The existing experimental data for the temperature dependence of the nuclear quadrupole interaction in Zn and Cd have been accounted for by considering reanalyzed data for structure and vibrational amplitude as a function of temperature, in combination with density functional calculations of the electric-field gradient (EFG) variation due to the structure change. For Zn the complex EFG temperature effect, previously unexplained, can be fully reproduced, while for Cd it is shown that the apparent agreement with an earlier proposed universal temperature dependence as proportional to $T^{3/2}$ is due to a combination of structural and vibrational contributions. It is demonstrated that for Zn, in particular, the resulting EFG at 0 K, including the now directly calculated shift due to zero-point vibrations, and the subsequently obtained nuclear quadrupole moments, can be considerably different when taking the present revised analysis and all experimental data into account. As an additional example also one impurity system, ${}^{69}\mathrm{Ge}$ in Zn, is tentatively analyzed in this context. The possible extension of the present approach to other noncubic $s\text{−}p$ metals is envisioned.

The Dirac hierarchy (DH), comprising an eightfold bulk Dirac cone (DC), a fourfold surface DC, a twofold hinge, and a corner state, has been proposed and observed in acoustic systems recently. DH establishes a versatile platform for exploring exotic phenomena related to the hierarchy of Dirac physics and topological phases at varying dimensions. However, the investigation of DH in the context of photonic crystals is still lacking, as the electromagnetic interactions in the 3D configuration are complex and difficult to match with the tight-binding model. In this study, we first propose a photonic DH in the Mie-confined resonance framework with band chirality. DH with 2D surface states, 1D hinge states, and 0D corner states is obtained by lattice distortions. Besides, we extend the 3D framework to the disclination-introduced photonic system and prove the coexistence of robust disclination, corner, and hinge states. Our work explores the Dirac physics in photonics, offers insights to manipulate electromagnetic waves at varying dimensions, and reveals unconventional bulk-disclination correspondence in 3D photonic materials.

Driven many-body systems typically experience heating due to the lack of energy conservation. Heating may be suppressed for time-periodic drives, but little is known for less regular drive protocols. In this paper, we investigate the heating dynamics in aperiodically kicked systems, specifically those driven by quasiperiodic Thue-Morse or a family of random sequences with $n$-multipolar temporal correlations. We demonstrate that multiple heating channels can be eliminated even away from the high-frequency regime. The number of eliminated channels increases with multipolar order $n$. We illustrate this in a classical kicked rotor chain where we find a long-lived prethermal regime. When the static Hamiltonian only involves the kinetic energy, the prethermal lifetime $t^{*}$ can strongly depend on the temporal correlations of the drive, with a power-law dependence on the kick strength $t^{*}\sim K^{-2n}$, for which we can account using a simple linearization argument.

In this work we propose a scheme to engineer subharmonic responses via scar states in a generalized PXP model. We first show that the generalized PXP model also possesses a band of scar states like the pristine PXP model does. In addition, we reveal that a generalized forward-scattering approximation (FSA) still works for these scar states. We further argue that the FSA subspace exhibits an $SO\left(3\right)$ symmetry, which enables an $SO\left(3\right)\text{−}\mathrm{FSA}$ approach for the scar states. When such a model is placed under periodic driving, nontrivial Floquet scar states emerge in the quasienergy spectrum. One appealing feature of such Floquet scar states is that they can support subharmonic responses akin to the discrete time crystalline phase. In particular, such subharmonic responses can exist beyond the conventional prethermalization regime, where either large frequencies or large driving amplitudes are required.

Understanding the ultrafast demagnetization of transition metals requires pump-probe experiments sensitive to the time evolution of the electronic, spin, and lattice thermodynamic baths. By means of time-resolved photoelectron energy and spin-polarization measurements in the low-pump-fluence regime on iron, we disentangle the different dynamics of hot electrons and demagnetization in the subpicosecond and picosecond time range. We observe a broadening of the Fermi-Dirac distribution, following the excitation of nonthermal electrons at specific region of the iron valence band. The corresponding reduction of the spin polarization is remarkably delayed with respect to the dynamics of electronic temperature. The experimental results are corroborated with a microscopic 3-temperature model highlighting the role of thermal disorder in the quenching of the average spin magnetic moment, and indicating Elliot-Yafet type spin-flip scattering as the main mediation mechanism, with a spin-flip probability of 0.1 and a rate of energy exchange between electrons and lattice of $2.5\mathrm{K}{\mathrm{fs}}^{-1}$.

We study the electronic orders at the lower van Hove filling in the kagome lattice. In the weak limit of the Hubbard interaction $U$ versus the hopping parameter $t$, we find that the system develops itinerant ferromagnetism; In the intermediate range of $U$, we find the system develops noncollinear magnetic order with orthogonal spin moments on nearest-neighbor bonds. This is in fact a Chern insulator-supporting quantized anomalous Hall conductance; In the strong $U$ limit, we map the Hubbard model to the $t-J$ model with $J=4t^2/U$. For moderate values of $J$ we recover the noncollinear magnetic order obtained in the Hubbard model. However, in the limit of $J\to 0$ (or $U\to \infty$) we find the ferromagnetic order revives. The results are obtained by combination of the random-phase approximation and functional renormalization group in the weak to moderate limit of $U$, and the variational quantum Monte Carlo for the $t-J$ model in the strong coupling limit. The phase diagram is distinctly different to that at the higher van Hove filling studied earlier, and the difference can be attributed to the lack of particle-hole symmetry in the band structure with respect to the Dirac point.

Many complex crystals show a flat or even increasing lattice thermal conductivity at high temperatures, which deviates from the traditional 1/$T$ decay trend given by conventional phonon theory. In this paper, we predict the thermal conductivity of ${\mathrm{Al}}_2{\mathrm{O}}_3$ that matches with experimental data from room temperature to near melting point (2200 K). The lattice thermal conductivity is found to be composed of contributions of phonon, diffuson, and radiation. Phonon particle thermal conductivity decays approximately as $\sim T^{-1.14}$ after considering four-phonon (4ph) scattering as well as finite-temperature corrections to the lattice constant and harmonic and anharmonic force constants (AFCs). Diffuson (interband tunneling) thermal conductivity increases roughly as $\sim T^{0.43}$. Radiation thermal conductivity increases as $\sim T^{2.51}$, being slightly smaller than $\sim T^3$ due to the increase of phonon linewidth with temperature, which increases photon extinction coefficient and reduces photon mean free path (MFP). At room temperature, phonon, diffuson, and radiation contribute ∼99, 1, and 0%, respectively. At 2200 K, their contributions change to 61, 20, and 19%, respectively. 4ph scattering is important at ultrahigh temperatures, decreasing the phonon thermal conductivity by a maximum of 24%. The finite-temperature softening effects of the harmonic and AFCs increase the phonon thermal conductivity by a maximum of 36% at ultrahigh temperatures. We also verify that Green-Kubo molecular dynamics can capture both the particle and wave nature of phonons, like the Wigner formalism. At ultrahigh temperatures, the photon MFP is found to be on the order of 100 nm, which should be considered for experimental measurement of thin films. In this paper, we aim to enhance the understanding of lattice thermal conductivity in complex crystals at ultrahigh temperatures, potentially spurring further exploration of materials suitable for such extreme conditions.

In the past few decades, two-dimensional (2D) transition metal dichalcogenides (TMDCs), such as ${\mathrm{MoS}}_2$ and ${\mathrm{WTe}}_2$, have attracted intensive research due to their unique crystal structure, interesting physical properties, and potential applications in various fields. However, 2D transition metal dioxides with the same crystal structure as TMDCs are much less studied both theoretically and experimentally. Here, we present a systematic theoretical study on the 2D ${\mathrm{RuO}}_2$ and ${\mathrm{OsO}}_2$ by using the first-principles calculations. It is found that the monolayer ${\mathrm{RuO}}_2$ and ${\mathrm{OsO}}_2$ both have a 1${\mathrm{T}}^{\prime }$ crystal structure and their stabilities are confirmed by the phonon dispersions and molecular dynamics simulations. The hybrid functional calculations show that both materials are nonmagnetic semiconductors with moderate bandgaps of 0.64 and 0.69 eV for monolayer $1{\mathrm{T}}^{\prime }\text{−}{\mathrm{RuO}}_2$ and ${\mathrm{OsO}}_2$, respectively. When stacking monolayer $1{\mathrm{T}}^{\prime }\text{−}{\mathrm{RuO}}_2$ and ${\mathrm{OsO}}_2$ up into the three-dimensional structures, two stable ${\mathrm{T}}_{\mathrm{d}}$ and 2M phases can be formed, which are also nonmagnetic semiconductors. Interestingly, the ${\mathrm{T}}_{\mathrm{d}}$ phase lacks the inversion symmetry, which possesses sliding ferroelectricity. The calculated spontaneous out-of-plane polarization is 0.16 and 0.33 $\mu \mathrm{C}/{\mathrm{cm}}^2$ for ${\mathrm{T}}_{\mathrm{d}}\text{−}{\mathrm{RuO}}_2$ and ${\mathrm{OsO}}_2$, respectively. Our work clarifies the crystal structure and electronic properties of 2D ${\mathrm{RuO}}_2$ and ${\mathrm{OsO}}_2$ and could be helpful for more experimental studies on both materials.

In this paper, we study the near-field radiative energy, linear-momentum, and angular-momentum transfer from a current-biased graphene to nanoparticles. The electric current through the graphene sheet induces nonequilibrium fluctuations, causing energy and momentum transfer even in the absence of a temperature difference. The inherent spin-momentum locking of graphene surface plasmons leads to an in-plane torque perpendicular to the direction of the electric current. In the presence of a temperature difference, the energy transfer is greatly enhanced while the lateral force and torque remain within the same order. Our work explores the potential of utilizing current-biased graphene to manipulate nanoparticles.

Conventional photoemission orbital tomography based on the Fourier iterative method enables us to extract a projected two-dimensional (2D) molecular orbital from a 2D photoelectron momentum map (PMM) of planar $\pi$-conjugated molecules in a single-orientation system but not in a multiorientation system. In this work, we demonstrate photoemission orbital tomography for $\pi$-conjugated molecules with a tight-binding ansatz using an atomic orbital basis. We analyze 2D PMMs of single-orientation pentacene/Ag(110) and multiorientation 3,4,9,10-perylenetetracarboxylic dianhydride/Ag(110) and reproduce their three-dimensional highest occupied molecular orbitals. We demonstrate that the PhaseLift algorithm can be used to analyze PMMs including experimental or theoretical uncertainties. With the 2D PMM for pentacene, we simultaneously optimize the structure and the molecular orbital. The present approach enables us to extract the three-dimensional orbitals and structures of existing materials.

Ultraflat bands have already been detected in twisted bilayer graphene and twisted bilayer transition-metal dichalcogenides, which provide a platform to investigate strong correlations. In this paper, the electronic properties of twisted trilayer molybdenum disulfide (TTM) are investigated via an accurate tight-binding Hamiltonian. We find that the highest valence bands are derived from the $\mathrm{\Gamma }$-point of the constituent monolayer, and they exhibit a graphenelike dispersion or become isolated flat bands that are dependent on the starting stacking arrangements. The lattice relaxation, local deformation, and external fields can significantly tune the electronic structures of TTM. After introducing the spin-orbital coupling effect, we find a spin-valley-layer locking effect at the minimum of the conduction band at the $K$- and $K^{\prime }$-point of the Brillouin zone, which may provide a platform to study optical properties and magnetoelectric effects.

In an attempt to understand the density-density response of the cuprate superconductors, we study plasmons in a layered strange metal using the Gubser-Rocha model. The latter is a well-known bottom-up holographic model for a strange metal that is used here to describe the strongly repulsive on-site interactions between the electrons in each copper-oxide $\left({\mathrm{CuO}}_2\right)$ layer, whereas the long-range Coulomb interactions are incorporated by a so-called double-trace deformation. To be able to model the bilayer cuprates more realistically, we consider in particular the case of two closely spaced ${\mathrm{CuO}}_2$ layers per unit cell. In the response we then obtain for vanishing out-of-plane momentum both an optical and an acoustic plasmon, whereas for nonvanishing out-of-plane momentum there are two acoustic plasmon modes. We present the full density-density spectral functions with parameters typical for cuprates and discuss both the dispersion and the lifetime of these plasmon excitations. Moreover, we compute the conductivity after introducing disorder into the system. Finally, we also compute the loss function to facilitate a comparison with experimental results from electron energy-loss spectroscopy.

Néel spin current is defined as the staggered spin current across different magnetic sublattices and can manipulate the Néel vector of the antiferromagnet by its associated spin-transfer torques. Currently, it is believed that Néel spin currents are only generated through electrical driving in $\mathcal{PT}$-symmetric antiferromagnetic metals, which is a linear effect. In this paper, we propose that Néel spin currents can be induced through the nonlinear optical effect (spin photogalvanic effect) in $\mathcal{PT}$-symmetric antiferromagnetic semiconductors. Using CrSBr and ${\mathrm{CrI}}_3$ as representatives, we predict that light can generate Néel spin current in antiferromagnetic semiconductors, with both staggered and antiparallel spin currents distributed across different magnetic sublattices, depending on the $\mathcal{PT}$ symmetries of their corresponding spin photogalvanic coefficients. We show that the origin of the diverse manifestations of light-assisted Néel spin currents lies in the nonlinearity of the spin photogalvanic effect, resulting in the current not necessarily being the staggered spin current. Our work proposes a nonlinear effect that may have tremendous application potential in future antiferromagnetic devices.

In the field of materials research, machine learning (ML) techniques have emerged as indispensable tools. However, the opaqueness in decision making by models can compromise the trustworthiness of results, underscoring the crucial need for model interpretability. Explainable machine learning (XML) strives to augment researchers’ comprehension of material properties and performance. Yet, reliance on high-quality datasets and scarcity of prior knowledge pose challenges for XML research, particularly when dealing with smaller datasets. In this study, using spinel as a representative example, we successfully addressed the data challenges in XML through a cationic perturbation strategy. We demonstrate an effective approach for handling information scarcity in small datasets, thus offering a feasible method for material research and broadening the scope of XML applications in materials science. Furthermore, our investigation successfully uncovered potential causal relationships underlying material properties and validated their consistency with physical cognition. These causal relationships can serve as experimental guides, facilitating the design and optimization of new materials. Consequently, this research holds significant scientific merit in advancing XML in the realm of materials science, while providing profound insights into material properties and fostering the development of reliable ML-based materials research.

We investigate the mesoscopic transport through a twisted bilayer graphene (TBG) consisting of a clean graphene nanoribbon on the bottom and a disordered graphene disk on the top. We show that, with strong top-layer disorder, the transmission through such a device shows a sequence of resonant peaks with respect to the rotation angle $\theta$, where at the resonant angles ${\theta }_c$ the disk region contains one giant hexagonal moiré supercell. A further investigation shows that the value of ${\theta }_c$ shows negligible dependence on the disorder strength, the Fermi energy, and the shape distortion, indicating the resonance is a robust commensuration feature of the moiré supercell. We explain this commensuration resonance based on the bound states formed inside TBG disk as a result of the nonuniform interlayer coupling, with their average local density of states dominating at the AA stacking region while minimizing at the AB/BA stacking regions. By increasing the interlayer distance, the peak becomes less pronounced which further confirms the role of interlayer coupling. The results presented here suggest a new mechanism to tune the quantum transport signal through the twist angle in disordered moiré systems.

As elementary particles carry energy and momentum in the Universe, quasiparticles are the elementary carriers of energy and momentum quanta in condensed matter. And, as elementary particles, under certain conditions quasiparticles can be unstable and decay, emitting pairs of less energetic ones. Pitaevskii [Sov. Phys. JETP 9, 830 (1959)] proposed that such processes exist in superfluid helium, a quantum fluid where the very concept of quasiparticles was borne by Landau and which presented the first notable success of that concept. Pitaevskii's decays have important consequences, including the possible breakdown of a quasiparticle [M. B. Stone et al., Nature (London) 440, 187 (2006)]. Here, we present neutron scattering experiments, which provide evidence that such decays explain the collapsing lifetime (strong damping) of higher-energy phonon-roton sound-wave quasiparticles in superfluid helium. This damping develops when helium is pressurized towards crystallization, or warmed towards approaching the superfluid transition. Our results resolve a number of puzzles raised by previous experiments and reveal the ubiquity of quasiparticle decays and their importance for understanding quantum matter.

We present a detailed study of the electronic and magnetic ground-state properties of ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\mathrm{Si}$ using a combination of macroscopic and microscopic experimental techniques. From these experiments we quantitatively characterize the metal-insulator transition and magnetic/nonmagnetic quantum phase transition occurring at low-doping levels in ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\mathrm{Si}$. From our study, we find a surprising closeness of the critical composition of the metal-insulator transition at $x_{\mathrm{MIT}}=0.014$ and the quantum phase transition at $x_{\mathrm{LRO}}\sim 0.024-0.031$. This suggests that these effects are cooperative and depend on each other.

We report the effect of Ir doping on the anomalous Hall effect (AHE) and anomalous Nernst effect (ANE) in ${\mathrm{Fe}}_3\mathrm{Co}$ single-crystal thin films. ${\left({\mathrm{Fe}}_3\mathrm{Co}\right)}_{100\text{--}x}{\mathrm{Ir}}_x$ $(x\le 12\%)$ composition-spread thin films are fabricated on MgO(100) substrates by a combinatorial sputtering technique for a high-throughput and systematic characterization. From a structural analysis using x-ray diffraction, the films are grown epitaxially on the substrates and B2-ordered phase is detected from $x=7.3\%$ to 12%. The compositional dependence of the AHE, magnetoresistance, ANE, and Seebeck effect is measured to obtain anomalous Hall resistivity $\left({\rho }_{yx}^A\right)$, longitudinal resistivity $\left({\rho }_{xx}\right)$, anomalous Nernst coefficient $\left(S_{\mathrm{ANE}}\right)$, and Seebeck coefficient $\left(S_{\mathrm{SE}}\right)$, respectively. From these transport measurements, we calculate anomalous Nernst conductivity $\left({\alpha }_{xy}^A\right)$. A large enhancement of the ${\rho }_{yx}^A$ value is observed upon Ir doping by a factor of ≈ 9.2 for $x=12\%$ at 300 K. By employing a scaling analysis to the AHE results, extrinsic contribution is found to be increased after Ir doping in the low-Ir concentration regime, while intrinsic contribution becomes more dominant in the high-Ir concentration regime. On the other hand, unlike the ${\rho }_{yx}^A$, the $S_{\mathrm{ANE}}$ does not show significant compositional dependence. We find that AHE-related contribution $(-S_{\mathrm{SE}}{\rho }_{yx}^A/{\rho }_{xx})$ is dominant to the $S_{\mathrm{ANE}}$ compared to the contribution from direct conversion of a temperature gradient to a transverse charge current by anomalous Nernst conductivity $\left({\alpha }_{xy}^A{\rho }_{xx}\right)$. We also find that the ${\alpha }_{xy}^A$ value sharply changes from a positive to negative value immediately after Ir doping, showing a negative maximum at $x\approx 1\%$, followed by a decrease in magnitude to almost zero for $x=12\%$. Based on the Mott's relation and the scaling analysis of the AHE, we suggest a possible connection between the ${\alpha }_{xy}^A$ and the extrinsic contribution of the AHE. These experimental results and analysis will provide insights into the relationship between the AHE and ANE in ferromagnetic alloys upon heavy metal doping.

Materials featuring the kagome configuration hold significant research potential following their discovery. Drawing inspiration from ${\mathrm{MgB}}_2$, we introduce a kagome topological superconducting family: ${X\mathrm{B}}_3$ $(X=\mathrm{Ni}, \mathrm{Pd})$. This prediction is based on first-principles calculations and an analysis of bulk-edge correspondence. In this family, the boron atoms transition from their original honeycomb arrangement to form a stable kagome lattice, as confirmed by the phonon spectrum analysis. Through the calculations of the topological invariant and surface states, we establish that these materials belong to the ${\mathbb{Z}}_2$ Dirac metal category with nodal surface characteristics. Employing the Allen-Dynes modified McMillan formula, we anticipate superconducting critical temperatures, denoted as $T_c$, of 14.5 K for ${\mathrm{NiB}}_3$ and 19.1 K for ${\mathrm{PdB}}_3$. These values surpass most of both conventional topological superconductors' candidates and kagome superconductors due to the relatively robust electron-phonon coupling. Moreover, the spin texture analysis of the Dirac cone at the high symmetry point $K$ lends further support to their status as topological superconductors. Consequently, the ${X\mathrm{B}}_3$ family presents an exciting platform for experimental investigations into topological superconductors and their potential applications in fault-tolerant quantum computation.