There has been significant interest in recent years in finding fractional quantum Hall physics in lattice models, but it is not always clear how these models connect to the corresponding models in continuum systems. Here we introduce a family of models that is able to interpolate between a recently proposed set of lattice models with Laughlin-like ground states constructed from conformal field theory and models with ground states that are practically the usual bosonic/fermionic Laughlin states in the continuum. Both the ground state and the Hamiltonian are known analytically, and we find that the Hamiltonian in the continuum limit does not coincide with the usual delta interaction Hamiltonian for the Laughlin states. We introduce quasiholes into the models and show analytically that their braiding properties are as expected if the quasiholes are screened. We demonstrate screening numerically for the 1/3 Laughlin model and find that the quasiholes are slightly smaller in the continuum than in the lattice. Finally, we compute the effective magnetic field felt by the quasiholes and show that it is close to uniform when approaching the continuum limit. The techniques presented here to interpolate between the lattice and the continuum can also be applied to other fractional quantum Hall states that are constructed from conformal field theory.

Two samples of the ${\left[\mathrm{C}{\mathrm{a}}_2\mathrm{Co}{\mathrm{O}}_{3–t}\right]}_{0.62}\left(\mathrm{Co}{\mathrm{O}}_2\right)$ misfit cobaltate, often denoted as the $\mathrm{C}{\mathrm{a}}_3\mathrm{C}{\mathrm{o}}_4{\mathrm{O}}_9$ phase, were prepared from the same ceramic material by oxygen and argon annealing, resulting in different carrier concentrations in the conducting $\mathrm{Co}{\mathrm{O}}_2$ layers, $n=0.31$ and 0.19 hole/Co, respectively. Electrical and thermal transport properties were studied in dependence of magnetic field up to 140 kOe. The magnetothermopower data reveal an extra spin-entropy contribution to the Seebeck coefficient that is not expected for carriers of Fermi liquid character. Its magnitude is unprecedentedly large and makes at zero field up to $50\%$ of the theoretical limit $\frac{k_B}{|q_e|}ln2=59\mu \mathrm{V}/\mathrm{K}$. This spin-entropy contribution is gradually suppressed with increasing magnetic field, and the saturation is even observed when temperatures are low enough. To understand the results, the thermopower is treated in terms of a purely thermodynamic Kelvin formula, and the so-called spin-liquid model is evoked, providing a reason for the spin-entropy manifestation in the ${\left[\mathrm{C}{\mathrm{a}}_2\mathrm{Co}{\mathrm{O}}_{3–t}\right]}_{0.62}\left(\mathrm{Co}{\mathrm{O}}_2\right)$ misfits.

We derive asymptotically exact expressions for the thermopower and figure of merit of a quantum impurity connecting two noninteracting leads in the linear response regime where the chemical potential and temperature differences between the leads are small. Based on sum rules for the single-particle impurity spectral function, these expressions become exact at high temperatures as well as in the very strongly correlated regime, where the impurity Coulomb repulsion is much larger than the temperature. Although modest interactions impede thermoelectric performance, a very large Coulomb scale restores the optimal transport properties of noninteracting electrons, albeit renormalized to account for the absence of double occupancy in the impurity. As with noninteracting electrons, the electronic contribution to the figure of merit is limited only by the spectral broadening that arises from the coupling between the impurity and the leads.

We derive expressions of interatomic force and heat current for many-body potentials such as the Tersoff, the Brenner, and the Stillinger-Weber potential used extensively in molecular dynamics simulations of covalently bonded materials. Although these potentials have a many-body nature, a pairwise force expression that follows Newton's third law can be found without referring to any partition of the potential. Based on this force formula, a stress applicable for periodic systems can be unambiguously defined. The force formula can then be used to derive the heat current formulas using a natural potential partitioning. Our heat current formulation is found to be equivalent to most of the seemingly different heat current formulas used in the literature, but to deviate from the stress-based formula derived from two-body potential. We validate our formulation numerically on various systems described by the Tersoff potential, namely three-dimensional silicon and diamond, two-dimensional graphene, and quasi-one-dimensional carbon nanotube. The effects of cell size and production time used in the simulation are examined.

The Kondo lattice model is investigated through a fermionic mean-field approximation. The obtained phase diagram, including the pure ferromagnetic (FM), antiferromagnetic (AF), Kondo (K), and mixed phases, is in good agreement with previous studies. Calculations on the simple cubic and square lattices confirm a robust coexistence of ferromagnetism and Kondo effect (FM + K), sustained by a partial Kondo screening, which leads to the concept of a spin selective Kondo insulator. We have also obtained a coexistence of antiferromagnetism and Kondo effect (AF + K), which requires the intervenience of a next-nearest-neighbor hopping $t^{\prime }$ and a Heisenberg exchange $J_{ij}$. The effect of temperature and pressure is described by the behavior of the order parameters. The corresponding Néel temperature $T_N$ and Kondo temperature $T_K$ are plotted in the form of a Doniach diagram. The presence of the intermediate mixed phases is fundamental to determine the order of the magnetic phase transitions as one approaches the quantum critical point.

The origin of the metamagnetic antiferromagnetic-ferromagnetic phase transition of FeRh is a subject of debate. Competing explanations invoke magnetovolume effects or a purely thermodynamic transition within the spin system. It is experimentally difficult to observe the changes in the magnetic system and the lattice simultaneously, leading to conflicting evidence over which mechanism causes the phase transition. A noncollinear electronic structure study by Mryasov [Phase Transitions 78, 197 (2005)] showed that nonlinear behavior of the Rh moment leads to higher-order exchange terms in FeRh. Using atomistic spin dynamics, we show that the phase transition can occur due to the competition between bilinear and the higher-order four spin exchange terms in an effective spin Hamiltonian. The phase transition we see is of first order and shows thermal hysteresis in agreement with experimental observations. Simulating subpicosecond laser heating, we show an agreement with pump-probe experiments with a ferromagnetic response on a picosecond time scale.

We investigate the magnetization relaxation of a one-dimensional helimagnetic system coupled to interacting itinerant electrons. The relaxation is assumed to result from the emission of plasmons, the elementary excitations of the one-dimensional interacting electron system, caused by slow changes of the magnetization profile. This dissipation mechanism leads to a highly nonlocal form of magnetization damping that is strongly dependent on the electron-electron interaction. Forward-scattering processes lead to a spatially constant damping kernel, while backscattering processes produce a spatially oscillating contribution. Due to the nonlocal damping, the thermal fluctuations become spatially correlated over the entire system. We estimate the characteristic magnetization relaxation times for magnetic quantum wires and nuclear helimagnets.

We investigate the magnetic anisotropy of epitaxial Fe films on GaN(0001) and $\mathrm{GaN}\left(000\overline{1}\right)$. Due to the particular orientation relationship between Fe and GaN{0001}, the leading term proportional to $K_1$ does not contribute to the magnetic anisotropy, allowing us to determine $K_3$ with unprecedented accuracy. Using two experimental techniques, we obtain values for $K_3$ of $4.7–9.2\times {10}^5 \mathrm{erg}/\mathrm{cm}{}^3$, i.e., comparable to and even larger than $K_1$.

Two critical points have been revealed in the normal-state phase diagram of the electron-doped cuprate superconductor ${\mathrm{Nd}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$ by exploring the Fermi surface properties of high-quality single crystals by high-field magnetotransport. First, the quantitative analysis of the Shubnikov-de Haas effect shows that the weak superlattice potential responsible for the Fermi surface reconstruction in the overdoped regime extrapolates to zero at the doping level $x_c=0.175$ corresponding to the onset of superconductivity. Second, the high-field Hall coefficient exhibits a sharp drop right below optimal doping $x_{\mathrm{opt}}=0.145$ where the superconducting transition temperature is maximum. This drop is most likely caused by the onset of long-range antiferromagnetic ordering. Thus the superconducting dome appears to be pinned by two critical points to the normal state phase diagram.

We investigated current induced depairing in the ${\mathrm{Bi}}_2{\mathrm{Te}}_3/\mathrm{FeTe}$ topological insulator-chalcogenide interface superconductor. The measured depairing current density provides information on the magnetic penetration depth and superfluid density, which in turn shed light on the nature of the normal state that underlies the interfacial superconductivity.

We have studied the anisotropy in the in-plane resistivity and the electronic structure of isovalent Ru-substituted ${\mathrm{BaFe}}_2{\mathrm{As}}_2$ in the antiferromagnetic-orthorhombic phase using well-annealed crystals. The anisotropy in the residual resistivity component increases in proportion to the Ru dopant concentration, as in the case of Co-doped compounds. On the other hand, both the residual resistivity and the resistivity anisotropy induced by isovalent Ru substitution are found to be 1 order of magnitude smaller than those induced by heterovalent Co substitution. Combined with angle-resolved photoemission spectroscopy results, which show almost the same anisotropic band structure for both the parent and the Ru-substituted compounds, we confirm the scenario that the anisotropy in the residual resistivity arises from anisotropic impurity scattering in the magnetostructurally ordered phase rather than directly from the anisotropic band structure of that phase.

We present the experimental generation and observation of an underwater acoustic accelerating beam. The beam was generated by phase modulating a single projector using a tailored acoustic phase mask. The beam is propagating for a range in excess of 800 wavelengths, which are about six Rayleigh lengths, while preserving its shape and transversely accelerating. Such beams have promising applications in the fields of sonar, hydrography, and medical ultrasound and can provide new means to study nonlinear interaction of acoustic beams.

We derive a non-Markovian master equation for the evolution of a class of open quantum systems consisting of quadratic fermionic systems coupled to wideband reservoirs. This is done by providing an explicit correspondence between master equations and nonequilibrium Green's function approaches. Our findings permit us to address non-Markovian regimes characterized by negative decoherence rates and to characterize the dynamics with respect to a recently proposed measurement of “non-Markovianity.” We study the real-time dynamics and the steady-state solution of two illustrative models: a tight-binding electronic model and $\mathit{XY}$ spin chains. The rich set of nonequilibrium steady-state phases encountered extends previous results to the non-Markovian regime.

We consider the effect of adding quantum dynamics to a classical topological spin liquid, with a particular view of how to best detect its presence in experiment. For the Coulomb phase of spin ice, we find quantum effects to be most visible in the gauge-charged monopole excitations. In the presence of weak dilution with nonmagnetic ions we find a particularly crisp phenomenon, namely, the emergence of hydrogenic excited states in which a magnetic monopole is bound to a vacancy at various distances. Via a mapping to an analytically tractable single particle problem on the Bethe lattice, we obtain an approximate expression for the dynamic neutron scattering structure factor.

In this work we formulate the nonequilibrium dynamical renormalization group (ndRG). The ndRG represents a general renormalization-group scheme for the analytical description of the real-time dynamics of complex quantum many-body systems. In particular, the ndRG incorporates time as an additional scale which turns out to be important for the description of the long-time dynamics. It can be applied to both translational-invariant and disordered systems. As a concrete application, we study the real-time dynamics after a quench between two quantum critical points of different universality classes. We achieve this by switching on weak disorder in a one-dimensional transverse-field Ising model initially prepared at its clean quantum critical point. By comparing to numerically exact simulations for large systems, we show that the ndRG is capable of analytically capturing the full crossover from weak to infinite randomness. We analytically study signatures of localization in both real space and Fock space.

Here we demonstrate an experimental observation of GHz-scale spin dynamics resolved to sublattice octahedral ($O_h$) tetrahedral ($T_d$) sites in a spinel ferrimagnet, in this case a Mn-ferrite thin film. X-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) are used, in combination with multiplet calculations, to uniquely identify the spectral signature from ${\mathrm{Mn}}^{2+}$ and ${\mathrm{Fe}}^{2+,3+}$ on $O_h$ and $T_d$ lattice sites. With the sample under $\mathit{rf}$ excitation, the spin alignment of the sublattices is tracked with time-resolved XMCD (TR-XMCD). The spin alignment of the sublattices is mostly antiferromagnetic. The phase difference between the $O_h {\mathrm{Fe}}^{2+}$ [$O_h {\mathrm{Fe}}^{3+}$] and $T_d {\mathrm{Mn}}^{2+}$ sites is $181.2\pm 3.8^{\circ }$ [$183.3^{\circ }\pm 3.7^{\circ }$] at 150 K and $186.6\pm 2.2^{\circ }$ [$182.0^{\circ }\pm 2.2^{\circ }$] at 300 K. Such direct measurement of the dynamic coupling, exchange stiffness, and damping enabled by TR-XMCD across sublattices will be essential for optimizing the development of future-generation microwave devices.

Nonreciprocal microwave transmission through a long Josephson junction in the flux-flow regime is studied analytically and numerically within the framework of the perturbed sine-Gordon model. We demonstrate that the maximum attenuation of the transmitted microwave power occurs when the direction of the flux flow is opposite the direction of the microwave propagation. This attenuation is nonreciprocal with respect to the flux-flow direction and can be enhanced by increasing the system length and proper impedance matching of the junction ends to the external transmission line.

We discuss effects of surface perturbations on equilibrium surface currents which contribute to orbital magnetization and orbital angular momentum in systems without time-reversal symmetry. We show that, in a U(1) particle-number-conserving system, disorder and other perturbations at a surface do not affect the equilibrium surface current and corresponding orbital magnetization, due to a sum rule which is analogous to Luttinger's theorem. On the other hand, for a superfluid, the sum rule is no longer applicable and hence the surface mass current and corresponding orbital angular momentum can depend on details of a surface.

We develop a theory for electron-electron interaction-induced many-body effects in three-dimensional Weyl or Dirac semimetals, including interaction corrections to the polarizability, electron self-energy, and vertex function, up to second order in the effective fine-structure constant of the Dirac material. These results are used to derive the higher-order ultraviolet renormalization of the Fermi velocity, effective coupling, and quasiparticle residue, revealing that the corrections to the renormalization group flows of both the velocity and coupling counteract the leading-order tendencies of velocity enhancement and coupling suppression at low energies. This in turn leads to the emergence of a critical coupling above which the interaction strength grows with decreasing energy scale. In addition, we identify a range of coupling strengths below the critical point in which the Fermi velocity varies nonmonotonically as the low-energy, noninteracting fixed point is approached. Furthermore, we find that while the higher-order correction to the flow of the coupling is generally small compared to the leading order, the corresponding correction to the velocity flow carries an additional factor of the Dirac cone flavor number (the multiplicity of electron species, e.g. ground-state valley degeneracy arising from the band structure) relative to the leading-order result. Thus, for materials with a larger multiplicity, the regime of velocity nonmonotonicity is reached for modest values of the coupling strength. This is in stark contrast to an approach based on a $\text{large}-N$ expansion or the random phase approximation (RPA), where higher-order corrections are strongly suppressed for larger values of the Dirac cone multiplicity. This suggests that perturbation theory in the coupling constant (i.e., the loop expansion) and the $\text{RPA}/\text{large}-N$ expansion are complementary in the sense that they are applicable in different parameter regimes of the theory. We show how our results for the ultraviolet renormalization of quasiparticle properties can be tested experimentally through measurements of quantities such as the optical conductivity or dielectric function (with carrier density or temperature acting as the scale being varied to induce the running coupling). Although experiments typically access the finite-density regime, we show that our zero-density results still capture clear many-body signatures that should be visible at higher temperatures even in real systems with disorder and finite doping.

We report on the direct and quantitative evaluation of density of gap states (DOGS) in large-size ${\mathrm{C}}_{60}$ single crystals by using ultralow-background, high-sensitivity ultraviolet photoemission spectroscopy. The charging of the crystals during photoionization was overcome using photoconduction induced by simultaneous laser irradiation. By comparison with the spectra of as-deposited and gas exposed ${\mathrm{C}}_{60}$ thin films the following results were found: (i) The DOGS near the highest occupied molecular orbital edge in the ${\mathrm{C}}_{60}$ single crystals $({10}^{19}-{10}^{21}\mathrm{states}\mathrm{e}{\mathrm{V}}^{-1}\mathrm{c}{\mathrm{m}}^{-3})$ mainly originates from the exposure to inert and ambient gas atmosphere during the sample preparation, storage, and transfer; (ii) the contribution of other sources of gap states such as structural imperfections at grain boundaries is negligible $(<{10}^{18}\mathrm{states}\mathrm{e}{\mathrm{V}}^{-1}\mathrm{c}{\mathrm{m}}^{-3})$.