Search for: All records

Abstract In this work, we propose a geometric non-linear current response induced by magnetic resonance in magnetic Weyl semimetals. This phenomenon is in analog to the quantized circular photogalvanic effect (de Juan et al., Nat. Commun. 8:15995, 2017) previously proposed for Weyl semimetal phases of chiral crystals. However, the non-linear current response in our case can occur in magnetic Weyl semimetals where time-reversal symmetry, instead of inversion symmetry, is broken. The occurrence of this phenomenon relies on the special coupling between Weyl electrons and magnetic fluctuations induced by magnetic resonance. To further support our analytical solution, we perform numerical studies on a model Hamiltonian describing the Weyl semimetal phase in a topological insulator system with ferromagnetism. 

Abstract Valleytronics is a rapidly advancing field that explores the use of the valley degree of freedom in electronic systems to encode and process information. It relies on electronic states with spin–valley locking, first predicted and observed in monolayer transition metal dichalcogenides like MoS₂. However, very few bulk materials have been reported to host spin–valley locked electronic states. In this work, we present experimental evidence for a predicted, unique spin–valley locked electronic state generated by the Bi zig-zag chains in the layered compound BaMnBi₂. We observed remarkable quantum transport properties in this material, including stacked quantum Hall effect (QHE) and nonlinear Hall effect (NLHE). From the analysis of the QHE, we identified a spin–valley degeneracy of 4, while the NLHE provides supporting evidence for the anticipated valley-contrasted Berry curvature—a typical signature of a spin–valley locked state. This spin–valley locked state contrasts with that observed in the sister compound BaMnSb₂, where the degeneracy is 2. This difference arises from significant variations in their orthorhombic structures and spin-orbital coupling. These findings not only set up a new platform for exploring coupled spin–valley physics in bulk materials but also underscores its potential for valleytronic device applications. 

Abstract High-entropy oxide (HEO) thermodynamics transcend temperature-centric approaches, spanning a multidimensional landscape where oxygen chemical potential plays a decisive role. Here, we experimentally demonstrate how controlling the oxygen chemical potential coerces multivalent cations into divalent states in rock salt HEOs. We construct a preferred valence phase diagram based on thermodynamic stability and equilibrium analysis, alongside a high throughput enthalpic stability map derived from atomistic calculations leveraging machine learning interatomic potentials. We identify and synthesize seven equimolar, single-phase rock salt compositions incorporating Mn, Fe, or both, as confirmed by X-ray diffraction and fluorescence. Energy-dispersive X-ray spectroscopy confirms homogeneous cation distribution, whereas X-ray absorption fine structure analysis reveals predominantly divalent Mn and Fe states, despite their inherent multivalent tendencies. Ultimately, we introduce oxygen chemical potential overlap as a key complementary descriptor for predicting HEO stability and synthesizability. Although we focus on rock salt HEOs, our methods are chemically and structurally agnostic, providing a broadly adaptable framework for navigating HEOs thermodynamics and enabling a broader compositional range with contemporary property interest. 

Abstract Tomonaga-Luttinger liquid (TLL) behavior in one-dimensional systems has been predicted and shown to occur at semiconductor-to-metal transitions within two-dimensional materials. Reports of one-dimensional defects hosting a Fermi liquid or a TLL have suggested a dependence on the underlying substrate, however, unveiling the physical details of electronic contributions from the substrate require cross-correlative investigation. Here, we study TLL formation within defectively engineered WS₂atop graphene, where band structure and the atomic environment is visualized with nano angle-resolved photoelectron spectroscopy, scanning tunneling microscopy and spectroscopy, and non-contact atomic force microscopy. Correlations between the local density of states and electronic band dispersion elucidated the electron transfer from graphene into a TLL hosted by one-dimensional metal (1DM) defects. It appears that the vertical heterostructure with graphene and the induced charge transfer from graphene into the 1DM is critical for the formation of a TLL. 

ABSTRACT Interface‐induced superconductivity has recently been achieved by stacking a magnetic topological insulator layer on an antiferromagnetic FeTe layer. However, the mechanism driving this emergent superconductivity remains unclear. Here, we employ molecular beam epitaxy to grow a 1T‐CrTe₂layer, a 2D ferromagnet with a Curie temperature up to room temperature, on a FeTe layer. These 1T‐CrTe₂/FeTe heterostructures show superconductivity with a critical temperature of ∼12 K. Through magnetic force microscopy measurements, we observe the Meissner effect on the surface of the 1T‐CrTe₂layer. Our electrical transport measurements reveal that the 1T‐CrTe₂/FeTe heterostructures exhibit nonreciprocal charge transport behavior, characterized by a large magneto‐chiral anisotropy coefficient. The enhanced nonreciprocal charge transport in 1T‐CrTe₂/FeTe heterostructures provides a promising platform for exploring the magnetically controllable superconducting diode effect. 

ABSTRACT We investigate the local atomic and electronic structure, thermodynamic stability, and defect chemistry ofA₆B₂O₁₇(A= Zr/Hf,B= Nb/Ta) oxides using first‐principles density functional theory (DFT) calculations. We examine both ordered unit cells as well as fully disordered special quasirandom structures to clearly discern the effects of cation disorder. Structural predictions align closely with previous experimental results and follow established ionic radii trends. The electronic structure is strongly dependent onB‐cation species:A₆Ta₂O₁₇compositions have ~30% larger band gaps than theirA₆Nb₂O₁₇counterparts. Defect chemistry is similar for all compositions, with anion vacancies being more energetically favorable than corresponding cation defects. All exploredA₆B₂O₁₇compositions are enthalpically unstable with respect to theirAO₂andB₂O₅competing oxides and are therefore classified as entropy‐stabilized materials, supporting prior experimental results. The pronounced agreement between our disordered supercell predictions and experimental measurements indicates all exploredA₆B₂O₁₇compositions contain substantial cation disorder across all 6‐, 7‐, and 8‐coordinated sites. Our findings collectively provide a fundamental understanding of theA₆B₂O₁₇material family through DFT calculations, establishing a framework for future compositional tuning to engineer targeted material properties. 

ABSTRACT Viscosity is a fundamental physical property that governs the flow and processing behavior of glass‐forming liquids. During glass manufacturing processes, it is thus important to know how rheological properties are influenced by variables such as temperature, chemical composition, and the presence of any inclusions within the melt. There is extensive literature describing theoretical models for calculating the viscosity of oxide glass‐forming systems; resources dedicated to experimental methodologies for measuring oxide glass viscosity are comparatively scarce. This review therefore focuses on direct viscometry techniques as well as indirect approaches for measuring viscosity including differential scanning calorimetry (DSC) and dilatometry combined with the Mauro–Yue–Ellison–Gupta–Allan (MYEGA) model. In addition, we highlight emerging machine‐learning approaches, which offer complementary insights into glass viscosity, particularly in complex multicomponent systems. Such machine learning‐based methods require large and high‐quality datasets for training and validation, underscoring the vital importance of experimental measurements in establishing reliable viscosity values. Overall, the primary goal of this review is to fill a gap in the literature regarding experimental methodologies for viscosity measurement of oxide glasses, explaining their underlying principles, highlighting the challenges faced by researchers, and emphasizing the continued necessity of experimental viscosity measurements alongside theoretical and computational approaches. 

ABSTRACT We report the first successful synthesis and characterization of a new family of high‐entropy rare earth borate (RⁿBBO) single crystals with compositionsR⁵Ba₃(B₃O₆)₃andR⁶Ba₃(B₃O₆)₃(R= Nd, Tb, Sm, Dy, Gd, Yb, Er). Using configurational entropy as a tuning knob, these systems have been grown as large, highly crystalline boules that exhibit a bandgap of ≈5 eV and significantly enhanced optical transparency (20–50%) over singlecomponent systems. The presence of multiple rare‐earth elements results in broadband photoluminescence in both the visible and the near‐infrared wavelength ranges, with co‐existing emission bands at 605, 705, 813, 910, and 1030 nm. Further, broken inversion symmetry enables optical second‐harmonic generation (SHG) with potential for both type‐I and type‐II phase matching. Our highest observed effective phase‐matched SHG coefficient of ≈ 2.1 pm V⁻¹at 800–400 nm wavelength conversion is 20% better than the commercial β‐BaB₂O₄(BBO), while its laser‐induced surface damage threshold is 5‐6 × larger for 100 fs 800 nm pulse, enabling potentially an order of magnitude improvement in the frequency conversion efficiency. This work illuminates the promise of high‐entropy synthesis strategy for designing next‐generation optoelectronic materials that combine increased transparency, strong broadband luminescence, and enhanced nonlinear response in a single platform. 

Abstract The search for thin film electro‐optic materials that can retain superior performance under cryogenic conditions has become critical for quantum computing. Barium titanate thin films show large linear electro‐optic coefficients in the tetragonal phase at room temperature, which is severely degraded down to ≈200 pm V⁻¹in the rhombohedral phase at cryogenic temperatures. There is immense interest in manipulating these phase transformations and retaining superior electro‐optic properties down to liquid helium temperature. Utilizing the thermodynamic theory of optical properties, a large low‐temperature electro‐optic response is designed by engineering the energetic competition between different ferroelectric phases, leading to a low‐symmetry monoclinic phase with a massive electro‐optic response. The existence of this phase is demonstrated in a strain‐tuned BaTiO₃thin film that exhibits a linear electro‐optic coefficient of 2516 ± 100 pm V⁻¹at 5 K, which is an order of magnitude higher than the best reported performance thus far. Importantly, the electro‐optic coefficient increases by 100 × during cooling, unlike the conventional films, where it degrades. Further, at the lowest temperature, significant higher order electro‐optic responses also emerge. These results represent a new framework for designing materials with property enhancements by stabilizing highly tunable metastable phases with strain. 

Abstract This manuscript presents a working model linking chemical disorder and transport properties in correlated‐electron perovskites with high‐entropy formulations and a framework to actively design them. This work demonstrates this new learning in epitaxial Sr_x(Ti,Cr,Nb,Mo,W)O₃thin films that exhibit exceptional crystalline fidelity despite a diverse chemical formulation where mostB‐site species are highly misfit with respect to valence and radius. X‐ray diffraction, X‐ray photoelectron spectroscopy, and transmission electron microscopy confirm a unique combination of chemical disorder and structural perfection in thin and thick epitaxial layers. This combination produces an optical transparency window that surpasses that of the constituent end‐members in the UV and IR, while maintaining relatively low electrical resistivity. This work addresses the computational challenges of modeling such systems and investigate short‐range ordering using cluster expansion. These results showcase that unusuald‐metal combinations access an expanded property design space that is predictable using end‐member characteristics and their interactions – though unavailable to them – thus offering performance advances in optical, high‐frequency, spintronic, and quantum devices.