We investigated the Landau-level structure in Weyl semimetal NbAs, in which a pair of band degenerate points (Weyl points) exists inside an anisotropic crescent-shaped Fermi surface. Through phase analysis of quantum oscillations in various magnetic-field directions, we found that the phase took various values between zero and $\pi$, reflecting variations of the energy dispersion in the extremal area. The nontrivial phase value around $\pi$ is seen when the extremal plane was relatively far from the Weyl pairs and the double-minimum energy dispersion caused by the band inversion disappears inside the plane.

We present a theoretical analysis of the split-off states emerging due to a tunnel coupling between a remote bound state and a semiconductor quantum well (QW). The on-site Coulomb repulsion and the spin splitting of the bound state have been considered. The split-off states emerge in the band gap of the QW and reveal themselves as two solitary peaks in the photoluminescence (PL) from the QW. The peaks have opposite circular polarization and their spectral position strongly depends on the tunnel coupling strength. We suggest a mechanism of ultrafast PL polarization switching by means of electrical modulation of the tunnel coupling by an external gate. The obtained results open a new possibility for the spin and optical polarization control in nanoscale systems.

Spin polarization by Rashba effect in the quasi-one-dimensional metallic bands of $\mathrm{Si}\left(111\right)5\times 2$-Au surface is revealed by spin- and angle-resolved photoelectron spectroscopy and the first-principles calculation. Small but clear spin polarization and its sign reversal with respect to the $\overline{\mathrm{\Gamma }}$ point is observed indicating the Rashba origin of the spin-polarized states. Deviating from the typical helical tangential spin texture of normal Rashba effect of two-dimensional electronic states, not only in-plane but significant out-of-plane spin polarization probably caused by the anisotropic in-plane charge distribution around Au atoms is observed at some specific $k$ points. The observed peculiar spin texture of the sample is qualitatively in good agreement with the results of the first-principles calculation based on the recently proposed surface reconstruction model by Kwon and Kang implying the validity of the structural model.

A popular Adam-Gibbs scenario has suggested that the excess entropy of glass and liquid over crystal dominates the dynamical arrest at the glass transition with exclusive contribution from configurational entropy over vibrational entropy. However, an intuitive structural rationale for the emergence of frozen dynamics in relation to entropy is still lacking. Here we study these issues by atomistically simulating the vibrational, configurational, as well as total entropy of a model glass former over their crystalline counterparts for the entire temperature range spanning from glass to liquid. Besides confirming the Adam-Gibbs entropy scenario, the concept of Shannon information entropy is introduced to characterize the diversity of atomic-level structures, which undergoes a striking variation across the glass transition, and explains the change found in the excess configurational entropy. Hence, the hidden structural mechanism underlying the entropic kink at the transition is revealed in terms of proliferation of certain atomic structures with a higher degree of centrosymmetry, which are more rigid and possess less nonaffine softening modes. In turn, the proliferation of these centrosymmetric (rigid) structures leads to the freezing-in of the dynamics beyond which further structural rearrangements become highly unfavorable, thus explaining the kink in the configurational entropy at the transition.

We combine theories of scattering for linearized water waves and flexural waves in thin elastic plates to characterize and achieve control of water wave scattering using floating plates. This requires manipulating a sixth-order partial differential equation with appropriate boundary conditions of the velocity potential. Making use of multipole expansions, we reduce the scattering problem to a linear algebraic system. The response of a floating plate in the quasistatic limit simplifies, considering a distinct behavior for water and flexural waves. Unlike for similar studies in electromagnetics and acoustics, scattering of gravity-flexural waves results in a nonvanishing scattering cross-section in the zero-frequency limit, dominated by its zeroth-order multipole. Potential applications lie in floating structures manipulating ocean water waves.

Experimental techniques to verify Majoranas are of current interest. A prominent test is the effect of Majoranas on the Josephson current between two wires linked via a normal junction. Here, we study the case of a quantum dot connecting the two superconductors and the sign of the supercurrent in the trivial and topological regimes under grand-canonical equilibrium conditions, explicitly allowing for parity changes due to, e.g., quasiparticle poisoning. We find that the well-known supercurrent reversal for odd occupancy of the quantum dot ($\pi$ junction) in the trivial case does not occur in the presence of Majoranas in the wires. However, we also find this to be a mere consequence of Majoranas being zero energy states. Therefore, the lack of supercurrent sign reversal can also be caused by trivial bound states and is thus not a discriminating signature of Majoranas.

Ultrafast laser excitation of the ferromagnetic semiconductor InMnAs is shown to trigger spin precession with the largest amplitude reported for magnetic semiconductors so far. To reveal the electronic transitions mediating the coupling between light and spins, we compared the spin dynamics triggered by short terahertz (photon energy 5 meV) and midinfrared (photon energy 500 meV) pulses. The experiments reveal that terahertz pump pulses excite qualitatively similar spin dynamics, but are 100 times more energy efficient than the mid-IR pulses. This finding shows that in a semiconductor with hole-mediated ferromagnetism intraband electronic transitions mediate ultrafast and the most efficient coupling between light and spins.

A Kitaev quantum spin liquid involves fractionalized quasiparticles called itinerant Majorana fermions and localized gauge fluxes. The topological character with chiral excitations under a magnetic field is currently in an active debate. For a candidate spin liquid $\alpha \text{−}{\mathrm{RuCl}}_3$, we report low-energy spin excitations through nuclear magnetic and quadrupole resonance measurements down to temperatures three orders of magnitude lower than the exchange energy. In a field-driven disordered state, we found the evolution of two kinds of gapped spin excitations with distinct field dependences. The result is indicative of a field-induced hybridization between fractionalized quasiparticles, as inferred by the perturbation theory for the Kitaev model. The detailed field dependence of spin dynamics across the quantum critical region shows the emergence of a gapless intermediate phase between the gapped zigzag order phase and spin-disordered phases.

Generic short-range interacting quantum systems with a conserved quantity exhibit universal diffusive transport at late times. We employ nonequilibrium quantum field theory and semiclassical phase-space simulations to show how this universality is replaced by a more general transport process in a long-range XY spin chain at infinite temperature with couplings decaying algebraically with distance as $r^{-\alpha }$. While diffusion is recovered for $\alpha >1.5$, longer-ranged couplings with $0.5<\alpha \le 1.5$ give rise to effective classical Lévy flights, a random walk with step sizes drawn from a distribution with algebraic tails. We find that the space-time-dependent spin density profiles are self-similar, with scaling functions given by the stable symmetric distributions. As a consequence, for $0.5<\alpha \le 1.5$, autocorrelations show hydrodynamic tails decaying in time as $t^{-1/(2\alpha -1)}$ and linear-response theory breaks down. Our findings can be readily verified with current trapped ion experiments.

The inertial effects of magnetic solitons play a crucial role in their dynamics and stability. Yet governing their inertial effects is a challenge for their use in real devices. Here, we show how to control the inertial effects of magnetic droplet solitons. Magnetic droplets are more strongly nonlinear and localized autosolitons than can form in current-driven nanocontacts. Droplets can be considered as dynamical particles with an effective mass. We show that the dynamical droplet bears a second excitation under its own inertia. These excitations comprise a chiral profile, and appear when the droplet resists the force induced by the Oersted field of the current injected into the nanocontact. We reveal the role of the spin torque on the excitation of these chiral modes and we show how to control these modes using the current and the field.

We report the existence of a regime for domain-wall motion in uniaxial and near-uniaxial ferromagnetic nanowires, characterized by applied magnetic fields sufficiently strong that one of the domains becomes unstable. There appears a stable solution of the Landau-Lifshitz-Gilbert equation, describing a nonplanar domain wall moving with constant velocity and precessing with constant frequency. Even in the presence of thermal noise, the solution can propagate for distances on the order of 500 times the field-free domain-wall width before fluctuations in the unstable domain become appreciable.

The optimal superconductivity ($T_c\approx 30$ K) in ${\mathrm{BaFe}}_2{\left({\mathrm{As}}_{1-x}{\mathrm{P}}_x\right)}_2$ can be reached when the coupled antiferromagnetic (AF) order $\left(T_N\right)$ and orthorhombic lattice distortion $\left(T_s\right)$ are suppressed to zero temperature with increasing of P concentration or hydrostatic pressure. Here we use transport and neutron scattering to study the $c$-axis pressure effects on electronic phases in underdoped ${\mathrm{BaFe}}_2{\left({\mathrm{As}}_{0.72}{\mathrm{P}}_{0.28}\right)}_2$, which has $T_N=T_s\approx 40$ K and $T_c\approx 28$ K at zero pressure. With increasing $c$-axis pressure, $T_N$ and $T_s$ are slightly enhanced around $P_c\sim 20$ MPa. Upon further increasing pressure, AF order is gradually suppressed to zero, while $T_c$ is enhanced to 30 K. Our results reveal the importance of magnetoelastic couplings in ${\mathrm{BaFe}}_2{\left({\mathrm{As}}_{1-x}{\mathrm{P}}_x\right)}_2$, suggesting that the $c$-axis pressure can be used as a tuning parameter to manipulate the electronic phases in iron pnictides.

We study the zero-temperature phase diagram of a dissipationless and disorder-free Josephson junction chain. Namely, we determine the critical Josephson energy below which the chain becomes insulating as a function of the ratio of two capacitances: the capacitance of each Josephson junction and the capacitance between each superconducting island and the ground. We develop an imaginary-time path integral quantum Monte Carlo algorithm in the charge representation, which enables us to efficiently handle the electrostatic part of the chain Hamiltonian. We find that a large part of the phase diagram is determined by anharmonic corrections which are not captured by the standard Kosterlitz-Thouless renormalization group description of the transition.

We use quantum Monte Carlo method employing stochastic-series-expansion technique to study the ground state properties of the $t_2-V_1$ model of hard-core bosons on a square lattice. We find that, away from half fillings, the minimal combination of nearest-neighbor repulsion $V_1$ and next-nearest-neighbor hopping $t_2$ may give rise to checkerboard supersolidity. The nature of the quantum phase transition, where the superfluid changes to a checkerboard supersolid, depends on the relative strength of $V_1/t_2$ and the average site occupancy. Interestingly, at the half filling, the model displays the extreme Thouless effect. As the filling is varied away from half filling, the model exhibits initially a mixed-order transition, next a tricritical point, and finally a second-order transition.

We study the time evolution of excitonic states after photoexcitation in the one-dimensional spinless extended Falicov-Kimball model. Several numerical methods are employed and benchmarked against each other: time-dependent mean-field simulations, the second-Born approximation (2BA) within the Kadanoff-Baym formalism, the generalized Kadanoff-Baym ansatz (GKBA) implemented with the 2BA, and the infinite time-evolving block decimation (iTEBD) method. It is found that the GKBA gives the best agreement with iTEBD and captures the relevant physics. Excitations to the particle-hole continuum and resonant excitations of the equilibrium exciton result in a qualitatively different dynamics. In the former case, the exciton binding energy remains positive and the frequency of the corresponding coherent oscillations is smaller than the band gap. On the other hand, resonant excitations trigger a collective mode whose frequency is larger than the band gap. We discuss the origin of these different behaviors by evaluating the nonequilibrium susceptibility using the nonthermal distribution and a random phase approximation. The peculiar mode with frequency larger than the band gap is associated with a partial population inversion with a sharp energy cutoff. We also discuss the effects of the cooling by a phonon bath. We demonstrate the real-time development of coherence in the polarization, which indicates excitonic condensation out of equilibrium.

We report a resistively detected nuclear magnetic resonance (RDNMR) measurement in a GaAs-based quantum point contact in the quantum Hall breakdown regime. We focus on the detection of the ${}^{75}\mathrm{As}$ RDNMR signal at different perpendicular magnetic fields in the presence of electrons occupying the lowest Landau level. We confirm successful RDNMR detection down to $B=1.25\mathrm{T}$ ($B=3.5\mathrm{T}$) using a high-mobility (low-mobility) device. All the RDNMR signals exhibit a threefold spectra attributed to electric quadrupole interaction. We find that the separation between the central transition and its satellite, ${\mathrm{\Delta }}_f\approx 20\mathrm{kHz}$, remains unaffected by magnetic-field variation. Interestingly, the central NMR linewidths vary with the field strength. Above $B=3\mathrm{T}$, the linewidth tends to saturate around 13 kHz. Below $B=3\mathrm{T}$, the linewidth decreases in proportion with field and approaches a lower limit of 1 kHz corresponding to the GaAs nuclear dipole interaction as the field decreases to $B=1.25\mathrm{T}$.

We study the adiabatic topological charge pumping driven by interlayer sliding in the moiré superlattices. We show that, when we slide a single layer of the twisted bilayer system relatively to the other, a moiré pattern flow and a quantized transport of electrons occur. The number of pumped charges is quantized to a sliding Chern number, which is related to the interlayer sliding degree of freedom. In the twisted bilayer graphene, the topological pumping current flows perpendicularly to the sliding direction when the Fermi energy is in the energy gap above or below the nearly-flat bands.

We investigate the effect of the sliding motion of layers in moiré heterostructures on the electronic state. We show that the sliding moiré heterostructure can generate nontrivial topology characterized by the first and second Chern number in the high-dimensional manifold spanned by the physical dimensions and synthetic dimensions associated with the sliding displacement. The nontrivial topology implies a topological charge pumping caused by the sliding motion. We demonstrate the nontrivial topology and charge pumping explicitly in a one-dimensional bichain model and small-angle twisted bilayer graphene. Contrary to the conventional belief that the interlayer sliding in incommensurate moiré heterostructures does not affect the electronic structure, our results reveal that the sliding motion can generate nontrivial topology dynamically and hence cannot be neglected in the dynamical process.