Interlayer coupling plays a critical role in van der Waals materials by governing lattice stability and emergent quantum phases, yet its impact on few-layer hexagonal ${\mathrm{CoTe}}_2$ remains unclear. Here, using first-principles calculations, we systematically investigate monolayer and bilayer ${\mathrm{CoTe}}_2$ with an emphasis on their electronic structures, lattice dynamics, and electron-phonon coupling (EPC) and elucidate the underlying mechanisms driven by interlayer interactions. Our results show that monolayer ${\mathrm{CoTe}}_2$ exhibits pronounced dynamical instability at low temperatures, whereas interlayer coupling stabilizes the bilayer crystal structure and gives rise to phonon-mediated superconductivity with a predicted critical temperature of about 4.7 K when spin-orbit coupling is included. The stabilization and superconductivity in bilayer ${\mathrm{CoTe}}_2$ are primarily attributed to interlayer coupling induced Te $p_z$ charge redistribution and the associated modification of the Fermi surface and electron-phonon coupling. Finally, we discuss how spin-orbit coupling in bilayer ${\mathrm{CoTe}}_2$ weakens the EPC and superconductivity. Our work clarifies how interlayer coupling can jointly tune structural stability and superconductivity in few-layer ${\mathrm{CoTe}}_2$, providing insights for engineering quantum phases in layered transition-metal dichalcogenides.

Dynamical mean-field theory (DMFT) is one of the most standard theoretical frameworks for addressing strongly correlated electron systems. In this study, we explore a holographic renormalization-group (RG)-like structure inherent in DMFT, which we refer to as “AdS/DMFT,” by focusing on the background Bethe-lattice network behind DMFT for electrons with a semicircle density of states. We formulate an RG transformation for the branch Green's function from the outer edge to the interior of the background Bethe-lattice network, and then find that its fixed point can be interpreted as a self-consistent solution of Green's function in DMFT. Moreover, we clarify that the scaling dimensions for the branch Green's function and the boundary correlation functions of electrons at the outer edge of the Bethe-lattice network are characterized by the fixed-point Green's function, analogous to the behavior of a scalar field in an effective two-dimensional anti-de Sitter space. We also perform DMFT computations for the Bethe-lattice Hubbard model, which illustrate that the scaling dimensions capture the Mott transition in the deep interior.

The Kondo screening of a localized magnetic moment crucially depends on the spectral properties of the electronic bath to which it is coupled. Unlike textbook examples, realistic systems as well as dynamical mean-field theory of correlated lattice models force us to consider sharp features in the hybridization function near the Fermi energy. Divergencies of this kind can play a relevant role in twisted bilayer graphene, for which local-moment formation and isospin entropy at finite temperature are currently under the spotlight. We clarify how a low-frequency singularity impacts the screening mechanisms by means of a toy model with a tunable $\delta$ peak in the hybridization function, superimposed to a regular part. Our analysis unveils an unexpectedly big impact on the local-moment physics already for a parametrically small weight of the flat band in the bath.

A High-quality single crystal of $\mathrm{CaF}{\mathrm{e}}_3{\mathrm{O}}_5$ was grown using the floating-zone method, enabling a precise investigation of its electronic phase transitions. Temperature-dependent resistivity measurements reveal two successive semiconductor-metal-insulator transitions at $\sim 299$ and $\sim 296\mathrm{K}$, which are identified via specific heat and thermal expansion data as the emergence of a charge-averaged (CA) phase and the formation of a $\mathrm{F}{\mathrm{e}}^{3+}\text{−}\mathrm{F}{\mathrm{e}}^{2+}\text{−}\mathrm{F}{\mathrm{e}}^{3+}$ trimeron in the charge-ordered (CO) phase in $\mathrm{CaF}{\mathrm{e}}_3{\mathrm{O}}_5$, respectively. Our results demonstrate that the occurrences of CO and CA phases in $\mathrm{CaF}{\mathrm{e}}_3{\mathrm{O}}_5$ exhibit a competitive relationship instead of forming simultaneously. Under applied pressure, the metal behavior vanishes above 0.13 GPa, with $\mathrm{CaF}{\mathrm{e}}_3{\mathrm{O}}_5$ exhibiting pure semiconductor/insulator behavior. This means that pressure stabilizes the CO phase in $\mathrm{CaF}{\mathrm{e}}_3{\mathrm{O}}_5$ by prompting the formation of a trimeron, offering an alternative route to control competing electronic orders in mixed-valent oxides.

Magnetic skyrmions in proximity to superconductors offer a route to engineering topological superconductivity due to the synthetic spin-orbit coupling engendered by the spin twist of the skyrmion texture. Previous theoretical works show that this leads to Majorana zero modes (MZMs) in skyrmion-vortex pairs for $s$-wave superconductors. Here we investigate this mechanism in fully gapped $d+is$ and $d+id$ superconductors. We find the surprising result that while stable MZMs are found in large parts of the phase diagram, strongly enhanced $d$-wave pairing or stronger skyrmion-induced spin twisting can in fact destroy topology unlike in $s$-wave superconductors. This effect can be understood from the nontrivial spatial structure of the $d$-wave pairing, and mixing of odd and even angular-momentum pairing channels in a rotated frame which untwists the skyrmion texture. Our results inform the feasibility of realizing MZMs with unconventional superconductors in such heterostructures.

Multiferroic tunnel junctions (MFTJs) with tunneling electroresistance (TER) and tunneling magnetoresistance (TMR) effects have emerged as promising candidates for low-power and high-density information technology. However, simultaneously achieving giant TER and TMR ratios still faces significant hurdles. Here, we propose an MFTJ architecture that integrates ferroelectric bilayer-${\mathrm{Ga}}_2{\mathrm{O}}_3$ barrier and room-temperature ferromagnetic $2H-{\mathrm{VS}}_2$ electrodes with spin-valley-mismatch states. Within this structure, reversible Ohmic and Schottky contact switching at the ${\mathrm{VS}}_2/{\mathrm{Ga}}_2{\mathrm{O}}_3$ interfaces modulated by antiferroelectric phase transition can be realized by polarization-induced interlayer electron transfer. Crucially, the Ohmic contacts localize the electronic states of ${\mathrm{Ga}}_2{\mathrm{O}}_3$ layers near the Fermi level at the Γ points, leading to exclusive valley-matching with the spin-up states of ${\mathrm{VS}}_2$ and allowing the ${\mathrm{Ga}}_2{\mathrm{O}}_3$ layers to act as effective spin-valley-filtering layers. Moreover, the intrinsic spin-valley-mismatch states in the ${\mathrm{VS}}_2$ electrodes enable spin-valley matching to be tunable via parallel and antiparallel magnetic configurations. Accordingly, the designed ${\mathrm{VS}}_2$/bilayer-${\mathrm{Ga}}_2{\mathrm{O}}_3/{\mathrm{VS}}_2$ MFTJs achieve giant TER and TMR ratios up to $2.4\times {10}^4\%$ and $1.3\times {10}^8\%$, respectively, accompanied by 100% spin-valley-filtering effects and minimal resistance-area products of 0.09 Ω µ${\mathrm{m}}^2$. Our results propose a viable strategy for significantly improving the performance of MFTJs, enabling low-power and fast-response spintronic memory applications.

Chiral molecules have attracted broad interdisciplinary interest for their ability to produce highly spin-polarized current. This phenomenon, known as the chiral-induced spin-selectivity effect, holds great potential in the field of spintronics. Here, we propose combining chiral molecules with altermagnets (AMs) to construct highly efficient and tunable spin valves. Using the nonequilibrium Green’s function method and the Landauer-Büttiker formula, we obtain the conductance and the magnetoresistance (MR) of a normal metal/chiral molecule/AM spin valve. Our theoretical results reveal that the conductance of the spin valve can be effectively tuned by reorienting the Néel vector of the AM, and the MR of the spin valve increases with molecular length and AM anisotropy. Moreover, the MR vanishes for achiral molecules or in the absence of molecular spin-orbit coupling. Our work paves the way for developing efficient, controllable, and stray-field-free spintronic devices.

The nonlinear transport regime is manifested in the nonlinear current-voltage characteristic of the system. An example of such a nonlinear regime is a setup in which current is injected into the sample and the measured voltage drop is quadratic in the injected current. Such a quadratic nonlinear regime requires inversion symmetry to be broken. This is the same symmetry condition as one needs to observe weak antilocalization, which can be prominent in two-dimensional systems. Here, we study the effects of weak (anti)localization on second-order nonlinear transport in two-dimensional systems using the semiclassical Boltzmann approach. We solve for quasiparticle distribution function up to the second order in the applied external electric field and calculate linear and nonlinear conductivity tensors for a toy model. We find that localization effects could lead to a sign change of the nonlinear conductivity tensor—a phenomenon observed in transition metal dichalcogenide and single-layer graphene devices.

Highly dense and ordered nanobubble arrays in van der Waals (vdW) heterostructures are crucial for strain engineering electronic devices, fabricating high-capacity energy storage systems, and creating quantum emitters. However, neighboring nanobubbles have been found to spontaneously coalesce because of their interactive strain fields, posing severe limitations in controllability. An interlayer rotation in vdW heterostructures forms superlattices featuring long-wavelength moiré patterns. Here, we show theoretically that these moiré patterns underpin superstructures of perfect arrays of nanobubbles confining molecular clusters in localized regions of the superlattice. We find that nanobubbles spontaneously move towards AA stacking regions, forming ordered arrays with a period that can be tuned by the twist angle. This unprecedented control arises from the modulation of moiré patterns on the local strain field, which turns it into a distinct six-point star shape with rotational symmetry that prevents bubble coalescence. This modulation becomes more prominent with larger dimensions of AA stacking regions—controllable through the bilayer twist angle—and dominates above a critical value. We demonstrate a strategy to engineer the position and density of confined molecule clusters in moiré superlattices. These findings could encourage the experimental exploration of superlattice systems with a tuneable electronic band structure, high energy storage capacity, and precisely positioned quantum emitters.

Nitrogen substitution for oxygen is an anion-engineering strategy for tailoring the rich physical properties of oxides. In this work, we investigate the effect of nitrogen doping in titanium monoxide (TiO) and the underlying mechanism, utilizing epitaxial titanium oxynitride Ti(O,N) films grown using nitric oxide (NO)-assisted molecular beam epitaxy (MBE). The resulting film with the ${\mathrm{TiO}}_{0.6}{\mathrm{N}}_{0.4}$ stoichiometry exhibits a superconducting transition temperature ($T_c$) of about 2.5 K, higher than the $T_c$ of pure TiO ($\sim 0.5\mathrm{K}$) yet lower than that of TiN ($\sim 6\mathrm{K}$). However, the $T_c$ variation as a function of anion ratio shows a large discrepancy with the theoretical $T_c$ trend computed based on the Eliashberg equation and density functional theory (DFT). Interestingly, we find that the series of Ti(O,N) films follows the Mooij correlation in the normal-state resistivity versus temperature—typically associated with amorphous metals—manifesting the critical importance of disorder. Our analysis reveals that strong disorder in TiO originates from stoichiometric Ti and O vacancies ($V_{\mathrm{O}}$ and $V_{\mathrm{Ti}}$), while the N substitution for O above 10% effectively mitigates the vacancy formation but introduces moderate chemical disorder at the anion sublattice. Our DFT calculations demonstrate that disorder suppresses superconductivity through the resultant strong momentum-dependent decoherence in the low-energy electronic and high-frequency phonon structures. N substituting for O weakens the lattice instability inherent to TiO, thereby enhancing the $T_c$ primarily due to reduced disorder. Our work suggests that substituting N for O could serve as a viable experimental method for tuning disorder and superconductivity in the series of Ti(O,N) materials, opening new avenues for their applications in quantum devices.

We introduce an entanglement witness that identifies off-diagonal long-range order (ODLRO)—a distinctive form of entanglement—in systems containing both fermionic and bosonic particles. By analyzing the particle-hole reduced density matrices of each subsystem, the approach detects ODLRO independently in both fermionic and bosonic sectors and identifies when long-range order develops across the entire mixed-particle system. The witness also quantifies the magnitude of ODLRO within each particle type, revealing how fermionic and bosonic correlations combine to form the total entanglement of the system, including a bosonic condensation of particle-hole pairs driven by many-body correlations rather than particle statistics. Using the Lipkin-Meshkov-Glick spin model, we show how the transition from ODLRO localized to one particle type to ODLRO shared by both particle types captures the onset of collective entanglement in a mixed-particle environment, providing intriguing insight into systems where fermionic and bosonic correlations coexist.

Tantalum pentoxide $\left({\mathrm{Ta}}_2{\mathrm{O}}_5\right)$ is a polymorphic wide-band-gap semiconductor with outstanding dielectric properties and widespread use in optical and electronic technologies. Its rich structural diversity, arising from multiple polymorphs accessible under different synthesis conditions, has made ${\mathrm{Ta}}_2{\mathrm{O}}_5$ a long-standing subject of interest. However, a unified understanding of the thermodynamic stability and phase transitions of its polymorphs across pressure-temperature (P-T) space has remained elusive. Here, using first-principles calculations, we map the thermodynamic landscape of ${\mathrm{Ta}}_2{\mathrm{O}}_5$ and establish a comprehensive P-T phase diagram together with a phase-stability hierarchy. We find that γ-${\mathrm{Ta}}_2{\mathrm{O}}_5$ and $\mathrm{B}\text{−}{\mathrm{Ta}}_2{\mathrm{O}}_5$ dominate the phase diagram over a broad range of P-T conditions: $\gamma \text{−}{\mathrm{Ta}}_2{\mathrm{O}}_5$ is stabilized at low pressures, while $\mathrm{B}\text{−}{\mathrm{Ta}}_2{\mathrm{O}}_5$ becomes thermodynamically favored at higher pressures up to $\sim 60$ GPa, beyond which Y-${\mathrm{Ta}}_2{\mathrm{O}}_5$ emerges as the most stable phase. Crucially, the zero-point energy (ZPE), one aspect of nuclear quantum effects (NQEs), plays a significant role in determining relative phase stability, contributing substantially to the Gibbs free energy and altering phase boundaries. A reentrant phase transition between γ- and $\mathrm{B}\text{−}{\mathrm{Ta}}_2{\mathrm{O}}_5$ is predicted near $\sim 2$ GPa, revealing unexpected complexity in the phase behavior of this oxide. More generally, we identify a characteristic temperature $\left(T_0\right)$, at which zero-point and thermal phonon contributions to the free energy become comparable, and show that $T_0$ is approximately one-third of the Debye temperature. This relationship provides a simple, physically transparent criterion for assessing the importance of NQEs in phase stability, with implications extending beyond ${\mathrm{Ta}}_2{\mathrm{O}}_5$ to a broad class of complex oxides.

Spin-orbit entangled excitons (SOEEs) in two-dimensional (2D) antiferromagnets provide direct access to explore unconventional many-body interactions in correlated electron systems. In this work, we carry out a detailed investigation using nondegenerate isotropic and anisotropic pump-probe reflection spectroscopy to probe the ultrafast dynamics of SOEEs and their coupling to spin fluctuations in ${\mathrm{NiPS}}_3$. Transient reflectivity data reveal acoustic phonon oscillations at $\sim 27\mathrm{GHz}$, along with two distinct relaxation timescales: fast (1–9 ps) and slower components (1–4 ns) associated with SOEE coherence and spin reordering, respectively. Both timescales exhibit pronounced temperature dependence near the exciton dissociation ($T_{\mathrm{ED}}=120\text{K}$) and Néel ($T_{\mathrm{N}}=155\text{K}$) temperatures. The SOEE coherence shortens from $\sim 9$ ps at $T<T_{\mathrm{ED}}$ to $\sim 3$ ps at $T>T_{\mathrm{ED}}$ with a finite tail persisting beyond $T_{\mathrm{N}}$. The spin reordering time grows near 120 K, and shows a critical slowing down around $T_{\mathrm{N}}$. Pump fluence studies further corroborate their spin origin. Our findings uncover the direct interplay between the excitonic and spin degrees of freedom across ultrafast and longer timescales, offering distinct opportunities to probe and engineer emergent many-body interactions in 2D antiferromagnets.

We report a comprehensive study of spin-$\frac{1}{2}$ quantum magnet brochantite, ${\mathrm{Cu}}_4{\mathrm{SO}}_4{\left(\mathrm{OH}\right)}_6$, combining high-field thermodynamic measurements, polarized neutron diffraction, inelastic neutron scattering, and nuclear magnetic resonance spectroscopy. Using bulk magnetization and specific heat measurements we construct the magnetic $H\text{−}T$ phase diagram for magnetic fields applied along main crystallographic directions up to 24.1 T. Polarized neutron diffraction reveals a noncollinear magnetic ground state confined to the $ab$ plane. A field-induced transition is observed for magnetic fields in the $ab$ plane whose critical field and character evolve continuously with field direction in the $ab$ plane. While the transition for $H\parallel b$ might be a spin-flop-like transition, the one for $H\parallel a$ resembles the short-range correlated state above $T_{\mathrm{N}}$, suggesting a magnetic configuration related to the quasi-two-dimensional correlations in the $bc$ planes. The experimental results demonstrate that the ground-state and field-induced phases cannot be explained by a simple XXZ model with a single dominant exchange interaction and that weaker interchain and anisotropic interactions have to be taken into account. Our work establishes brochantite as a low-symmetry Cu-based quantum magnet with noncollinear order and complex field-induced behavior.

A combined experimental and first-principles investigation of the magnetic hyperfine field at dilute Ce impurities in the antiferromagnetic intermetallics ${\mathrm{GdIn}}_3$ and ${\mathrm{TbIn}}_3$ is reported here. Perturbed angular correlation spectroscopy using ${}^{140}\mathrm{Ce}$ probes reveals strongly reduced hyperfine fields of $\sim 13\mathrm{T}$ in both hosts, which are substantially smaller than the free-ion value and even reduced relative to ${\mathrm{CeIn}}_3$. To elucidate the local origin of this suppression, we perform spin-polarized density functional calculations including spin-orbit coupling within supercell models that explicitly account for the antiferromagnetic order. A systematic comparison of local spin-density approximation (LSDA), $\mathrm{LSDA}+U$, and hybrid B3PW91 functionals demonstrates that the hyperfine field at the Ce site is overwhelmingly dominated by the orbital contribution associated with the $4f$ shell, while spin-dipolar and Fermi-contact terms nearly cancel out. Conventional $\mathrm{DFT}+U$ (DFT being density functional approximation) artificially localizes the Ce $4f$ states and strongly overestimates hyperfine field. In contrast, calculations with a hybrid functional with enhanced exact exchange reveal a resonance-like $4f$ spectral weight at the Fermi level, yielding nearly quenched spin moments and hyperfine fields in excellent agreement with the experiment. Analysis of the electronic structure and charge-density redistribution indicates that the reduced lattice volume (from lanthanide contraction) of the ${\mathrm{GdIn}}_3$ and ${\mathrm{TbIn}}_3$ hosts exerts an effective chemical pressure on the Ce impurity comparable to the critical pressure of ${\mathrm{CeIn}}_3$, thereby driving the Ce $4f$ electrons into an intermediate-valence regime. These results establish hyperfine interactions as a sensitive microscopic probe of $4f$ hybridization and demonstrate the importance of beyond-semilocal exchange-correlation functionals for reliable predictions of hyperfine properties in correlated rare-earth materials.

We study how topological crystalline defects—dislocations—reshape the real-space quantum geometric tensor and act as tunable sources of quantum geometry. We show that dislocations strongly enhance the quantum metric, establishing a direct link between lattice topology and the Hilbert-space geometry of states. We characterize the quantum geometry of topological magnons in ordered arrays of dislocations, demonstrating that defect-induced geometric enhancement controls their localization and topological protection. In disordered arrays, dislocation-driven geometry expands the accessible topological phase space and enables transitions to disorder-induced topological phases. Our results identify the quantum metric as a tunable bridge between crystalline topology, magnonic excitations, and emergent topological matter in aperiodic solid-state and synthetic systems.