We respond to the Comment by Errandonea et al. [Phys. Rev. B 92, 026101 (2015)] on their reinterpretation of our published data [Nguyen et al., Phys. Rev. B 89, 174109 (2014)]. In the original paper, we argued that there is no solid-solid phase transition along the Hugoniot at 2.1 Mbars. There is, however, a softening of the shear modulus starting at 2.6 Mbars. Errandonea et al. [Phys. Rev. B 92, 026101 (2015)] reinterpreted our data and concluded that there is a structural change near 2.3 Mbars on the Hugoniot. We will explore the differences and agreements in the two interpretations of our data.

Modern extensions of density functional theory such as the density functional theory plus U and the density functional theory plus dynamical mean field theory require choices, including selection of variable (charge vs spin density) for the density functional and specification of the correlated subspace. This paper examines these issues in the context of the “plus U” extensions of density functional theory, in which additional correlations on specified correlated orbitals are treated using a Hartree-Fock approximation. Differences between using charge-only or spin-density-dependent exchange-correlation functionals and between Wannier and projector-based definitions of the correlated orbitals are considered on the formal level and in the context of the structural energetics of the rare-earth nickelates. It is demonstrated that theories based on spin-dependent exchange-correlation functionals can lead to large and in some cases unphysical effective on-site exchange couplings. Wannier and projector-based definitions of the correlated orbitals lead to similar behavior near ambient pressure, but substantial differences are observed at large pressures. Implications for other beyond density functional methods such as the combination of density functional and dynamical mean field theory are discussed.

Tailoring the properties of correlated oxides is accomplished by chemical doping, pressure, temperature, or magnetic field. Photoexcitation is a valid alternative to reach out-of-equilibrium states otherwise inaccessible. Here, we quantitatively estimate the coupling between a lattice distortion and the charge-transfer excitation in ${\mathrm{La}}_2{\mathrm{CuO}}_{4+\delta }$. We photoinduce a coherent La ion vibration and monitor the response of the optical constants in a broad energy range, providing quantitative information on the electron-phonon matrix element that can be compared to theoretical models. We propose the same methodology to probe electron-phonon and electron-electron interactions in other materials.

We propose the possible detection of broken mirror symmetries in correlated two-dimensional materials by elastotransport measurements. Using linear response theory we calculate the“shear conductivity” ${\mathrm{\Gamma }}_{xx,xy}$, defined as the linear change of the longitudinal conductivity ${\sigma }_{xx}$ due to a shear strain ${\epsilon }_{xy}$. This quantity can only be nonvanishing when in-plane mirror symmetries are broken and we discuss how candidate states in the cuprate pseudogap regime (e.g., various loop current or charge orders) may exhibit a finite shear conductivity. We also provide a realistic experimental protocol for detecting such a response.

We study luminescence spectra observed from InAs quantum dots (QDs) embedded in an $n$-type InGaAs-based heterostructure, where electron Cooper pairs penetrate from an adjacent niobium (Nb) superconductor with the proximity effect. Below the superconducting (SC) critical temperature of Nb, we observe substantial luminescence intensity enhancement and a sharp edge in luminescence spectra of InAs QDs. We explain the observed sharp edge in the luminescence spectra with the proximity effect, that is, with the consideration of opening of SC gap and modification of density of states (DOS) near the electron Fermi level in the $n$-type semiconductor heterostructure. We demonstrate that the sharp edge luminescence spectra are well reproduced by the SC DOS, with quasiparticle lifetime broadening and a Gaussian distribution of lowest QD state emission lines. We discuss the reason why it has been difficult to observe the sharp edge luminescence spectra in the previous quantum well-based SC light emitting diodes.

Surface conductance measurements on $p$-type doped germanium show a small but systematic change to the surface conductivity at different length scales. This effect is independent of the structure of the surface states. We interpret this phenomenon as a manifestation of conductivity changes beneath the surface. This hypothesis is confirmed by an analysis of the classical current flow equation. We derive an integral formula for calculating the effective surface conductivity as a function of the distance from a point source. Furthermore, we derive asymptotic values of the surface conductivity at small and large distances. The actual surface conductivity can only be sampled close to the current source. At large distances, the conductivity measured on the surface corresponds to the bulk value.

Using first principles calculations we describe the energy band structure of bulk ${\mathrm{CuInS}}_2$. The energy band parameters for the multiband effective mass approximation that describes the band edges of this semiconductor are obtained by fitting them to the first principles spectra. Within the multiband effective mass approximation we develop a theoretical description for the structure of band-edge levels and optical properties of the ${\mathrm{CuInS}}_2$ nanocrystals. For the nanocrystals of spherical shape, the optical transitions are weakly allowed between the electron and hole ground states due to the tetragonal symmetry of the crystal lattice, resulting in a large Stokes shift of photoluminescence up to 300 meV in the smallest nanocrystals. This theory of the band-edge optical transitions in ${\mathrm{CuInS}}_2$ NCs can be applied to spherical NCs made of other chalcopyrite compounds.

We investigate the optical properties of high-quality Si nanocrystals $\left(\mathrm{NCs}\right)/\mathrm{Si}{\mathrm{O}}_2$ multilayers under high hydrostatic pressure with Raman scattering and photoluminescence (PL) measurements. The aim of our study is to shed light on the origin of the optical emission of the Si $\mathrm{NCs}/\mathrm{Si}{\mathrm{O}}_2$. The Si NCs were produced by chemical-vapor deposition of Si-rich oxynitride $\left(\mathrm{SRON}\right)/\mathrm{Si}{\mathrm{O}}_2$ multilayers with 5- and 4-nm SRON layer thicknesses on fused silica substrates and subsequent annealing at 1150 °C, which resulted in the precipitation of Si NCs with an average size of 4.1 and 3.3 nm, respectively. From the pressure dependence of the Raman spectra we extract a phonon pressure coefficient of $8.5\pm 0.3\mathrm{c}{\mathrm{m}}^{-1}/\mathrm{GPa}$ in both samples, notably higher than that of bulk $\mathrm{Si}(5.1\mathrm{c}{\mathrm{m}}^{-1}/\mathrm{GPa})$. This result is ascribed to a strong pressure amplification effect due to the larger compressibility of the $\mathrm{Si}{\mathrm{O}}_2$ matrix. In turn, the PL spectra exhibit two markedly different contributions: a higher-energy band that redshifts with pressure, and a lower-energy band which barely depends on pressure and which can be attributed to defect-related emission. The pressure coefficients of the higher-energy contribution are $(-27\pm 6)$ and $(-35\pm 8)\mathrm{meV}/\mathrm{GPa}$ for the Si NCs with a size of 4.1 and 3.3 nm, respectively. These values are sizably higher than those of bulk $\mathrm{Si}(-14\mathrm{meV}/\mathrm{GPa})$. When the pressure amplification effect observed by Raman scattering is incorporated into the analysis of the PL spectra, it can be concluded that the pressure behavior of the high-energy PL band is consistent with that of the indirect transition of Si and, therefore, with the quantum-confined model for the emission of the Si NCs.

We investigate the optical response of a system consisting of periodic silver V-shaped grooves interacting with quantum emitters. Two surface plasmon-polariton resonances are identified in the reflection spectrum of bare silver grooves, with the intensity of one resonance being localized near the bottom of the groove and that of the other resonance being distributed throughout the entire groove. The linear response of the hybrid silver-emitter system is thoroughly analyzed by considering the coupling between surface plasmon polaritons and emitters as the geometry of the grooves and the spatial distribution of emitters within the grooves are varied. The nonlinear response of the system is also considered by pumping the emitters with a short, high-intensity pulse. By changing the duration or the intensity of the pump, the population of emitters in the ground state at the end of the pump is varied, and it is found (upon probing with a short pulse) that an increase in the fraction of emitters in the ground state corresponds to an increase in Rabi splitting. Spatial variations in the ground-state population throughout the emitter region are shown to be a result of field retardation.

The novel pseudogap state has been systematically studied on flat-top In, Al, and Pb islands/films grown on $\mathrm{Si}\left(111\right)$ surfaces with scanning tunneling microscopy. Our observations and analysis suggest that the interplay between electron-phonon interaction and quantum confinement, the dynamic Coulomb blockade, and the orthodox Coulomb blockade are, respectively, the dominant mechanism of the formation of such pseudogap states in the flat-top metal islands at different island size scales. Our results can help to settle the dispute on the origins of the pseudogap state in such systems.

In this paper, we present full-band atomistic quantum transport simulations of single- and few-layer ${\mathrm{MoS}}_2$ field-effect transistors (FETs) including electron-phonon scattering. The Hamiltonian and the electron-phonon coupling constants are determined from ab initio density-functional-theory calculations. It is observed that the phonon-limited electron mobility is enhanced with increasing layer thicknesses and decreases at high charge concentrations. The electrostatic control is found to be crucial even for a single-layer ${\mathrm{MoS}}_2$ device. With a single-gate configuration, the double-layer ${\mathrm{MoS}}_2$ FET shows the best intrinsic performance with an ON current, $I_{\text{ON}}=685\mu \mathrm{A}/\mu \mathrm{m}$, but with a double-gate contact the transistor with a triple-layer channel delivers the highest current with $I_{\text{ON}}=1850\mu \mathrm{A}/\mu \mathrm{m}$. The charge in the channel is almost independent of the number of ${\mathrm{MoS}}_2$ layers, but the injection velocity increases significantly with the channel thickness in the double-gate devices due to the reduced electron-phonon scattering rates in multilayer structures. We demonstrate further that the ballistic limit of transport is not suitable for the simulation of ${MX}_2$ FETs because of the artificial negative differential resistance it predicts.

We propose the use of an approximate bootstrap exchange-correlation kernel to account for vertex corrections in self-consistent $GW$ calculations. We show that the approximate kernel gives accurate band gaps for a variety of extended systems, including simple $sp$ semiconductors, wide band-gap insulators, and transition-metal compounds with either closed or open $d$ shells. The accuracy is comparable with that obtained via the solution of the Bethe-Salpeter equation but only at a fraction of the computational cost.

A well-known universal feature among iron pnictide superconductors is the correlation between the As-Fe-As bonding angle and the superconducting transition temperature. However, the origin of such a correlation has not been clearly understood despite its potential importance in understanding the mechanism of superconductivity. Here, we present comparative electronic structure studies of LiFeAs and ${\mathrm{Sr}}_2{\mathrm{VO}}_3\mathrm{FeAs}$, two representative systems without any dopant that can show bonding angle dependence of the electronic structure. Captured distinct features of the higher $T_c$ compound ${\mathrm{Sr}}_2{\mathrm{VO}}_3\mathrm{FeAs}$ such as an unusual $k_z$ modulation and anomalous polarization dependence suggest that the difference between the two systems is in the interorbital coupling strength. This could be the essential element of the bonding angle dependence that allows an enhanced pairing instability and $T_c$.

We present a theory of autolocalization as a mechanism of formation of the macroscopically ordered exciton state (MOES) in semiconductor quantum wells. We show that the onset of a crystalline order having a macroscopic spatial period is possible in the systems where, in addition to long-range dipolar repulsion, the excitons exhibit resonant pairing at short distances. Our theory suggests that the central part of each condensate in the MOES may represent the long-sought bosonic analog of the Bardeen-Cooper-Schrieffer (BCS) superconductor.

The critical effect of disorder on the two-dimensional (2D) surface superconductor $\mathrm{Si}\left(111\right)-(\sqrt{7}\times \sqrt{3})$-In is clarified by comparing two regions with different degrees of disorder. Low-temperature scanning tunneling microscopy measurements reveal that superconductivity is retained in the less disordered region, judging from the characteristic differential conductance $(dI/dV)$ spectra and from the formation of vortices under magnetic fields. In striking contrast, the absence of those features in the highly disordered region shows that superconductivity is strongly suppressed there. Analysis of observed zero-bias anomalies in $dI/dV$ spectra allows us to estimate the reduction in the transition temperature $T_{\mathrm{c}}$, which explains the fate of superconductivity in each region.

We investigate the quasiparticle interference (QPI) in Fe-based superconductors in both the $s_{++}$-wave and $s_{\pm }$-wave superconducting states on the basis of the five-orbital model. In the octet model for cuprate superconductors with $d_{x^2-y^2}$-wave state, the QPI signal due to the impurity scattering at $\mathit{q}={\mathit{k}}_i-{\mathit{k}}_j$ ($E=\left|\mathrm{\Delta }\right({\mathit{k}}_i\left)\right|, i=1-8$) disappears when the gap functions at ${\mathit{k}}_i$ and ${\mathit{k}}_j$ have the same sign. However, we show that this extinction rule does not hold in Fe-based superconductors with fully gapped $s$-wave state. The reason is that the resonance condition $E=\left|\mathrm{\Delta }\right({\mathit{k}}_i\left)\right|$ is not satisfied under the experimental condition for Fe-based superconductors. We perform the detailed numerical study of the QPI signal using the $T$-matrix approximation, and show that the experimentally observed QPI peak around ${\mathit{q}}_2=(\pi ,0)$ can be explained on the basis of both the $s_{++}$-wave and $s_{\pm }$-wave states. Furthermore, we discuss the magnetic field dependence of the QPI by considering the Zeeman effect, and find that the field-induced suppression of the peak intensity around ${\mathit{q}}_2$ can also be explained in terms of both the $s_{++}$-wave and $s_{\pm }$-wave states.

We show that a thermoelectric transport through a quantum dot–single-mode quantum point contact nanodevice demonstrating pronounced fingerprints of nonFermi liquid (NFL) behavior in the absence of external magnetic field is protected from magnetic field NFL destruction by strong spin-orbit interaction (SOI). The mechanism of protection is associated with the appearance of additional scattering processes due to lack of spin conservation in the presence of both SOI and small Zeeman field. The interplay between in-plane magnetic field $\vec{B}$ and SOI is controlled by the angle between $\vec{B}$ and ${\vec{B}}_{\mathrm{SOI}}$. We predict strong dependence of the thermoelectric coefficients on the orientation of the magnetic field and discuss a window of parameters for experimental observation of NFL effects.

A comprehensive experimental investigation of exciton and biexciton recombination in GaAs/AlGaAs quantum wells is presented. Exciton and biexciton recombination times are found to be 16 and 55 ps, respectively. A method of determining the dynamics of the exciton temperature is developed. It is shown that both exciton and biexciton recombination processes increase the exciton temperature by an amount as high as $\sim 10$ K. These processes impose a new restriction on the possibility of exciton Bose-Einstein condensation and make impossible its achievement in a system of direct excitons in GaAs quantum wells even for resonantly excited exciton gas.

We consider an adiabatic Landau-Zener model of a two-level system diagonally coupled to an Ohmic bosonic bath of large spectral width and, through fermionization, derive its exact solution at a special value of the coupling constant. From this solution we obtain the characteristic function of the distribution of energy transferred to the bath during the evolution of the system ground state as a functional determinant of a single-particle operator. At zero temperature this distribution is further found to be exponential, and at finite temperature the first three moments of the distribution are calculated.

We investigate the optical properties of ultrathin film of a topological insulator in the presence of an in-plane magnetic field. We show that due to the combination of the overlap between the surface states of the two layers and the magnetic field, the optical conductivity can show strong anisotropy. This leads to the effective optical activity of the ultrathin film by influencing the circularly polarized incident light. Intriguingly, for a range of magnetic fields, the reflected and transmitted lights exhibit elliptic character. Even for certain values almost linear polarizations are obtained, indicating that the thin film can act as a polaroid in reflection. All these features are discussed in the context of the time-reversal symmetry breaking as one of the key ingredients for the optical activity.