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Quantum materials can display physical phenomena rooted in the geometry of electronic wavefunctions. The corresponding geometric tensor is characterized by an emergent field known as the Berry curvature (BC). Large BCs typically arise when electronic states with different spin, orbital or sublattice quantum numbers hybridize at finite crystal momentum. In all the materials known to date, the BC is triggered by the hybridization of a single type of quantum number. Here we report the discovery of the first material system having both spin- and orbital-sourced BC: LaAlO3/SrTiO3 interfaces grown along the [111] direction. We independently detect these two sources and probe the BC associated to the spin quantum number through the measurements of an anomalous planar Hall effect. The observation of a nonlinear Hall effect with time-reversal symmetry signals large orbital-mediated BC dipoles. The coexistence of different forms of BC enables the combination of spintronic and optoelectronic functionalities in a single material.We report both spin- and orbital-sourced Berry curvature in LaAlO3/SrTiO3 interfaces grown along the [111] direction.

Chiral spin textures such as skyrmions are of interest to the field of spintronics for their potential use in future computing devices. Hall effect measurements are a simple and powerful method to probe the electronic and magnetic properties of materials. The topological Hall effect, which appears as anomalies in Hall resistance versus magnetic field measurements compared to magnetic measurements, has frequently been used to establish the occurrence of chiral spin textures. However, in addition to experimental issues, intrinsic electronic mechanisms combined with inhomogeneity in materials and at interfaces can lead to an inhomogeneous anomalous Hall effect which could be mistaken for a topological Hall signal. This review covers recent research using Hall effect measurements to probe chiral spin textures, focusing on SrRuO 3 as a model system. The ambiguity between Hall effects due to topological sources has led to disagreement in the interpretation of experimental results and casts doubts on the effectiveness of these techniques for investigating chiral spin textures. Hall effect measurements are often used to identify chiral spin textures in materials through the topological Hall effect, but similar Hall signals can arise due to sample inhomogeneity or experimental issues. Here, SrRuO3 is used as a model system to discuss the ambiguity in Hall signals, questioning the reliability of Hall effect measurements as evidence of chiral spin textures.

Supercurrent diodes are nonreciprocal electronic elements whose switching current depends on their flow direction. Recently, a variety of composite systems combining different materials and engineered asymmetric superconducting devices have been proposed. Yet, ease of fabrication and tunable sign of supercurrent rectification joined to large efficiency have not been assessed in a single platform so far. We demonstrate that all-metallic superconducting Dayem nanobridges naturally exhibit nonreciprocal supercurrents under an external magnetic field, with a rectification efficiency up to ~ 27%. Our niobium nanostructures are tailored so that the diode polarity can be tuned by varying the amplitude of an out-of-plane magnetic field or the temperature in a regime without magnetic screening. We show that sign reversal of the diode effect may arise from the high-harmonic content of the current phase relation in combination with vortex phase windings present in the bridge or an anomalous phase shift compatible with anisotropic spin-orbit interactions. The sign of switching currents in supercurrent diodes depends on their flow direction, however effective strategies to control it in single platforms with large efficiency are missing. The authors realise a supercurrent diode in superconducting weak links that is tunable both in amplitude and sign of switching current by an out of-plane magnetic field in a regime without magnetic screening.

We study the Josephson effects arising in junctions made of non-centrosymmetric superconductors with spin-triplet pairing having s-wave orbital-singlet symmetry. We demonstrate that the orbital dependent character of the spin-triplet order parameter determines its non-trivial texture in the momentum space due to the inversion symmetry breaking and spin-orbit interactions. The emergence of this pattern is responsible for the occurrence of an anomalous Josephson coupling and a dominance of high-harmonics in the current phase relation. Remarkably, due to the spin-orbital couplings, variations in the electronic structure across the heterostructure can generally turn the ground state of the junction from 0- to a generic value of the Josephson phase, thus realizing the so-called φ-junction. Hallmarks of the resulting Josephson behavior, apart from non-standard current-phase relation, are provided by an unconventional temperature and magnetic field dependence of the critical current. These findings indicate the path for the design of superconducting orbitronics devices and account for several observed anomalies of the supercurrent in oxide interface superconductors.

We investigate the changes in spin and orbital patterns induced by magnetic transition-metal ions without an orbital degree of freedom doped in a strongly correlated insulator with spin-orbital order. In this context, we study the 3d ion substitution in 4d transition-metal oxides in the case of 3d3 doping at either 3d2 or 4d4 sites, which realizes orbital dilution in a Mott insulator. Although we concentrate on this doping case as it is known experimentally and more challenging than other oxides due to finite spin-orbit coupling, the conclusions are more general. We derive the effective 3d−4d (or 3d−3d ) superexchange in a Mott insulator with different ionic valencies, underlining the emerging structure of the spin-orbital coupling between the impurity and the host sites, and demonstrate that it is qualitatively different from that encountered in the host itself. This derivation shows that the interaction between the host and the impurity depends in a crucial way on the type of doubly occupied t2g orbital. One finds that in some cases, due to the quench of the orbital degree of freedom at the 3d impurity, the spin and orbital order within the host is drastically modified by doping. The impurity either acts as a spin defect accompanied by an orbital vacancy in the spin-orbital structure when the host-impurity coupling is weak or favors doubly occupied active orbitals (orbital polarons) along the 3d−4d bond leading to antiferromagnetic or ferromagnetic spin coupling. This competition between different magnetic couplings leads to quite different ground states. In particular, for the case of a finite and periodic 3d atom substitution, it leads to striped patterns either with alternating ferromagnetic or antiferromagnetic domains or with islands of saturated ferromagnetic order. We find that magnetic frustration and spin degeneracy can be lifted by the quantum orbital flips of the host, but they are robust in special regions of the incommensurate phase diagram. Orbital quantum fluctuations modify quantitatively spin-orbital order imposed by superexchange. In contrast, the spin-orbit coupling can lead to anisotropic spin and orbital patterns along the symmetry directions and cause a radical modification of the order imposed by the spin-orbital superexchange. Our findings are expected to be of importance for future theoretical understanding of experimental results for 4d transition-metal oxides doped with 3d3 ions. We suggest how the local or global changes of the spin-orbital order induced by such impurities could be detected experimentally.

Systems with pronounced spin anisotropy are pivotal in advancing magnetization switching and spin-wave generation mechanisms that are fundamental to spintronic technologies. Quasi-van der Waals ferromagnets like Cr 1+ δ Te 2 represent seminal materials in this field, renowned for their delicate balance between frustrated layered geometries and magnetism. Despite extensive investigation, the nature of their magnetic ground state and the mechanism of spin reorientation under external fields and varying temperatures remain contested. Here, we exploit complementary techniques to reveal a previously overlooked magnetic phase in Cr 1+ δ Te 2 ( δ  = 0.25 − 0.50), which we term orthogonal-ferromagnetism. This phase consists of atomically sharp single layers of in-plane and out-of-plane maximally canted ferromagnetic blocks, which differs from the stacking of multiple heterostructural elements required for crossed magnetism. Contrary to earlier reports of gradual spin reorientation in CrTe 2 -based systems, we present evidence for abrupt spin-flop-like transitions. This discovery further highlights Cr 1+ δ Te 2 compounds as promising candidates for spintronic and orbitronic applications, opening new pathways for device engineering. Self-intercalated Chromium tellurides consist of CrTe 2 van der Waals layers, with additional Chromium atoms residing in the van der Waals gap. This highly tuneable class of magnetic materials has presented a range of unique magnetic phenomena, and here Bigi, Jego, Polewczyk et al add to this by showing that CrTe 2 ( δ  = 0.25 − 0.50) hosts orthogonal ferromagnetism.

The Berry curvature (BC)—a quantity encoding the geometric properties of the electronic wavefunctions in a solid—is at the heart of different Hall-like transport phenomena, including the anomalous Hall and the non-linear Hall and Nernst effects. In non-magnetic quantum materials with acentric crystalline arrangements, local concentrations of BC are generally linked to single-particle wavefunctions that are a quantum superposition of electron and hole excitations. BC-mediated effects are consequently observed in two-dimensional systems with pairs of massive Dirac cones and three-dimensional bulk crystals with quartets of Weyl cones. Here, we demonstrate that in materials equipped with orbital degrees of freedom local BC concentrations can arise even in the complete absence of hole excitations. In these solids, the crystals fields appearing in very low-symmetric structures trigger BCs characterized by hot-spots and singular pinch points. These characteristics naturally yield giant BC dipoles and large non-linear transport responses in time-reversal symmetric conditions.

The Josephson diode effect describes the property of a Josephson junction to have different values of the critical current for different directions of applied bias current and it is the focus of intense research thanks to the potential technological applications. The ubiquity of the experimentally reported phenomenology calls for a study of the impact that disorder can have in the appearance of the effect. We study the Fraunhofer pattern of planar Josephson junctions in presence of different kinds of disorder and imperfections and we find that a junction that is mirror symmetric at zero-field forbids the diode effect and that the diode effect is typically magnified at the nodal points of the Fraunhofer pattern. The work presents a comprehensive treatment of the role of pure spatial inhomogeneity in the emergence of a diode effect in planar junctions, with an extension to the multi-terminal case and to systems of Josephson junctions connected in parallel. Here, the authors consider the superconducting diode effect in the Fraunhofer pattern of planar Josephson junctions and focus on the role of spatial disorder of several kinds in the junction to yield the diode effect.

Nonreciprocal supercurrent refers to the phenomenon where the maximum dissipationless current in a superconductor depends on its direction of flow. This asymmetry underlies the operation of superconducting diodes and is often associated with the presence of vortices. Here, we investigate supercurrent nonreciprocal effects in a superconducting weak-link hosting distinct types of vortices. We demonstrate how the winding number of the vortex, its spatial configuration, and the shape of the superconducting lead can steer the sign and amplitude of the supercurrent rectification. We identify a general criterion for optimizing the rectification amplitude based on vortex patterns, focusing on configurations where the first harmonic of the supercurrent vanishes. We prove that supercurrent nonreciprocal effects can be used to diagnose high-winding vortex and to distinguish between different types of vorticity. Our results provide a toolkit for controlling supercurrent rectification through vortex phase textures and detecting unconventional vortex states. Vortices are a feature of both superconductivity and superfluidity and are a governing factor in the performance of superconducting-based technologies. Here, the authors theoretically demonstrate how parameters of the vortex, such as position and winding number, can influence the rectification strength of the superconducting diode effect in Josephson junctions.

We investigate nonreciprocal supercurrent phenomena in superconducting quantum interference devices (SQUIDs) that integrate Josephson junctions with single and multiband order parameters, which may exhibit time-reversal symmetry breaking. Our results show that the magnetic field can independently control both the amplitude and the direction of supercurrent rectification, depending on the multiband characteristics of the superconductors involved. We analyze the effects of in-phase (zero) and antiphase ( π ) pairing among different bands on the development of nonreciprocal effects and find that the rectification is not influenced by π -pairing. Furthermore, we demonstrate that incorporating multiband superconductors that break time-reversal symmetry produces significant signatures in rectification. The rectification exhibits an even dependence on the magnetic field and the average rectification amplitude across quantum flux multiples does not equal zero. These findings indicate that magnetic flux pumping can be accomplished with time-reversal symmetry broken multiband superconductors by adjusting the magnetic field. Overall, our results provide valuable insights for identifying and utilizing phases with broken time-reversal symmetry in multiband superconductors. Nonreciprocal supercurrent phenomena and the corresponding diode effect in dc SQUIDs based on Josephson junctions with single and multiband superconductors are studied. It is shown that magnetic fields can independently control supercurrent rectification’s amplitude and direction, particularly in superconductors with broken time-reversal symmetry.