As a quasiparticle formed by light and excitons in semiconductors, the exciton polariton (EP) as a quantum bus is promising for the development of quantum interconnect devices at room temperature. However, the significant damping of EPs in the material generally causes a loss of quantum information. We propose a mechanism to overcome the destructive effect of a damping EP on its mediated correlation dynamics of quantum emitters (QEs). Via an investigation of the near-field coupling between two QEs and the EP in a monolayer ${\mathrm{MoS}}_2$ nanodisk, we find that, with the complete dissipation of the QEs efficiently avoided, a persistent quantum correlation between the QEs can be generated and stabilized even to their steady state. This is due to the fact that, upon decreasing the QE-${\mathrm{MoS}}_2$ distance, the QEs become so hybridized with the EP that one or two bound states are formed between them. Our result supplies a useful way to avoid the destructive impact of EP damping, and it refreshes our understanding of the light-matter interaction in an absorbing medium.

The comparability and reliability of the analysis of the electronic structure of selected cyanates and thiocyanates at the nitrogen $K$ edge based on BSE calculations have been investigated in this work. Using high-resolution x-ray spectroscopy with calibrated instrumentation reliable and reproducible experimental results for x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) were achieved. These results were used to validate theoretical modeling with first-principles calculations based on the Bethe-Salpeter equation approach for the excited-state interactions. Furthermore, radiation-induced damages occurring in the samples are correlated with absolute doses.

Uranium dioxide (${\mathrm{UO}}_2$) remains a formidable challenge for first-principles approaches due to the complex interplay among spin-orbit coupling, Mott physics, magnetic ordering, and crystal distortions. Here we use $\mathrm{DFT}+U$ to explore ${\mathrm{UO}}_2$ at zero temperature, incorporating all the aforementioned phenomena. The technical challenge is to navigate the many metastable electronic states produced by $\mathrm{DFT}+U$, which is accomplished using $f$-orbital occupation matrix control to search for the ground state. We restrict our search to the high-symmetry ferromagnetic phase, including spin-orbit coupling, which produces a previously unreported occupation matrix. This newfound occupation matrix is then used as an initialization to explore the broken symmetry phases. We find the oxygen cage distortion of the 3k antiferromagnetic state to be in excellent agreement with experiments, and both the spin-orbit coupling and the Hubbard $U$ are critical ingredients. We demonstrate that only select phonon modes have a strong dependence on the Hubbard $U$, whereas magnetic ordering has only a small influence overall. We perform measurements of the phonon dispersion curves using inelastic neutron scattering, and our calculations show good agreement when using reasonable values of $U$. The quantitative success of $\mathrm{DFT}+U$ warrants exploration of thermal transport and other observables within this level of theory.

Low-temperature scanning tunneling microscopy is used here to study the dynamic bonding of gold atoms on surfaces under low coordination conditions. In the experiments, using an atomically sharp gold tip, a gold adatom is deposited onto a gold surface with atomic precision either on the first hollow site near a step edge or far away from it. Classical molecular dynamics simulations at 4.2 K and density-functional theory calculations serve to elucidate the difference in the bonding behavior between these two different placements, while also providing information on the crystalline classification of the STM tips based on their experimental performance.

Particlelike scattering states allow for noiseless transport through quantum dots by closely retracing bundles of classical trajectories. We identify such raylike states for electron transport through graphene ribbons. Remarkably, we find that these quasiclassical scattering states can be unambiguously associated with well-defined quantum numbers of the valley degree of freedom specific to graphene. Trigonal warping—i.e., deviations of the band structure from a perfectly isotropic two-dimensional Dirac equation due to the hexagonal lattice structure—results in preferred propagation directions and scattering time delays that depend on the valley the particlelike wave travels in. By implementing a truncated mode basis of Bloch states, we achieve simulations of micrometer-sized quantum dots starting from an atomic-scale tight-binding Hamiltonian.

We report a spin filtration operation considering an antiferromagnetic helix system, possessing zero net magnetization. Common wisdom suggests that for such a system, a spin-polarized current is no longer available from a beam of unpolarized electrons. But once we apply an electric field perpendicular to the helix axis, a large separation between up- and down-spin energy channels takes place, which yields a high degree of spin polarization. Employing a tight-binding framework to illustrate the antiferromagnetic helix, we compute spin filtration efficiency by determining spin-selective currents using Landauer-Büttiker formalism. Geometrical conformation plays an important role in spin-channel separation, and here we critically investigate the effects of short-range and long-range hoppings of electrons in the presence of the electric field. We find that the filtration performance gets improved with increasing the range of hopping of electrons. Moreover, the phase of spin polarization can be altered selectively by changing the strength and direction of the electric field, and also by regulating the physical parameters that describe the antiferromagnetic helix. Finally, we explore the specific role of dephasing to make the system more realistic and to make the present communication a self-contained one. Our analysis may provide a route of getting conformation-dependent spin polarization possessing longer range hopping of electrons, and can be generalized further to different kinds of other fascinating antiferromagnetic systems.

Intrinsic topological superconductors have protected gapless Majorana modes, bound and/or propagating, at the natural boundaries of the sample, without requiring field, defect, or heterostructure. We establish the complete classification/construction of intrinsic topological superconductors jointly protected by point-group and time-reversal symmetries in three dimensions. This is obtained from enumerating distinct ways for stacking $n\mathrm{th}$-order irreducible building blocks, minimal anomalous surface states of $n\mathrm{th}$-order topological superconductors. Particularly, our method provides a unified description of possible surface anomalies away from high-symmetry points/lines in terms of the homotopy group of the surface mass field.

Charge-density-wave order in a solid can be temporarily “melted” by a strong laser pulse. Here, we use the discrete Gross-Pitaevskii equation on a cubic lattice to simulate the recovery of the CDW long-range phase coherence following such a pulse. Our simulations indicate that the recovery process is dramatically slowed down by the three-dimensional topological defects—CDW dislocations—created as a result of strongly nonequilibrium heating and cooling of the system. Overall, the simulated CDW recovery was found to be remarkably reminiscent of a recent pump-probe experiment in ${\mathrm{LaTe}}_3$.

Palladium diselenide (${\mathrm{PdSe}}_2$), a recently exploited transition metal dichalcogenide material with a thickness-dependent band gap, anisotropic optical response, and high air stability, has shown excellent performance in electronics and polarization photodetection. However, the origin of the intriguing optical response in this material from a perspective of electronic band structure, including the orbital character and the experimental demonstration of its indirect band gap, has not yet been explored. By applying polarization-dependent, angle-resolved photoemission spectroscopy and density functional theory calculations, we measured an indirect band gap of bulk ${\mathrm{PdSe}}_2$ to be $\sim 0.36\mathrm{eV}$. Moreover, the orbital-resolved electronic band structure reveals a top valence band dominated by Pd-$d_{3z^2-r^2}$ and Se-$p_z$ orbitals, which gives rise to an unprecedented giant linear dichroic ratio of 10, showing a huge orbital-induced anisotropy. Our results elucidate the semiconducting nature of ${\mathrm{PdSe}}_2$ and propose ${\mathrm{PdSe}}_2$ to be an intrinsically orbital-engineered material with giant anisotropy for polarization-related optical applications.

In this paper, the equation of motion of graphenelike topological gyroscopic metamaterials under acceleration is derived, and the influence of the external acceleration on the band structure is investigated. The calculated results of band structure under acceleration of $1g$ are in good agreement with the experimental results reported in the literature and the numerical simulations show that the edge states are highly confined to the boundary, which is significantly different from the bulk states. Hence, an acceleration sensing method based on topological gyroscopic metamaterials is proposed by detecting the acceleration-induced bandwidth variation of the edge bands. Moreover, it is found that the proposed sensing approach shows extremely high sensitivity in a small acceleration range compared to the traditional capacitive accelerometers. And arising from its topological properties, the robustness of the proposed sensing method against local defects is numerically verified. Finally, some possible electronic methods are proposed to read the output signal of the sensing system.

The conventional spin-orbit torque (SOT) and magnetoresistance effect observed in normal-metal (NM)/ferromagnet (FM) bilayers originate from the interaction between magnetic moments and spin with in-plane transverse polarization (${\widehat{\sigma }}_y$). In FM/NM/FM trilayer structures, the presence of an extra FM layer breaks the symmetry, resulting in spin polarization other than ${\widehat{\sigma }}_y$ and the corresponding SOT. However, the study on the unidirectional magnetoresistance (UMR) effect induced by the spin polarization with spin rotation (SR) symmetry is still missing. In this work, we investigate the SOT and UMR effect in a Co/Cu/Co structure with crossed anisotropy by utilizing the harmonic longitudinal voltage measurement. We demonstrate that, in addition to the harmonic terms originating from the fieldlike SOT of the spin polarization with spin Hall and SR symmetry, two different unidirectional harmonic signals are observed in the angular and field scan measurements. Further, combining the SOT effective fields results from the harmonic Hall voltage measurement, we successfully separate the contributions of the observed unidirectional harmonic signals, which include the dampinglike SOT contribution through the giant magnetoresistance effect, and the UMR induced by the spin current with different polarization directions through spin-dependent scattering mechanism.

A Raman scattering study covering the entire substitution range of the ${\mathrm{FeSe}}_{1-x}{\mathrm{S}}_x$ solid solution is presented. Data were taken as a function of sulfur concentration $x$ for $0\le x\le 1$, of temperature and of scattering symmetry. All types of excitations including phonons, spins, and charges are analyzed in detail. It is observed that the energy and width of the iron-related $B_{1g}$ phonon mode vary continuously across the entire range of sulfur substitution. The $A_{1g}$ chalcogenide mode disappears above $x=0.23$ and reappears at a much higher energy for $x=0.69$. In a similar way the spectral features appearing at finite doping in $A_{1g}$ symmetry vary discontinuously. The magnetic excitation centered at approximately 500 ${\mathrm{cm}}^{-1}$ disappears above $x=0.23$ where the $A_{1g}$ lattice excitations exhibit a discontinuous change in energy. The low-energy mode associated with fluctuations displays maximal intensity at the nematostructural transition and thus tracks the phase boundary.

We report the synthesis and characterization of ${\mathrm{RbNi}}_2{\mathrm{Se}}_2$, an analog of the iron chalcogenide superconductor ${\mathrm{Rb}}_x{\mathrm{Fe}}_2{\mathrm{Se}}_2$, via transport, angle-resolved photoemission spectroscopy, and density functional theory calculations. A superconducting transition at $T_c=1.20$ K is identified. In the normal state, ${\mathrm{RbNi}}_2{\mathrm{Se}}_2$ shows paramagnetic and Fermi-liquid behaviors. A large Sommerfeld coefficient yields an effective electron mass of $m^{*}\approx 6m_e$. In the superconducting state, zero-field electronic specific-heat data $C_{es}$ can be described by a two-gap BCS model, indicating that ${\mathrm{RbNi}}_2{\mathrm{Se}}_2$ is a possible multigap superconductor. Our density functional theory calculations and angle-resolved photoemission spectroscopy measurements demonstrate that ${\mathrm{RbNi}}_2{\mathrm{Se}}_2$ exhibits relatively weak correlations and multiband characteristics, consistent with the multigap superconductivity.

In this work we explore the interplay between superconductivity and nematicity in the framework of a Ginzburg-Landau theory with a nematic order parameter coupled to the superconductor order parameter. In particular, we focus on the study of the vortex-vortex interaction in order to determine the way nematicity affects its attractive or repulsive character. To do so, we use a dynamical method based on the solutions of the time-dependent Ginzburg-Landau equations in a bulk superconductor. An important contribution of our work is the implementation of a pseudospectral method to solve the dynamics, known to be highly efficient and of very high order in comparison to the usual finite-differences and -elements methods. The coupling between the superconductor and the (real) nematic order parameters is represented by two terms in the free energy: a biquadratic term and a coupling of the nematic order parameter to the covariant derivatives of the superconductor order parameter. Our results show that there is a competing effect: while the former independently of its competitive or cooperative character generates an attractive vortex-vortex interaction, the latter always generates a repulsive interaction.

We present a hidden Markov model analysis for fluorescent time series of colloidal quantum dots. A fundamental quantity to measure optical performance of the quantum dots is a distribution function for the light-emission duration. So far, to estimate it, a threshold value for the fluorescent intensity was introduced, and the light-emission state was evaluated as a state above the threshold. With this definition, the light-emission duration was estimated, and its distribution function was derived as a blinking plot. Due to the noise in the fluorescent data, however, this treatment generates a large number of artificially short-lived emission states, thus leading to an erroneous blinking plot. In the present paper, we propose a hidden Markov model to eliminate these artifacts. The hidden Markov model introduces a hidden variable specifying the light-emission and quenching states behind the observed fluorescence. We found that it is possible to avoid the above artifacts by identifying the state from the hidden-variable time series. We found that, from the analysis of experimental and theoretical benchmark data, the accuracy of our hidden Markov model is beyond human cognitive ability.

We report on the chemical structure and spin Hall magnetoresistance (SMR) in epitaxial $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{hematite}\right)\left(0001\right)\text{/}\mathrm{Pt}\left(111\right)$ bilayers with hematite thicknesses of 6 and 15 nm grown by molecular beam epitaxy on a MgO(111) substrate. Unlike previous studies that involved Pt overlayers on hematite, the present hematite films were grown on a stable Pt buffer layer and displayed structural changes as a function of thickness. These structural differences (the presence of a ferrimagnetic phase in the thinner film) significantly affected the magnetotransport properties of the bilayers. We observed a sign change of the SMR from positive to negative when the thickness of the hematite increased from 6 to 15 nm. For $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3\left(15\mathrm{nm}\right)\text{/}\mathrm{Pt}$, we demonstrated room-temperature switching of the Néel order with rectangular, nondecaying switching characteristics. Such structures open the way to extending magnetotransport studies to more complex systems with double asymmetric metal/hematite/Pt interfaces.

The intrinsic magnetic properties of nanoparticles (NPs) can be accurately determined using highly dispersed NPs in a matrix. In this paper, we study chemically ordered CoPt and FePt NPs with a diameter of 3 nm embedded in an amorphous carbon matrix. Although both alloys exhibit almost the same magnetic and crystallographic properties in the bulk materials, they are completely different as NPs. We show that their magnetic anisotropy differs greatly. To understand the origin of such a difference, a fine crystallographic structure study has been performed using extended x-ray absorption fine structure. In that respect, the atomic relaxations appear to be different in both nanoalloys. Ab initio calculations of the atomic relaxation shed light on these experimental results, showing that the wide distance distribution in Co sublattice should strongly alter the magnetic anisotropy of CoPt NPs.

Magnetic two-dimensional materials have great potential in the preparation of nanoelectronic and spintronic devices. Recently, a new two-dimensional material with no corresponding bulk-structure, ${\mathrm{MoSi}}_2{\mathrm{N}}_4$, has been prepared, attracting public attention to the ${XA}_2{Z}_4$ series of materials. Naturally, doping with $3d$ magnetic element will result in various magnetic orderings. In our work, we replaced the Mo element with different transition-metal elements whose property varies from magnetic to nonmagnetic and screened out a variety of two-dimensional exchange scenarios. Then, we provided an analysis that shows the existence of a huge on-site Coulomb interaction at $3d$ orbitals which is strongly related to the Mott transition and therefore causes the superexchange interaction.

We derive the quantization of magnetic helicity in the solid state, and we demonstrate tunable macroscopic quantum tunneling, coherence, and oscillation for a skyrmion spin texture stabilized in frustrated magnets. We also discuss the parameter space for the experimental realization of quantum effects. Typically, for a skyrmion of 5 nm radius, quantum tunneling between two macroscopic states with distinct helicities occurs with an inverse escape rate within seconds below 100 mK, and an energy splitting in the MHz regime. The feasibility of quantum tunneling of an ensemble of magnetic spins inspires new platforms for quantum operations utilizing topologically protected chiral spin configurations.