We study anisotropic superconductivity in the nearly quarter-filled $\alpha$–${\mathcal{T}}_3$ lattice. We analyze an extended Hubbard model with off-site attractive interactions within the mean-field framework and find two distinct chiral $d+i{d}^{\prime }$-wave superconducting phases characterized by different Chern numbers. We further investigate the superconducting mechanism mediated by spin fluctuations arising from purely repulsive interactions by applying the fluctuation-exchange (FLEX) approximation to the Hubbard model. The gap symmetry obtained by solving the linearized Eliashberg equation is $d$-wave, which corresponds to a $d+i{d}^{\prime }$-wave superconducting state with a Chern number of 8, including the spin degree of freedom. The $\mathit{q}=\mathit{0}$ antiferromagnetic spin fluctuation, which possesses the largest spectral weight at finite energies arising from the incipient flat band, gives rise to an effective spin-singlet pairing glue between rim sites.

Closing the gap between ray tracing simulations and experimentally observed electron jetting in bilayer graphene (BLG), we study all-electronic, gate-defined BLG cavities using tight-binding simulations and semiclassical equations of motion. Such cavities offer a rich playground to investigate anisotropic electron transport due to the trigonaly warped Fermi surfaces. In this work, we achieve two things: First, we verify the existence of triangular modes (as predicted by classical ray tracing calculations) in the quantum solutions of closed circular BLG cavities. Then, we explore signatures of said triangular modes in transport through open BLG cavities connected to leads. We show that the triangular symmetry translates into anisotropic transport and present an optimal setup for experimental detection of the triangular modes as well as for controlled modulation of transport in preferred directions.

In this work, we describe a localization phenomena, the “topological defect coalescence,” occurring in a non-Hermitian chain with an arbitrary number of defect sites. Specifically, it refers to the localization and coalescence of multiple defect eigenstates at a single defect site closest to the localization edge of the bulk non-Hermitian skin modes. This phenomenon is distinct from the conventional topological defect states in Hermitian systems, where the defect states are separately localized at their respective defect sites. The requirement for the onset of topological defect coalescence is the presence of nonreciprocal coupling which renders the chain non-Hermitian, as well as imaginary on-site potentials at the defect nodes. This allows the defect state coalescence and distribution to be modulated by both the defect site distribution and their corresponding on-site potentials, paving the way for possible applications. Furthermore, this phenomenon is realizable in various synthetic and experimentally realizable platforms, such as topolectrical and photonic systems.

The Magneto-optical effect is a fundamental and well-studied phenomenon in the linear regime, but it is rarely studied in extreme conditions where both the magnetic and the laser fields are strong. Here, we study this effect theoretically in graphene in the nonlinear regime, where high-order harmonics are generated. It is found that the harmonic conversion efficiency can be enhanced by orders of magnitude, and the cutoff energy could be extended from visible to extreme ultraviolet ranges. When the laser intensity reaches a critical value, the cutoff energy is linearly dependent on the laser wavelength, outperforming many semiconductors with a wavelength-independent cutoff. These effects closely link to the dense Landau levels. Our Letter sheds light on a promising prospect for the application of the magneto-optical effect in harmonic generation processes in solids.

Topological phases, edge states, and flat bands in synthetic quantum systems are a key resource for topological quantum computing and noise-resilient information processing. We introduce a scheme based on step-dependent quantum walks on cyclic graphs, termed cyclic quantum walks, to simulate exotic topological phenomena using discrete Fourier transforms and an effective Hamiltonian. Our approach enables the generation of both gapped and gapless topological phases, including Dirac conelike energy dispersions, topologically nontrivial flat bands, and protected edge states, all without resorting to resource-intensive split-step or split-coin quantum walk protocols. Odd- and even-site cyclic graphs exhibit markedly different spectral characteristics, with rotationally symmetric flat bands emerging exclusively in $4n$-site graphs ($n\in \mathbf{N}$). We analytically establish the conditions for the emergence of topological, gapped flat bands and show that gap closings in rotation space imply the formation of Dirac cones in momentum space. Further, we engineer protected edge states at the interface between distinct topological phases in both odd and even cycle graphs. We numerically demonstrate that the edge states are robust against moderate static and dynamic gate (coin) disorder as well as remain stable against phase-preserving perturbations and are independent of initial states. This scheme serves as a resource-efficient and versatile platform to engineer topological phases, transitions, edge states, and flat bands in small-scale quantum systems, opening different avenues for robust quantum memory, protected state transfer, and compact implementations of fault-tolerant quantum technologies.

We investigate the dynamics of number entropy in a chain of free fermions subjected to both defects and stochastic processes. For a special class of defects, namely conformal defects, we present analytical and numerical results for the temporal growth of number entropy, the time evolution of the number distribution, and the eigenvalue profile of the associated correlation matrix within a subsystem. We show that the number entropy exhibits logarithmic growth in time, originating from the Gaussian structure of the number distribution. We find that the eigenvalue dynamics reveal a profound connection to the reflection and transmission coefficients of the associated scattering problem for a broad range of defects. When stochastic processes are introduced, specifically Stochastic Unitary Processes (SUP) and Quantum State Diffusion (QSD), the number entropy scales as $ln\left(t\right)$ in the SUP case and shows strong hints of $ln[ln(t\left)\right]$ scaling in the QSD case. These findings establish compelling evidence that number entropy grows logarithmically slower than the corresponding von Neumann entanglement entropy across a wide class of systems.

We report a pressure-induced high- to low-spin transition in the magnetic insulator ${\mathrm{FeBr}}_2$ at around 31.7 GPa using X-ray emission spectroscopy. The underlying mechanism is interpreted through a combination of structural and electrical transport measurements, together with density functional theory calculations. The magnetic moments are found to decrease under high pressure due to the strengthened crystal field during the structural evolution from the trigonal $\left(P\overline{3}m1\right)$ to the monoclinic $(C2/m)$ phase, which causes the electrons to preferentially occupy the lower-energy $t_{2\mathrm{g}}$ orbitals and pair up to form a low-spin state. Furthermore, metallization is observed upon further compression above 50 GPa, accompanied by another structural transition to a hexagonal $\left(P{6}_{3}mc\right)$ phase. The discovery of a spin transition in the two-dimensional magnetic insulator ${\mathrm{FeBr}}_2$ opens avenues for exploring magnetism by leveraging the unique aspects of van der Waals engineering to induce novel magnetic phenomena.

Weyl semimetals and higher-order topological phases represent two fundamental yet distinct classes of topological matter. While both have been extensively studied in classical-wave systems, their coexistence and controllable transition remain largely unexplored. Meanwhile, emulating three-dimensional spin-orbit couplings, which are crucial for realizing a broad class of higher-dimensional synthetic topological phases, continues to pose significant experimental challenges. Here, we experimentally emulate three-dimensional spin–orbit coupling in a circuit metamaterial and show that tuning the coupling strength into a dimerized configuration enables the coexistence of and a controllable transition between a Weyl semimetal phase and a third-order topological insulator phase. We observe hallmark signatures of both phases, including Fermi arcs revealed by frequency-resolved spectroscopy and topological corner modes probed via local density-of-states measurements. Interestingly, the corner mode degeneracy doubles compared to that in the canonical Benalcazar-Bernevig-Hughes model, signaling an enriched topological structure. Our study establishes a fundamental connection between two paradigmatic topological phases and paves the way for further exploring spin-orbit-coupling-induced exotic higher-dimensional topological phases.

We explore quantum localization phenomena in a system of two coupled tight-binding chains with incommensurate periods. Employing the inverse participation ratio as a measure of localization, we investigate the effects of geometric incommensurability and external magnetic fields. Numerical results reveal the existence of a mobility edge in the spectrum characterized by an abrupt onset of localization in higher-energy states. We find that localization tends to be enhanced by a weak magnetic field, whereas a strong field delocalizes most states.

Magnonic frequency combs (MFCs) are emerging as powerful tools for coherent information processing, yet most existing schemes are limited to a single spacing. Here we demonstrate, through micromagnetic simulations, that a skyrmionium hosted in a synthetic antiferromagnet can generate triple MFCs. We found that the skyrmionium supports in-phase, out-of-phase, and other gyrotropic modes, whose nonlinear interactions with propogating spin waves produce three interleaved sets of comb teeth under suitable conditions. We showed that the interlayer antiferromagnetic coupling can modulate the mode frequency, thereby enabling continuous control of the comb spacing. These results establish skyrmionium-based synthetic antiferromagnets as a promising platform for broadband and tunable MFCs, opening avenues for spintronic and quantum magnonic applications.

Interfacial spin transparency have been well established as a critical factor in determining the spin current transmission efficiency from heavy metal layer to ferromagnetic layer, thereby influencing the spin-orbit torque (SOT) efficiency in heavy metal/ferromagnetic metal heterostructures. Here, we demonstrate that in situ argon plasma treatment effectively enhances the interfacial spin transparency in Pt/NiFe (Py) bilayers, leading to a substantial improvement in spin-orbit torque efficiency. By optimizing plasma exposure time, a maximum interfacial spin transparency (∼0.98) is achieved, approaching the ideal limit for spin current transmission This results in a 81% enhancement in the dampinglike SOT efficiency, as quantified by spin-torque ferromagnetic resonance measurements. The enhancement of interfacial spin transparency is attributed to a suppression of spin memory loss and spin-flip scattering at the Pt/Py interface, resulting from the reduced interfacial roughness, as directly evidenced by x-ray reflectivity analysis. Furthermore, a linear relationship between interfacial spin transparency and interfacial roughness was obtained. Our findings highlight argon plasma as a simple, scalable, and noninvasive technique for tailoring spin-transport properties at heavy metal/ferromagnetic metal, offering a promising pathway for the development of high-performance spintronic devices.

Recent experiments observing how femtosecond laser pulse (fsLP) excites magnons in two-dimensional (2D) antiferromagnetic (AF) semiconductors—such as CrSBr, ${\mathrm{NiPS}}_3$, and ${\mathrm{MnPS}}_3$, or their van der Waals heterostructures—suggest an important role played by excitons. However, microscopic details of such an effect remain obscure, as resonant coupling of magnons, living in the sub-meV energy range, to excitons, living in the $\sim 1\mathrm{eV}$ range, can hardly be operative. Here, we develop a quantum transport theory of this effect, in which the time-dependent nonequilibrium Green's function (TDNEGF) for electrons driven by fsLP is coupled self-consistently to the Landau-Lifshitz-Gilbert (LLG) equation describing classical dynamics of localized magnetic moments (LMMs) residing on magnetic atoms of 2D AF semiconductors. This theory explains how fsLP, of central frequency above the semiconductor gap, generates a photocurrent that becomes spin-polarized due to the background of LMMs, which, in turn, exerts spin-transfer torque (STT) onto LMMs as a genuinely nonequilibrium spintronic mechanism. By analyzing the collective motion of LMMs via the windowed Fast Fourier transform (FFT), we extract frequencies of excited magnons, as well as their lifetime governed by nonlocal damping with the LLG equation due to (explicitly included via TDNEGF) electronic bath. The TDNEGF part of the loop can also include excitons, which is achieved in the present study by utilizing the off-diagonal elements of the nonequilibrium density matrix as the mean-field treatment of Coulomb-binding of electron-hole pairs into excitons. Finally, our theory makes it possible to predict that excited magnons will pump time-dependent charge currents into the attached electrodes, or locally within the 2D AF semiconductor, thereby emitting electromagnetic radiation. The windowed FFT of these two signals contains imprints of excited magnons, as well as the possible presence of excitons, which could be exploited as a novel probe in future experiments.

Chiral magnetic textures, owing to their topological properties and potential for spintronic applications, have attracted considerable attention. Controlling the interplay among different interactions to realize the switching between distinct magnetic textures has therefore become a central research focus. Here, we employ first-principles calculations together with atomic spin dynamics simulations to explore the switching between skyrmions and Yoshimori-type spin spirals induced by Li adsorption in Janus two-dimensional (2D) CrTeSe. We show that selective Li adsorption on either the Se- or Te-terminated surface stabilizes distinct magnetic phases: Li adsorption on the Se side favors a Yoshimori-type spin spiral, whereas adsorption on the Te side stabilizes the skyrmionic state. This contrast originates from site-dependent modifications of exchange interactions, magnetic anisotropy, and the Dzyaloshinskii-Moriya interaction. In addition, the response of magnetic textures to out-of-plane magnetic fields differs strongly between the two systems. These results demonstrate that surface adsorption provides an effective strategy for reversible control of chiral magnetic states in 2D magnets, while also offering fundamental insights into the competing interactions that govern the stability of skyrmions and Yoshimori spin spirals. Our findings not only deepen the understanding among the formation and manipulation of distinct chiral magnetic textures, but highlight the potential of Janus 2D materials as a versatile platform for engineering spintronic phenomena.

Experimental studies have reported that nitrogen (N)-doped orthorhombic $\alpha \text{−}{\mathrm{Mo}}_2\mathrm{C}$ exhibits a significant enhancement in its superconducting transition temperature ($T_c$). To elucidate the underlying mechanisms, we conducted a systematic first-principles investigation of N-doped $\alpha \text{−}{\mathrm{Mo}}_2\mathrm{C}$, focusing on its structural stability, electronic structure, phonon dynamics, and superconductivity. The results show that the superconductivity originates from the electron-phonon coupling (EPC) between $\mathrm{Mo}\text{−}4d$ orbital electrons and low-frequency vibrational modes of Mo atoms. As the N content increases, the $T_c$ exhibits a dome-shaped variation, well-consistent with experimental observations. Notably, varying the N-doping concentration drives a Lifshitz transition and a trivial-nontrivial-trivial topological evolution, as confirmed by Wannier-based $Z_2$ invariants. These findings provide important insights into the superconductivity and topology in N-doped $\alpha \text{−}{\mathrm{Mo}}_2\mathrm{C}$, and offer valuable guidance for the design of high-performance superconducting and topological quantum materials.

Spin-triplet superconductors are considered a promising platform for dissipationless spin transport, where spin currents are carried by spin-triplet Cooper pairs. In this paper, we propose that the spin-triplet superconductivity and spin supercurrent can be engineered in an altermagnetic superconducting nanowire, where a one-dimensional nanowire is placed on the surface of an $s$-wave superconductor and in proximity to the altermagnet. Using the nonequilibrium Green's function method, we demonstrate a nonzero equal-spin Andreev reflection coefficient at the normal metal–altermagnetic superconducting nanowire interface, thereby verifying the injection of spin-triplet Cooper pairs. Furthermore, we systematically investigate the spin transport properties in this hybrid system under a spin bias. Our results demonstrate that these properties can be effectively tuned by the chemical potential and spin bias orientation. Our proposal provides a pathway toward realizing dissipationless spin transport.

Phonons not only serve as the fundamental medium underlying superconductivity but also play a critical role in tuning the performance of superconducting nanowires. Here, we present an efficient approach for detecting midinfrared single photons by leveraging enhanced phonon trapping in superconducting nanowires, which arises from intrinsic acoustic mismatch. In the experiment, the nanowires are patterned on nitrogen-doped amorphous tungsten films, which consist of disordered heavy atoms and weakly doped light atoms. This unique structural composition enables the films to exhibit a phonon group velocity that is significantly lower than that of the silicon substrate. The current-voltage characteristics reveal an ultrahigh ratio of the superconducting switching current to retrapping current ($\sim 22$), which is more than three times higher than that of conventional niobium nitride nanowires. We attribute the increased ratio to phonon trapping facilitated by strong intrinsic acoustic mismatch. Furthermore, the fabricated detector achieves saturated internal detection efficiencies across a wavelength range 1.75–6 µm. This work provides a facile strategy for improving the sensitivity of midinfrared single-photon detectors through in situ phonon engineering.

Superconducting nanocircuits serve as an important platform for realizing quantum computing and quantum detecting. van der Waals integration (vdWI) has been reported in semiconductor devices due to its excellent electrical and thermal properties, but it is rarely reported in superconducting nanocircuits. In this work, we demonstrate a heterostructure through vdWI strategy to achieve the directional control of the thermal relaxation in a superconducting platform. The heterostructure is composed of NbN and $\mathrm{Mo}{\mathrm{S}}_2$ deposited by chemical and sputtering methods, respectively, thereby constructing a vdWI heterostructure with intrinsic anisotropic thermal conductivity. The simulated results indicate that the temperature uniformity of NbN superconducting nanocircuits was improved by the ultrahigh conductivity in plane of $\mathrm{Mo}{\mathrm{S}}_2$. The experimental results show that the superconductivity was improved as a transport characteristic curve. The improved superconductivity is benefited from the robustness to self-heating in a vdWI heterostructure, which is applicable to superconductor devices.

Optically active spin defects in semiconductors and insulators, also known as color centers, have emerged as highly promising platforms for qubits. In recent years, the search for color centers that possess both excellent optical and spin properties has become a major focus of research. In this work, using first-principles calculations, we theoretically predict ${{\mathrm{V}}_{\mathrm{Si}}}^{2-}$ defect in 4H- and 6H-SiC as a promising color center with high spin ($\mathrm{S}=1$), exhibiting a relatively weak electron-phonon coupling that leads to a large Debye-Waller factor (>10%). Additionally, its NV-like electronic structure and local environment result in a significant zero-field splitting ($1.16-1.29\mathrm{GHz}$) and a long spin coherence time (>1.3 ms). Combining the advantages of known color centers, ${{\mathrm{V}}_{\mathrm{Si}}}^{2-}$ in SiC exhibits outstanding optical and spin properties, which can serve as an ideal system for qubits. Furthermore, we find that ${{\mathrm{V}}_{\mathrm{Si}}}^{2-}$ is also a promising single-photon source in the IR-B and IR-C region for long-distance communications, addressing the current gap in quantum-coherent materials.

We investigate the effects of thermal fluctuations in graphene bilayers by means of a nonperturbative renormalization group (NPRG) approach, following the pioneering work of Mauri et al. [Phys. Rev. B 102, 165421 (2020)] based on a self-consistent screening approximation (SCSA). We consider a model of two continuum polymerized membranes, separated by a distance $\ell$, in their flat phase, coupled by interlayer shear, compression/dilatation, and elastic terms. Within a controlled truncation of the effective average action, we retain only the contributions that generate a pronounced crossover of the effective bending rigidity along the renormalization group flow between two regimes: at high running scale $k$, the rigidity is dominated by the in-plane elastic properties, with ${\kappa }_{\mathrm{eff}}\sim {\ell }^2(\lambda +2\mu )/2$, whereas at low $k$ it is controlled by the bending rigidity of two independent monolayers, ${\kappa }_{\mathrm{eff}}\sim 2\kappa$. This crossover is reminiscent of that observed by Mauri et al. as a function of the wavevector scale $q$, but here it is obtained within a renormalization group framework. This has several advantages. First, although approximations are performed, the NPRG approach allows one, in principle, to take into account all nonlinearities present in the elastic theory, in contrast to the SCSA treatment, which requires, already at the formal level, significant simplifications. Second, it demonstrates that the bilayer problem can be treated as a straightforward extension of the monolayer case, with flow equations that keep the same structure and differ only by bilayer-specific adjustments. Third, unlike the SCSA, the NPRG framework admits a controlled, systematically improvable, hierarchy of approximations.

We study the magnon spectrum of $\alpha$-MnTe by utilizing the density functional perturbation theory. In contrast to conventional antiferromagnets, the spectra of chiral magnons in $\alpha$-MnTe are found to coincide in four nodal planes, possess the same peak energy but different peak intensities at the Brillouin zone boundaries, and completely diverge elsewhere, which indicates the magnon chiral splitting. Symmetry analysis from electronic states reveals that the inversion symmetry breaking or half-cell translation breaking leads to the magnon bands' splitting in altermagnets. We also verify the $g$-wave magnetism in MnTe from first principles. Our findings provide direct microscopic insights into collective spin excitations in altermagnets.