The Kitaev chain has been extensively explored in the context of uniform couplings, with studies focusing either on purely nearest-neighbor interactions or on systems dominated by long-range superconducting pairing. Building on these investigations, we introduce a hybrid Kitaev chain in which the lattice is partitioned into two segments: the left segment comprises nearest-neighbor couplings, while the right segment incorporates long-range pairing. To probe the role of the interface, we study two scenarios: a decoupled (suppressed hopping) case, where the segments are isolated, and a coupled case, where they are connected via interface hopping that enables tunneling. Using this setup, we investigate the behavior of Majorana zero modes at the interface between the two segments, finding that in the decoupled case, Majorana zero modes remain sharply localized at the left segment chain edges while massive Dirac modes remain in right segment chain edges, with their energies and localization strongly dependent on the long-range pairing exponent. Introducing a finite interface coupling enables transfer of Majorana zero modes from the edges of the left segment to those of the right segment of the chain. We characterize this dynamics by the fidelity of state transfer, dynamical rotation, and inverse participation ratio. We show the signature of Majorana zero mode transfer across the interface by the spatiotemporal profile of the probability distribution of the time evolved state.

We study the mean-field broken symmetry phases of charge neutral multilayer rhombohedral graphene within tight-binding approximations including self-consistent extended Hubbard interactions. We used onsite and intersite Hubbard interactions obtained from a newly developed first-principles calculation method. Our calculations for systems up to eight layers give rise to electron-hole asymmetries, band flatness, band gaps, and layer anti-ferromagnetic ground states in keeping with available experiments. By including the intersite Hubbard interactions up to the next-nearest neighboring sites, the band gaps are shown to open when the number of layers is larger than three, while the trilayer system maintains its metallic nature with two low energy density of state peaks near the Fermi energy whose separation increases with the range of intersite Hubbard parameters. Within our framework, the calculated band gaps reflect mean-field ground states with extended Hubbard interactions, in closer agreement with experimental estimates. The tight-binding formulation further enables efficient treatment of large rhombohedral chiral systems, including twisted multilayer graphene.

A system of several Wannier-Mott excitons interacting with phonons in a bulk material is considered. We show that strong exciton-phonon coupling causes the formation of a coherent two-exciton state—the exciton pair. Unlike the biexcitons, where the photons play the role of force carrier, the exciton pair is formed via entanglement with the long-living phonon mode: (i) The essentially multiparticle theory requires excitons (cobosons composed of an electron and a hole) to satisfy the mixed Bose-Fermi statistics; and (ii) this allows us to formulate a system of nonlinear dynamic equations, using the multiconfiguration Hartree method applied to the Fröhlich Hamiltonian. The system of equations possesses a stationary solution, which, for the case of a single exciton, describes the excitonic polaron and corresponds to the exciton pair in the two-exciton case. We also compare the fluorescent spectra of exciton polarons and exciton pairs estimated from our theory with those observed in experiments on room-temperature superfluorescence (collective emission of fluorescent light) in hybrid perovskites to give an additional insight into the superfluorescence phenomenon.

Negatively charged nitrogen vacancy (NV) center in diamond is the representative solid state defect qubit for quantum information science, offering long coherence time at room temperature. To achieve high sensitivity and spatial resolution, shallow NV centers near the surface are preferred. However, a shallow NV center suffers from surface states and spin noise that reduce the photostability and coherence time. In this work, we systematically study the NV center in the recently reported two-dimensional diamond, known as diamane, using first-principles calculations. We show that the quantum confinement in finite-layer diamane, with appropriate surface passivation, could significantly modify the band structure. In particular, we identify oxygen surface termination capable of hosting a NV center in diamane while optimizing photostability compared to bulk diamond. Furthermore, a layer-dependent NV center demonstrates a tunable zero-phonon line and suppressed phonon side band, while retaining long coherence time. These findings highlight the need to account for the finite-size effects in tuning qubit properties and to develop mitigation strategies that preserve the optical-magneto properties of qubit in nanostructured hosts. Our findings highlight diamane as a promising platform for NV-based quantum information processing with improved optical properties and stability.

We present a theoretical framework for controlling thermal emission in both the azimuth and zenith directions by integrating an in-plane uniaxially anisotropic spacer into a planar three-layered heterostructure. We analytically derive design conditions for directional thermal emission in planar structures with in-plane anisotropic spacer layers. We predict a regime of polarization-selective thermal emissivity along different crystal axes, as well as a regime of high emissivity over a narrow angular cone. As a realistic example, we propose structures with a calcite (${\mathrm{CaCO}}_3$) spacer combined with a silicon carbide (SiC) emitter and a gold back-reflector, achieving high directivity in the midinfrared. These results demonstrate a lithography-free route to narrow band, polarization-dependent control of the thermal emission direction in simple multilayer structures.

Time-reversal-invariant $p$-wave superconductors (SCs) are characterized by their $\mathit{d}$ vectors, whose orientations could be manipulated by a tiny magnetic field. We study in this paper the adiabatic pumping process induced by periodically rotating the $\mathit{d}$ vector in a topological $p$-wave SC, which is coupled to two normal leads. If the $\mathit{d}$ vector rotates nearly within a plane, the pumped spin $2S_z/\hslash$ over one cycle is nearly quantized at 2 without net charge pumping. When the pumping lead is fully spin polarized, both the pumped charge $Q/e$ and spin $2S_z/\hslash$ will peak nearly at 1. When a mixing $s$-wave pairing component is taken into account, a topological phase transition can be driven by modulating the ratio between the pairing components. We find a sharp resonance phenomenon near the phase transition when the $p$-wave $\mathit{d}$ vector is adiabatically rotating, which may help experimentally distinguish the topological SCs from trivial ones.

Friction control remains a pivotal challenge in enhancing energy efficiency and extending the operational lifespan of mechanical components across multiple length scales. Sliding ferroelectric materials present a promising pathway for friction modulation via external electric fields due to their capacity to generate tunable out-of-plane polarization through interlayer sliding. However, a critical barrier in realizing this approach lies in quantifying the correlation between friction behavior in sliding ferroelectrics and applied electric fields. Here, we systematically investigate the friction and electronic constructures of eight h-BN-like sliding ferroelectric systems under varying external electric fields by combining a self-built high-throughput computational framework based on density functional theory and the Prandtl-Tomlinson model with electronic effect considerations. We elucidate the fundamental principles governing electric-field-regulated friction in sliding ferroelectric materials and quantitatively determine the alternating electric field intensity required to achieve superlubricity. This study lays the theoretical foundation for designing of field-tunable, ultra-low-friction atomic-scale devices using sliding ferroelectric materials.

Using ab initio band structure and dynamical mean-field theory methods we examine the effects of electron-electron interactions on the electronic structure, magnetic state, and structural phase stability of the recently discovered double-layer perovskite superconductor ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ (LNO) under pressure. Our results show the emergence of a double spin-charge-density stripe state characterized by a wave vector $\mathbf{q}=(\frac{1}{4},\frac{1}{4})$ arrangement (diagonal hole stripes oriented at ${45}^{\circ }$ to the Ni-O bond) of the nominally high-spin ${\mathrm{Ni}}_A^{2+}$ and low-spin ${\mathrm{Ni}}_B^{3+}$ (with a predominant $3d^8\underline{L}$ configuration with a hole localized in the O $2p$ band) ions which form zigzag ferromagnetic chains alternating in the $ab$ plane. The phase transition is accompanied by cooperative breathing-mode distortions of the lattice structure and leads to a reconstruction of the low-energy electronic structure and magnetic properties of LNO. Our results indicate a strong orbital dependence of correlation effects in LNO. We obtain a narrow-gap correlated insulator with a band gap value of $\sim 0.2\mathrm{eV}$ characterized by strong localization of the Ni $3d$ states and significant spin-orbital polarizations of the charge deficient ${\mathrm{Ni}}_B^{3+}$ ions. We note the importance of double exchange to determine the magnetic properties of LNO, similarly to that in charge-ordered manganites and nickelates. We propose that spin and charge stripe fluctuations play an important role in tuning superconductivity in LNO under pressure.

The intrinsic nonlinear planar Hall effect (NPHE) proposed in recent studies offers a new way to probe inherent band geometric properties in a large class of nonmagnetic materials. However, the search of material platforms with a large response remains a problem. Here, we show that the orbital contribution to NPHE, which was often neglected in previous studies, can be significantly amplified by topological band crossings and overwhelm the spin contribution. This suggests a general approach to achieve a large orbital-dominated NPHE response in topological metals. As an example, we show that the enhancement for a Weyl model, and find the orbital NPHE response coefficient exhibits a characteristic resonance-like lineshape around the Weyl-point energy. Using first-principles calculations, we confirm these features for a concrete material example ${\mathrm{CuTlSe}}_2$. Previous studies have reported two different topological states of ${\mathrm{CuTlSe}}_2$. We clarify this difference originates from two slightly different lattice structures. We show that the NPHE is much stronger in the Weyl semimetal state than in the topological insulator state, and the large response is indeed dominated by orbital contribution amplified by Weyl points. Our work reveals the importance of orbital mechanism in NPHE, demonstrates a close connection between orbital NPHE and topological band features, and suggests ${\mathrm{CuTlSe}}_2$ as a suitable platform for realizing enhanced NPHE.

The doping dependence of the superfluid density ${\rho }_{\text{s}}$ exhibits distinct behaviors in the underdoping and overdoping regimes of cuprates, while the superconducting (SC) transition temperature $T_c$ generally scales with ${\rho }_{\text{s}}$. In this paper, we present a unified understanding of the superconducting transition temperature $T_c$ and ${\rho }_{\text{s}}$ across the entire doping range by incorporating the underlying mutual Chern-Simons gauge structure that couples the spin and charge degrees of freedom in a doped Mott insulator. Within this framework, the SC phase fluctuations are deeply intertwined with the spin dynamics, such that thermally excited neutral spins determine $T_c$, while quantum spin excitations effectively reduce the superfluid density at zero temperature. As a result, a Uemura-like scaling of $T_c$ vs ${\rho }_{\text{s}}$ in the underdoped regime naturally emerges, while the suppression of both $T_c$ and ${\rho }_{\text{s}}$ at overdoping is attributed to a drastic reduction of antiferromagnetic spin correlations.

A new dielectric spectroscopic technique, termed equilibrium photocapacitance measurement (EPCM), using the Lorentz oscillator model, has been developed to understand the photocapacitance of semiconductor devices. This new technique reveals that the density of dipoles and the dipole moment of each dipole in a semiconductor change under illumination. These changes counteract and lead to an equilibrium at a specific applied AC frequency ${\omega }_e$, at which the photocapacitance response (PCR), a frequency-dependent phenomenon, vanishes. The measured ${\omega }_e$ is found to be equivalent to a fundamental parameter governing charge dynamics, the effective Lorentz resonant frequency (${\omega }_0$), that cannot be measured directly. Here, we use EPCM to probe ${\omega }_0$ indirectly via measuring ${\omega }_e$ to investigate how external perturbations (light, DC bias, etc.) influence the dielectric properties of a semiconductor device. Using ITO/PTB7/Ag and $\mathrm{ITO}/\mathrm{ZnO}/\mathrm{PTB}7/{\mathrm{MoO}}_3/\mathrm{Ag}$ devices, we demonstrate that EPCM allows probing both free and bound charge carriers, unlike conventional current measurements, which only account for the mobile charges. Additionally, EPCM enables precise identification of bound and free charge dominated regimes in the C-V profile and provides a robust method to determine the intrinsic dielectric constant of materials, which is challenging to ascertain due to its sensitivity to measurement conditions.

We implement an experimental approach to directly measure the lifetime of guided polaritons arising from the strong-coupling of GaN excitons and the guided photonic modes of a slab waveguide. Using a Fourier imaging setup, combined with spatial filtering of the emission, the emission associated to polaritonic modes with well-defined propagation constants can be selectively analyzed in the temporal domain. By directing it to the entrance slit of a streak camera, time-resolved photoluminescence (TRPL) measurements along the polariton dispersion branch were performed at 40 K, enabling to assess the time decay of polariton modes. By combining this information with the photonic/excitonic fraction corresponding to each polariton mode, extracted from a coupled-oscillators model that indicate a Rabi splitting of $\mathrm{\Omega }=80\mathrm{meV}$, we could extract the photon lifetime in the waveguide ${\tau }_{\gamma }=3\pm 1$ ps. This corresponds to a record $Q$-factor in the UV of 16 000. The excitonic reservoir lifetime, which contributes to polariton formation, was determined through TRPL measurements on excitonic luminescence. Finally, measurements conducted at lower temperature highlight secondary feeding mechanisms for the guided polaritonic mode, either via photon recycling from the AlGaN cladding layer or through resonant injection of photons from transitions below the band gap.

The electronic structure of semiconducting 2D materials such as transition metal dichalcogenides (TMDs) is known to be tunable by its environment, from simple external fields applied with electrical contacts up to complex van der Waals heterostructure assemblies. However, conventional alloying from reference binary TMD compounds to composition-controlled ternary alloys also offers unexplored opportunities. In this work, we use nano-angle resolved photoemission spectroscopy (nano-ARPES) and density functional theory (DFT) calculations to study the structural and electronic properties of different alloy compositions of bulk $\mathrm{W}{\mathrm{S}}_{2(1-x)}\mathrm{S}{\mathrm{e}}_{2x}$. Our results demonstrate the continuous variation of the band structure and the progressive evolution of the valence band splitting at the K points from 420 to 520 meV in bulk $\mathrm{W}{\mathrm{S}}_{2(1-x)}\mathrm{S}{\mathrm{e}}_{2x}$. We also carried out scanning tunneling microscopy (STM) measurements and DFT to understand the possible S or Se substitutions variants in $\mathrm{W}{\mathrm{S}}_{2(1-x)}\mathrm{S}{\mathrm{e}}_{2x}$ alloys, with different local atomic configurations. Our work opens up perspectives for the fine control of the band dispersion in van der Waals materials and demonstrates how the band structure can be tuned in bulk TMDs. The collected information can serve as a reference for future applications.

We performed field-angle-resolved magnetostriction and thermal-expansion measurements on ${\mathrm{PrIr}}_2{\mathrm{Zn}}_{20}$, a cubic non-Kramers compound exhibiting antiferroquadrupolar order below $T_{\mathrm{Q}}=0.125\mathrm{K}$. Thermal expansion exhibits two qualitatively different anomalies under magnetic fields applied along the [001] direction, providing experimental support for the existence of an intermediate A phase previously reported. Furthermore, comparison between the experimental results and theoretical modeling indicates a strong anisotropic coupling of the $O_{20}$ quadrupolar moment, which plays a key role in stabilizing the A phase. These findings demonstrate that multipolar states in non-Kramers systems can be effectively tuned by magnetic-field orientation, providing insights into the anisotropic nature of quadrupolar interactions.

The origin of the charge-density-wave (CDW) phase in ${\mathrm{TiSe}}_2$ is a highly debated topic, with lattice and excitonic correlations proposed as the main driving mechanisms. One of the proposed scenarios is the excitonic insulator (EI) mechanism, where a soft electronic mode drives the phase transition. However, the existence of this purely electronic mode is controversial. Here, we perform fully ab initio calculations of the electron excitation spectra in ${\mathrm{TiSe}}_2$ with electron-hole excitonic effects included via Bethe-Salpeter equations. In the normal high-temperature phase, the excitation spectra are dominated by the exciton mode at 1.6 eV, while no well-defined soft electronic modes that could support the EI phase are present. In the CDW phase, the structural distortions induce a CDW band-gap opening between Ti-$d$ and Se-$p$ states, which supports the formation of the two low-energy excitonic modes in the optical spectrum at 0.4 eV and 80 meV. Close to the transition temperature $T_{\mathrm{CDW}}$, these two excitonic modes are softened and approach zero energy. These results suggest that the EI mechanism is not a main driving force in the formation of the CDW phase in ${\mathrm{TiSe}}_2$, but there is a region in the phase diagram near $T_{\mathrm{CDW}}$ where EI fluctuations could be relevant.

CdTe undergoes a pressure-induced phase transformation from the zinc-blende ($B3$) to the rock-salt ($B1$) structure in the pressure range of $2-4\mathrm{G}\mathrm{Pa}$. However, at temperatures below $773\mathrm{K}$, powder-diffraction experiments further have established a narrow pressure range in which an intermediate cinnabar phase exists although the transformation mechanisms remain unclear. Ab initio metadynamics simulations are performed to examine the pressure-induced $B3\text{−}B1$ phase transformation of CdTe close to the experimental transition pressure at room temperature. The transformation upon compression into the rock-salt phase is proceeded by parallel sliding of alternating ${\left\{111\right\}}_{B3}$ planes along a ${\langle 110\rangle }_{B3}$ direction relative to in-between stationary ${\left\{111\right\}}_{B3}$ planes. This sliding mechanism produces shearing of the six-membered rings of the zinc-blende phase resulting in the brief formation of a five-coordinated structure before the transformation into the six-coordinated rock-salt phase is complete. A similar, albeit reversed, transformation mechanism is observed upon decompression starting from the rock-salt phase. The observed transformation mechanism exhibits an orientation relationship between one of the three-fold axes of the cubic phases as found experimentally. Significantly, an intermediate cinnabar phase is not observed in the simulated phase transformation, contrary to expectations from diffraction experiments. Accordingly, the phase stability for the experimentally proposed cinnabar structure of CdTe and the pressure dependence of its structural, mechanical, and electrical properties are investigated.

The quantum transverse Ising model and its extensions play a critical role in various fields, such as statistical physics, quantum magnetism, quantum simulations, and mathematical physics. Although it does not suffer from the sign problem in most cases, the corresponding quantum Monte Carlo algorithm performs inefficiently, especially at a large longitudinal field. The main hindrance is the lack of loop update method which can strongly decrease the auto-correlation between Monte Carlo steps. Here, we successfully develop a loop algorithm with a novel merge-unmerge process. It demonstrates a great advantage over the state-of-the-art algorithm when implementing it to simulate the Rydberg atom chain and Kagome qubit ice. This advanced algorithm suits various systems, such as Rydberg atom arrays, trapped ions, quantum materials, and quantum annealers.

We investigate the structure, magnetic, and ferroelectric properties of orthochromite ${\mathrm{GdCrO}}_3$ using density functional theory simulations. Structure relaxation with the experimental lattice found centrosymmetric Pbnm and $P{2}_1/c$ phases together with noncentrosymmetric $Pna{2}_1$ and $\mathit{Pc}$ phases, and corresponding atom coordinates were calculated. The $Pna{2}_1$ phase was found to be the ground state structure responsible for a 0.12 $\mu {\mathrm{C}/\mathrm{cm}}^2$ spontaneous polarization. We found that both the Cr and Gd moments are antiferromagnetic aligned with G-type antiferromagnetism for Cr, while, intriguingly, the Gd sublattice was found to be C type antiferromagnetic. The antiferromagnetic Néel temperature was estimated to be 170.10 K for Cr and 4.74 K for Gd; spin moments calculated with spin-orbit coupling remained C type antiferromagnetic for the Gd sublattice with the spins canting in other directions. Our results not only agree well with recent experimental results and Bertaut's spin transformation theory but also reveal the fundamental relations of magnetic and ferroelectric properties of multiferroic ${\mathrm{GdCrO}}_3$.

Cavity-magnon polaritons are hybrid excitations from the interaction between cavity photons and magnons, the quanta of collective spin oscillations. Along with the tunability of the magnon-photon coupling strength, fast information transfer and conversion speed are desired in hybrid devices. This can be achieved utilizing the propagating nature of spin waves with nonzero momentum for their ultrafast time dynamics and reduced ohmic dissipation. Antiferromagnets are particularly interesting as hosts for magnons since stray-field interactions are minimized and they support multiple modes with distinctive magnetic-field behavior across the phase diagram. Chromium trichloride (${\mathrm{CrCl}}_3$) is a van der Waals layered antiferromagnet having a strong easy-plane anisotropy and a weak in-plane easy-axis anisotropy. Despite some magnetic resonance studies, the impact of magnetic reorientation of spins in ${\mathrm{CrCl}}_3$ on the cavity-magnon-polariton interaction strength as a function of magnetic field remains largely unexplored. In this study, we investigate the coupling between magnons in ${\mathrm{CrCl}}_3$ and photons in a coplanar waveguide resonator as a function of magnetic field. In particular, we find that the magnon-photon coupling strength varies nonmonotonically and distinctly with the magnetic field for the acoustic and the optical magnons, which can be utilized to tune the magnon-photon coupling strength using an external magnetic field as a knob. We find the signature of spin-flop transition in the two harmonics of the cavity due to a stronger dispersive coupling between optical magnons and cavity photons at lower fields. Additionally, we find standing modes formed by spin waves with nonzero momentum associated with the two hybrid magnons when the external field is applied at an angle with the crystal plane. These modes do not undergo substantial coupling with the cavity mode unlike the antiferromagnetic modes and can be used as low-loss propagation channels in hybrid devices.