The structure of Mach cones in a crystalline complex plasma has been studied experimentally using an intensity sensitive imaging, which resolved particle motion in three dimensions. This revealed a previously unknown out-of-plane cone structure, which appeared due to excitation of the vertical wave mode. The complex plasma consisted of micron sized particles forming a monolayer in a plasma sheath of a gas discharge. Fast particles, spontaneously moving under the monolayer, created Mach cones with multiple structures. The in-plane cone structure was due to compressional and shear lattice waves.

The spatiotemporal self-organization of viscoresistive magnetohydrodynamics in a toroidal geometry is studied. Curl-free toroidal magnetic and electric fields are imposed. It is observed in our simulations that a flow is generated, which evolves from dominantly poloidal to toroidal when the Lundquist numbers are increased. It is shown that this toroidal organization of the flow is consistent with the tendency of the velocity field to align with the magnetic field. Up-down asymmetry of the geometry causes the generation of a nonzero toroidal angular momentum.

Using a numerical renormalization group based on exploiting an underlying exactly solvable nonrelativistic theory, we study the out-of-equilibrium dynamics of a 1D Bose gas (as described by the Lieb-Liniger model) released from a parabolic trap. Our method allows us to track the postquench dynamics of the gas all the way to infinite time. We also exhibit a general construction, applicable to all integrable models, of the thermodynamic ensemble that has been suggested to govern this dynamics, the generalized Gibbs ensemble. We compare the predictions of equilibration from this ensemble against the long time dynamics observed using our method.

Using a Fermi-Bose mixture of ultracold atoms in an optical lattice, we construct a quantum simulator for a $U(1)$ gauge theory coupled to fermionic matter. The construction is based on quantum links which realize continuous gauge symmetry with discrete quantum variables. At low energies, quantum link models with staggered fermions emerge from a Hubbard-type model which can be quantum simulated. This allows us to investigate string breaking as well as the real-time evolution after a quench in gauge theories, which are inaccessible to classical simulation methods.

A new physical mechanism of plastic flow in solids is suggested and theoretically described. The mechanism represents stress-driven rotations of grain boundaries (GBs) in subsurface areas of solids. The stress and energy characteristics of the GB rotations are calculated. In the case of nickel, we find that such rotations are energetically favorable processes in a wide range of GB parameters. Our theory is consistent with the experimental observation [D. Jang and J. R. Greer, Scr. Mater. 64, 77 (2011).] of GB rotations in deformed nanocrystalline nickel nanopillars.

Complex structures of warm and hot dense matter are essential to understanding the behavior of materials in high energy density processes and provide new features of matter constitutions. Here, around a new unified first-principles determined Hugoniot curve of iron from the normal condensed condition up to 1 Gbar, the novel structures characterized by the ionic clusters with electron bubbles are found using quantum Langevin molecular dynamics. Subsistence of complex clusters can persist in the time scale of 50 fs dynamically with quantum flowing bubbles, which are produced by the interplay of Fermi electron degeneracy, the ionic coupling, and the dynamical nature. With the inclusion of those complicated features in quantum Langevin molecular dynamics, the present equation of states could serve as a first-principles based database in a wide range of temperatures and densities.

We have measured, as a function of the age $t_a$, the aging of the nonlinear dielectric susceptibility ${\chi }_3$ of glycerol below the glass transition. Whereas the linear susceptibility can be accurately accounted for in terms of an age dependent relaxation time ${\tau }_{\alpha }(t_a)$, this scaling breaks down for ${\chi }_3$, suggesting an increase of the amplitude of ${\chi }_3$. This is a strong indication that the number $N_{\mathrm{corr}}$ of molecules involved in relaxation events increases with $t_a$. For $T=0.96\times T_g$, we find that $N_{\mathrm{corr}}$ increases by $\sim 10\%$ when $t_a$ varies from 1 to 100 ks. This sheds new light on the relation between length scales and time scales in glasses.

The critical properties of the finite temperature Mott end point are drastically altered by a coupling to crystal elasticity, i.e., whenever it is amenable to pressure tuning. Similar as for critical piezoelectric ferroelectrics, the Ising criticality of the electronic system is preempted by an isostructural instability, and long-range shear forces suppress microscopic fluctuations. As a result, the end point is governed by Landau criticality. Its hallmark is, thus, a breakdown of Hooke’s law of elasticity with a nonlinear strain-stress relation characterized by a mean-field exponent. Based on a quantitative estimate, we predict critical elasticity to dominate the temperature range $\Delta T^{*}/T_c\simeq 8\%$, close to the Mott end point of $\kappa \mathrm{\text{−}}(\mathrm{BEDT}\mathrm{\text{−}}\mathrm{TTF}{)}_{2}X$.

The spectral response and physical features of the 2D Hubbard-Holstein model are calculated both in equilibrium at zero and low chemical dopings, and after an ultrashort powerful light pulse, in undoped systems. At equilibrium and at strong charge-lattice couplings, the optical conductivity reveals a three-peak structure in agreement with experimental observations. After an ultrashort pulse and at nonzero electron-phonon interaction, phonon and spin subsystems oscillate with the phonon period $T_{\mathrm{ph}}\approx 80\mathrm{fs}$. The decay time of the phonon oscillations is about 150–200 fs, similar to the relaxation time of the charge system. We propose a criterion for observing these oscillations in high $T_c$ compounds: the time span of the pump light pulse ${\tau }_{\mathrm{pump}}$ has to be shorter than the phonon oscillation period $T_{\mathrm{ph}}$.

We have performed high-resolution angle-resolved photoemission spectroscopy of layered chalcogenide $1T\mathrm{\text{−}}{\mathrm{Fe}}_x{\mathrm{Ta}}_{1-x}{\mathrm{S}}_2$ which undergoes a superconducting transition in the nearly commensurate charge-density-wave phase (melted Mott phase). We found a single electron pocket at the Brillouin-zone center in the melted Mott phase, which is created by the backfolding of bands due to the superlattice potential of charge-density-wave. This electron pocket appears in the $x$ region where the samples show superconductivity, and is destroyed by the Mott- and Anderson-gap opening. Present results suggest that the melted Mott state and the superconductivity coexist in real space, providing a new insight into the interplay between electron correlation, charge order, and superconductivity.

As-grown topological insulators (TIs) are typically heavily doped $n$-type crystals. Compensation by acceptors is used to move the Fermi level to the middle of the band gap, but even then TIs have a frustratingly small bulk resistivity. We show that this small resistivity is the result of band bending by poorly screened fluctuations in the random Coulomb potential. Using numerical simulations of a completely compensated TI, we find that the bulk resistivity has an activation energy of just 0.15 times the band gap, in good agreement with experimental data. At lower temperatures activated transport crosses over to variable range hopping with a relatively large localization length.

Molecules in junctions often fluctuate considerably, especially when subject to the influence of solvent molecules. These fluctuations in site energies and couplings can be sampled, for example, by using molecular dynamics simulations, and can lead to incoherent effects in charge transport. To this end, a popular snapshot-averaged Landauer approach is compared to a time-dependent Green’s function scheme. Since sequential transport dominates in systems with rapidly varying bridges, schemes not taking the time order of conformations into account, such as the Landauer approach, are inappropriate.

Based on the dynamical mean field theory and angle resolved photoemission spectroscopy, we have investigated the mechanism of high $T_c$ superconductivity in stoichiometric LiFeAs. The calculated spectrum is in excellent agreement with the measured angle resolved photoemission spectroscopy. The Fermi surface (FS) nesting, which is predicted in the conventional density functional theory method, is suppressed due to the orbital-dependent correlation effect within the dynamical mean field theory method. We have shown that such marginal breakdown of the FS nesting is an essential condition to the spin-fluctuation mediated superconductivity, while the good FS nesting in NaFeAs induces a spin density wave ground state. Our results indicate that a fully charge self-consistent description of the correlation effect is crucial in the description of the FS nesting-driven instabilities.

We solve the Sherrington-Kirkpatrick model in a transverse field $\Gamma$ deep in its quantum glass phase at zero temperature. We show that the glass phase is critical everywhere, exhibiting collective excitations with a gapless Ohmic spectral function. Using an effective potential approach, we interpret the latter as arising from disordered collective excitations behaving like weakly coupled, underdamped oscillators. For a small transverse field $\Gamma$, the low-frequency spectrum takes a form independent of the fluctuation strength $\Gamma$.

All-electrical control of spin transport in nanostructures has been the central interest and challenge of spin physics and spintronics. Here we demonstrate on-chip spin polarizing or filtering actions by driving the gate-defined one dimensional (1D) conductor, one of the simplest geometries for integrated quantum devices, away from the conventional Ohmic regime. Direct measurement of the spin polarization of the emitted current was performed when the momentum degeneracy was lifted, wherein both the 1D polarizer for spin injection and the analyzer for spin detection were demonstrated. The results showed that a configuration of gates and applied voltages can give rise to a tunable spin polarization, which has implications for the development of spintronic devices and future quantum information processing.

For isolated vacancies in ordered local-moment antiferromagnets we show that the magnetic-field linear-response limit is generically singular: The magnetic moment associated with a vacancy in zero field is different from that in a finite field $h$ in the limit $h\to 0^{+}$. The origin is a universal and singular screening cloud, which moreover leads to perfect screening as $h\to 0^{+}$ for magnets which display spin-flop bulk states in the weak-field limit.

The three-dimensional Edwards-Anderson and mean-field Sherrington-Kirkpatrick Ising spin glasses are studied via large-scale Monte Carlo simulations at low temperatures, deep within the spin-glass phase. Performing a careful statistical analysis of several thousand independent disorder realizations and using an observable that detects peaks in the overlap distribution, we show that the Sherrington-Kirkpatrick and Edwards-Anderson models have a distinctly different low-temperature behavior. The structure of the spin-glass overlap distribution for the Edwards-Anderson model suggests that its low-temperature phase has only a single pair of pure states.

We have studied the temperature dependence of the exchange bias effect in epitaxial $\mathrm{Co}/\mathrm{CoO}$ bilayer structures with in-plane uniaxial magnetocrystalline anisotropy. We have measured the anisotropic positive exchange bias, which is independent from the initial cooling field value. Synchronous with the occurrence of positive exchange bias, distinct changes in the magnetization reversal process indicate a temperature-dependent rotation of the effective anisotropy and exchange bias axis. Model calculations based upon the electron microscopy-determined epitaxial $\mathrm{Co}/\mathrm{CoO}$-interface structure corroborate this interpretation.

Brownian motion in a granular gas in a homogeneous cooling state is studied theoretically and by means of molecular dynamics. We use the simplest first-principles model for the impact-velocity dependent restitution coefficient, as it follows for the model of viscoelastic spheres. We reveal that for a wide range of initial conditions the ratio of granular temperatures of Brownian and bath particles demonstrates complicated nonmonotonic behavior, which results in a transition between different regimes of Brownian dynamics: It starts from the ballistic motion, switches later to a superballistic one, and turns at still later times into subdiffusion; eventually normal diffusion is achieved. Our theory agrees very well with the molecular dynamics results, although extreme computational costs prevented us from detecting the final diffusion regime. Qualitatively, the reported intermediate diffusion regimes are generic for granular gases with any realistic dependence of the restitution coefficient on the impact velocity.

The conformations of semiflexible (bio)polymers are studied in flow-through geometrically structured microchannels. Using mesoscale hydrodynamics simulations, we show that the polymer undergoes a rod-to-helix transition as it moves from the narrow high-velocity region into the wide low-velocity region of the channel. The transient helix formation is the result of a nonequilibrium and nonstationary buckling transition of the semiflexible polymer, which is subjected to a compressive force originating from the fluid-velocity variation in the channel. The helix properties depend on the diameter ratio of the channel, the polymer bending rigidity, and the flow strength.