We propose a class of topological metals, which we dub Hund nodal line semimetals, arising from the strong Coulomb interaction encoded in the Hund's coupling between itinerant electrons and localized spins. We here consider a particular twisted spin configuration, which is realized in the double-exchange model which describes the manganite oxides. The resulting effective tetragonal lattice of electrons with hoppings tied to the local spin features an antiunitary nonsymmorphic symmetry that, in turn, together with another nonsymmorphic but unitary glide-mirror symmetry, protects crossings of a double pair of bands along a high-symmetry line on the Brillouin zone boundary. We also discuss the stability of Hund nodal line semimetals with respect to symmetry breaking arising from various perturbations of the twisted phase. Our results motivate further studies of other realizations of this state of matter, for instance, in different spin backgrounds, properties of its drumhead surface states, as well as its stability to disorder and interactions among the itinerant electrons.

${\mathrm{BaFe}}_2{\mathrm{S}}_3$ is a quasi-one-dimensional Mott insulator that orders antiferromagnetically below 117(5) K. The application of pressure induces a transition to a metallic state, and superconductivity emerges. The evolution of the magnetic behavior on increasing pressure has up to now been either studied indirectly by means of transport measurements, or by using local magnetic probes only in the low pressure region. Here, we investigate the magnetic properties of ${\mathrm{BaFe}}_2{\mathrm{S}}_3$ up to 9.9 GPa by means of synchrotron ${}^{57}\mathrm{Fe}$ Mössbauer spectroscopy experiments, providing the first local magnetic phase diagram. The magnetic ordering temperature increases up to 185(5) K at 7.5 GPa, and is fully suppressed at 9.9 GPa. The low-temperature magnetic hyperfine field is continuously reduced from 12.9 to 10.3 T between 1.4 and 9.1 GPa, followed by a sudden drop to zero at 9.9 GPa indicating a first-order phase transition. The pressure dependence of the magnetic order in ${\mathrm{BaFe}}_2{\mathrm{S}}_3$ can be qualitatively explained by a combination of a bandwidth-controlled insulator-metal transition as well as a pressure enhanced exchange interaction between Fe atoms and $\mathrm{Fe}3d\text{−}\mathrm{S}3p$ hybridization.

A ${}^{59}\mathrm{Co}$ nuclear quadrupole resonance (NQR) was performed on a single-crystalline ferromagnetic (FM) superconductor UCoGe under pressure. The FM phase vanished at a critical pressure $P_c$, and the NQR spectrum just below $P_c$ showed phase separation of the FM and paramagnetic (PM) phases below Curie temperature $T_{\text{Curie}}$, suggesting first-order FM quantum phase transition (QPT). We found that the internal field was absent above $P_c$, but the superconductivity is almost unchanged. This result suggests the existence of the nonunitary to unitary transition of the superconductivity around $P_c$. Nuclear spin-lattice relaxation rate $1/T_1$ showed the FM critical fluctuations around $P_c$, which persist above $P_c$ and are clearly related to superconductivity in the PM phase. This FM QPT is understood to be a weak first order with critical fluctuations. $1/T_1$ sharply decreased in the superconducting (SC) state above $P_c$ with a single component, in contrast to the two-component $1/T_1$ in the FM SC state, indicating that the inhomogeneous SC state is a characteristic feature of the FM SC state in UCoGe.

We present the results of structural and magnetic phase comparisons of the iron oxychalcogenides ${\mathrm{La}}_2{\mathrm{O}}_2{\mathrm{Fe}}_2\mathrm{O}M{}_2(M=\text{S},\text{Se})$. Elastic neutron scattering reveals that $M=\text{S}$ and Se have similar nuclear structures at room and low temperatures. Our neutron diffraction data reveals that both materials obtain antiferromagnetic ordering at a Néel temperature $T_{N}90.1\pm 0.16$ K and $107.2\pm 0.06$ K for $M=\text{Se}$ and S, respectively. The magnetic arrangements for both $M=\text{S}$, Se compounds are obtained through Rietveld refinement. We find the order parameter exponent $\beta$ to be 0.$129\pm 0.006$ for $M=\text{Se}$ and $0.133\pm 0.007$ for $M=\text{S}$. Each of these values is near the Ising symmetry value of 1/8. This suggests that although lattice and electronic structural modifications result from chalcogen replacement, the nature of the magnetic interactions is similar in these materials.

Gilbert damping plays a significant role in magnetic reversal processes, and it determines the timescale of the switching. Here we investigate the properties of exchange-coupled composite media and the dependence of the switching time on the damping constant of the soft layer using atomistic spin dynamics. For a bilayer Fe/FePt medium, we find an anomalous increase of the switching time with increasing soft layer damping constant. The reversal occurs via a high-temperature exchange spring, and we show that the increase in the switching time is related to a corresponding increase in the time to establish the exchange spring. This phenomenon is delicately balanced in that the switching time increase occurs only in fields close to the coercivity.

By employing magnetization and small angle neutron scattering measurements, we have investigated the behavior of the skyrmion lattice (SKL) and the helical order in $\mathrm{MnS}{\mathrm{i}}_{0.992}\mathrm{G}{\mathrm{a}}_{0.008}$ Our results indicate that the order of the SKL is sensitive to the orientation of an applied magnetic field with respect to the crystal lattice and to variations in the sequence of small temperature and applied magnetic field changes. The disorder caused by the substitution of the heavier element Ga for Si is sufficient to reduce the pinning of the SKL to the underlying crystalline lattice, reducing the propensity for the SKL to be aligned with the crystal lattice. This tendency is most evident when the applied field is not well oriented with respect to the high symmetry axes of the crystal resulting in disorder in the long range SKL while maintaining sharp short range (radial) order. We have also investigated the effect of substituting heavier elements into MnSi on the reorientation process of the helical domains with field cycling in $\mathrm{MnS}{\mathrm{i}}_{0.992}\mathrm{G}{\mathrm{a}}_{0.008}$ and $\mathrm{M}{\mathrm{n}}_{0.985}\mathrm{I}{\mathrm{r}}_{0.015}\mathrm{Si}$ A comparison of the reorientation process in these materials with field reduction indicates that the substitution of heavier elements on either Mn or Si sites creates a higher energy barrier for the reorientation of the helical order and for the formation of domains.

This paper reports that ∼10-nm-thick iron selenide (FeSe) thin films exhibit insulator-like behavior in terms of the temperature dependence of their electrical resistivity even though bulk FeSe has a metallic electronic structure that has been confirmed by photoemission spectroscopy and first-principles calculations. This apparent contradiction is explained by potential barriers formed in the conduction band. Very thin FeSe epitaxial films with various atomic composition ratios ([Fe]/[Se]) were fabricated by molecular beam epitaxy and classified into two groups with respect to lattice strain and electrical properties. Lattice parameter $a$ increased and lattice parameter $c$ decreased with increasing [Fe]/[Se] up to 1.1 and then $a$ leveled off and $c$ began to decrease at higher [Fe]/[Se]. Consequently, the FeSe films had the most strained lattice when [Fe]/[Se] was 1.1, but these films had the best quality with respect to crystallinity and surface flatness. All the FeSe films with [Fe]/[Se] of 0.8–1.9 exhibited insulator-like behavior, but the temperature dependences of their electrical resistivities exhibited different activation energies $E_{\mathrm{a}}$ between the Se-rich and Fe-rich regions; i.e., $E_{\mathrm{a}}$ were small (a few meV) up to $\left[\mathrm{Fe}\right]/\left[\mathrm{Se}\right]=1.1$ but jumped up to ∼25 meV at higher [Fe]/[Se]. The film with $\left[\mathrm{Fe}\right]/\left[\mathrm{Se}\right]=1.1$ had the smallest $E_{\mathrm{a}}$ of 1.1 meV and exhibited an insulator–superconducting transition at 35 K with zero resistance under gate bias. The large $E_{\mathrm{a}}$ of the Fe-rich films was attributed to the unusual lattice strain with tensile in-plane and relaxed out-of-plane strains. The large $E_{\mathrm{a}}$ of films with [Fe]/[Se] > 1.1 resulted in low mobility with a high potential barrier of ∼50 meV in the conduction band for percolation carrier conduction compared with that of the $\left[\mathrm{Fe}\right]/\left[\mathrm{Se}\right]=1.1$ film (∼17 meV). Therefore, the Fe-rich films exhibited remarkable insulator-like behavior similar to a semiconductor despite their metallic electronic structure. The high potential barrier of Fe-rich films is tentatively attributed to the presence of large amounts of excess Fe, which could plausibly cause a broad superconducting transition without zero resistance under gating.

We investigate the statistics of microcavity polariton Bose–Einstein condensation by measuring photoluminescence dynamics from a GaAs microcavity excited by single laser excitation pulses. We directly observe fluctuations (jitter) of the polariton condensation onset time and model them using a master equation for the occupancy probabilities. The jitter of the condensation onset time is an inherent property of the condensate formation and its magnitude is approximately equal to the rise time of the condensate density. We investigate temporal correlations between the emission of condensate in opposite circular or linear polarizations by measuring the second-order correlation function $g^{\left(2\right)}(t_1,t_2)$. Polariton condensation is accompanied by spontaneous symmetry breaking revealed by the occurrence of random (i.e., varying from pulse to pulse) circular and linear polarizations of the condensate emission. The degree of circular polarization generally changes its sign in the course of condensate decay, in contrast to the degree of linear polarization.

Near-field radiative heat transfer has attracted increased attention in recent years for surpassing the far-field blackbody limit. Recently, it has been developed into three-body scenario to further enhance the heat transfer rate. Here we propose the exact formulation of near-field radiative heat transfer in three-body systems with periodic structures. We demonstrate that a three-grating system could provide the possibility to enhance radiative heat transfer over two-grating and three-slab counterparts. This enhancement is attributed to an additional heat transport channel provided by the intermediate grating, which can support hyperbolic surface modes in a specific wavelength range. Moreover, asymmetric situations are analyzed for weighting the impacts of both structure and position asymmetries on modulation of the near-field properties in the system. These findings open new pathways toward extended control over radiative heat transfer in the near-field regime.

The difficulty of describing excitons in semiconducting single-wall nanotubes analytically lies with the fact that excitons can neither be considered strictly one- nor two-dimensional objects. However, the situation changes in the case of metallic nanotubes where, by virtue of screening from gapless metallic subbands, the radius of the exciton becomes much larger than the radius of the nanotube $R_{\text{ex}}\gg R$. Taking advantage of this, we develop the theory of excitons in metallic nanotubes, determining that their binding energy is about $0.08v/R$, in agreement with the existing experimental data. Additionally, because of the presence of the gapless subbands, there are processes where bound excitons are scattered into unbound electron-hole pairs belonging to the gapless subbands. Such processes lead to a finite exciton lifetime and the broadening of its spectral function. We calculate the corresponding decay rate of the excitons.

We explore the influence of the nanoporous structure on the thermal relaxation of electrons and holes excited by ultrashort laser pulses ($\sim 7\mathrm{fs}$) in thin gold films. Plasmon decay into hot electron-hole pairs results in the generation of a Fermi-Dirac distribution thermalized at a temperature $T_{\mathrm{e}}$ higher than the lattice temperature $T_{\mathrm{l}}$. The relaxation times of the energy exchange between electrons and lattice, here measured by pump-probe spectroscopy, is slowed down by the nanoporous structure, resulting in much higher peak $T_{\mathrm{e}}$ than for bulk gold films. The electron-phonon coupling constant and the Debye temperature are found to scale with the metal filling factor $f$ and a two-temperature model reproduces the data. The results open the way for electron temperature control in metals by engineering of the nanoporous geometry.

We study electronic transport in two-dimensional spin-orbit coupled electron gas subjected to an in-plane magnetic field. The interplay of the spin-orbit interaction and the magnetic field leads to the Van Hove singularity of the density of states and strong anisotropy of Fermi contours. We develop a method that allows one to exactly calculate the nonequilibrium distribution function for these conditions within the framework of the semiclassical Boltzmann equation without using the scattering time approximation. The method is applied to calculate the conductivity tensor and the tensor of spin polarization induced by the electric field (Aronov-Lyanda-Geller-Edelstein effect). It is found that both the conductivity and the spin polarization have a sharp singularity as functions of the Fermi level or magnetic field, which occurs when the Fermi level passes through the Van Hove singularity. In addition, the transport anisotropy dramatically changes near the singularity.

We optimize the operation of single-electron charge pumps using full counting statistics techniques. To this end, we evaluate the statistics of pumped charge on a wide range of driving frequencies using Floquet theory, focusing here on the current and the noise. For charge pumps controlled by one or two gate voltages, we demonstrate that our theoretical framework may lead to enhanced device performance. Specifically, by optimizing the driving parameters, we predict a significant increase in the frequencies for which a quantized current can be produced. For adiabatic two-parameter pumps, we exploit that the pumped charge and the noise can be expressed as surface integrals over Berry curvatures in parameter space. Our findings are important for the efforts to realize high-frequency charge pumping, and our predictions may be verified using current technology.

In this work, we adapt the formalism of the dynamical vertex approximation ($\mathrm{D}\mathrm{\Gamma }\mathrm{A}$), a diagrammatic approach including many-body correlations beyond the dynamical mean-field theory, to the case of attractive on-site interactions. We start by exploiting the ladder approximation of the $\mathrm{D}\mathrm{\Gamma }\mathrm{A}$ scheme, in order to derive the corresponding equations for the nonlocal self-energy and vertex functions of the attractive Hubbard model. Second, we prove the validity of our derivation by showing that the results obtained in the particle-hole symmetric case fully preserve the exact mapping between the attractive and the repulsive models. It will be shown how this property can be related to the structure of the ladders, which makes our derivation applicable for any approximation scheme based on ladder diagrams. Finally, we apply our $\mathrm{D}\mathrm{\Gamma }\mathrm{A}$ algorithm to the attractive Hubbard model in three dimensions, for different fillings and interaction values. Specifically, we focus on the parameters region in the proximity of the second-order transition to the superconducting and charge-density wave phases, respectively, and calculate (i) their phase-diagrams, (ii) their critical behavior, as well as (iii) the effects of the strong nonlocal correlations on the single-particle properties.

We study the magnetic susceptibility, electrical resistivity, Hall effect, and heat capacity of single crystals of ${\mathrm{Sm}}_x{\mathrm{B}}_6$ for $x=1,0.94,0.8,$ and 0.75. Remarkably, the overall properties of the crystals do not qualitatively depend on the density of vacancies. The topological surface states are seen at low temperatures in the electrical transport properties as the bulk conductivity freezes out. Even a large number of Sm vacancies does not close the hybridization gap. The linear term in the specific heat $\gamma$, of unclear origin, remains large but decreases gradually with $x$. The shoulder in the density of states, brought by the hybridized $4f$ states and observed in the susceptibility and the specific heat, does not move but decreases its height with decreasing $x$. The specific heat also displays a weak Schottky anomaly at about 1.5 K for all $x$, except for the $x$ = 0.75 sample. This Schottky anomaly is only slightly field dependent and of unknown origin.

We study a one-dimensional model of interacting bosons coupled to a dynamical ${\mathbb{Z}}_2$ field, the ${\mathbb{Z}}_2$ Bose-Hubbard model, and analyze the interplay between spontaneous symmetry breaking and topological symmetry protection. In a previous work, we showed how this model exhibits a spontaneous breaking of the translational symmetry through a bosonic Peierls transition. Here we find how, at half filling, the resulting phase also displays topological features that coexist with the presence of long-range order and yields a topological bond order wave. Using both analytical and numerical methods, we describe the properties of this phase, showing that it cannot be adiabatically connected to a topological phase of noninteracting bosons, and thus constitutes an instance of an interaction-induced symmetry-breaking topological insulator.