The semihydrogenated bilayer graphene (${\mathrm{C}}_2{\mathrm{C}}_2\mathrm{H}$), which is a bilayer graphene semihydrogenated on one graphene layer, can be considered as the merging of a monolayer graphene and a semihydrogenated graphene (${\mathrm{C}}_2\mathrm{H}$) through the interlayer bonds. Based on this picture, and an approximation to the low-energy band of ${\mathrm{C}}_2\mathrm{H}$, we construct the low-energy effective model of ${\mathrm{C}}_2{\mathrm{C}}_2\mathrm{H}$. In both the nonmagnetic state and the magnetic ordered state, the low-energy effective model of ${\mathrm{C}}_2{\mathrm{C}}_2\mathrm{H}$ is equivalent to the model of ${\mathrm{C}}_2\mathrm{H}$. Similar to ${\mathrm{C}}_2\mathrm{H}$, the Berry curvature distributions in the low-energy bands of ${\mathrm{C}}_2{\mathrm{C}}_2\mathrm{H}$ concentrate close to the two valleys of the hexagonal Brillouin zone and have opposite signs at the two valleys. Because of the close connection between the Berry curvature distribution and the optical selection rule, the optical excitations under circularly polarized light are valley polarized in both the nonmagnetic state and the magnetic state. In the magnetic ordered state, the optical excitations are also spin resolved, and are therefore spin and valley coupled. By tuning the resonant energies of the two spin channels via a vertical electric field, the low-energy optical excitations under circularly polarized light can be switched to any one of the four spin-valley polarization channels, indicating that ${\mathrm{C}}_2{\mathrm{C}}_2\mathrm{H}$ is a two-dimensional magnetic material with promising spin- and valley-resolved optoelectronic applications.

One of the major advances of quantum technology is the engineering of complex quantum channels in lattice systems, which paves the way for a variety of nonequilibrium phenomena. For a boundary driven lattice with such engineered quantum channels, the analysis of the full counting statistics of current across boundaries has received limited attention. In this work, we consider a boundary driven free-fermionic lattice with carefully engineered correlated gain and loss channels and obtain the cumulant generating function of the steady-state particle current. We also discuss the limit for simplifying the correlated gain-loss channel to a local gain-loss channel and obtain the average current and its fluctuation in such cases. Generally, in the presence of gain-loss, the current statistics are different at the two ends of the lattice. Hence, for both local and correlated gain-loss, we devise the conditions for which the statistics can coincide, giving rise to a $\mathcal{PT}$ symmetric balanced gain-loss scenario. A striking difference between the correlated gain-loss and their local counterpart is the emergence of nonreciprocity in the system and we observe that it has a dramatic impact in the current as well as fluctuations. Our work therefore provides interesting insights about the importance of engineered dissipators in boundary driven systems.

Multiferroic altermagnets, which integrate ferroelectricity with altermagnetism, provide a promising platform for realizing unconventional magnetoelectric coupling. However, the realization of multiple multiferroic orders in such systems remains largely unexplored. Here, we uncover electrically reconfigurable altermagnetism in three-dimensional (3D) van der Waals (vdW) crystals assembled from orthogonally stacked ferromagnetic (FM) transition metal oxytrihalide nanowires. Taking ${\mathrm{MoOBr}}_3$ as an example, first-principles calculations identify a ferroelectric (FE) ground state and four metastable polar variants—ferrielectric (FiE) plus three symmetry-inequivalent antiferroelectric (AFE) configurations—created by Mo off-center movement along the nanowire axis. All five phases retain altermagnetic (AM)-like nonrelativistic spin splitting characteristics, while spinorbit coupling (SOC) merely endows each with a distinct magnetic-anisotropy landscape. Crucially, controlled switching among the FE, AFE, and FiE states concurrently reshapes the momentum-resolved spin splitting and rotates the Néel vector by up to ${90}^{\circ }$, revealing a strong coupling between electric polarization and AM order. Additionally, uniaxial strain breaks the $C_{4x}$ symmetry protection, inducing a piezomagnetic response that transforms the compensated AM state into a weakly ferrimagnetic (FiM) state while simultaneously modulating the FE polarization magnitude. This synergy and coupling of multiple multiferroic orders hold potential candidates for developing nonvolatile memories, reconfigurable logic devices, and energy-efficient mechanospintronics.

The parity anomaly of a single massless Dirac fermion in $(2+1)$ dimensions produces a half-quantized Hall conductance, a phenomenon recently confirmed on the surface of three-dimensional (3D) ${\mathbb{Z}}_2$ topological insulators. Whether and how this anomaly generalizes to 3D topological phases carrying an integer winding number $W$ has remained an open question. Here, we address this problem for 3D chiral topological systems in the Altland-Zirnbauer symmetry classes AIII and DIII. By constructing minimal lattice models, we show that the winding number fixes the net chirality of the boundary Dirac or Majorana cones. By introducing a time-reversal-breaking surface mass to provide the necessary high-energy regularization, we explicitly expose their intrinsic parity anomaly. Through a layer-resolved Chern-number analysis, we establish a macroscopic topological magnitude law, $|{\mathcal{C}}_{\mathrm{surf}}|=|W|/2$, revealing that the shared chirality enforces a constructive accumulation of the fractional topological charges. We further demonstrate that this amplified anomaly coefficient is unambiguously readable in transport: a four-terminal setup in class AIII yields a quantized transmission asymmetry $\left|\mathrm{\Delta }T\right|=\left|W\right|/2$, while a six-terminal thermal Hall measurement in class DIII topological superconductors gives $|{\kappa }_{xy}^{\mathrm{surf}}|=|W|/4{\kappa }_0$. Notably, this thermal signature remains strictly robust against 3D Anderson disorder. Our results establish that the bulk winding number universally controls the macroscopic surface parity-anomaly coefficient in 3D chiral topological phases, providing concrete transport protocols for its detection in artificial metamaterial platforms and topological superconductor candidates.

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.