${\mathrm{WTe}}_2$ stands out as a semimetal presenting Fermi level quantum oscillations in most measured quantities under magnetic fields. However, the electronic band structure above and below the Fermi level has not been completely explored. Here we study the electronic band structure of ${\mathrm{WTe}}_2$ by quasiparticle interference with scanning tunneling microscopy and observe, with the support of density functional theory, the electron and hole bands around the Fermi level. We also report on the observation of Landau quantization in atomically resolved measurements and discuss the possible connection with band structure calculations.

Understanding the pairing mechanism in bilayer nickelate superconductors constitutes a fascinating quest. Here we investigate the intriguing interplay between Hund's rule coupling and interorbital hybridization in a two-orbital model for bilayer nickelates, using a comprehensive tensor network approach: density matrix renormalization group for finite-size systems, infinite projected entangled-pair states in the thermodynamic limit, and thermal tensor networks for finite-temperature properties. We explain the pressure-dependent high-$T_c$ superconductivity observed in experiments by identifying three distinct superconductive (SC) regimes: hybridization dominant, Hund's rule dominant, and the hybrid-Hund synergistic SC regimes. In these SC regimes, both $d_{x^2-y^2}$ and $d_{z^2}$ orbitals exhibit algebraic pairing correlations with similar Luttinger parameters $K_{\mathrm{SC}}$. However, the former exhibits a much stronger amplitude than the latter, with a distinctly higher SC characteristic temperature $T_c^{*}$, below which the pairing susceptibility diverges as ${\chi }_{\mathrm{SC}}\left(T\right)\sim 1/T^{2-K_{\mathrm{SC}}}$. With realistic model parameters, we find the pressurized ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ falls into the Hund's rule dominated SC regime. As hybridization further enhances with pressure, it leads to significant interorbital frustration and in turn suppresses the SC correlations, explaining the rise and fall of high-$T_c$ superconductivity under high pressure. Our results offer a comprehensive understanding of the interlayer pairing in superconducting ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$.

We systematically investigate the stability of the symmetry-protected topological (SPT) Haldane phase in spin-$\frac{1}{2}$ Heisenberg and half-filled Hubbard ladders coupled by ferromagnetic Hund's interactions. Using the density-matrix renormalization group method, we analyze key signatures of the Haldane phase: long-range string order, finite spin gap, and characteristic entanglement spectrum degeneracies. In spin-only Heisenberg ladders, we find immediate onset and continuous strengthening of the Haldane phase with increasing Hund's coupling. In contrast, the inclusion of charge fluctuations in Hubbard ladders leads to a nontrivial stability regime, revealing a robust yet bounded region where SPT order persists despite significant charge fluctuations. We identify distinct boundaries separating a trivial insulating phase from the Haldane SPT phase, governed by both Coulomb repulsion and Hund's coupling. Our results highlight the subtle interplay of spin and charge degrees of freedom in correlated itinerant systems and establish essential criteria for observing Haldane physics experimentally in fermionic ladder materials.

Motivated by recent advances in the realization of Truchet-tiling structures in molecular networks and metal-organic frameworks, we investigate the wave localization issue in this kind of structure. We introduce an electron model based on random Truchet tilings, square lattices with randomly oriented diagonal links, and uncover a rich interplay between spectral and localization phenomena. By varying the strength of diagonal couplings, we explore successive transitions from an extended phase, through a regime with a mobility edge, to a fully localized phase. The energy-resolved fractal dimension analysis captures the emergence and disappearance of mobility edges, while an anomalous shift and asymmetry in the Van Hove singularity are identified as key signatures of the underlying disordered Truchet-tiling structure. Notably, by using the finite-size scaling of level spacing statistics, we clarify that the transition occurs at a finite level of disorder even in the two-dimensional system. Our findings position Truchet-tiled electron systems as a versatile platform for engineering disorder-driven localization and interaction effects in amorphous quantum materials and photonic architectures.

Realizing gate control of spin-orbit coupling (SOC) is crucial for implementing semiconductor spintronic devices, with Rashba SOC being the key mechanism due to its electric-field sensitivity. GaN-based semiconductors are promising for room-temperature spintronics, owing to the availability of diluted magnetic semiconductors with Curie temperatures above room temperature. However, since Rashba SOC is inversely proportional to the band gap, effective electrical manipulation of SOC in wide band-gap GaN-based semiconductors has yet to be clearly established. In this study, we demonstrate that SOC can be effectively tuned by a front gate voltage by beating patterns of Shubnikov–de Haas SdH oscillations in AlGaN/GaN heterostructures. An anomalous gate-dependent decrease in the total SOC coefficient from $4.33\times {10}^{-12}\mathrm{eVm}$ (−6V) to $3.23\times {10}^{-12}\mathrm{eVm}$ (2V) (34% variation) in the two-dimensional electron gas is observed with the internal electric field increasing. This behavior is attributed to the enhancement of Rashba and Dresselhaus SOC with comparable magnitudes but opposite signs under gate control. This gate-tunable SOC provides an alternative platform for electrical control of spin precession in spin transistors. Furthermore, the ability to balance Rashba and Dresselhaus SOC strengths offers a route to prolong the spin lifetime and engineer the SU(2)-symmetric spin states in wurtzite heterostructures.

We report on polarization-resolved electron spin resonance (ESR) in a two-dimensional electron system in AlAs quantum wells. The transmission spectra in the subterahertz frequency range reveals unusual behavior as a function of the light polarization and of experimental geometry. In the Faraday geometry, the excitation conditions for spin resonance are reversed compared with the cyclotron resonance, while in the Voigt geometry the absorption exhibits a twofold dependence on the azimuthal angle of an in-plane static magnetic field. These results contradict a pure magnetic nature of ESR in AlAs quantum wells, revealing a dominating Dresselhaus spin-orbit coupling as a microscopic mechanism of the electric-dipole absorption. A theoretical model that includes an inversion asymmetry and the spin-orbit coupling successfully explains the experimental observations.

Ultrathin FeSe films on ${\mathrm{SrTiO}}_3$ substrate show interface-enhanced superconductivity. However, how the superconductivity is established including superconducting (SC) fluctuations remains unclear. This study investigates the Nernst effect, which is sensitive to superconducting fluctuations in ultrathin FeSe films on ${\mathrm{SrTiO}}_3$. Temperature dependence of Nernst signals in the normal state is similar to bulk FeSe, suggesting that the electrons of ${\mathrm{SrTiO}}_3$ are transferred only to a few layers near the $\mathrm{FeSe}/{\mathrm{SrTiO}}_3$ interface. The Nernst effect caused by SC fluctuations was observed only below $T\sim 1.2T_{\mathrm{c}}^{\mathrm{onset}}$ within our measurement resolution, which is similar to other Fe chalcogenide systems. Our results suggest that the pseudogap in monolayer FeSe/STO possibly originates in other electronic states rather than superconductivity.

We report a superinsulatinglike behavior, in a device having granular Pb film on back-gated few-layer ${\mathrm{MoS}}_2$, below an onset temperature same as the critical temperature $T_{\mathrm{C}}\approx 7\mathrm{K}$ of bulk Pb. Below $T_{\mathrm{C}}$, the current-voltage characteristics exhibit a threshold voltage marking a crossover between the low-bias insulating and the high-bias normal-resistance states, consistent with the known superinsulating state behavior. A temperature-dependent critical magnetic field is also found above which the insulating behavior is suppressed. The threshold voltage is found to vary with the gate voltage but the critical field remains unchanged. With reducing temperature, the sample conductance saturates to a finite value, which depends on magnetic field and gate voltage. This saturation behavior is found to be inconsistent with the charge-Berezinskii-Kosterlitz-Thouless and the thermal activation models but it can be fitted well to a combination of thermal activation and quantum fluctuations.

Ever since the discovery of large electromechanical response at the morphotropic phase boundary of the classical piezoceramic system ${\mathrm{PbZr}}_y{\mathrm{Ti}}_{1-y}{\mathrm{O}}_3$ (PZT) more than six decades ago, different variants of PZT are in use in wide-ranging applications. For the stability of electromechanical performance of piezoelectric devices against inadvertent temperature increase during device operation, the use of piezoceramics with a high Curie point is desirable. In general, chemical modifications of ferroelectrics that significantly improve their piezoelectric response lower the Curie point/depolarization temperature. In contrast to this general trend, here we report a phenomenon wherein a slight Eu modification of PZT, synthesized as per the nominal formula ${\mathrm{Pb}}_{1-3x/2}{\mathrm{Eu}}_x\left({\mathrm{Zr}}_{0.53}{\mathrm{Ti}}_{0.47}\right){\mathrm{O}}_3$, not only increases its piezoelectric charge coefficient $\left(d_{33}\right)$ remarkably from 204 pC/N $(x=0)$ to 415 pC/N $(x=0.005)$, but also increases the Curie point notably from 373 °C $(x=0)$ to 389 °C $(x=0.005)$. We report here this phenomenon and the underlying mechanism by investigating the structures at the local and global length scales using a combination of tools like $\mathrm{E}{\mathrm{u}}^{3+}$ photoluminescence, Raman spectroscopy, and x-ray powder diffraction. We found that while the increase in Curie point is caused by Eu-doping pushing the system from a two-phase (rhombohedral + tetragonal) state to a single-phase tetragonal state with increased tetragonality, the remarkable increase in the $d_{33}$ is associated with Eu-doping increasing the structural heterogeneity of the system by limiting rhombohedral correlations on the local scale. We reproduce the same phenomenon by doping PZT with a dilute concentration of Sm and La, thereby demonstrating the generality of this phenomenon.

The low-energy effective description of Weyl semimetals is defined by the axion electrodynamics, which captures the effects arising due to the presence of nodes of opposite chirality in the electronic structure. Here, we explore the magnetoelectric response of time-reversal breaking (TRB) Weyl superconductors in the London regime. The influence of the axion contribution leads to an increase in the London penetration depth—a behavior that can be anticipated by first considering the photon spectrum of a TRB Weyl semimetal. Moreover, we find that both the Meissner state and the vortex phase feature an interplay between the electric and magnetic fields. This leads to a nonvanishing electromagnetic angular momentum, which we calculate for a number of geometrical configurations.

Recent scanning tunneling spectroscopy (STS) experiments revealed a remarkable role of a supercell consisting of $4\times 4 {\mathrm{CuO}}_2$ unit cells in the emergence of local nematic state and preformed local Cooper pairs and phase coherent cuprate superconductivity. By employing the numerically exact determinant Quantum Monte Carlo simulations, we mimic the effects of an experimental Ca vacancy by an external local potential to investigate the charge and spectral properties of the system hosting two-doped holes. The model numerically supports the role of the $4\times 4$ supercell as the building block of hole-doped cuprates via the hole density distribution and local spectra around the local potential. Our results might provide a theoretical support for the experimental observations and a platform for investigating local charge order and local Cooper pairs on the $4\times 4$ supercell as the plausible route to understanding unconventional cuprate superconductivity.

Recent experimental advances in mixed-stacked tetralayer graphene (4MG) revealed a lack of space-inversion symmetry, leading to intrinsic polarization and an associated band gap. Motivated by these results, we conducted a detailed investigation of the Lifshitz transition under out-of-plane electric fields $E$ and doping $n$ using first-principles calculations. Our calculations reveal that the electronic properties of 4MG are highly tunable, featuring multiple field-driven insulator-metal transitions. The most significant phenomena emerge on the hole-doped side, where a negative electric field unlocks a Lifshitz transition with a unique dual character: an extreme sensitivity that allows it to be triggered by minimal doping near the charge neutrality point and the capacity for a colossal density of states (DOS). The resulting DOS peak is more than an order of magnitude larger than that in benchmark tetralayer rhombohedral graphene. These findings establish 4MG as a versatile platform with remarkably tunable electronic properties, ideal for exploring correlation physics and designing advanced electronic devices.

The self-spin valve, an important giant-magnetoresistance effect observed down to a monolayer thickness, is highly desirable because of the ease of experimental sample preparation. Here, we target the A-type antiferromagnetic ${\mathrm{Ti}}_2\mathrm{C}$ monolayer MXene. Our first-principles calculations based on the density functional theory demonstrate that biaxial strain in the $xy$ plane is an effective approach to achieve the transition from an antiferromagnetic semiconductor to a room-temperature ferromagnetic metal in the A-type antiferromagnetic ${\mathrm{Ti}}_2\mathrm{C}$ monolayer MXene. The out-of-plane easy magnetization axis is robust under the strain. Interestingly, a nonzero magneto-optical Kerr effect signal emerges with a peak Kerr angle of 0.06 rad under a 7% tensile strain. Our results indicate that strain can effectively modulate the optospintronic valve.

Nanopatterning has been shown to be a powerful tool for manipulating the vibrational modes of elastic structures, with applications such as optical-mechanical mode coupling. Inspired by these recent developments in phononic band engineering, we propose a nanopatterning scheme to enhance the superconducting transition temperature $T_c$ in phonon-mediated nanofilm superconductors, such as aluminum. Using the finite element method, we simulate the lattice vibrational modes of nanopatterned films within the Debye model. Our results show that periodic nanopatterning softens the lattice vibrational modes compared to bulk films. It also increases the density of states at high energies, resulting in a couple of percent enhancement in $T_c$. Moreover, we investigate connections to Weyl's law and provide an experimental design prescription to optimize nanopatterning for further enhancement of the superconducting transition temperature.

Increasing the spin coherence time $T_2$ is a major area of interest for spin defect systems such as the silicon ($V_{\text{Si}}$) and carbon ($V_{\text{C}}^{\pm }$) vacancies in $4H\text{−}\mathrm{SiC}$. Usually as temperature increases, $T_2$ decreases due to the thermal bath. Observations of electron-paramagnetic resonance and direct systematic measurements of $T_2$ has seen an anomaly where $T_2$ increases with increasing temperature. In this work, we investigate the mechanisms that cause the $T_2$ temperature anomaly. We find that due to a spontaneous symmetry lowering from a motional Jahn-Teller distortion, a polaron quasiparticle is generated from the vibronic coupling. Initially, for temperatures from 8 to $20–40\mathrm{K}$, the coherence temperature dependence is dominated by phonon-assisted spin relaxation. At temperatures around $20–40\mathrm{K}$, depending on the vacancy, a thermally activated polaron hopping turns on and motional narrowing dominates and increases $T_2$ with increasing temperature. As temperatures reach $120–160\mathrm{K}$, the energy barrier gets high enough to slow the polaron hopping. At this point the Larmor precession dominates, leading to decoherence. Our calculated temperature-dependent coherence agrees with what has been seen experimentally, giving a full theoretical framework for the mechanisms that cause the $T_2$ temperature anomaly of increasing $T_2$ with increasing temperature. The theoretical framework presented here also gives insight into these mechanisms being a probable universal phenomenon that could occur in many other defect center spin systems.

Recent experiments reveal critical roles of anisotropic stresses in transforming glassy carbon (GC) into amorphous diamond, yet ab initio molecular dynamics (AIMD) softwares handling such situations remain scarce. Here, we develop an on-the-fly machine learning augmented constrained AIMD (ML-augmented CAIMD) method by modifying standard AIMD, enabling fast GC simulations under anisotropic stresses and capturing its structural complexity via iterative ML potential updates. Using this approach, new routes from GC to quenchable amorphous diamond with easy synthesis conditions are searched, where the effect of severe rotational shear strains on stabilizing ${\mathrm{sp}}^3$ bonds, previously overlooked in synthesis processes, is now considered. We first demonstrate that GC has unexpectedly high plasticity in ambient conditions, with its tensile strength kept constant up to a strain of 0.6 and its compression and shear strengths stiffened by large strains. Under pressure, increasing annealing temperature promotes the formation of quenchable amorphous diamond by enhancing ${\mathrm{sp}}^3$ preservation upon decompression, but this trend reverses above 2900 K due to thermal graphitization. Remarkably, we find that severe rotational shear strains applied under a pressure of 30 GPa can promote high ${\mathrm{sp}}^3$ hybridization (up to 80%) at low temperatures $(300\sim 1000 \mathrm{K})$, which are quenchable to ambient conditions. A hardened amorphous carbon structure retaining a substantial ${\mathrm{sp}}^3$ fraction of 64% is obtained by decompression from 30 GPa pressuring at 300 K after applying a rotational shear strain of 1.0, the lowest pressure and temperature ever predicted. Our on-the-fly ML-augmented CAIMD algorithm enables designing synthesis routes for quenchable amorphous carbon under unexplored conditions and offers a general framework for structural transformations in disordered materials under extreme conditions and anisotropic stresses.

We illustrate the magnetic differences between the triangular-dimer-lattice compounds ${\mathrm{Rb}}_2{\mathrm{Ni}}_2{\left({\mathrm{SeO}}_3\right)}_3$ and ${\mathrm{K}}_2{\mathrm{Co}}_2{\left({\mathrm{SeO}}_3\right)}_3$. Synthesized ${\mathrm{Rb}}_2{\mathrm{Ni}}_2{\left({\mathrm{SeO}}_3\right)}_3$ is magnetically ordered at 5.8 K and undergoes two-step antiferromagnetic (AFM) transitions when magnetic field is applied along the easy $c$ axis $(H//c)$. The high-field magnetization at 2 K for $H//c$ demonstrates a 1/3 magnetization plateau, followed by a possible narrow 1/2 plateau. Density functional theory calculations reveal that the exchange within the structural dimer $\left(J_0\right)$ is significantly smaller than the exchange in the triangular-lattice layer $\left(J_1\right)$ and, thus, ${\mathrm{Rb}}_2{\mathrm{Ni}}_2{\left({\mathrm{SeO}}_3\right)}_3$ behaves like an easy-axis triangular lattice antiferromagnet. However, for ${\mathrm{K}}_2{\mathrm{Co}}_2{\left({\mathrm{SeO}}_3\right)}_3$, which is disordered down to 2 K, the high-field magnetization at 1.6 K shows two wide 1/3 and 1/2 magnetization plateaus as well as a narrow 2/3 plateau for $H//c$. The magnetic characterization results show that ${\mathrm{K}}_2{\mathrm{Co}}_2{\left({\mathrm{SeO}}_3\right)}_3$ is a coupled dimer antiferromagnet. The competing interplay between the AFM dimer and triangular lattice, as well as additional anisotropic exchanges (for the Co compound), might lead to the emergence of multiple magnetization plateaus in triangular-dimer-lattice antiferromagents.

We report a neutron diffraction study of the magnetic structure of CeAlGe, a candidate topological semimetal that hosts a noncollinear, multi-$\mathbf{k}$ magnetic phase. By measuring both low- and high-momentum-transfer magnetic Bragg peaks within a single experimental setup, we refine a magnetic structure model based solely on localized Ce moments. This model, which differs from that obtained using only high-$Q$ data, quantitatively reproduces the observed intensities, including the (000) zeroth-order magnetic satellites that are especially sensitive to subtle components of the modulation. While a contribution from itinerant electrons to the zeroth satellite cannot be definitively excluded, our analysis reveals no unambiguous evidence for such effects within experimental uncertainty. The refined magnetic structures exhibit topologically nontrivial winding patterns, derived from the fitted magnetic parameters, that support localized, particle-like spin textures with half-integer topological charges. These features provide a natural microscopic origin for the observed topological Hall effect, establishing CeAlGe as a model system where magnetism and topology are intimately linked.