Including on-site electronic interactions described by the multiorbital Hubbard model we study the correlation effects in the electronic structure of bulk palladium. We use a combined density functional and dynamical mean-field theory, LDA+DMFT, based on the fluctuation exchange approximation. The agreement between the experimentally determined and the theoretical lattice constant and bulk modulus is improved when correlation effects are included. It is found that correlations modify the Fermi surface around the neck at the $L$ point while the Fermi surface tube structures show little correlation effects. At the same time we discuss the possibility of satellite formation in the high-energy binding region. Spectral functions obtained within the LDA+DMFT and $\mathit{GW}$ methods are compared to discuss nonlocal correlation effects. For relatively weak local Coulomb interaction and Hund's exchange coupling the LDA+DMFT spectra show no major difference in comparison to $\mathit{GW}$.

We study the excitation spectrum of a family of transverse-field spin chain models with variable interaction range and arbitrary spin $S$, which in the case of $S=1/2$ interpolates between the Lipkin-Meshkov-Glick and the Ising model. For any finite number $N$ of spins, a semiclassical energy manifold is derived in the large-$S$ limit employing bosonization methods, and its geometry is shown to determine not only the leading-order term but also the higher-order quantum fluctuations. Based on a multiconfigurational mean-field ansatz, we obtain the semiclassical backbone of the quantum spectrum through the extremal points of a series of one-dimensional energy landscapes—each one exhibiting a bifurcation when the external magnetic field drops below a threshold value. The obtained spectra become exact in the limit of vanishing or very strong external, transverse magnetic fields. Further analysis of the higher-order corrections in $1/\sqrt{2S}$ enables us to analytically study the dispersion relations of spin-wave excitations around the semiclassical energy levels. Within the same model, we are able to investigate quantum bifurcations, which occur in the semiclassical $\left(S\gg 1\right)$ limit, and quantum phase transitions, which are observed in the thermodynamic $\left(N\to \infty \right)$ limit.

Semiconductor quantum dot (QD) structures can be used as a model for understanding the effect of the microscopic structure, symmetry of crystals, and molecules on their macroscopic properties. In this work, the results of two theoretical approaches demonstrate that the spin dynamics in ordered QD structures depends on the size, spatial configuration, and topology of the object built of QDs. It was shown that the spin dynamics in QD structures with the hopping regime of conductivity significantly differs from the spin dynamics in two-dimensional (2D) and three-dimensional (3D) structures being at the other side of the metal-insulator transition. The special character of the effective magnetic field $\delta \mathbf{H}$ fluctuations appearing only during tunneling between quantum dots is responsible for the insensitivity of spin relaxation times to the magnitude of the external magnetic field in infinite QD structures (2D square lattice and 1D linear QD chain). In finite QD structures (QD rings and linear chains), an external magnetic field ${\mathbf{H}}_0$ is directly involved in the spin relaxation process and spin is lost due to interaction with a special combination of fields $\mathrm{\Delta }\mathbf{H}\sim [{\mathbf{H}}_{\mathbf{0}}\times \delta \mathbf{H}]/\delta H$ that leads to an unusual orientation dependence of ESR linewidth, recently observed for QD chains. It was shown that the ordering of QD structures can be used for the conservation of spin orientation. For 1D finite quantum dot chains, the ordering can provide the stabilization of all spin components $S_x,S_y$, and $S_z$, while for ringlike molecules only $S_z$ polarization can be stabilized. The results obtained in this work can be useful for development of novel semiconductor devices and in quantum information processing.

We employ time-resolved photoluminescence combined with scanning electron microscopy and modeling to evaluate the lifetimes of excitons and free carriers in core-shell $\mathrm{ZnTe}-{\mathrm{Zn}}_{1-x}{\mathrm{Mg}}_x\mathrm{Te}$ nanowires. We find that electron tunneling through the shell to the surface controls the decay dynamics. The photoluminescence of single nanowires reveals contributions from an electron-hole plasma. The analysis of its temporal behavior allows one to extract the carrier and exciton lifetimes and monitor the cooling dynamics. In particular, we demonstrate that most of the electrons tunnel out before they cool down or bind into excitons. A semiclassical model allows us to extract the contributions of tunneling and recombination to the photoluminescence decay. We find that the recombination time shortens with increasing temperature as a result of an activation of a phonon-assisted nonradiative process.

$\mathrm{Mo}{X}_2(X=\mathrm{S} \text{or Se})$ is a semiconductor family with two-dimensional structure. And a recent calculation predicted the superconductivity in the electron-doped ${\mathrm{MoS}}_2$ monolayer. In this work, the electronic structure and lattice dynamics of $\mathrm{Mo}{X}_2$ bilayers with monolayer Na intercalated have been calculated. According to the electron-phonon interaction, it is predicted that these bilayers can be transformed from indirect-gap semiconductors to superconductors by Na intercalation. More interestingly, the biaxial tensile strain can significantly enhance the superconducting temperature up to $\sim 10$ K in Na-intercalated ${\mathrm{MoS}}_2$. In addition, the phonon mean free path at room temperature is also greatly improved in Na-intercalated ${\mathrm{MoSe}}_2$, which is advantageous for related applications.

With an example of the periodic plasmonic dolmen structure we performed a theoretical study of the effect of the conducting water layer on the plasmon resonances of the system with narrow gaps. Using the scanning tunneling microscopy studies of the conductance of the water junctions as inputs, we show that water layer(s) should affect plasmon modes of the systems with nm and sub nm gaps in two ways. The frequency of the plasmon modes shifts because of the dielectric screening, as commonly used in plasmonic sensors, and the corresponding resonance in the optical spectra looses intensity and broadens because of the resistive tunneling current. The water layer in the junction lowers potential barrier for electron tunneling, so that quantum effects in plasmon response appear for the junction width at least twice larger as compared to the vacuum gaps.

Organic-inorganic halide ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbI}}_3$ solar cells have attracted enormous attention in recent years due to their remarkable power conversion efficiency. When inversion symmetry is broken, these materials should exhibit interesting spin-dependent properties as well, owing to their strong spin-orbit coupling. In this work, we consider the spin-dependent optical response of ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbI}}_3$. We first use density functional theory to compute the ballistic spin current generated by absorption of unpolarized light. We then consider diffusive transport of photogenerated charge and spin for a thin ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbI}}_3$ layer with a passivated surface and an Ohmic, nonselective contact. The spin density and spin current are evaluated by solving the drift-diffusion equations for a simplified three-dimensional Rashba model of the electronic structure of the valence and conduction bands. We provide analytic expressions for the photon flux required to induce measurable spin densities, and propose that these spin densities can provide useful information about the role of grain boundaries in the photovoltaic behavior of these materials. We also discuss the prospects for measuring the optically generated spin current with the inverse spin Hall effect.

In the Comment by Söderlind et al. [Phys. Rev. B 90, 157101 (2014)], the authors argue that (1) density functional theory (DFT), especially with all-electron methods, already models U metal and U-Zr alloy accurately; and (2) $\mathrm{DFT}+U$ results calculated at $U_{\mathrm{eff}}=1.24$ for volume, enthalpy, and magnetic moments that they select from our study [Phys. Rev. B 88, 235128 (2013)] suggest adding the Hubbard $U$ potential in $\mathrm{DFT}+U$ reduces accuracy compared to DFT. With respect to argument (1) by Söderlind et al., we argue that previously neglected and very recent experimental data suggest that DFT in Söderlind's full-potential linear muffin-tin orbital calculations [Phys. Rev. B 66, 085113 (2002)] still models the bulk modulus and elastic constants of αU with errors considerably larger than other related elements, e.g., most transition metals. In addition, we demonstrate that the assertion by Söderlind et al. that our DFT results are not satisfactory because deficiency exists in our projector augmented wave calculation is unfounded. With respect to argument (2) by Söderlind et al., we argue that they have inappropriately focused on just one phase [the bcc phase γ(U,Zr)], neglecting the other phases which represent the majority of our evidence; made overgeneralizations based on results at only one $U_{\mathrm{eff}}$ value of 1.24 eV; and supported their argument with inaccurate assertions that $\mathrm{DFT}+U$ predicts for γ(U,Zr) an unprecedentedly large positive volume of mixing and an enthalpy of mixing that is inconsistent with the experimental miscibility gap. We therefore hold to our original conclusion that the accuracy of DFT for modeling U and U-Zr has room for improvement and $\mathrm{DFT}+U$ is a good candidate.

${\mathrm{LiOsO}}_3$ has been recently identified as the first unambiguous “ferroelectric metal,” experimentally realizing a prediction by Anderson and Blount [Phys. Rev. Lett. 14, 217 (1965)]. In this Rapid Communication, we investigate the metallic state in ${\mathrm{LiOsO}}_3$ by means of infrared spectroscopy supplemented by density functional theory and dynamical mean-field theory calculations. Our measurements and theoretical calculations clearly show that ${\mathrm{LiOsO}}_3$ is a very bad metal with a small quasiparticle weight, close to a Mott-Hubbard localization transition. The agreement between experiments and theory allows us to ascribe all the relevant features in the optical conductivity to strong electron-electron correlations within the $t_{2g}$ manifold of the osmium atoms.

We present electrically detected electron nuclear double resonance measurements of the nuclear spins of ionized and neutral arsenic donors in strained silicon. In addition to a reduction of the hyperfine coupling, we find significant quadrupole interactions of the nuclear spin of the neutral donors of the order of 10 kHz. By comparing these to the quadrupole shifts due to crystal fields measured for the ionized donors, we identify the effect of the additional electron on the electric field gradient at the nucleus. This extra component is expected to be caused by the coupling to electric field gradients created due to changes in the electron wave function under strain.

We consider an infrared photodiode under negative illumination, wherein the photodiode is maintained at a temperature $T$ and radiatively exposed to an emissive body colder than itself. We experimentally demonstrate that a diode under such conditions can generate electrical power. We show theoretically that the efficiency of energy conversion can approach the Carnot limit. This work is applicable to waste heat recovery as well as emerging efforts to utilize the cold dark universe as a thermodynamic resource for renewable energy.

We present a finite-temperature diagrammatic perturbation theory of third-harmonic generation in doped graphene. We carry out calculations of the third-order conductivity in the scalar potential gauge, highlighting a subtle cancellation between a Fermi surface contribution, which contains only power laws, and power-law contributions of interband nature. Only logarithms survive in the final result. We conclude by presenting quantitative results for the upconversion efficiency at zero and finite temperature. Our approach can be easily generalized to other materials and to include many-body effects.

Recent experimental studies have demonstrated the possibility of information storage in short antiferromagnetic chains on an insulator substrate [S. Loth et al., Science 335, 196 (2012)]. Here, using the density functional theory and atomistic spin dynamics simulations, we show that a local magnetic control of such chains with a magnetic tip and magnetic pulses can be used for fast switching of their magnetization. Furthermore, by changing the position of the tip one can engineer the magnetization dynamics of the chains.

The potential of resonant inelastic soft x-ray scattering to measure $4f$ crystal electric-field excitation spectra in Ce Kondo lattices has been examined. Spectra have been obtained for several Ce systems and show a well-defined structure determined by crystal-field, spin-orbit, and charge-transfer excitations only. The spectral shapes of the excitation spectra can be well understood in the framework of atomic multiplet calculations. For ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$ we found notable disagreement between the inelastic x-ray-scattering spectra and theoretical calculations when using the crystal-field scheme proposed from inelastic neutron scattering. Modified sets of crystal-field parameters yield better agreement. Our results also show that, with the very recent improvements of soft x-ray spectrometers in resolution to below 30 meV at the Ce $M_{4,5}$ edges, resonant inelastic x-ray scattering could be an ideal tool to determine the crystal-field scheme in Ce Kondo lattices and other rare-earth compounds.

Different from the spin-1 Haldane gapped phase, we propose an SO(3) spin-1 matrix product state (MPS), whose parent Hamiltonian includes three-site spin interactions. From the entanglement spectrum of a single block with $l$ sites, an enlarged SU(3) symmetry is identified in the edge states, which are conjugate to each other for the $l=\text{even}$ block but identical for the $l=\text{odd}$ block. By blocking this state, the blocked MPS explicitly displays the SU(3) symmetry with two distinct structures. Under a symmetric bulk bipartition with a sufficient large block length $l=\text{even}$, the entanglement Hamiltonian (EH) of the reduced system characterizes a spontaneous dimerized phase with twofold degeneracy. However, for the block length $l=\text{odd}$, the corresponding EH represents an SU(3) quantum critical point with delocalized edge quasiparticles, and the critical field theory is described by the SU(3) level-1 Wess-Zumino-Witten conformal field theory.

Hexagonal $\mathrm{BaIr}{\mathrm{O}}_3$ is a magnetic insulator driven by the spin-orbit interaction (SOI), whereas $\mathrm{BaRu}{\mathrm{O}}_3$ is an enhanced paramagnetic metal. Our investigation of structural, magnetic, transport, and thermal properties reveals that substitution of $\mathrm{R}{\mathrm{u}}^{4+} \left(4d^4\right)$ ions for $\mathrm{I}{\mathrm{r}}^{4+} \left(5d^5\right)$ ions in $\mathrm{BaIr}{\mathrm{O}}_3$ reduces the magnitudes of the SOI and a monoclinic structural distortion and rebalances the competition between the SOI and the lattice degrees of freedom to render an evolution from a magnetic insulting state to a robust metallic state. The central findings of this paper are as follows: (1) light Ru doping $\left(0<x\le 0.15\right)$ prompts simultaneous, precipitous drops in both the magnetic ordering temperature $T_{\mathrm{N}}$ and the electrical resistivity, and (2) heavier Ru doping $\left(0.41\le x\le 0.9\right)$ induces a robust metallic state without any long-range magnetic order. All results suggest a critical role of the lattice degrees of freedom in determining the ground state in the heavy transition-metal oxides.

We propose a tunable electronic band gap and zero-energy modes in periodic heterosubstrate-induced graphene superlattices. Interestingly, there is an approximate linear relation between the band gap and the proportion of an inhomogeneous substrate (i.e., percentages of different components) in the proposed superlattice, and the effect of structural disorder on the relation is discussed. In an inhomogeneous substrate with equal widths, zero-energy states emerge in the form of Dirac points by using asymmetric potentials, and the positions of Dirac points are addressed analytically. Further, the Dirac point exists at $\mathbf{k}=\mathbf{0}$ only for specific potentials; every time it appears, the group velocity vanishes in the $k_y$ direction, and the resonance occurs. For general cases of an inhomogeneous substrate with unequal widths, part of the zero-energy states are described analytically, and differently, they are not always Dirac points. Our prediction may be realized on a heterosubstrate such as ${\mathrm{SiO}}_2/\mathrm{BN}$.

Evolution of the average and local crystal structure of Ca-doped ${\mathrm{LaMnO}}_3$ has been studied across the metal to insulator (MI) and the orthorhombic to rhombohedral (OR) structural phase transitions over a broad temperature range for two Ca concentrations $\left(x=0.18,0.22\right)$. Combined Rietveld and high real space resolution atomic pair distribution function (PDF) analysis of neutron total scattering data was carried out with aims of exploring the possibility of nanoscale phase separation (PS) in relation to MI transition, and charting the evolution of local Jahn-Teller (JT) distortion of ${\mathrm{MnO}}_6$ octahedra across the OR transition at $T_S\sim 720$ K. The study utilized explicit two-phase PDF structural modeling, revealing that away from $T_{\text{MI}}$ there is no evidence for nanoscale phase coexistence. The local JT distortions disappear abruptly upon crossing into the metallic regime both with doping and temperature, with only a small temperature-independent signature of quenched disorder being observable at low temperature as compared to ${\mathrm{CaMnO}}_3$. The results hence do not support the percolative scenario for the MI transition in ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ based on PS, and question its ubiquity in the manganites. In contrast to ${\mathrm{LaMnO}}_3$ that exhibits long-range orbital correlations and sizable octahedral distortions at low temperature, the doped samples with compositions straddling the MI boundary exhibit correlations (in the insulating regime) limited to only $\sim 1$ nm with observably smaller distortions. In the $x=0.22$ sample local JT distortions are found to persist across the OR transition and deep into the $R$ phase (up to $\sim 1050$ K), where they are crystallographically prohibited. Their magnitude and subnanometer spatial extent remain unchanged.

Insulating quantum spin liquids can undergo a confinement transition to a valence bond solid via the condensation of topological excitations of the associated gauge theory. We extend the theory of such transitions to fractionalized Fermi liquids (FL*): These are metallic doped spin liquids in which the Fermi surfaces only have gauge neutral quasiparticles. Using insights from a duality transform on a doped quantum dimer model for the U(1)-FL* state, we show that projective symmetry group of the theory of the topological excitations remains unmodified, but the Fermi surfaces can lead to additional frustrating interactions. We propose a theory for the confinement transition of ${\mathbb{Z}}_2$-FL* states via the condensation of visons. A variety of confining, incommensurate density wave states are possible, including some that are similar to the incommensurate $d$-form factor density wave order observed in several recent experiments on the cuprate superconductors.

Using hybrid density functional theory, we address point defects susceptible to cause charge compensation upon Mg doping of GaN. We determine the free energy of formation of the nitrogen vacancy and of several Mg-related defects. The entropic contribution as a function of temperature is determined within the quasiharmonic approximation. We find that the Mg interstitial shows a noticeably lower free energy of formation than the Mg substitutional to Ga in $p$-type conditions. Therefore, the Mg impurity is amphoteric behaving like an acceptor when substitutional to Ga and like a double donor when accommodated in an interstitial position. The hybrid-functional results are then linked to experimental observations by solving the charge neutrality equations for semiconductor dominated by impurities. We show that a thermodynamic equilibrium model is unable to account for the experimental hole concentration as a function of Mg doping density, due to nitrogen vacancies and Mg interstitials acting as compensating donors. To explain the experimental result, which includes a dropoff of the hole concentration at high Mg densities, we thus resort to nonequilibrium models. We show that either nitrogen vacancies or Mg interstitials could be at the origin of the self-compensation mechanism. However, only the model based on interstitial Mg donors provides a natural mechanism to account for the sudden appearance of self-compensation. Indeed, the amphoteric nature of the Mg impurity leads to Fermi-level pinning and accounts for the observed dropoff of the hole concentration of GaN samples at high Mg doping. Our work suggests that current limitations in $p$-type doping of GaN could be overcome by extrinsically controlling the Fermi energy during growth.