respectively. Additionally, we find that both cylindrical Fermi sheets possess considerable undulation but negligible small-scale corrugation, which may allow for their near-nesting and therefore promote magnetic fluctuations that enhance the triplet pairing mechanism. Importantly, we find no evidence for the presence of any 3D Fermi surface sections. Our results place strong constraints on the possible symmetry of the superconducting order parameter in UTe$_2$.