In this paper, the exact transient quantum transport in noninteracting nanostructures is investigated in the presence of initial correlations for a device system coupled to general electronic leads. The exact master equation incorporating initial system-lead correlations is derived through the extended quantum Langevin equation. The effects of the initial correlations are manifested in terms of the time-dependent fluctuations contained explicitly in the exact master equation. The transient electron transport incorporating initial correlations is obtained from the exact master equation. The resulting electron transport current can be expressed in terms of the single-particle propagation and correlation Green functions of the device system. We show that the initial correlations can affect quantum transport not only in the transient regime, but also in the steady-state limit when system-lead couplings are strong enough that electron localized states occur in the device system.

Perovskite structured materials contain myriad tunable ordered phases of electronic and magnetic origin with proven technological importance and strong promise for a variety of energy solutions. An always-contributing influence beneath these cooperative and competing interactions is the lattice, whose physics may be obscured in complex perovskites by the many coupled degrees of freedom, which makes these systems interesting. Here, we report signatures of an approach to a quantum phase transition very near the ground state of the nonmagnetic, ionic insulating, simple cubic perovskite material ${\mathrm{ScF}}_3$, and show that its physical properties are strongly effected as much as 100 K above the putative transition. Spatial and temporal correlations in the high-symmetry cubic phase determined using energy- and momentum-resolved inelastic x-ray scattering as well as x-ray diffraction reveal that soft mode, central peak, and thermal expansion phenomena are all strongly influenced by the transition.

Molecular dynamics simulations of densified glass-forming liquids, $2{\mathrm{SiO}}_2-{\mathrm{Na}}_2\mathrm{O}$, are presented. We perform a cooling/heating cycle across the glass transition, and important energy variations are obtained when the material relaxes at low temperature, leading to a hysteresis loop. However, for selected system densities, minuscule energy changes are found, revealing glasses which can be viewed as “thermally reversing,” in close correspondence with experiments performed in the context of isostatically rigid glasses. The topological constraint count of the atomic network structure shows that such “reversible” liquids adapt under the density-driven coordination increase, by experiencing larger bond-angle excursions at the atomic scale, quantified from the evolution with density of the Mauro-Gupta function $q(T,\rho )$, which exhibits a broad minimum around $2.75{\mathrm{g}/\mathrm{cm}}^3$. The stiffening of the network structure is also evidenced from an inspection of the vibrational density of states, which shows an important decrease in the low-frequency contributions across the reversibility window. Dynamic anomalies are detected from the evolution of isothermal diffusivity with density, which underscore the possible generality of “glass reversibility” in densified tetrahedral glass-forming liquids.

The unoccupied electronic structure of quasi-one-dimensional reconstructions of Pb atoms on a Si(557) surface is investigated by means of femtosecond time- and angle-resolved two-photon photoemission. Two distinct unoccupied electronic states are observed at $E-E_{\mathrm{F}}=3.55$ and 3.30 eV, respectively. Density functional theory calculations reveal that these states are spatially located predominantly on the lead wires and that they are energetically degenerated with an energy window of reduced electronic density of states in Si. We further find momentum-averaged lifetimes of 24 and 35 fs of these two states, respectively. The photoemission yield and the population dynamics depend on the electron momentum component perpendicular to the steps of the Si substrate, and the momentum-dependent dynamics cannot be described by means of rate equations. We conclude that momentum- and direction-dependent dephasing of the electronic excitations, likely caused by elastic scattering at the step edges on the vicinal surface, modifies the excited-state population dynamics in this system.

Recently, we proposed the loop-string algorithm (LSA) for the Monte Carlo simulations of the nearest-neighbor (NN) spin-ice model [Phys. Rev. B 90, 220406(R) (2014)]. Here we discuss its advancement to a dipolar spin ice (DSI) such as ${\mathrm{Ho}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ and ${\mathrm{Dy}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$. For this purpose, based on the dumbbell representation, we express DSI as a NN spin-ice model described by Hamiltonian $H_0$ perturbed by the Coulomb interactions among defects $H_1$. Then we apply LSA to $H_0$ and decompose the system into a mixture of loops and strings interacting via $H_1$. In simulation of the mixture, we employ the Metropolis algorithm. Our approach possesses two advantages: First, it is free of the so-called spin freezing problem; second, the computational cost for $H_1$ decreases exponentially with temperature, which can be viewed as an algorithmic realization of the projective equivalence concept. We compare numerical data with experimental results for ${\mathrm{Ho}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ and ${\mathrm{Dy}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ to demonstrate its predictability for these frustrated magnets.

The penetration of an ac magnetic signal into a type-II superconductor residing in the Shubnikov phase depends on the pinning properties of Abrikosov vortices. Within a phenomenological theory, the so-called Campbell penetration depth ${\lambda }_{\mathrm{C}}$ is determined by the curvature $\alpha$ at the bottom of the effective pinning potential. Preparing the sample into a critical state, this curvature vanishes and the Campbell length formally diverges. We make use of the microscopic expression for the pinning force density derived within strong pinning theory and show how flux penetration on top of a critical state proceeds in a regular way.

We studied the optical properties of ${\mathrm{CoV}}_2{\mathrm{O}}_4$, in which a broad spectrum arising from the Mott excitation of the V $d$ states and sharp peaks from the intra-atomic $d-d$ transitions in the Co ions coexist. We found that the width of the $d-d$ transition peaks decreases and that Fano resonance appears in the steady-state optical spectrum with decreasing temperature. We also found that the width of the $d-d$ transition peaks increases less than 1 ps after a pump pulse is applied to the Mott excitation. These results indicate that the Mott excitation and the $d-d$ transitions are strongly coupled in this compound.

The origin of compression-induced failure in brittle solids has been a subject of debate. Using in situ, high-speed, strain field mapping of a representative material, polymethylmethacrylate, we reveal that shock loading leads to heterogeneity in a compressive strain field, which in turn gives rise to localized lateral tension and shear through Poisson's effects, and, subsequently, localized microdamage. A failure wave nucleates from the impact surface and its propagation into the microdamage zone is self-sustained, triggering interior failure. Its velocity increases with increasing shock strength and eventually approaches the shock velocity. The seemingly puzzling phenomena observed in previous experiments, including incubation time, failure wave velocity variations, and surface roughness effects, can all be explained consistently with the nucleation and growth of the microdamage, and the effects of loading strength and preexisting defects.

We present first-principles calculations of the thermal and electronic transport properties of the oxide semiconductor CdO. In particular, we find from theory that the accepted thermal conductivity $\kappa$ value of $0.7\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ is approximately one order of magnitude too small; our calculations of $\kappa$ of CdO are in good agreement with recent measurements. We also find that alloying of MgO with CdO is an effective means to reduce the lattice contribution to $\kappa$, despite MgO having a much larger thermal conductivity. We further consider the electronic structure of CdO in relation to thermoelectric performance, finding that large thermoelectric power factors may occur if the material can be heavily doped $p$ type. This work develops insight into the nature of thermal and electronic transport in an important oxide semiconductor.

We present a comprehensive experimental and theoretical study of the electronic and magnetic properties of two quasi-two-dimensional (2D) honeycomb lattice monoclinic compounds $A_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6(A=\mathrm{Li},\mathrm{Na})$. Magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic long-range order with Néel temperatures of ∼14 and 16 K for $\mathrm{L}{\mathrm{i}}_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6$ and $\mathrm{N}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6$, respectively. The effective magnetic moments of $4.3{\mu }_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.\left(\mathrm{L}{\mathrm{i}}_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6\right)$ and $4.4{\mu }_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.\left(\mathrm{N}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6\right)$, where f.u. is formula units, indicate that $\mathrm{N}{\mathrm{i}}^{2+}$ is in a high-spin configuration ($S=1$). The temperature dependence of the inverse magnetic susceptibility follows the Curie-Weiss law in the high-temperature region and shows positive values of the Weiss temperature, $\sim 8\mathrm{K}$ ($\mathrm{L}{\mathrm{i}}_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6$) and ∼12 K ($\mathrm{N}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6$), pointing to the presence of nonnegligible ferromagnetic interactions, although the system orders antiferromagnetically at low temperatures. In addition, the magnetization curves reveal a field-induced (spin-flop type) transition below $T_{\mathrm{N}}$ that can be related to the magnetocrystalline anisotropy in these systems. These observations are in agreement with density functional theory calculations, which show that both antiferromagnetic and ferromagnetic intralayer spin exchange couplings between $\mathrm{N}{\mathrm{i}}^{2+}$ ions are present in the honeycomb planes, supporting a zigzag antiferromagnetic ground state. Based on our experimental measurements and theoretical calculations, we propose magnetic phase diagrams for the two compounds.

Magnetic materials without structural inversion symmetry can display the Dzyaloshinskii-Moriya interaction, which manifests itself as chiral magnetic ground states. These chiral states can interact in complex ways with applied fields and boundary conditions provided by finite sample sizes that are of the order of the length scale of the chiral states. Here we study epitaxial thin films of FeGe with a thickness close to the helix pitch of the helimagnetic ground state, which is about 70 nm, by conventional magnetometry and polarized neutron reflectometry. We show that the helix in an FeGe film reverses under the application of a field by deforming into a helicoidal form, with twists in the helicoid being forced out of the film surfaces on the way to saturation. An additional boundary condition was imposed by exchange-coupling a ferromagnetic Fe layer to one of the interfaces of an FeGe layer. This forces the FeGe spins at the interface to point in the same direction as the Fe, preventing node expulsion and giving a handle by which the reversal of the helical magnet may be controlled.

We present a worm sampling method for calculating one- and two-particle Green's functions using continuous-time quantum Monte Carlo simulations in the hybridization expansion (CT-HYB). Instead of measuring Green's functions by removing hybridization lines from partition function configurations, as in conventional CT-HYB, the worm algorithm directly samples the Green's function. We show that worm sampling is necessary to obtain general two-particle Green's functions which are not of density-density type and that it improves the sampling efficiency when approaching the atomic limit. Such two-particle Green's functions are needed to compute off-diagonal elements of susceptibilities and occur in diagrammatic extensions of the dynamical mean-field theory and in efficient estimators for the single-particle self-energy.

In this work we present an analysis of a quench for the repulsive Lieb-Liniger gas confined to a large box with hard wall boundary conditions. We study the time average of local correlation functions and show that both the quench action approach and the generalized Gibbs ensemble formalism are applicable for the long-time average of local correlation functions. We find that the time average of the system corresponds to an eigenstate of the Lieb-Liniger Hamiltonian and that this eigenstate is related to an eigenstate of a Lieb-Liniger Hamiltonian with periodic boundary conditions on an interval of twice the length and with twice as many particles (a doubled system). We further show that local operators with support far away from the boundaries of the hard wall have the same expectation values with respect to this eigenstate as corresponding operators for the doubled system. We present an example of a quench where the gas is initially confined in several moving traps and then released into a bigger container, an approximate description of the Newton's cradle experiment. We calculate the time average of various correlation functions for long times after the quench.

We have demonstrated coupling between a pair of ultrastrong light-matter coupled microcavities composed of neat glassy organic dye films between metallic (silver) mirrors at room temperature. Based upon our modified coupled oscillator model, we have observed that the degeneracy between the Rabi splittings associated with the symmetric and antisymmetric cavity modes is broken by the higher-order antiresonant terms in the Hamiltonian associated with the breakdown of the rotating wave approximation in the ultrastrong coupling regime. These results are in quantitative agreement with both experiment and transfer matrix modeling. The component cavities are characterized by $Q$ factors around 12 and display a large vacuum Rabi splitting around $1.12$ eV between the upper and lower polariton branches, which is about $52\%$ of the excited state energy, thus indicating ultrastrong coupling in each individual cavity. This large splitting is due to the large oscillator strength of the neat dye glass. We have also observed large polariton-induced incidence-side asymmetry in reflection spectra in a coupled cavity pair with one cavity having no exciton.

High positive electrostatic (dc) field can break the bonds in molecules and strip away atoms from the solid surfaces. The dynamics of this field evaporation under laser pulse is studied for a ${\mathrm{H}}_2$ molecule and a ${\mathrm{Si}}_4$ cluster using time-dependent density functional theory combined with molecular dynamics. This allows us to monitor the position and charge state of the evaporated atom in real time. Our simulations demonstrate that the critical dc field for the evaporation is lower if the molecule/cluster is illuminated by a laser pulse. The behavior of the evaporation threshold as a function of laser intensity and dc field is in qualitative agreement with experiments and provides important insights into the mechanisms of laser-assisted field evaporation. Additionally, the laser-assisted field evaporation is found to be sensitive to the laser energy according to the photoabsorption spectra that demonstrate a pronounced redshift in the lower energy region at higher dc field values.

We demonstrate electrical control of ferromagnetism in field-effect transistors with a trilayer quantum well (QW) channel containing an ultrathin n-type ferromagnetic semiconductor $(\mathrm{In},\mathrm{Fe})\mathrm{As}$ layer. A gate voltage is applied to control the electron wave functions ${\phi }_i$ in the QW, such that the overlap of ${\phi }_i$ and the $(\mathrm{In},\mathrm{Fe})\mathrm{As}$ layer is modified. The Curie temperature is largely changed by 42%, whereas the change in sheet carrier concentration is two to three orders of magnitude smaller than that of previous gating experiments. This result provides an approach for versatile, low power, and ultrafast manipulation of magnetization.

Adsorption of the organic semiconductor perylene tetracarboxylic dianhydride onto $\mathrm{Cr}\left(001\right)$ decreases the metal $d$-derived surface-state lifetime without causing a shift in its energy. This suggests an indirect electronic interaction that contrasts sharply with expectations of p-d electronic coupling based on direct chemisorption. Lifetime changes are measured with scanning tunneling spectroscopy as a function of temperature and quantified as arising from a molecule-induced increase in electron-electron scattering rate into bulk bands within Fermi-liquid theory. Adsorbate-induced effects extend far beyond the adsorption site of the molecule, decaying exponentially away with a characteristic length scale of $\sim 2.4\mathrm{nm}$, similar to the carrier mean free path in Cr.

Cu(1,3-benzenedicarboxylate) [Cu(1,3-bdc)] contains structurally perfect kagome planes formed by ${\mathrm{Cu}}^{2+}$ ions without the presence of diamagnetic defects. This organometallic compound should serve as a precious platform to explore quantum frustrated magnetism, yet the experimental results so far are mysterious, leading to questions such as, “Is Cu(1,3-bdc) just a trivial weak ferromagnet?” Using the density functional theory, we have systematically studied the electronic and magnetic properties of Cu(1,3-bdc), putting forth a theoretical basis to clarify this novel material. We present numerical evidence of a dominating antiferromagnetic (AFM) exchange between nearest-neighbor (NN) ${\mathrm{Cu}}^{2+}$ as experimentally extracted from the high-temperature susceptibility data. We further show that beyond the NN AFM exchange, the additional interactions in Cu(1,3-bdc) have similar strength as those in the well-studied kagome antiferromagnet, herbertsmithite, by designing a comparative study. In the end, we discuss our understanding of the phase transition and FM signals observed under low temperature.

The heavy-hole (HH) and light-hole (LH) components of the valence states in three-dimensional (3D) bulk semiconductors can mix quantum mechanically as the dimensionality is reduced in forming low-D nanostructures, such as 2D quantum wells, 1D quantum wires, and 0D quantum dots (QDs). This coupling controls the tuning of the excitonic fine-structure splitting, provides an efficient channel for the spin coherence, and leads to polarization anisotropy of light emission, central to several quantum-information schemes. The current understanding is that the mixing scales with the square of $\delta V_{\text{HL}}/{\mathrm{\Delta }}_{\text{HL}}$, where $\delta V_{\text{HL}}$ and ${\mathrm{\Delta }}_{\text{HL}}$ are the coupling matrix elements of the crystal potential and the energy separation between the primary HH0 and LH0 states, respectively. We discuss two classes of HH-LH coupling mechanisms. First, coupling factors occurring through the numerator $\delta V_{\text{HL}}$, referred to as “direct coupling,” including the well-known (i) quantum confinement, (ii) built-in strain, and (iii) shape elongation, as well as three additional direct coupling mechanisms discussed here: (iv) the intrinsic $C_{2v}$ crystal-field effect, (v) the local symmetry of the interface, and (vi) the alloy disorder. We quantify these six direct HH-LH coupling effects by performing atomistic pseudopotential calculations on a range of strained and unstrained QDs of different morphologies. We find that in unstrained self-assembled QDs such as GaAs/AlGaAs, effects (i)–(vi) contribute 0%, 0%, 0%, 0%, 40%, and 60%, respectively, whereas in strained self-assembled QDs such as InGaAs/GaAs they contribute 0%, 0%, 78%, 0%, 8%, and 14%, respectively, to the direct HH-LH coupling $\delta V_{\text{HL}}$. These relative contributions to direct HH-LH coupling differ significantly from what was previously believed. Second, we discover an unexpected HH-LH supercoupling that effectively reduces the denominator ${\mathrm{\Delta }}_{\text{HL}}$ by the presence of a dense ladder of intermediate states between the HH0 and LH0 states (analogous to superexchange in magnetism). Supercoupling amplifies and propagates the HH-LH interaction and is the dominant source of HH-LH mixing in strained nanostructures where ${\mathrm{\Delta }}_{\text{HL}}$ is fairly large, so by the direct coupling mechanism alone $\delta V_{\text{HL}}/{\mathrm{\Delta }}_{\text{HL}}$ would be expected to be rather small. Supercoupling explains a number of outstanding puzzles, including the surprising fact that in strained (InAs/GaAs) QDs the mixing is very strong despite the fact that ${\mathrm{\Delta }}_{\text{HL}}$ is large, and it offers a way to manipulate HH-LH mixing and hence associated properties in nanostructures.