The electronic structure of ${\mathrm{SrRuO}}_3$ thin film with a thickness from 1 to 50 unit cell (u.c.) is investigated via the resonant inelastic x-ray scattering (RIXS) technique at the O $K$ edge to unravel the intriguing interplay of orbital and charge degrees of freedom. We found that the orbital-selective quantum confinement effect (QCE) induces the splitting of Ru $4d$ orbitals. At the same time, we observed a clear suppression of the electron-hole continuum across the metal-to-insulator transition occurring in the 4-u.c. sample. From these two clear observations we conclude that the QCE gives rise to a Mott insulating phase in ultrathin ${\mathrm{SrRuO}}_3$ films. Our interpretation of the RIXS spectra is supported by the configuration interaction calculations of ${\mathrm{RuO}}_6$ clusters.

As a crucial part in thermal management, interfacial thermal transport is still not well understood. In this paper, we employ the newly developed modal nonequilibrium molecular dynamics to study the Si/Ge interfacial thermal transport and clarify several long-standing issues. We find that the few atomic layers at the interface are dominated by interfacial modes, which act as a bridge that connects the bulk Si and Ge modes. Such bridging effect boosts the inelastic transport to contribute more than 50% to the total thermal conductance even at room temperature. The apparent inelastic transport can even allow effective four-phonon processes across the interface when the mass difference between the two materials is large. Surprisingly, optical phonon modes can contribute equal or more thermal conductance than the acoustic modes due to the bridging effect. From the modal temperature analysis, we find that the phonon modes are in strong thermal nonequilibrium near the interface, which impedes the thermal transport. The widely used Landauer approach that does not consider the phonon nonequilibrium can lead to inaccurate results. We have modified the Landauer approach to include the inelastic transmission and modal thermal nonequilibrium. The approach is used to analyze our modal NEMD results, and the mode-dependent phonon transmission function that includes inelastic scattering has been derived. Our results unveil the fundamental thermal transport physics across interfaces and will shed light on the future engineering in thermal management. It provides a method of calculating modal phonon transmission functions that includes inelastic scattering from molecular dynamics.

The thermoelectric power factor of hierarchically nanostructured materials is investigated using the nonequilibrium Green's function method for quantum transport, including interactions of electrons with acoustic and optical phonons. We describe hierarchical nanostructuring by superlattice-like potential barriers/wells, combined with quantum dot barriers/wells nanoinclusions as well as voids in the intermediate region. We show that these structures can be designed in a way that the power factor is not only largely immune to the presence of the nanostructure features, but under certain conditions benefits can be achieved as well. Interestingly, we show that these design approaches are linked to the energy relaxation of the current flow and whether charge carrier scattering is limited by elastic or inelastic processes. In particular, when nanostructures form potential barriers, the power factor can be substantially enhanced under elastic scattering conditions, irrespective of nanostructuring density and potential barrier heights. When inelastic scattering processes dominate, however, the power factor is inevitably degraded. In the case in which nanostructures form potential wells, despite a slight decrease, the power factor is quite resilient under either elastic or inelastic scattering processes. These nanostructuring design approaches could help open the path to the optimization of new generation nanostructured thermoelectric materials by not only targeting reductions in thermal conductivity, but simultaneous improvements in the power factor as well.

Decomposing the field scattered by an object into vector spherical wave functions (VSWF) is a useful tool when discussing its optical properties on more analytical grounds. Thus far, it was frequently required in the decomposition that the scattered field is available on a spherical surface enclosing the scatterer. This requirement is adapted to the spatial dependency of the VSWFs but is rather incompatible with many numerical solvers. To mitigate this problem, we propose an orthogonal expression for the decomposition that holds for any surface that encloses the scatterer, independently of its shape. We also show that the orthogonal relations remain unchanged when the radiative VSWF used for the expansion of the scattered field are substituted by the regular VSWF used for the expansion of the incident illumination as test functions. This is a key factor for the numerical stability of our decomposition. As an example, we use a finite-element based solver to compute the multipole response of a nanorod illuminated by a plane wave and study its convergence properties.

ZnO is a transparent semiconductor with optoelectronic, thermoelectric, and sensor applications, where using amorphous thin films presents great advantages. However, growing amorphous (a) films of pure ZnO proved challenging due to their rapid crystallization. We investigated the ability of bulk ZnO to form glass structures using well-tested interatomic potentials and a melt and quench procedure within isothermal-isobaric (NPT) ensemble. The geometries of some of the resulting structures were further optimized using density functional theory (DFT) calculations with the PBE functional. We demonstrate that cooling rates in melt and quench procedure equal or exceeding 100 ${\mathrm{K}\mathrm{ps}}^{-1}$ lead to formation of stable amorphous structures. However, ZnO samples tend to crystallize at lower cooling rates. This result does not depend on the size of the periodic cell used in the calculations for cells containing more than 324 atoms. Using simulation cells with up to 768 000 atoms, we demonstrate that the expected average glass density is about 5.04 $\mathrm{g}{\mathrm{cm}}^{-3}$ and the coordination numbers of Zn and O atoms are around 3.9. We calculate radial distribution functions and characterize the structures of amorphous ZnO samples. Using both the activation-relaxation technique and simulated annealing, we show that the obtained amorphous structures have low propensity to crystallization.

Flexible ferromagnetic rings are spin-chain magnets, in which the magnetic and mechanical subsystems are coupled. The coupling is achieved through the tangentially oriented anisotropy axis. The possibility to operate the mechanics of the nanomagnets by controlling their magnetization is an important issue for the nanorobotics applications. A minimal model for the deformable curved anisotropic Heisenberg ferromagnetic wire is proposed. An equilibrium phase diagram is constructed for the closed loop geometry: (i) A vortex state with vanishing total magnetic moment is typical for relatively large systems; in this case, the wire has the form of a regular circle. (ii) A topologically trivial onion state with the planar magnetization distribution is realized in small enough systems; magnetic loop is elliptically deformed. By varying geometrical and elastic parameters, a phase transition between the vortex and onion states takes place. The detailed analytical description of the phase diagram is well confirmed by numerical simulations.

Recently, with advances in acoustic metamaterial science, the possibility of sound attenuation using subwavelength structures, while maintaining permeability to air, has been demonstrated. However, the ongoing challenge addressed herein is the fact that among such air-permeable structures to date, the open area represents only small fraction of the overall area of the material. In the presented paper in order to address this challenge, we first demonstrate that a transversely placed bilayer medium with large degrees of contrast in the layers' acoustic properties exhibits an asymmetric transmission, similar to the Fano-like interference phenomenon. Next, we utilize this design methodology and propose a deep-subwavelength acoustic metasurface unit cell comprising nearly 60% open area for air passage, while serving as a high-performance selective sound silencer. Finally, the proposed unit-cell performance is validated experimentally, demonstrating a reduction in the transmitted acoustic energy of up to 94%. This ultra-open metamaterial design, leveraging a Fano-like interference, enables high-performance sound silencing in a design featuring a large degree of open area, which may find utility in applications in which highly efficient, air-permeable sound silencers are required, such as smart sound barriers, fan or engine noise reduction, among others.

We revisit a quantum-mechanical formula of the spin magnetic quadrupole moment (MQM) in periodic crystals. Two previous attempts were inconsistent with each other; one is gauge dependent and the other is gauge invariant. Here we define the spin MQM by calculating the spin density in a nonuniform system. Our definition is analogous to that of the charge polarization, but the result is gauge invariant and coincides with the latter previous one. We also formulate what we call gravitomagnetoelectric (gravito-ME) effect, in which the magnetization is induced by a temperature gradient. Although the Kubo formula for the gravito-ME effect provides an unphysical divergence at zero temperature, we prove that the correct susceptibility is obtained by subtracting the spin MQM from the Kubo formula. It vanishes at zero temperature and is related to the ME susceptibility by the Mott relation. We explicitly calculate the gravito-ME susceptibility in a Rashba ferromagnet and show its experimental feasibility.

Aiming at a unified treatment of correlation and inhomogeneity effects in superconductors, Oliveira, Gross, and Kohn proposed in 1988 a density functional theory for the superconducting state. This theory relies on the existence of a Kohn- Sham scheme, i.e., an auxiliary noninteracting system with the same electron and anomalous densities of the original superconducting system [Phys. Rev. Lett. 60, 2430 (1988)]. However, the question of noninteracting $v$-representability has never been properly addressed and the existence of the Kohn-Sham system has always been assumed without proof. Here, we show that indeed such a noninteracting system does not exist at zero temperature. In spite of this result, we also show that the theory is still able to yield good results, although in the limit of weakly correlated systems only.

We have elucidated the nature of the electron correlation effect in uranium compounds by imaging the partial $\mathrm{U}5f$ density of states (pDOS) of typical itinerant, localized, and heavy fermion uranium compounds by using the $\mathrm{U}4d\text{−}5f$ resonant photoemission spectroscopy. The obtained $\mathrm{U}5f$ pDOS exhibit a systematic trend depending on the physical properties of compounds. The coherent peak at the Fermi level can be described by the band-structure calculation, but an incoherent peak emerges on the higher binding energy side ($\lesssim 1\mathrm{eV}$) in the $\mathrm{U}5f$ pDOS of localized and heavy fermion compounds. As the $\mathrm{U}5f$ state is more localized, the intensity of the incoherent peak is enhanced and its energy position is shifted to higher binding energy. These behaviors are consistent with the prediction of the Mott metal-insulator transition, suggesting that the Hubbard-$U$ type mechanism takes an essential role in the $5f$ electronic structure of actinide materials.

Magnetic lanthanide half-Heuslers ($R\mathrm{PtBi}$; $R$ being the lanthanide) represent an attractive subgroup of the Heusler family and have been identified as ideal candidates for time-reversal symmetry-breaking topological Weyl semimetals. In this paper, we present the detailed analysis of the magnetotransport properties of frustrated antiferromagnet TbPtBi. This material shows large, nonsaturating magnetoresistance (MR) with unusual magnetic field dependence. The MR of TbPtBi is significantly anisotropic with respect to the magnetic field, applied along different crystallographic directions, and indicates the anisotropic nature of the Fermi surface. The chiral-anomaly-induced negative longitudinal magnetoresistance confirms the presence of Weyl fermions. At low temperature, Berry-phase-driven large anomalous Hall conductivity has been observed. The calculated anomalous Hall angle is the largest reported so far.

We study topological properties of two-dimensional (2D) bi-triangular lattices with multiple $p$ and $d$ orbitals. Tight-binding (TB) model calculations show that the multiple $p$ ($p_x/p_y$) and $d$ ($d_{xy}/d_{x^2-y^2}$ or $d_{xz}/d_{yz}$) bands in the 2D bi-triangular lattices, with $C_3$ symmetry, are all degenerate at the $\mathrm{\Gamma }$ point with quadratic non-Dirac band dispersions and gapped at the $K/K^{\prime }$ points. Spin-orbit coupling (SOC) is found not only resulting in the topologically nontrivial states, but also the topologically trivial states. In the 2D bi-triangular lattices, a topological phase transition from a topologically nontrivial state to a trivial state can be triggered by increasing the atomic SOC strength. Our first-principles calculations predict a large band-gap quantum anomalous Hall state (about 30 meV) and topological phase transitions in a 2D metal-organic frameworks $X({\mathrm{C}}_{21}{\mathrm{N}}_3{\mathrm{H}}_{15}$) ($X=\mathrm{Ta}$, Hf), rationalized well by the TB model built above. Our results are helpful to deeply understand the topological states and provide theoretical guidance for the search of 2D topological materials based on the multiple $p$ and $d$ orbitals.

We report a classical electromagnetically induced transparency (EIT) analog based on magnetic plasmonic artificial molecules consisting of magnetic localized surface plasmons and split ring resonators. The key to achieve EIT-like transparency are the excited symmetric and antisymmetric states based on bright-dark mode coupling, where the bright mode of the split ring resonator excited by incident waves is coupled to the dark mode of the neighbor spoof magnetic localized surface plasmons resonator. We conduct experiments, simulations, and analysis based on the Lorentz oscillator model. In addition, we numerically demonstrate that the EIT-like transparency can be employed to permittivity sensing applications.

We have investigated the hyperfine structure in high-resolution broadband optical absorption spectra of a strongly diluted paramagnet ${}^7\mathrm{LiYF}_4:{\mathrm{Ho}}^{3+}$ (0.1 at. %) in external magnetic fields parallel to the tetragonal symmetry axis of the crystal. Anticrossings in the hyperfine spectral pattern were observed. It is the first direct observation of the hyperfine level anticrossings in optical spectra. Analysis of the spectral envelopes corresponding to transitions between the electron-nuclear sublevels of crystal-field non-Kramers doublets and singlets of the ${\mathrm{Ho}}^{3+}$ ions, based on the microscopic model of the electronic $4f^{10}$ configuration, allowed us to retrieve information on the hyperfine structure of electronic singlets, nuclear quadroupole interactions, and random lattice strains.

A topological superconductor candidate $\beta \text{−}{\mathrm{RhPb}}_2$ is predicted by using first-principles electronic structure calculations. Our calculations show that there is a band inversion around the Fermi level at the $Z$ point of Brillouin zone. The calculated nonzero topological invariant ${\mathrm{Z}}_2$ indicates that $\beta \text{−}{\mathrm{RhPb}}_2$ is a topological insulator defined on a curved Fermi level. Slab calculations further demonstrate that the gapless nontrivial topological surface states (TSS) are not overlapped by the bulk states and they cross the Fermi level. Phonon calculations confirm the dynamical stability of $\beta \text{−}{\mathrm{RhPb}}_2$, while electron-phonon coupling (EPC) calculations predict that the superconducting transition temperature $\left(T_c\right)$ of $\beta \text{−}{\mathrm{RhPb}}_2$ can reach 9.7 K. The coexistence of nontrivial topological band structure with the TSS crossing the Fermi level as well as the superconducting $T_c$ above the liquid-helium temperature suggest that the layered compound $\beta \text{−}{\mathrm{RhPb}}_2$ is a topological superconductor, which deserves further experimental verification.