Optically detected magnetic resonance (ODMR) is an efficient and reliable method that enables initialization and readout of spin states through the spin-photon interface. In general, high quantum efficiency and large spin-dependent photoluminescence contrast are desirable for reliable quantum information readout. However, reliable prediction of the ODMR contrast from first-principles requires an accurate description of complex spin polarization mechanisms of spin defects. These mechanisms often include multiple radiative and nonradiative processes, in particular, intersystem crossing (ISC) among multiple excited electronic states. In this work, we present our implementation of the first-principles ODMR contrast by solving the kinetic master equation with calculated rates from ab initio electronic structure methods then benchmark the implementation on the case of the negatively charged nitrogen vacancy center in diamond. We show the importance of the correct description of multireference electronic states and pseudo Jahn-Teller effect for quantitatively, even qualitatively correct prediction of spin-orbit coupling (SOC) and the rate of ISC. We present the complete calculation of SOC for different ISC processes that align with both group theory and experimental observations. Moreover, we provide a comprehensive picture of excitation and relaxation dynamics, including previously unexplored internal conversion processes. We show good agreement between our first-principles calculations and the experimental ODMR contrast under magnetic field. We then demonstrate reliable predictions of magnetic field direction, pump power, and Rabi frequency as important parameters for ODMR experiments. Our work clarifies the important excited-state relaxation mechanisms determining ODMR contrast and provides a predictive computational platform for spin polarization and optical readout of solid-state quantum defects from first principles.

We consider a planar superconducting–normal metal junction with both inelastic and spin-flip scattering processes present. In the diffusive limit, we use a one-dimensional formulation of the Usadel equation to compute the self-consistent energy dependence of the single-particle density of states as a function of distance from the interface on both the superconducting and metallic sides for various spatial profiles of a pair-breaking spin-flip term. The pair-breaking processes fill in the superconducting gap at zero energy, which is reflected in the zero-bias tunneling conductance in scanning tunneling microscopy/spectroscopy experiments, in the vicinity of the junction. We also investigate the impact of having a partially transparent interface at the junction. We compare our findings with the observed exponential rise in the zero-bias conductance at the 1H step edge in recent experiments on 4Hb-${\mathrm{TaS}}_2$ [A. K. Nayak et al., Nat. Phys. 17, 1413 (2021)].

Fractional Chern insulators (FCIs) have attracted intensive attention for the realization of fractional quantum Hall states in the absence of an external magnetic field. Most FCIs have been proposed on two-dimensional (2D) Euclidean lattice models with various boundary conditions. In this work, we investigate hyperbolic FCIs which are constructed in hyperbolic geometry with constant negative curvature. Through the studies on hyperbolic analogs of kagome lattices with hard-core bosons loaded into topological flat bands, we find convincing numerical evidences of two types of $\nu =1/2$ FCI states, i.e., conventional and unconventional FCIs. Multiple branches of edge excitations and geometry-dependent wave functions for both conventional and unconventional $\nu =1/2$ FCI states are revealed. Intriguingly, the geometric degree of freedom plays various roles for these two FCIs. Additionally, a center-localized orbital plays a crucial role in the unconventional FCI state.

We investigate a quasi-two-dimensional system consisting of two species of alkali atoms confined in a specific optical lattice potential [Phys. Rev. A 95, 053608 (2017)]. In the low-energy regime, this system is governed by a unique ${\mathbb{Z}}_N$ gauge theory, where field theory arguments have suggested that it may exhibit two exotic gapless deconfined phases, namely a dipolar liquid phase and a Bose liquid phase, along with two gapped (confined and deconfined) phases. We address these predictions numerically by using large-scale density matrix renormalization group simulations. Our findings provide conclusive evidence for the existence of a gapless Bose liquid phase for $N\ge 7$. We demonstrate that this gapless phase shares the same critical properties as one-dimensional critical phases, resembling weakly coupled chains of Luttinger liquids. In the range of ladder and cylinder geometries and $N$ considered, the gapless dipolar phase predicted theoretically is still elusive and its characterization will probably require a full two-dimensional treatment.

The cubic phase of the ternary ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ alloy has attracted significant interest as a material for next-generation high-performance electronic and optoelectronic applications. It has recently been demonstrated that epitaxial growth techniques can overcome the miscibility gap in this alloy system, thereby revealing the existence of CuPt-type ordering around $x\approx 0.5$ [ACS Appl. Mater. Interfaces 15, 39513 (2023)]. We present a comprehensive theoretical analysis of the structural and electronic properties of the (In, Ga)N alloy in the zinc-blende structure. This study covers both pure phases of InN and GaN, as well as random alloys of ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$. Furthermore, it examines the composition of ${\mathrm{In}}_{0.5}{\mathrm{Ga}}_{0.5}\mathrm{N}$ in the ordered phases with CuPt-type ordering and chalcopyrite-type ordering. We establish that the investigated structures are metastable. The results presented include the lattice parameters, elastic constants, and the phononic and electronic band structures. We compare the random phase with the ordered structures and report how the structure affects the properties. This results facilitate the differentiation between the phases in experimental settings.

Kagome materials are of significant interest in condensed-matter physics due to their unique band structures and emergent topological phases when combined with spin-orbit coupling and magnetism. In this work, we investigate the impact of rare-earth elemental substitution on the magnetic and electronic properties of the manganese-based kagome material $\mathrm{DyM}{\mathrm{n}}_6\mathrm{G}{\mathrm{e}}_6$, achieving tunable magnetic states ranging from ferrimagnetism to antiferromagnetism. High-resolution angle-resolved photoemission spectroscopy further reveals that the robust kagome lattice structure remains intact despite the elemental substitution. Our observations reveal stable Dirac points, which persist across different compositions, highlighting the material's potential for exploring exotic magnetic topological phases and quantum transport phenomena. These findings offer valuable insights into the independent tuning of magnetism and electronic structure in kagome materials, thereby paving the way for advanced studies and applications in the realm of quantum materials.

Tin diselenide ($\mathrm{Sn}{\mathrm{Se}}_2$) is a promising semiconducting material that exhibits diverse potential applications, including nanoscale electronics, resistive memories, sensors, and thermoelectric devices. Although $\mathrm{Sn}{\mathrm{Se}}_2$ offers low thermal conductivity (κ) and high-power factor (PF) compared with other two-dimensional (2D) materials, layer-dependent as well as phase-sensitive studies in particular polytypes are very limited. Here, we have probed $2H$-polytype $\mathrm{Sn}{\mathrm{Se}}_2$ to study the layer-dependent thermal conductivity by using the optothermal Raman technique. The $2H$ polytype of $\mathrm{Sn}{\mathrm{Se}}_2$ has been confirmed by Raman spectroscopy and second harmonic generation (SHG). We have achieved a low thermal conductivity value from 1.37 ± 0.04 to 2.81 ± 0.10 $\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ in $\mathrm{Sn}{\mathrm{Se}}_2$ for the layer thicknesses in the range of 3L–8L. The first-principles calculation has been performed to model the thermal conductivity for the $2H$ polytype from the monolayer (1L) up to the bulk limit. The calculated thermal conductivity value falls in the range of 1.29–2.87 $\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ for 1L to the bulk range, which is consistent with our experimental findings. The remarkably low thermal conductivity in layered $2H$-polytype $\mathrm{Sn}{\mathrm{Se}}_2$ could be attributed to its inherent high anharmonicity and fragile interatomic bonding between the heavy elements Sn and Se. Moreover, the enhancement of phonon boundary scattering with decreasing thickness could be the possible cause of having an extremely low κ value in 2D $\mathrm{Sn}{\mathrm{Se}}_2$ nanoflakes. The origin of thickness-dependent low thermal conductivity in $2H\text{−}\mathrm{Sn}{\mathrm{Se}}_2$ is further supported by studies on phonon lifetime, group velocity, and electron localization function analysis. In this paper, we stipulate the groundwork for the finetuning of any other 2D system phase-dependent thermal conductivity.

In the present article, we explore the electron properties of magnetic semiconductors with strong Rashba spin-orbit coupling, taking into account the presence of domain walls at the sample surface. We consider antiphase domain walls separating domains with both in-plane and out-of-plane magnetization as well as noncollinear domain walls. First, we propose the model and unveil the general physical picture of the phenomenon supported by analytical arguments. Further, we perform comprehensive tight-binding numerical calculations to provide a profound understanding of our findings. A domain wall separating domains with any polarization direction is demonstrated to host a bound state. What is more interesting is that we predict that either of these domain walls also induces a one-dimensional resonant state. The surface energy spectrum and spin polarization of the states are highly sensitive to the magnetization orientation in the adjacent domains. The spectral broadening and the spatial localization of the resonant state depend significantly on a relation between the Rashba splitting and the exchange one. Our estimation shows that chiral conducting channels associated with the long-lived resonant states can emerge along the magnetic domain walls and can be accessed experimentally at the surface of BiTeI doped with transition metal atoms.

A versatile method for angle-resolved photoemission spectra (ARPES) calculations is reported within the one-step model of photoemission. The initial states are obtained from a repeated-slab calculation using the projector-augmented wave (PAW) method. ARPES final states are constructed by matching the repeated-slab eigenstates of positive energy with free electron states that satisfy the time-reversed low-energy electron diffraction boundary conditions. Nonphysical solutions of the matching equations, which do not respect the flux conservation, are discarded. The method is applied to surface-normal photoemission from graphene as a function of photon energy from threshold up to 100 eV. The results are compared with independently performed multiple scattering calculations and very good agreement is obtained, provided that the photoemission matrix elements are computed with all-electron waves reconstructed from the PAW pseudowaves. However, if the pseudowaves are used directly, the relative intensity between $\sigma$- and $\pi$-band emission is wrong by an order of magnitude. The graphene ARPES intensity has a strong photon energy dependence including resonances. The normal emission spectrum from the $\pi$ band shows a hitherto unreported sharp resonance at a photon energy of 31 eV. The resonance is due to a two-dimensional interband transition and highlights the importance of matrix element effects beyond the final-state plane-wave approximation.

The exploration of magnetic topological insulators is instrumental in exploring axion electrodynamics and intriguing transport phenomena, such as the quantum anomalous Hall effect. Here, we report that a family of magnetic compounds ${\mathrm{Eu}}_{2n+1}{\mathrm{In}}_2$(As,${\mathrm{Sb})}_{2n+2}$ ($n=0,1,2$) exhibit both gapless Dirac surface states and chiral hinge modes. Such a hybrid-order topology hatches surface-dependent quantum geometry. By mapping the responses into real space, we demonstrate the existence of chiral hinge modes along the $c$ direction, which originate from the half-quantized anomalous Hall effect on two gapped $ac/bc$ facets due to Berry curvature, while the unpinned Dirac surface states on the gapless $ab$ facet generate an intrinsic nonlinear anomalous Hall effect due to the quantum metric. When ${\mathrm{Eu}}_3{\mathrm{In}}_2{\mathrm{As}}_4$ is polarized to the ferromagnetic phase by an external magnetic field, it becomes an ideal Weyl semimetal with a single pair of type-I Weyl points and no extra Fermi pocket. Our work predicts rich topological states sensitive to magnetic structures, quantum geometry-induced transport, and topological superconductivity if proximitized with a superconductor.

Understanding polariton behavior at the boundary of two-dimensional (2D) materials is a critical yet unresolved issue. Here, we provide an analytical description of the reflection and transmission coefficients of polaritons under oblique incidence, establishing a Fresnel formula tailored to polaritons. We demonstrate that boundary-scattered fields, whether evanescent or radiative, couple with polaritons, inducing phase shifts in reflected and transmitted polaritons and changing the momentum of polaritons in a direction perpendicular to the boundary by an imaginary amount. These polariton dynamics at the boundary lead to various features, including a Brewster-like effect, the Goos-Hänchen effect without total internal reflection, and the cross-polarization coupling of polaritons. Our analytical understanding of polariton dynamics could be applied to the development of future polaritonic devices utilizing 2D materials.

Thin films of the topological insulator $({\mathrm{BiSb})}_2{\mathrm{Te}}_3$ oriented along the [0001] direction were grown via molecular beam epitaxy on substrates of ${\mathrm{Al}}_2{\mathrm{O}}_3$ (0001) and ${\mathrm{MgF}}_2$ (110) single crystals, as well as on an epitaxial thin film of the antiferromagnetic insulator and predicted altermagnet ${\mathrm{MnF}}_2$ (110). Magnetoconductivity measurements of these samples showed close proximity of the Fermi level to the Dirac point and weak antilocalization at low temperature that was partially suppressed in the sample grown on the ${\mathrm{MnF}}_2$ layer. The magnetoconductivity data were fit to a model that describes the quantum corrections to the conductivity for the Dirac surface state of a three-dimensional topological insulator, from which values of the Fermi velocity and the phase coherence length of the surface state charge carriers were derived. The magnetoconductivity of the $({\mathrm{BiSb})}_2{\mathrm{Te}}_3\text{−}{\mathrm{MnF}}_2$ bilayer samples were fit to a model describing the crossover from weak antilocalization to weak localization due to magnetic doping. The results are consistent with the opening of an energy gap at the Dirac point in $({\mathrm{BiSb})}_2{\mathrm{Te}}_3$ due to magnetic proximity interactions of the topological surface states with the antiferromagnetic ${\mathrm{MnF}}_2$ insulator.

Adsorption of porphyrins on solid surfaces plays a key role to its application in various fields. In this work, we investigate the adsorption properties of a commonly studied model metalloporphyrin, magnesium porphyrin (MgP), on bare Au(111) surface and graphene/hexagonal boron nitride (h-BN) covered Au(111) surfaces. The moiré structure of the graphene/Au(111) and h-BN/Au(111) heterosurfaces as a result of the lattice mismatch and its influence of the adsorption of MgP were also studied. The adsorption energies and charge transfer properties calculated at the stable adsorption configurations indicates that the inclusion of the two-dimensional (2D) materials can significantly suppress the direct interaction between the MgP molecule and the Au(111) substrate. Further analysis of the partial density of states and wave function of the frontier molecular orbitals demonstrate that the electronic structure of the MgP molecule can be well preserved, highlighting the decoupling efficiency of two types of 2D materials especially the wide band gap h-BN.

We investigate the Berezinskii-Kosterlitz-Thouless (BKT) transition in a semiconductor-superconductor two-dimensional Josephson junction array. Tuned by an electrostatic top gate, the system exhibits separate superconducting (S), anomalous metal (M*), and insulating (I) phases, bordered by separatrices of the temperature-dependent sheet resistance $R_s$. We find that the gate-dependent BKT transition temperature falls to zero at the S-M* boundary, suggesting incomplete vortex-antivortex pairing in the M* phase. In the S phase, $R_s$ is roughly proportional to the perpendicular magnetic field at the BKT transition, as expected, while in the M* phase, $R_s$ deviates from its zero-field value as a power law in the field with exponent close to 1/2 at low temperature. An in-plane magnetic field eliminates the M* phase, leaving a small scaling exponent at the S-I boundary, which we interpret as a remnant of the incipient M* phase.

The spin-1/2 trimer system ${\mathrm{Na}}_2{\mathrm{Cu}}_3{\mathrm{Ge}}_4{\mathrm{O}}_{12}$ is proposed to host topologically nontrivial 1/3 magnetization $\left(M\right)$ plateau state. In this paper, we report a high-field nuclear magnetic resonance (NMR) study on the low-energy spin excitations of the $1/3\text{−}M$ plateau state in ${\mathrm{Na}}_2{\mathrm{Cu}}_3{\mathrm{Ge}}_4{\mathrm{O}}_{12}$ and Si-doped samples. First, the spin excitation gap supporting the high-field Haldane phase is indicated by the thermally activated behavior of spin-lattice relaxation rates in the $1/3\text{−}M$ plateau state. Second, by substituting ${\mathrm{Ge}}^{4+}$ with ${\mathrm{Si}}^{4+}$, the critical field for the 1/3-$M$ plateau significantly decreases, e.g., ${\mu }_0{H}_c=17$ T in the $x=1.0$ sample, which results from the suppressed intertrimer coupling $J_2$. The gapped spin excitation is observed above 17 T whose size shows the temperature-dependent behavior for ${\mu }_{0}H\ge 25.72$ T. These observations support the topological nontrivial characteristic of the $1/3\text{−}M$ plateau state.

Using machine learning–assisted crystal structure search and first-principles calculations, we have unveiled two hitherto undiscovered thermodynamically stable stoichiometries, namely, Cmmm $\mathrm{Li}{\mathrm{Be}}_5$ and $R\overline{3}m\mathrm{Li}{\mathrm{Be}}_6$, alongside a metastable phase, Cmca LiBe, within the high-pressure realm of Li-Be alloys. Moreover, our investigation has illuminated the distinctive electronic characteristics of Cmca LiBe and $R\overline{3}$ $m\mathrm{Li}{\mathrm{Be}}_6$, both capable of accommodating quasi-two-dimensional electrons, a feature conspicuously absent in $\mathrm{Li}{\mathrm{Be}}_5$. Additional molecular dynamic simulations also prove the existence of a superionic state in previously discovered $P{2}_1/m$ LiBe and $C2$/$m\mathrm{L}{\mathrm{i}}_3\mathrm{Be}$. More interestingly, the Li atoms in $P{2}_1/m$ LiBe only diffuse in one direction due to the potential well and interstitial electrons. Our study not only enriches the phase diagram of Li-Be alloys but also provides a solid theoretical foundation for future experimental investigations.

Understanding initial electron thermalization has relevance to both fundamental scientific knowledge and application to the construction of novel devices. In this study, attosecond transient absorption is used to directly measure initial electron thermalization times of 38 ± 8 fs, 15 ± 3 fs, 4.2 ± 1 fs, and 2.0 ± 0.3 fs for Mg, Pt, Fe, and Co, respectively. Through time-dependent density-function theory calculations, it is shown that the fast electron thermalization observed in Fe and Co is correlated with a strong local-field effect. We find that a simple analytical model can be used to calculate the initial electron thermalization time measured by the transient extreme ultraviolet absorption spectroscopy method performed here. Our results suggest that the most significant contributions to the initial electron thermalization times are the basic metal properties of the density of states volume available for scattering and screened electron interaction. Ultimately the information gained through this study shows the unique view that attosecond transient absorption spectroscopy contributes to unraveling and monitoring electron dynamics and its connection to many-body effects in metals and beyond.

In this work, we consider the imaginary time evolution of matrix product states. We present a quantum-inspired classical method that, when combined with time evolving block decimation (TEBD), is able to potentially speed up the convergence to a ground state compared to TEBD alone. Our method, referred to as boosted imaginary time evolution, relies on the use of reflections to boost to lower energy states. Interleaving TEBD steps with boosts reduces the total number of TEBD steps and potentially the computational cost required to imaginary time evolve a matrix product state to a ground state. We give the mathematical details of the method followed by an algorithmic implementation and finally some results for a simple test case.