We study the effect of inelastic processes on the magnetotransport of a quasi-one-dimensional Weyl semimetal, using a modified Boltzmann-Langevin approach. The magnetic field drives a crossover to a ballistic regime in which the propagation along the wire is dominated by the chiral anomaly, and the role of fluctuations inside the sample is exponentially suppressed. We show that inelastic collisions modify the parametric dependence of the current fluctuations on the magnetic field. By measuring shot noise as a function of a magnetic field, for different applied voltage, one can estimate the electron-electron inelastic length $l_{\mathrm{ee}}$.

Protonic defects on ice lattices induced by doping with acids such as HCl and HF or bases such as KOH can facilitate order-disorder transitions. In laboratory experiments KOH doping is efficient in promoting the ordering transition from hexagonal ice I to ice XI, but it is ineffective for other known ice phases, for which HCl can trigger hydrogen ordering. Aiming at understanding these differences, random-walk simulations of the defect diffusion are performed on two- and three-dimensional ice lattices under the constraints imposed by the Bernal-Fowler ice rules. Effective defect diffusion coefficients are calculated for a range of dopants, concentrations, and ice phases. The interaction of different defects, incorporated by different dopants, is investigated to clarify the particular motion-enhancing role played by complementary defect pairs.

Two recent publications report different boundaries for the dimerized phase of the bilinear-biquadratic spin-1 Heisenberg model with quadratic Zeeman effect. We address these discrepancies for the biquadratic model with a quadratic Zeeman term and explain the differences. Based on our numerical results the phase boundaries of the dimerized phase are determined.

The structural and magnetic properties of siderite $\mathrm{FeC}{\mathrm{O}}_3$ have been studied by means of neutron powder diffraction at pressures up to 7.5 GPa and first-principles theoretical calculations. The lattice compression in the rhombohedral calcite-type structure is dominated by the reduction of the Fe-O bonds, while the changes of the C-O bonds are much less pronounced. The Néel temperature of the antiferromagnetic (AFM) ground state increases substantially under pressure with a coefficient $d{T}_N/dP=1.8\mathrm{K}/\mathrm{GPa}$, which is about 1.5 times larger in comparison with those predicted by the empirical Bloch rule. The ab initio calculations were performed in the framework of the density functional theory including Hubbard-U correction. The calculated structural parameters and Néel temperature as functions of pressure provide a reasonable agreement with the experimental results. The analysis of the density of electronic states points toward increased covalent bonding between the Fe and O atoms upon pressure, giving rise to unexpectedly large pressure coefficient of the Néel temperature and reduced ordered magnetic moments of Fe atoms.

Inelastic neutron-scattering and finite-temperature density matrix renormalization group (DMRG) calculations are used to investigate the spin excitation spectrum of the $S=1/2$ Heisenberg spin chain compound ${\mathrm{K}}_2{\mathrm{CuSO}}_4{\mathrm{Cl}}_2$ at several temperatures in a magnetic field near saturation. Critical correlations characteristic of the predicted $z=2,d=1$ quantum phase transition occurring at saturation are shown to be consistent with the observed neutron spectra. The data is well described with a scaling function computed using a free fermion description of the spins, valid close to saturation, and the corresponding scaling limits. One of the most prominent nonuniversal spectral features of the data is a novel thermally activated longitudinal mode that remains underdamped across most of the Brillouin zone.

The many-body localization (MBL) is commonly related to a strong spatial disorder. We show that MBL may alternatively be generated by adding a temporal disorder to periodically driven many-body systems. We reach this conclusion by mapping the evolution of such systems on the dynamics of the time-independent, disordered, Hubbard-like models. Our result opens the way to experimental studies of MBL in systems that reveal crystalline structures in the time domain. In particular, we discuss two relevant setups which can be implemented in experiments on ultracold atomic gases.

The superconducting and normal state characteristics of yttrium hexaboride $\left({\mathrm{YB}}_6\right)$ have been investigated for the single crystals with a transition temperatures $T_c$ ranging between 4.2 K and 7.6 K. The extracted set of microscopic parameters [the coherence length $\xi \left(0\right)\sim 320$–340 $\AA$, the penetration depth $\lambda \left(0\right)\sim 1100$–3250 $\AA$ and the mean free path of charge carriers $\mathit{l}=11–58 \AA$, the Ginzburg-Landau-Maki parameters ${\kappa }_{1,2}\left(0\right)\sim 3.3$–9.5, and the superconducting gap $\mathrm{\Delta }\left(0\right)\sim 6.2$–14.8 K] confirms the type II superconductivity in “dirty limit” ($\xi \gg l$) with a medium to strong electron-phonon interaction (the electron-phonon interaction constant ${\lambda }_{\mathrm{e}-\mathrm{ph}}=0.32–0.96$) and $s$-type pairing of charge carriers in this compound [$2\mathrm{\Delta }\left(0\right)/k_B{T}_c\approx 3$–4]. The comparative analysis of charge transport (resistivity, Hall and Seebeck coefficients) and thermodynamic (heat capacity, magnetization) properties in the normal state in ${\mathrm{YB}}_6$ allowed to assume a transition into the cage-glass state at $T^{*}\sim 50$ K with a static disorder in the arrangement of the ${\mathrm{Y}}^{3+}$ ions. We argue that the significant $T_c$ variations in ${\mathrm{YB}}_6$ single crystals are determined by two main factors: (i) the superconductivity enhancement is related with the increase of the number of vacancies, both at yttrium and boron sites, leading to nonstoichiometric composition, which is accompanied by the enhancement of electron-phonon interaction in the hexaboride lattice; (ii) stronger $T_c$ depression is observed in near stoichiometric and more dense crystals and it is induced by the development of bcc lattice instability producing strong distortion, disordering, and formation of defect complexes in the matrix of ${\mathrm{YB}}_6$.

We have investigated the superconducting ground state of the newly discovered superconductor ThFeAsN with a tetragonal layered crystal structure using resistivity, magnetization, heat capacity, and transverse-field muon-spin rotation ($\mathrm{TF}-\mu \mathrm{SR}$) measurements. Our magnetization and heat-capacity measurements reveal an onset of bulk superconductivity with $T_c\sim 30\mathrm{K}$. A nonlinear magnetic-field dependence of the specific heat coefficient $\gamma \left(H\right)$ has been found in the low-temperature limit, which indicates that there is a nodal energy gap. Our analysis of the $\mathrm{TF}-\mu \mathrm{SR}$ results shows that the temperature dependence of the superfluid density is better described by a two-gap model either isotropic $s+s$ wave or $s+d$ wave than a single-gap isotropic $s$-wave model for the superconducting gap, consistent with other Fe-based superconductors. The combination of $\gamma \left(H\right)$ and $\mathrm{TF}-\mu \mathrm{SR}$ results suggest that the ($s+d$)-wave model is the most consistent candidate for the gap structure of ThFeAsN. The observation of two gaps in ThFeAsN suggests a multiband nature of the superconductivity possibly arising from the $d$ bands of Fe ions. Furthermore, from our $\mathrm{TF}-\mu \mathrm{SR}$ study we have estimated the magnetic penetration depth in the polycrystalline sample of ${\lambda }_L\left(0\right)=375\mathrm{nm}$, superconducting carrier density $n_s=4.97\times {10}^{27}{\mathrm{m}}^{-3}$, and carrier's effective-mass $m^{*}=2.48m_e$. We compare the results of our present paper with those reported for the Fe-pnictide families of superconductors.

We present a further development of methods for analytical calculations of Green's functions of lattice fermions based on recurrence relations. Applying it to tight-binding systems and topological superconductors in different dimensions, we obtain a number of noteworthy results. In particular, we derive an explicit expression for an arbitrary Green's function of an open Kitaev chain, and we discover nonlocal fermionic corner states in a two-dimensional $p$-wave superconductor.

A chain of cofacial molecules with $C_N$ or $C_{Nh}$ symmetry supports excitonic states with a screwlike structure. These can be quantified with the combination of an axial wave number and an azimuthal winding number. Combinations of these states can be used to construct excitonic wave packets that spiral down the chain with well-determined linear and angular momenta. These twisted exciton wave packets can be created and annihilated using laser pulses, and their angular momentum can be optically modified during transit. This allows for the creation of optoexcitonic circuits in which information, encoded in the angular momentum of light, is converted into excitonic wave packets that can be manipulated, transported, and then reemitted. A tight-binding paradigm is used to demonstrate the key ideas. The approach is then extended to quantify the evolution of twisted exciton wave packets in a many-body, multilevel time-domain density functional theory setting. In both settings, numerical methods are developed that allow the site-to-site transfer of angular momentum to be quantified.

We report on the observation of a significant increase of the radiative decay rates for exciton transitions in a wide (In,Ga)As/GaAs quantum well ($L=95$ nm) in magnetic fields up to 6 T applied along the growth axis of the heterostructure. The absolute values of the radiative decay rates are obtained from a quantitative analysis of resonant features in the experimentally measured reflectance spectra in the range of the optical transitions to the quantum-confined exciton states. High crystalline quality of the heterostructure allows us to observe the ground and several excited exciton transitions with the nonradiative broadening comparable to the radiative one. We employ a numerical procedure appropriate for the studied wide quantum well to model the increase of the radiative decay rate in magnetic field. The results of the modeling agree well with the experimental data.

Charge and heat transfer through a nanoscale conductor is not only determined by the transmission properties of the electrons, but can also be strongly impacted by coupling to other degrees of freedom in the environment of the conductor. Here, we analyze the influence of the electromagnetic environment on a simple, yet significant, thermoelectric property, the thermopower, in the simple transport scenario of single-charge transfer across a tunnel junction. Considering both thermal and out-of-equilibrium steady-state environments, we find that the thermopower can be strongly affected by the environmental state and can, in turn, act as a sensitive probe of environmental properties.

LaBi is a three-dimensional rocksalt-type material with a surprisingly quasi-two-dimensional electronic structure. It exhibits excellent electronic properties such as the existence of nontrivial Dirac cones, extremely large magnetoresistance, and high charge-carrier mobility. The cigar-shaped electron valleys make the charge transport highly anisotropic when the magnetic field is varied from one crystallographic axis to another. We show that the electrons can be polarized effectively in these electron valleys under a rotating magnetic field. We achieved a polarization of 60% at 2 K despite the coexistence of three-dimensional hole pockets. The valley polarization in LaBi is compared to the sister compound LaSb where it is found to be smaller. The performance of LaBi is comparable to the highly efficient bismuth.

We propose the lead sulphide (PbS) monolayer as a two-dimensional semiconductor with a large Rashba-like spin-orbit effect controlled by the out-of-plane buckling. The buckled PbS conduction band is found to possess Rashba-like dispersion and spin texture at the $M$ and $\mathrm{\Gamma }$ points, with large effective Rashba parameters of $\lambda \sim 5$ eV Å and $\lambda \sim 1$ eV Å, respectively. Using a tight-binding formalism, we show that the Rashba effect originates from the very large spin-orbit interaction and the hopping term that mixes the in-plane and out-of-plane $p$ orbitals of Pb and S atoms. The latter, which depends on the buckling angle, can be controlled by applying strain to vary the spin texture as well as the Rashba parameter at $\mathrm{\Gamma }$ and $M$. Our density functional theory results together with tight-binding formalism provide a unifying framework for designing Rashba monolayers and for manipulating their spin properties.

We study the relaxation dynamics of photocarriers in the paramagnetic Mott insulating phase of the half-filled two-band Hubbard model. Using nonequilibrium dynamical mean-field theory, we excite charge carriers across the Mott gap by a short hopping modulation, and simulate the evolution of the photodoped population within the Hubbard bands. We observe an ultrafast charge-carrier relaxation driven by the emission of local spin excitations with an inverse relaxation time proportional to the Hund's coupling. The photodoping generates additional side-bands in the spectral function, and for strong Hund's coupling, the photodoped population also splits into several resonances. The dynamics of the local many-body states reveals two effects, thermal blocking and kinetic freezing, which manifest themselves when the Hund's coupling becomes of the order of the temperature or the bandwidth, respectively. These effects, which are absent in the single-band Hubbard model, should be relevant for the interpretation of experiments on correlated materials with multiple active orbitals. In particular, the features revealed in the nonequilibrium energy distribution of the photocarriers are experimentally accessible, and provide information on the role of the Hund's coupling in these materials.

In the low-energy two-band as well as four-band continuum models, we study the supercritical charge instability in gapped bilayer graphene in the field of an impurity charge when the lowest-energy bound state dives into the hole continuum. It is found that the screening effects are crucially important in bilayer graphene. If they are neglected, then the critical value for the impurity charge tends to zero as the gap $\mathrm{\Delta }$ vanishes. If the screened Coulomb interaction is considered, then the critical charge tends to a finite value for $\mathrm{\Delta }\to 0$. The different scalings of the kinetic energy of quasiparticles and the Coulomb interaction with respect to the distance to the charged impurity ensure that the wave function of the electron bound state does not shrink toward the impurity as its charge increases. This results in the absence of the fall-to-center phenomenon in bilayer graphene although the supercritical charge instability is realized.

We investigate the effects of the in-plane biaxial strain and charge doping on the charge density wave (CDW) order of monolayer $1T-{\mathrm{TiSe}}_2$ by using the first-principles calculations. Our results show that the tensile strain can significantly enhance the CDW order, while both compressive strain and charge doping (electrons and holes) suppress the CDW instability. The tensile strain may provide an effective method for obtaining higher CDW transition temperature on the basis of monolayer $1T-{\mathrm{TiSe}}_2$. We also discuss the potential superconductivity in charge-doped monolayer $1T-{\mathrm{TiSe}}_2$. Controllable electronic phase transition from the CDW state to the metallic state or even the superconducting state can be realized in monolayer $1T-{\mathrm{TiSe}}_2$, which makes $1T-{\mathrm{TiSe}}_2$ possess a promising application in controllable switching electronic devices based on CDW.

Using laser-generated shock waves, we have measured pressure, density, and temperature of LiH on the principal Hugoniot between 260 and 1100 GPa (2.6–11 Mbar) and on a second-shock Hugoniot up to 1400 GPa to near fivefold compression, extending the maximum pressure reached in non-nuclear experiments by a factor of two. We observe the onset of metal-like reflectivity consistent with temperature-induced ionization of the Li 2s electron, and no sign of additional changes in ionization up to the maximum pressure. Our measurements are in good agreement with gas gun, Z-machine, and underground test data and are accurately described by quantum molecular dynamics simulations. The results confirm the validity of equation of state models built on an average-atom description of the electron-thermal contribution to the free energy and a density-dependent Grüneisen parameter to describe shock response of LiH over this pressure range.

Spin Hall angle characterizes the rate of spin-charge current conversion and it has become one of the most important material parameters for spintronics physics and device application. A long-standing controversy is that the spin Hall angles for a given material measured by spin pumping and by spin Hall torque experiments are inconsistent and they could differ by as much as an order of magnitude. By using the linear response spin transport theory, we explicitly formulate the relation between the spin Hall angle and measured variables in different experiments. We find that the nonlocal conductivity inherited in the layered structure plays a key role to resolve conflicting values of the spin Hall angle. We provide a generalized scheme for extracting spin transport coefficients from experimental data.