${\mathrm{Ce}}_{2}M{\mathrm{Al}}_7{\mathrm{Ge}}_4$ ($M=\text{Co,}\text{Ir,}\text{Ni}\text{or}\text{Pd}$) are heavy-fermion materials and host a variety of ground states ranging from magnetism to non-Fermi liquid behavior. The Co, Ir, and Ni members of the series undergo magnetic ordering with decreasing transition temperatures. In contrast, the Pd compound does not magnetically order down to 0.4 K and shows non-Fermi liquid behavior, suggesting proximity to a magnetic quantum critical point. Among the series, ${\mathrm{Ce}}_2{\mathrm{CoAl}}_7{\mathrm{Ge}}_4$ orders antiferromagnetically below $T_N=1.9$ K along with heavy-fermion behavior below 15 K. We report the magnetic structure of the antiferromagnetic phase in ${\mathrm{Ce}}_2{\mathrm{CoAl}}_7{\mathrm{Ge}}_4$ and the evolution of the magnetic transition under external pressure. Rietveld refinement of the neutron diffraction data suggests a coplanar antiferromagnetic structure with a wave vector $k=(1,1,1)$ and an ordered moment of $0.383\pm 0.018{\mu }_B$ in the antiferromagnetic phase. Electrical resistivity and AC calorimetry measurements under hydrostatic pressure reveal a suppression of the antiferromagnetic transition toward zero temperature around $p=1.1$ GPa. However, there is no evidence of non-Fermi liquid behavior associated with the suppression of magnetism by pressure, unlike the effect of transition-metal substitution.

Layered transition-metal dichalcogenide (TMD) materials host a variety of quantum states and exhibit fascinating physical phenomena, such as charge density waves (CDWs) and a metal-insulator transition, which have attracted considerable attention in condensed matter physics. $1T\text{−}{\mathrm{TaS}}_2$ is an intriguing TMD and has multiple CDW phases. In particular, the commensurate (C) CDW phase, an insulating ground state, has attracted much attention. Herein, we systematically investigate and verify the effect of electron injection through intercalation of Cu atoms in single crystals of the TMD material $1T\text{−}{\mathrm{Cu}}_x{\mathrm{TaS}}_2$ ($0\le x\le 0.05$) by combining electrical transport measurements, scanning tunneling microscopy and spectroscopy measurements, and first-principles calculations. Our experiment results reveal that the charge transfer from Cu atoms to adjacent ${\mathrm{TaS}}_2$ layers, which suppresses the CCDW-insulating state, destroys the long-range CDW order, changes the dominant carrier (from $p$ type to $n$ type), and renders $1T\text{−}{\mathrm{TaS}}_2$ metallic. The itinerant electrons of the intercalated Cu atoms, which induce the metallic state, primarily act as electron donors to raise the Fermi level. Our intercalation results support a scenario in which the doping electron primarily fills an existing band gap, consistent with a band-insulator picture. In addition, the stacking order is important for obtaining an accurate electronic structure, namely, the density of states. Our work provides opportunities for enriching the electronic phase diagram and exploring exotic physics in $1T\text{−}{\mathrm{TaS}}_2$ and other TMD materials.

We theoretically study quasi-two-dimensional nickel compounds, where the nickel ions assume ${\mathrm{Ni}}^{2+}{d}^8$ valence state and feature a low-spin $S=0$ ground state quasidegenerate with $S=1$ ionic excitations. Such a level structure is supported by square-planar coordination of nickel ions or a suitable substitution of apical oxygens. We construct the corresponding singlet-triplet exchange model and explore its phase diagram and excitation spectrum. By hole doping, we further introduce mobile ${\mathrm{Ni}}^{3+}{d}^7$ ionic configurations with effective spins $S=1/2$, and analyze their interactions with the $d^8$ singlet-triplet background. The interplay with the triplet excitations in the $d^8$ sector is found to have a deep impact on the propagation of the doped holelike charge carriers and is identified as a powerful source of Cooper pairing among them.

Donor-based quantum devices in silicon are attractive platforms for universal quantum computing and analog quantum simulations. The nearly atomic precision in dopant placement promises great control over the quantum properties of these devices. We present atomistic calculations and a detailed analysis of many-electron states in a single phosphorus atom and selected phosphorus dimers in silicon. Our self-consistent method involves atomistic calculations of the electron energies utilizing representative tight-binding Hamiltonians, computations of Coulomb and exchange integrals without any reference to an atomic orbital set, and solutions to the associated Hartree-Fock equations. First, we assess the quality of our tight-binding Hartree-Fock protocol against configuration-interaction calculations for two electrons in a single phosphorus atom, finding that our formalism provides an accurate estimation of the electron-electron repulsion energy requiring smaller computational boxes and self-consistent single-electron wavefunctions. Then, we compute charging and binding energies in phosphorus dimers observing their variation as a function of impurity-impurity separation. Our calculations predict an antiferromagnetic ground state for the two-electron system and a weakly bound three-electron state in the range of separations considered. We rationalize these results in terms of the single-electron energies, charging energies, and the wavefunction reshaping.

The $\mathrm{Sn}/\mathrm{Si}\left(111\right)-(\sqrt{3}\times \sqrt{3})R{30}^{\circ }$ surface, a 2D Mott insulator, has long been predicted and then found experimentally to metallize and even turn superconducting upon boron doping. To clarify the structural, spectroscopic, and theoretical details of that evolution, here we present angle resolved photoemission spectra data supplementing morphology and scanning tunneling measurements. These combined experimental results are compared with predictions from a variety of electronic structure approaches, mostly density functional $\mathrm{DFT}+U$, but not neglecting Mott-Hubbard models, both ordered and disordered. These theoretical pictures address different spectroscopic aspects, including the 2D Fermi surface, the Hubbard bands, etc. While no single picture accounts for all observations at once, the emergent hypothesis compatible with all data is that metallization arises from sub-subsurface boron doping, alternatively to the main standard subsurface boron geometry that would leave the surface insulating. These results advance the indispensable frame for the further understanding of this fascinating system.

In this study, we investigate the localized surface-plasmon modes of a subwavelength spherical nanoparticle composed of a Weyl semimetal, taking into account the axion modification of electrodynamics. We derive analytical solutions for dipole and quadrupole normal modes by employing the quasistatic approximation. The axion term leads to modified Fröhlich conditions, resulting in multiple nondegenerate plasmonic resonances with distinct polarization dependencies. In contrast with isotropic conventional metals, the magnetoelectric properties of Weyl semimetals enable an incident electromagnetic field, with the electric field transverse to the surface of the sphere, to excite a localized surface plasmon.

We present a protocol to generate enhanced nonlinear responses of incident pulses in the density wave phase within the extended Bose-Hubbard model using the concept of resonance-induced amplification. This method enables the selection of an incident pulse frequency to amplify the desired harmonic order. We characterize the enhancement of the nonlinear harmonic spectra under various frequencies and field strengths of the incident pulses and demonstrate that an optimal field strength is necessary to realize our protocol.

Accurate and reliable algorithms to solve complex impurity problems are instrumental to a routine use of quantum embedding methods for material discovery. In this context, we employ an efficient selected configuration-interaction impurity solver to investigate the role of bath discretization—specifically, bath size and parametrization—in Hamiltonian-based cluster dynamical mean-field theory (CDMFT) for the one- and two-orbital Hubbard models. We consider two- and four-site clusters for the single-orbital model and a two-site cluster for the two-orbital model. Our results demonstrate that, for small bath sizes, the choice of parametrization can significantly influence the solution, highlighting the importance of systematic convergence checks. Comparing different bath parametrizations not only reveals the robustness of a given solution but can also provide insights into the nature of different solutions and potential instabilities of the paramagnetic state. We present an extensive analysis of the zero-temperature Mott transition of the paramagnetic half-filled single-band Hubbard model, benchmarking our findings against previous literature. We find that, for the single-band model the dependence on parametrization is weak for the largest bath sizes accessible with ASCI, while a tendency towards a nematic solution can be seen when the bath size is small. Building on this, we extend our study to the multiband regime, where we present a systematic analysis at zero temperature for two orbitals and a two-site cluster. This setup allows us to assess the effect of nearest-neighbor dynamical correlations on the multi-orbital Mott transition. In this case, some quantitative dependence on the parametrization is retained for the two-orbital model, for instance in the value of the critical interaction for a Mott transition.

We present an effective medium theory–plane-wave (EMT-PW) based on density functional theory (DFT) that is implemented in vasp using the projector augmented-wave method with a plane-wave basis set. The transmission coefficient, $\tau \left(E\right)$, is derived through three complementary approaches: the current density relation $J=nqv$, the field operator method, and the nonequilibrium Green's function (NEGF) formalism. We compare $\tau \left(E\right)$ calculated using EMT-PW with results from NEGF-DFT, based on the NanoDCAL package utilizing a linear combination of atomic orbitals basis set, for both periodic and nonperiodic boundary conditions. The minor discrepancies observed are attributed to differences in basis sets, pseudopotentials, and the treatment of lead regions. Notably, the EMT-PW framework avoids the common issue of overcompleteness encountered in nonequilibrium transport theories and allows for the decomposition of the total transmission coefficient into contributions from individual eigenstates, providing an alternative approach to calculate transport properties through nanoscale systems.

Epsilon-near-zero (ENZ) systems exhibit an unconventional electromagnetic response close to their zero-permittivity regime. Here, we explore the ability of ultrathin ENZ films to modulate the transmission of radiation from an underlying quantum emitter through active control of the carrier density of the ENZ film. The achievable on-off switching ratio is shown to be constrained by the material's loss parameter, particularly in the ENZ regime, where transmissivity increases with higher material loss. The finite loss in real materials limits the more extraordinary potential of ideal near-zero-index systems. Along with an in-depth discussion of the material parameters vis-à-vis the underlying physics, this work provides avenues to overcome the shortcomings of finite loss in real materials. These findings are intended to guide material development and offer valuable insights for designing on-chip optical modulators and beam steering devices operating in the near-infrared regime.

The stability of aluminum alloy surfaces has a critical influence on their ability to join to another material. This study employs first-principles density functional theory calculations to investigate the surface stability, configuration, and diffusion tendencies of alloying elements Mg, Si, Zr, and Sc on the crystal planes (001), (110), and (111) of an aluminum alloy. Utilizing asymmetric slab models, we introduce and apply an energy difference concept ($\mathrm{\Delta }{E}^{\text{2D}}$) to assess the stability of surface alloys relative to pure element covered surfaces. The findings reveal that surface stability is strongly dependent on both composition and atomic arrangement. Generally, mixed surface compositions, particularly a 50% coverage ${\text{Al}}_2{M}_2$, exhibit enhanced stability. And the next nearest neighbor is favored over the nearest-neighbor position of alloying atoms which are precursors to nearest precipitates. An analysis of the diffusion paths indicates that Mg and Si preferentially segregate to the outermost surface layer with Mg more strongly, whereas Zr and Sc exhibit a lower driving force to diffuse towards the outermost aluminum surface.

Recent rapid advances in quantum nanoplasmonics offer the potential for accessing quantum phenomena at room temperature. Despite this, entangled states have not yet been realized, and remain an outstanding challenge. In this work, we demonstrate how entanglement emerges in plasmonic nanocavities, which are inherently multimode, and demonstrate the conditions necessary for entanglement to persist. We find that, in general, these conditions are broken due to coupling with multiple plasmonic modes of different parity. We address this challenge with a new nanocavity design that supports high selective coupling to a single mode, enabling the robust generation of persistent entanglement in nanoplasmonics. Our results open exciting prospects for leveraging simple plasmonic setups in ambient conditions for applications in quantum communication, sensing, and rapid quantum memories.

The control of spin and orbital angular momentum without relying on magnetic materials is commonly accomplished by breaking of inversion symmetry, which enables charge-to-spin conversion and spin selectivity in electron transfer processes occurring in chiral media. In contrast to this perspective, we show that orbital moment filtering can be accomplished in centrosymmetric systems: the electron states can be selectively manipulated allowing for the preferential transfer of electrons with a particular orbital momentum orientation. We find that orbital moment filtering is indeed efficiently controlled through orbital couplings that break both mirror and rotational symmetries. We provide the symmetry conditions required for the electron transmission to achieve orbital filtering and relate them to the orientation of the orbital moment. The presence of atomic spin-orbit interaction in the centrosymmetric transmission medium leads to the selective filtering of spin and orbital moments. Our findings allow one to identify optimal regimes for having highly efficient simultaneous spin and orbital moment filtering.

We study the entanglement structure of the Greenberger–Horne–Zeilinger (GHZ) state as it thermalizes under a strongly symmetric quantum channel describing the Metropolis-Hastings dynamics for the $d$-dimensional classical Ising model at inverse temperature $\beta$. This channel outputs the classical Gibbs state when acting on a product state in the computational basis. When applying this channel to a GHZ state in spatial dimension $d>1$, the resulting mixed-state changes character at the Ising phase transition temperature from being long-range entangled to short-range entangled as temperature increases. Nevertheless, we show that the topological entanglement negativity of a large region is insensitive to this transition and takes the same value as that of the pure GHZ state at any finite temperature $\beta >0$. We establish this result by devising a local operations and classical communication decoder that provides matching lower and upper bounds on the negativity in the thermodynamic limit which may be of independent interest. This perspective connects the negativity to an error-correction problem on the $(d-1)$-dimensional bipartitioning surface and explains the persistent negativity in certain correlated noise models found in previous studies. Numerical results confirm our analysis.

We develop an atomic cluster expansion (ACE) interatomic potential for lithium that accurately models both the solid and liquid phase and the corresponding melting point. The training data is obtained from 0 K density functional theory (DFT) and finite temperature ab initio molecular dynamics simulations of both solid and liquid Li. The ACE predicted properties for both phases obtained from molecular dynamics simulations are in close agreement with DFT and experimental data from the literature. The potential is able to capture the energy differences of the different competing phases of the solid at 0 K and finite temperature properties of the experimentally observed bcc phase. The potential also accurately predicts the temperature dependence of liquid density, viscosity, and the diffusion coefficient. The melting point is calculated using the two-phase coexistence method and is remarkably close to the experimental value. The potential is used to predict stress-induced phase transformations in solid Li and pressure-volume isotherms in liquid Li. We underline the necessity for a complete training set that includes both solid and liquid configurations in order to obtain a potential that precisely models both phases. By using the ACE formalism, we also systematically investigate the contributions of interactions involving $N$ bodies and the number of radial parameters needed to separately represent both phases since they have a direct consequence on the computational cost of the potential. We shed light on the complexity of the ACE potential needed to model solid and liquid lithium efficiently.

We report the synthesis of monoclinic ${\mathrm{Fe}}_{6.10\pm \delta }{\mathrm{Ge}}_5$ single crystals, as well as their magnetic, transport and thermodynamic properties, sharing similar key features within the range of $\delta \approx$ 0.25. The susceptibility and magnetization results reveal two distinct antiferromagnetic transitions at $T_{\mathrm{N}1}$ = 340 K and $T_{\mathrm{N}2}$ = 121 K, respectively, with the easy axis to be along the crystalline $c$ direction, as implied both by the anisotropy in the susceptibility and by a spin-flop transition. Insulating behavior with a narrow band gap of $\sim 1\mathrm{meV}$ is observed in resistivity measurement in the intermediate temperature range $T_{\mathrm{N}2}<T<T_{\mathrm{N}1}$, whereas metalliclike behavior manifests at lower temperatures $T<T_{\mathrm{N}2}$. These observations indicate that ${\mathrm{Fe}}_{6.10\pm \delta }{\mathrm{Ge}}_5$ exhibits rich magnetic phases, with charge carrier scattering highly sensitive to spin configurations in different magnetic phases, calling for further high-resolution experiments on its local atomic environment and magnetic structure.

The search for high-temperature superconductivity among pressure-stabilized hydrides has received great interest since theory-directed clathrate hydrides, such as ${\mathrm{CaH}}_6, {\mathrm{YH}}_6, {\mathrm{YH}}_9$, and ${\mathrm{LaH}}_{10}$, were synthesized and shown to exhibit a superconducting critical temperature ($T_{\mathrm{c}}$) above 200 K. However, further tuning the superconductivity and stability of these prominent hydrides to enhance their applicability remains a significant challenge. Here, taking the sodalitelike clathrate prototype $M{\mathrm{H}}_6$ ($M=\mathrm{Ca}$, Y, etc.) as an example, we investigate the stability and superconductivity of multicomponent metal hydrides containing four different metal atoms per structure. High-throughput simulations of 1820 $ABCD{\mathrm{H}}_{24}$ quinary hydrides, with initial symmetry of $F\overline{4}3m$ and varying metal atoms ($A, B, C$, and $D$), were conducted. The results identified 119 dynamically stable structures at 300 GPa, with 67 exhibiting superconductivity exceeding 200 K, and 20 having $T_{\mathrm{c}}$ values above 260 K. Notably, $\left(\mathrm{Na},\mathrm{Zr},\mathrm{Mg},\mathrm{Hf}\right){\mathrm{H}}_6$ is predicted to approach room temperature $T_{\mathrm{c}}$ at 250 GPa. Both configurational and vibrational entropy are crucial for stabilizing these alloys. $\left(\mathrm{Na},\mathrm{Y},\mathrm{Zr},\mathrm{Hf}\right){\mathrm{H}}_6, \left(\mathrm{Mg},\mathrm{Zr},\mathrm{Sc},\mathrm{Y}\right){\mathrm{H}}_6$, and $\left(\mathrm{Mg},\mathrm{Hf},\mathrm{Ca},\mathrm{Zr}\right){\mathrm{H}}_6$ were computed to be thermodynamically stable, making them promising candidates for experimental synthesis. These quinary superconducting hydrides may facilitate the realization of very high-temperature superconductors being stable over a broader range of conditions than binary or ternary systems.

In this work, we study the time-averaged populations obtained for a fluxonium circuit under a large amplitude nonresonant periodic drive. We present numerical simulations of the time evolution which consider the multilevel structure of the driven quantum circuit, looking for a realistic modeling closer to experimental implementations. The Landau-Zener-Stückelberg spectra show resonances that can be understood as originated from constructive interference favoring transitions to higher levels. For a truncated two-level system (TLS) the resonance patterns can be interpreted using a simplified description of the avoided crossing that takes into account the dynamic phase accumulated at each operation point. For the multilevel case, we derive an effective two-level Hamiltonian using a Schrieffer-Wolff transformation starting from the Floquet Hamiltonian in the Sambe space. Our study provides predictive insight into experimental outcomes, offering an intuitive interpretation that could also support the implementation of fast nonadiabatic single-qubit gates and entangling protocols.

We simulate the properties of magnons in erbium oxide, a noncollinear antiferromagnet, from an effective single-ion Hamiltonian, including exchange and long-range dipolar interactions. We parametrize the crystal-field splitting of ${\mathrm{Er}}_2{\mathrm{O}}_3$ using Steven's operators and obtain the effective symmetry-dependent exchange constants between different erbium ions quenched by the crystal field at different symmetry sites. We apply the Holstein-Primakoff transformation to the noncollinear spin system and employ paraunitary diagonalization for the effective spin Hamiltonian. The addition of the dipolar interaction to the exchange magnon dispersion changes the magnon bands drastically. The long-range nature of the dipolar interaction provides challenges to convergence, however, we find that the averaged and normalized difference in the magnon dispersion is less than an averaged factor of ${10}^{-6}$ if the dipolar interaction is included out to the 40th nearest neighbor.