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Abstract The phase landscape of UTe₂features 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 UTe₂Fermi 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 increasedf-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. 

𝐵 site ordered 5⁢𝑑2 double perovskites (𝐴2⁢𝐵⁢𝐵′⁢O6,𝐵′=5⁢𝑑2) display a remarkable range of physical properties upon variation of the chosen 𝐵 and 𝐵′ site ions. This sensitivity to chemical substitution reflects the delicate balance and profound impact of strong electronic correlation and spin-orbit coupling in such systems. We present rhenium 𝐿2 and 𝐿3 resonant inelastic x-ray scattering (RIXS) measurements of two such physically dissimilar materials, Mott-insultating Ba2⁢Y⁢Re⁢O6 and semiconducting Sr2⁢Cr⁢Re⁢O6. Despite these differences, our RIXS results reveal similar energy scales of Hund's (𝐽𝐻) and spin-orbit coupling (𝜁) in the two materials, with both systems firmly in the intermediate Hund's coupling regime where 𝐽𝐻/𝜁∼1. However, there are clear differences in their RIXS spectra. The conductive character of Sr2⁢Cr⁢Re⁢O6 broadens and obfuscates the atomic transitions within an electron-hole continuum, while the insulating character of Ba2⁢Y⁢Re⁢O6 results in sharp atomic excitations. This contrast in their RIXS spectra despite their similar energy scales reflects a difference in the itinerancy-promoting hopping integral and illustrates the impact of the local crystal environment in double perovskites. Finally, 𝐿2 and 𝐿3 edge analyses of the atomic excitations in Ba2⁢Y⁢Re⁢O6 reveal that the ordering of the low lying excited states is inverted compared to previous reports, such that the appropriate energy scales of Hund's and spin-orbit coupling are significantly modified. We present exact diagonalization calculations of the RIXS spectra at both edges which show good agreement with our results for new energy scales of 𝜁=0.290⁢(5)⁢eV and 𝐽𝐻=0.38⁢(2)⁢eV [𝐽𝐻/𝜁=1.30⁢(5)]. 

There has been significant recent interest in layered solid-state materials containing an [M2O] square lattice layer (M = transition metal), particularly because [M2O] is the anti-type of the [CuO2] planes in the layered cuprate superconductors. In addition to the superconducting titanium oxypnictides, the [M2O] anti-cuprate layer also occurs in a wide range of layered oxychalcogenide compounds with M spanning early (Ti, V) to later transition metals (Mn, Co, Fe). The chalcogenide in question – which sandwiches the anti-cuprate layer – may be S, Se or Te, and in combination with a wide range of intervening “spacer” layers, many different structural families have been investigated. This review surveys the structures and physical properties of all these oxychalcogenide materials and relates these properties to their common anti-cuprate square lattice [M2O] layer. It is organised around the different oxidation states of the metal ion M, in order to explore the effects of the electronic configuration of M on the physical properties of each compound as a whole. A key part of the review highlights the use of soft-chemical modifications to alter physical properties of these materials, in the synthesis of novel van der Waals materials and other metastable compounds. Future avenues for these materials in the bulk, few- and single-layer limits are discussed. 

Although nodal spin-triplet topological superconductivity appears probable in uranium ditelluride (UTe₂), its superconductive order parameter Δ_kremains unestablished. In theory, a distinctive identifier would be the existence of a superconductive topological surface band, which could facilitate zero-energy Andreev tunneling to an s-wave superconductor and also distinguish a chiral from a nonchiral Δ_kthrough enhanced s-wave proximity. In this study, we used s-wave superconductive scan tips and detected intense zero-energy Andreev conductance at the UTe₂(0-11) termination surface. Imaging revealed subgap quasiparticle scattering interference signatures witha-axis orientation. The observed zero-energy Andreev peak splitting with enhanced s-wave proximity signifies that Δ_kof UTe₂is a nonchiral state:B_1u,B_2u, orB_3u. However, if the quasiparticle scattering along theaaxis is internodal, then a nonchiralB_3ustate is the most consistent for UTe₂. 

Significant progress toward a theory of high-temperature superconductivity in cuprates has been achieved via the study of effective one- and three-band Hubbard models. Nevertheless, material-specific predictions, while essential for constructing a comprehensive theory, remain challenging due to the complex relationship between real materials and the parameters of the effective models. By combining cluster dynamical mean-field theory and density functional theory in a charge-self-consistent manner, here we show that the goal of material-specific predictions for high-temperature superconductors from first principles is within reach. To demonstrate the capabilities of our approach, we take on the challenge of explaining the remarkable physics of multilayer cuprates by focusing on the two representative CaCuOCl and HgBa2CaCuO families. We shed light on the microscopic origin of many salient features of multilayer cuprates, in particular, the n dependence of their superconducting properties. The growth of Tc from the single-layer to the trilayer compounds is here explained by the reduction of the charge transfer gap and, consequently, the growth of superexchange J as n increases. The origin of both is traced to the appearance of low-energy conduction bands reminiscent of standing wave modes confined within the stack of CuO2 planes. We interpret the ultimate drop of Tc for n ≥ 4 as a consequence of the inhomogeneous doping between the CuO2 planes, which prevents the emergence of superconductivity in the inner planes due to their insufficient effective hole doping, as we also highlight the existence of a minimal doping (4%) required for superconductivity to appear in one of the planes. We explain material-specific properties such as the larger propensity of HgBaCaCuO to super- conduct compared with CaCuOCl. We also find the coexistence of arcs and pockets observed with photoemission, the charge redistribution between copper and oxygen, and the link to the pseudogap. Our work establishes a framework for comprehensive studies of high-temperature superconducting cuprates, enables detailed comparisons with experiment, and, through its ab initio settings, unlocks opportunities for theoretical material design of high-temperature superconductors. 

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 ${\mathrm{UTe}}_2$ 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 ${\mathrm{UTe}}_2$ .