We analyze the spectrum of waveguide modes of an arbitrary uniaxial anisotropic metamaterial slab with nonlocal electromagnetic response whose permittivity tensor could be described within the Drude approximation. Spatial dispersion was introduced within the hydrodynamical model. By considering both anisotropy and spatial dispersion as perturbations, we distinguish their effect on the spectrum of the slab and analyze lifting of the degeneracy of eigenmodes at plasma frequency in detail. Spatial dispersion is shown to result in a break of the singularity in the density of optical states in the hyperbolic regime and in suppression of negative dispersion induced by anisotropy. We demonstrate that the interplay of spatial dispersion and anisotropy can bring light to a complete stop at certain frequencies.

Self-diffusion in silicon and the contribution of vacancies and self-interstitials have been controversially discussed for 50 yr. Most recent results show that the intrinsic silicon self-diffusion coefficient deviates from an Arrhenius-type, single exponential function for temperatures below $950{}^{\circ }\mathrm{C}$ [Y. Shimizu, M. Uematsu, and K. M. Itoh, Phys. Rev. Lett. 98, 095901 (2007); R. Kube, H. Bracht, E. Hüger, H. Schmidt, J. L. Hansen, A. N. Larsen, J. W. Ager, E. E. Haller, T. Geue, and J. Stahn, Phys. Rev. B 88, 085206 (2013)]. This led us to propose temperature-dependent thermodynamic properties of vacancies in order to achieve full consistency to vacancy-mediated dopant diffusion in silicon. Concepts of temperature-dependent properties of native defects or distinct forms of defects with different formation entropies suggested by Cowern et al. [N. E. B. Cowern, S. Simdyankin, C. Ahn, N. S. Bennett, J. P. Goss, J.-M. Hartmann, A. Pakfar, S. Hamm, J. Valentin, E. Napolitani, D. De Salvador, E. Bruno, and S. Mirabella, Phys. Rev. Lett. 110, 155501 (2013)] question the present understanding on atomic transport in semiconductors. To verify these concepts, additional self-diffusion experiments under particular gettering conditions were performed. As a result, silicon self-diffusion was found to be accurately described by one single diffusion activation enthalpy of $(4.73\pm 0.02)$ eV down to $755{}^{\circ }\mathrm{C}$. This provides full consistency to dopant diffusion without claiming native-defect concepts that were originally proposed by Seeger and Chik in 1968 [A. Seeger and K. P. Chik, Phys. Stat. Sol. 29, 455 (1968)] and confirms most recent density functional theory calculations on the activation energy of self-diffusion via vacancies and self-interstitials. Overall, this unravels the old debate of self-diffusion in silicon with the supposed intrinsic temperature dependence.

The layer-dependent structural, electronic, and vibrational properties of ${\mathrm{SnS}}_2$ and ${\mathrm{SnSe}}_2$ are investigated using first-principles density functional theory (DFT). The in-plane lattice constants, interlayer distances and binding energies are found to be layer-independent. Bulk ${\mathrm{SnS}}_2$ and ${\mathrm{SnSe}}_2$ are both indirect band gap semiconductors with $E_g=2.18$ and $1.07\mathrm{eV}$, respectively. Few-layer and monolayer 2D systems also possess an indirect band gap, which is increased to 2.41 and $1.69\mathrm{eV}$ for single layers of ${\mathrm{SnS}}_2$ and ${\mathrm{SnSe}}_2.$ The effective mass theory of 2D excitons, which takes into account the combined effect of the anisotropy, nonlocal 2D screening and layer-dependent 3D screening, predicts strong excitonic effects. The binding energy of indirect excitons in monolayer samples, $E_x\sim 0.9\mathrm{eV}$, is substantially reduced to $E_x=0.14\mathrm{eV}$ in bulk ${\mathrm{SnS}}_2$ and $E_x=0.09\mathrm{eV}$ in bulk ${\mathrm{SnSe}}_2$. The layer-dependent Raman spectra display a strong decrease of intensities of the Raman active $A_{1g}$ mode upon decreasing the number of layers down to a monolayer, by a factor of 7 in the case of ${\mathrm{SnS}}_2$ and a factor of 20 in the case of ${\mathrm{SnSe}}_2$, which can be used to identify the number of layers in a 2D sample.

Using both DFT as well as $G_0{W}_0$ calculations, we investigate static and dynamic effects on the phosphorene band gap upon deposition and encapsulation on/in BN multilayers. We demonstrate how competing long- and short-range effects cause the phosphorene band gap to increase at low $\mathrm{P}\text{−}\mathrm{BN}$ interlayer spacings, while the band gap is found to drop below that of isolated phosphorene in the BN/P bilayer at intermediate distances around 4 Å. Subsequent stacking of BN layers, i.e., BN/BN/P and BN/BN/BN/P is found to have a negligible effect at the DFT level while at the $G_0{W}_0$ level, increased screening lowers the band gap as compared to the BN/P bilayer. Encapsulation between two BN layers, on the other hand, is found to further increase the phosphorene band gap with respect to the BN/P bilayer. Lastly we investigate the use of the GLLB-SC functional as a starting point for $G_0{W}_0$ calculations showing it to, in the case of phosphorene, yield results close to those obtained from $G{W}_0@PBE$.

The phase diagram of iridium is investigated using the Z methodology. The Z methodology is a technique for phase diagram studies that combines the direct Z method for the computation of melting curves and the inverse Z method for the calculation of solid-solid phase boundaries. In the direct Z method, the solid phases along the melting curve are determined by comparing the solid-liquid equilibrium boundaries of candidate crystal structures. The inverse Z method involves quenching the liquid into the most stable solid phase at various temperatures and pressures to locate a solid-solid boundary. Although excellent agreement with the available experimental data (to $\lesssim 65$ GPa) is found for the equation of state (EOS) of Ir, it is the third-order Birch-Murnaghan EOS with $B_0^{\prime }=5$ rather than the more widely accepted $B_0^{\prime }=4$ that describes our ab initio data to higher pressure $\left(P\right)$. Our results suggest the existence of a random-stacking hexagonal close-packed structure of iridium at high $P.$ We offer an explanation for the 14-layer hexagonal structure observed in experiments by Cerenius and Dubrovinsky.

We find that if solid xenon is formed from liquid xenon, denoted “ice,” there is a 10% increase in ${}^{129}\mathrm{Xe}$ longitudinal relaxation $T_1$ time (taken at 77 K and 2 T) over a trickle-freeze formation, denoted “snow.” Forming xenon ice also gives an unprecedented reproducibility of ${}^{129}\mathrm{Xe}$ $T_1$ measurements across a range of 77–150 K. This temperature dependence roughly follows the theory of spin rotation mediated by Raman scattering of harmonic phonons, though it results in a smaller-than-predicted spin-rotation coupling strength $c_{K0}/h$. Enriched ice ${}^{129}\mathrm{Xe}$ $T_1$ experiments show no isotopic dependence of bulk relaxation mechanisms at 77 K and at kilogauss fields.

Although InP and GaAs have very similar band structure their magnetic properties appear to drastically differ. Critical temperatures in (In,Mn)P are much smaller than those of (Ga,Mn)As and scale linearly with Mn concentration. This is in contrast to the square-root behavior found in (Ga,Mn)As. Moreover the magnetization curve exhibits an unconventional shape in (In,Mn)P contrasting with the conventional one of well-annealed (Ga,Mn)As. By combining several theoretical approaches, the nature of ferromagnetism in Mn-doped InP is investigated. It appears that the magnetic properties are essentially controlled by the position of the Mn acceptor level. Our calculations are in excellent agreement with recent measurements for both critical temperatures and magnetizations. The results are only consistent with a Fermi level lying in an impurity band, ruling out the possibility to understand the physical properties of Mn-doped InP within the valence band scenario. The quantitative success found here reveals a predictive tool of choice that should open interesting pathways to address magnetic properties in other compounds.

We synthesized a series of V-doped ${\mathrm{LiFe}}_{1-x}{\mathrm{V}}_x\mathrm{As}$ single crystals. The superconducting transition temperature $T_c$ of LiFeAs decreases rapidly at a rate of 7 K per 1% V. The Hall coefficient of LiFeAs switches from negative to positive with 4.2% V doping, showing that V doping introduces hole carriers. This observation is further confirmed by the evaluation of the Fermi surface volume measured by angle-resolved photoemission spectroscopy (ARPES), from which a 0.3 hole doping per V atom introduced is deduced. Interestingly, the introduction of holes does not follow a rigid band shift. We also show that the temperature evolution of the electrical resistivity as a function of doping is consistent with a crossover from a Fermi liquid to a non-Fermi liquid. Our ARPES data indicate that the non-Fermi liquid behavior is mostly enhanced when one of the hole $d_{xz}/d_{yz}$ Fermi surfaces is well nested by the antiferromagnetic wave vector to the inner electron Fermi surface pocket with the $d_{xy}$ orbital character. The magnetic susceptibility of ${\mathrm{LiFe}}_{1-x}{\mathrm{V}}_x\mathrm{As}$ suggests the presence of strong magnetic impurities following V doping, thus providing a natural explanation to the rapid suppression of superconductivity upon V doping.

We present a thorough density functional theory study of the magnetoelectric (ME) effect in ${\mathrm{Cr}}_2{\mathrm{O}}_3$. The spin-lattice ME tensor $\alpha$ was determined in the low-field and spin flop (SF) phases, using the method of dynamical magnetic charges, and found to be the sum of three distinct components. Two of them, a large relativistic “cycloidal” term and a small longitudinal term, are independent on the spin orientation. The third, only active in the SF phases, is also of relativistic origin and arises from magnetic-field-induced chirality, leading to a nontoroidal ME response.

We investigated static and dynamic lattice properties in a quasi-one-dimensional charge-ordered semiconductor ${\left({\mathrm{NbSe}}_4\right)}_3\mathrm{I}$ by using Raman, femtosecond pump-probe spectroscopy and x-ray diffraction. In addition to a well-documented pseudo-Jahn-Teller ferrodistortive structural transition at $T_C=274$ K, where the displacements of Nb ions lead to ferroelectric (FE) in-chain polarization with opposite direction in adjacent chains, all methods suggest an additional lowering of symmetry at $T^{*}\approx 160$ K. Although antiferroelectric (AFE) phase is partially formed at $T_C$, our results consistently point to an enhancement of the interchain order at $T^{*}$, thus leading to AFE order-disorder transition, as supported by the earlier dielectric and structural studies.

We have investigated the crystal structure and magnetic properties of three kagome lattice antiferromagnets, ${\mathrm{Rb}}_2\mathrm{Na}{\mathrm{Ti}}_3{\mathrm{F}}_{12}, {\mathrm{Cs}}_2\mathrm{Na}{\mathrm{Ti}}_3{\mathrm{F}}_{12}$, and ${\mathrm{Cs}}_2\mathrm{K}{\mathrm{Ti}}_3{\mathrm{F}}_{12}$, using single crystals. These compounds represent a $S=1/2$ kagome system consisting of magnetic ${\mathrm{Ti}}^{3+}$ ions, which is expected to have negligibly small Dzyaloshinsky-Moriya interaction. The structural analyses revealed that each of the three compounds has a slightly distorted kagome lattice. The distortion of the kagome lattice becomes small as the ionic radii of constituent alkali metals increase. All three compounds have nearly the same Weiss temperature of $-45$ K, and the ground states are disordered and strongly depend on the distortion. The ground states of ${\mathrm{Rb}}_2\mathrm{Na}{\mathrm{Ti}}_3{\mathrm{F}}_{12}, {\mathrm{Cs}}_2\mathrm{Na}{\mathrm{Ti}}_3{\mathrm{F}}_{12}$, and ${\mathrm{Cs}}_2\mathrm{K}{\mathrm{Ti}}_3{\mathrm{F}}_{12}$ are found to be a two-component state including approximately 1/3 nearly free spins, a gapless disordered state, and a gapped disordered state, respectively. Our experimental results suggest that the ground state of the ideal $S=1/2$ Heisenberg kagome lattice antiferromagnet is gapped. In addition, the magnetization curves of ${\mathrm{Cs}}_2\mathrm{Na}{\mathrm{Ti}}_3{\mathrm{F}}_{12}$ and ${\mathrm{Cs}}_2\mathrm{K}{\mathrm{Ti}}_3{\mathrm{F}}_{12}$ show anomalies at approximately 1/3 of the full magnetic moment of ${\mathrm{Ti}}^{3+}$, which are a notable observation of signs of the theoretically proposed 1/3 magnetization plateau in $S=1/2$ kagome antiferromagnets.

The micromagnetic exchange stiffness is a critical parameter in numerical modeling of magnetization dynamics and reversal processes, yet the current literature reports a wide range of values even for such simple and widely used material as cobalt. Using the ab initio estimated Heisenberg parameters we calculate the low temperature micromagnetic exchange stiffness for hexagonal-close-packed (hcp) and face-centered-cubic cobalt. For hcp Co they are slightly different in the directions parallel and perpendicular to the $c$ axis. We establish the exchange stiffness scaling relation with magnetization $A\left(m\right)\sim m^{1.8}$ valid for a wide range of temperatures. For hcp Co we find an anisotropic domain wall width in the range 24–29 nm which increases with temperature. The results form a critical input for large-scale temperature-dependent micromagnetics simulations and demonstrate the importance of correct parametrization for accurate simulation of magnetization dynamics.

Magnetic Skyrmions have attracted broad attention during recent years because they are regarded as promising candidates as bits of information in novel data storage devices. A broad range of theoretical and experimental investigations have been conducted with the consideration of axisymmetric Skyrmions in isotropic environments. However, one naturally observes a huge variety of anisotropic behavior in many experimentally relevant materials. In the present work, we investigate the influence of anisotropic environments onto the formation and behavior of the noncollinear spin states of skyrmionic materials by means of Monte Carlo calculations. We find skyrmionic textures which are far from having an axisymmetric shape. Furthermore, we show the possibility to employ periodic modulations of the environment to create skyrmionic tracks.

A compound with very weakly interacting chains, ${\mathrm{MnCl}}_3$(bpy), has attracted a great deal of attention as a possible $S=2$ Haldane chain. However, long-range magnetic order of the chains prevents the Haldane gap from developing below 11.5 K. Based on a four-sublattice model, a description of the antiferromagnetic resonance (AFMR) spectrum up to frequencies of 1.5 THz and magnetic fields up to 50 T indicates that the interchain coupling is indeed quite small but that the Dzaloshinskii-Moriya interaction produced by broken inversion symmetry is substantial (0.12 meV). In addition, the antiferromagnetic, nearest-neighbor interaction within each chain (3.3 meV) is significantly stronger than previously reported. The excitation spectrum of this $S=2$ compound is well described by a $1/S$ expansion about the classical limit.

We study electron and spin transport in interacting quantum wires contacted by noninteracting leads. We theoretically model the wire and junctions as an inhomogeneous chain where the parameters at the junction change on the scale of the lattice spacing. We study such systems analytically in the appropriate limits based on Luttinger liquid theory and compare the results to quantum Monte Carlo calculations of the conductances and local densities near the junction. We first consider an inhomogeneous spinless fermion model with a nearest-neighbor interaction and then generalize our results to a spinful model with an on-site Hubbard interaction.

We study a system of microcavity pillars arranged into a kagome lattice. We show that polarization-dependent tunnel coupling of microcavity pillars leads to the emergence of the effective spin-orbit interaction consisting of the Dresselhaus and Rashba terms, similar to the case of polaritonic graphene studied earlier. The appearance of the effective spin-orbit interaction combined with the time-reversal symmetry breaking resulting from the application of the magnetic field leads to the nontrivial topological properties of the Bloch bundles of polaritonic wave function. These are manifested in the opening of the gap in the band structure and topological edge states localized on the boundary. Such states are analogs of the edge states arising in topological insulators. Our study of polarization properties of the edge states clearly demonstrates that opening of the gap is associated with the band inversion in the region of the Dirac points of the Brillouin zone where the two bands corresponding to polaritons of opposite polarizations meet. For one particular type of boundary we observe a highly nonlinear energy dispersion of the edge state which makes a polaritonic kagome lattice a promising system for observation of edge state solitons.

This Rapid Communication presents a structure and full theoretical analysis to exploit the photon drag effect for THz signal generation in a graphene layer integrated with a plasmonic structure. The plasmonic structure is composed of a periodic array of asymmetric nanoparticles patterned over a graphene layer. The nanoparticles are designed to accomplish two goals: field localization due to the plasmonic resonance and manipulating the phase of the near field to effectively drag the quasiparticles in graphene. Combining the asymmetry with the plasmon resonances of nanoparticles, we show that an enhancement as large as three orders of magnitude is attainable in the power of the generated THz wave. This level of unprecedented enhancement mostly stems from the phase manipulation of the near field caused by asymmetric nanoparticles. Using the achieved enhancement, it is demonstrated that an ultra-wideband THz signal carrying the power of $1\mu \mathrm{W}$ can be generated using a commercially available femtosecond pulsed laser.

To examine the effect of $k_{\perp }$ broadening on angle-resolved photoemission spectroscopy (ARPES) spectra, in situ ARPES using the variable polarization of synchrotron light has been performed for the (110) and (001) surfaces of ${\mathrm{SrVO}}_3$ films. Using the polarization dependence for the band structures of the V $3d{t}_{2g}$ states, we have separately observed the $d_{xy}$-derived states and the $d_{yz}/d_{zx}$ ones for the (110) surface. It is found that ARPES images for the $d_{yz}/d_{zx}$ states are considerably broader than those for the $d_{xy}$ states. Meanwhile, such a broadening is not observed in the identical $d_{yz}/d_{zx}$-derived band dispersion along the crystallographically equivalent direction on the (001) surface, indicating that the broadening of the ARPES image originates from the absence or presence of mirror symmetry in the respective states with respect to the ARPES-measurement planes. The observed spectroscopic behavior is well reproduced by the simulation where the $k_{\perp }$ broadening in the photoelectron emission process is taken into account. These results indicate that the consideration of the mirror symmetry of the band structures with respect to the ARPES-measurement plane is important for analyzing the ARPES-spectral line shape in the case that the $k_{\perp }$-broadening effect is dominant in ARPES spectra.

The analytic continuation of imaginary-time quantum Monte Carlo data to extract real-frequency spectra remains a key problem in connecting theory with experiment. Here we present a fast and efficient stochastic optimization method (FESOM) as a more accessible variant of the stochastic optimization method introduced by Mishchenko et al. [Phys. Rev. B 62, 6317 (2000)], and we benchmark the resulting spectra with those obtained by the standard maximum entropy method for three representative test cases, including data taken from studies of the two-dimensional Hubbard model. We generally find that our FESOM approach yields spectra similar to the maximum entropy results. In particular, while the maximum entropy method yields superior results when the quality of the data is strong, we find that FESOM is able to resolve fine structure with more detail when the quality of the data is poor. In addition, because of its stochastic nature, the method provides detailed information on the frequency-dependent uncertainty of the resulting spectra, while the maximum entropy method does so only for the spectral weight integrated over a finite frequency region. We therefore believe that this variant of the stochastic optimization approach provides a viable alternative to the routinely used maximum entropy method, especially for data of poor quality.

We present the possibility to engineer Fano resonances using multilayered hyperbolic metamaterials. The proposed cavity designs are composed of multilayers with a central slanted part. The highly tunable resonances originate from the interference between a propagating and an evanescent mode inside the slanted section. The propagating mode can reach an extremely high effective index, making the realization of deeply subwavelength cavities possible, as small as 5 nm. The evanescent mode is rarely analyzed but plays an important role here, as its contribution determines the particular shape of the cavity characteristic. Moreover, these phenomena cannot be described using effective medium theory, and we provide a more rigorous analysis. The reported resonances are very sensitive to any structural changes and could be used for sensing applications.