While the magnetic properties of nanoscaled antidot lattices in in-plane magnetized materials have widely been investigated, much less is known about the microscopic effect of hexagonal antidot lattice patterning on materials with perpendicular magnetic anisotropy. By using a combination of first-order reversal curve measurements, magnetic x-ray microscopy, and micromagnetic simulations we elucidate the microscopic origins of the switching field distributions that arise from the introduction of antidot lattices into out-of-plane magnetized GdFe thin films. Depending on the geometric parameters of the antidot lattice we find two regimes with different magnetization reversal processes. For small antidots, the reversal process is dominated by the exchange interaction and domain wall pinning at the antidots drives up the coercivity of the system. On the other hand, for large antidots the dipolar interaction is dominating which leads to fragmentation of the system into very small domains that can be envisaged as a basis for a bit patterned media.

We report on the magnetic properties of ${\mathrm{Eu}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ upon the application of hydrostatic pressure $P$ by means of macroscopic and local-probe techniques. In contrast to previously reported resistivity measurements, our dc magnetization data unambiguously demonstrate a nonmonotonic dependence of $T_N$, i.e., the critical transition temperature to the magnetic phase, on $P$. Strikingly, the recently calculated behavior for $T_N$ closely reproduces our results under the assumption that $P$ lowers the $U/W$ ratio (i.e., Coulomb repulsion energy over electronic bandwidth). Zero-field muon-spin spectroscopy measurements confirm that the ${\mathrm{Ir}}^{4+}$ magnetic moment and/or the local magnetic configuration are only weakly perturbed by low $P$ values. Accordingly, our current experimental findings strongly support the preservation of a 4-$\mathrm{in}/4$-out ground state across the accessed region of the phase diagram.

Parallel pumping of nuclear spin waves in antiferromagnetic ${\mathrm{CsMnF}}_3$ at liquid helium temperatures and magnetoelastic waves in antiferromagnetic ${\mathrm{FeBO}}_3$ at liquid nitrogen temperature in a helical resonator was studied. It was found that the absorbed microwave power is approximately equal to the irradiated power from the sample and that the main restriction mechanism of absorption in both cases is defined by the nonlinear radiation damping predicted about two decades ago. Nonlinear radiation damping is sure to be a common feature of the parallel pumping technique for all normal magnetic excitations and it must be taken into account for interpretation of nonlinear phenomena in parametrically excited magnetic systems.

We investigated $\mathrm{SrFe}{}_2\left(\mathrm{As}{}_{1-x}{\mathrm{P}}_x\right){}_2$ single crystals with four different phosphorus concentrations $x$ in the superconducting phase $\left(x=0.35,0.46\right)$ and in the magnetic phase $\left(x=0,0.2\right)$. The superconducting samples display a V-shaped superconducting gap, which suggests nodal superconductivity. Furthermore, we determined the superconducting coherence length by measuring the spatially resolved superconducting density of states. Using inelastic tunneling spectroscopy, we investigated excitations in the samples with four different phosphorus concentrations. Inelastic peaks are related to bosonic modes. The phonon and nonphonon mechanisms for the origin of these peaks are discussed.

Magnetic-electronic hyperfine interaction parameters of spectral components are obtained from in situ ${}^{57}\mathrm{Fe}$ Mössbauer spectroscopy pressure studies of the mixed-valence $\mathrm{LuF}{\mathrm{e}}_2{\mathrm{O}}_4$ multiferroic, up to $\sim 30\mathrm{GPa}$ and on recovered high-pressure phase samples. Temperature-dependent Mössbauer spectra of the low-pressure phase show that $\mathrm{F}{\mathrm{e}}^{2+}$ and $\mathrm{F}{\mathrm{e}}^{3+}$ sites are discernible, consistent with known site-centered charge order in the triangular (frustrated) Fe sublattice network. Magnetic spectra of the high-pressure phase, stabilized in a rectangular Fe sublattice network at $P>8\mathrm{GPa}$, exhibit fingerprints of iron in an intermediate valence state only. Temperature-dependent resistivity pressure studies evidence thermally activated small polaron motion in the high-pressure phase. These experimental signatures, complemented by ab initio calculations of electronic structure, are considered evidence of asymmetric dimer formation ${\mathrm{Fe}}^{(2+\mathrm{\Delta }+)}\iff {\mathrm{Fe}}^{(3-\mathrm{\Delta })+}$, where the minority-spin electron deconfinement coefficient is $\mathrm{\Delta }=0.3-0.4$. Bragg satellites discerned in electron diffraction patterns of the metastable high-pressure phase possibly stem from this admixture of site- and bond-centered localization (intermediate-state charge order) in a magnetic background. This breaks inversion symmetry and potentially renders $\mathrm{LuF}{\mathrm{e}}_2{\mathrm{O}}_4$ in its high-pressure phase as a new charge order instigated (electronic) ferroelectric.

We report two-dimensional quantum transport and Dirac fermions in ${\mathrm{BaMnBi}}_2$ single crystals. ${\mathrm{BaMnBi}}_2$ is a layered bad metal with highly anisotropic conductivity and magnetic order below 290 K. Magnetotransport properties, nonzero Berry phase, small cyclotron mass, and the first-principles band structure calculations indicate the presence of Dirac fermions in Bi square nets. Quantum oscillations in the Hall channel suggest the presence of both electron and hole pockets, whereas Dirac and parabolic states coexist at the Fermi level.

By realizing a nonvolatile third intermediate ferroelectric state through anisotropic misfit strain, we demonstrate electrical switching among three stable out-of-plane polarizations in bismuth ferrite thin films grown on ${\left(110\right)}_{\mathrm{pc}}$-oriented gadolinium scandate substrates (where pc stands for pseudocubic) by the use of an asymmetric external electric field at the step edge of a bottom electrode. We employ phenomenological Landau theory, in conjunction with electrical poling experiments using piezoresponse force microscopy, to understand the role of anisotropic misfit strain and an in-plane electric field in stabilization of multiple ferroelectric states and their competition. Our finding provides a useful insight into multistep ferroelectric switching in rhombohedral ferroelectrics.

We develop the theoretical formalism to calculate second-order correlations in dissipative exciton-polariton system and we propose intensity-intensity correlation experiments to reveal the physics of exciton-light coupling in semiconductor microcavities in the Rabi oscillation regime. We predict a counterintuitive behavior of the correlator between upper and lower polariton branches: Due to the decoherence caused by stochastic exciton-photon conversions this correlator is expected to decrease below 1, while the individual second-order coherence of upper and lower polaritons exhibits nonmonotonous bunching.

The thermodynamic stability of ${\mathrm{UO}}_2$ surfaces is investigated using ab initio calculations. We employ the GGA+$U$ framework to properly model the strong electronic correlations of the uranium $5f$ electrons. Among the seven terminations of the (100), (110), and (111) orientations studied in this paper, we predict that the stoichiometric O-(111) is the most stable one under oxygen-poor or -intermediary environments. At odds with other fluorite surfaces, the overstoichiometric and polar ${\mathrm{O}}_2$-(100) and ${\mathrm{O}}_2$-(111) terminations become the most stable in oxygen-rich environments. For the latter, strong modifications of the electronic structure appear within the upper layers, in order to fulfill the polarity compensation criterion. Some U-$5f$ states are emptied, leading to higher oxidation $5+$ and $6+$ states for uranium in the outermost layers, but leaving the surface insulating. This unexpected polarity compensation mechanism is not observed for other charge transfer compounds (such as ${\mathrm{PuO}}_2$) and can be related to the $f\text{−}f$ Mott-Hubbard band gap of the ${\mathrm{UO}}_2$ material. By considering the most stable stoichiometric and overstoichiometric terminations, the Castell's ratio can be fulfilled, explaining the Wulff shape of nanovoids in ${\mathrm{UO}}_2$ crystals.

Plasmons are commonly interpreted with classical electrodynamics, while nonclassical effects may influence the dynamics of plasmon resonances as the plasmon confinement approaches the few-nanometer scale. However, an unambiguous approach to quantify the degree of nonclassical dynamics remains. We propose a nonclassical-impact parameter (NCI) to characterize the degree of nonclassical effects from an energy perspective, i.e., which fraction of the total electromagnetic energy is attributed to classical electrodynamic terms and which fraction is correspondingly to be assigned to nonclassical degrees of freedom? We show that the NCI relates directly to two fundamental parameters of plasmon resonances: the loss function and the quality factor. Guided by the NCI, we discuss the nonclassical effects of plasmon waveguiding modes of metallic slab waveguides, and highlight the general features of the nonclassical effects at different microscopic levels by contrasting the numerical results from the semiclassical hydrodynamic Drude model (HDM) and the microscopic random-phase approximation (RPA). The formal relation between the HDM and the RPA is also established for metals by exploring the limit of an infinite work function.

We have carried out the measurements of high-pressure ${}^{11}\mathrm{B}$-nuclear magnetic resonance on the intermediate-valence compound ${\mathrm{SmB}}_6$ to investigate the effects of pressure on Sm $4f$ states and the quasiparticle band. From the measurements of spin-lattice relaxation time, just below the critical pressure $P_{\mathrm{c}}$ of nonmagnetic-magnetic phase transition, we find that quasiparticle bandwidth clearly decreases with pressure, while the insulating gap is almost constant or slightly increases. The latter is consistent with the result of a band-structure calculation. These pressure induced modifications in the band structure indicate the enhancement of the density of states of the quasiparticles when approaching $P_{\mathrm{c}}$. The pressure dependence of the Sm $4f$ states and the origin of the insulating gap are well explained in terms of exchange interactions between conduction and $4f$ electrons.

Noncentrosymmetric transition-metal monopnictides, including TaAs, TaP, NbAs, and NbP, are emergent topological Weyl semimetals (WSMs) hosting exotic relativistic Weyl fermions. In this Rapid Communication, we elucidate the physical origin of the unprecedented charge carrier mobility of NbP, which can reach $1\times {10}^7{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ at 1.5 K. Angle- and temperature-dependent quantum oscillations, supported by density function theory calculations, reveal that NbP has the coexistence of $p$- and $n$-type WSM pockets in the $k_z=1.16\pi /c$ plane (W1-WSM) and in the $k_z=0$ plane near the high symmetry points $\mathrm{\Sigma }$ (W2-WSM), respectively. Uniquely, each W2-WSM pocket forms a large dumbbell-shaped Fermi surface enclosing two neighboring Weyl nodes with the opposite chirality. The magnetotransport in NbP is dominated by these highly anisotropic W2-WSM pockets, in which Weyl fermions are well protected from defect backscattering by real spin conservation associated to the chiral nodes. However, with a minimal doping of $\sim 1\%$ Cr, the mobility of NbP is degraded by more than two orders of magnitude, due to the invalidity of helicity protection to magnetic impurities. Helicity protected Weyl fermion transport is also manifested in chiral anomaly induced negative magnetoresistance, controlled by the W1-WSM states. In the quantum regime below 10 K, the intervalley scattering time by impurities becomes a large constant, producing the sharp and nearly identical conductivity enhancement at low magnetic field.

A topological nodal-line semimetal is a state of matter with one-dimensional bulk nodal lines and two-dimensional so-called drumhead surface bands. Based on first-principles calculations and an effective $\mathit{k}·\mathit{p}$ model, we theoretically propose the existence of topological nodal-line fermions in the ternary transition-metal chalcogenide ${\mathrm{TlTaSe}}_2$. The noncentrosymmetric structure and strong spin-orbit coupling give rise to spinful nodal-line bulk states which are protected by a mirror reflection symmetry of this compound. This is remarkably distinguished from other proposed nodal-line semimetals such as ${\mathrm{Cu}}_3\mathrm{NPb}$(Zn) in which the nodal line exists only in the limit of vanishing spin-orbit coupling and thus is not as robust. In addition, we show that the drumhead surface states in ${\mathrm{TlTaSe}}_2$, which are associated with the topological nodal lines, exhibit an unconventional chiral spin texture and an exotic Lifshitz transition as a consequence of the linkage among multiple drumhead surface-state pockets.

This Rapid Communication was motivated by the quest for observing interference of fractionally charged quasiparticles. Here, we study the behavior of an electronic Mach-Zehnder interferometer at the integer quantum Hall effect regime at filling factors greater than 1. Both the visibility and the velocity were measured and found to be highly correlated as a function of the filling factor. As the filling factor approached unity, the visibility quenched, not to recover for filling factors smaller than unity. Alternatively, the velocity saturated around a minimal value at the unity filling factor. We highlight the significant role interactions between the interfering edge and the bulk play as well as that of the defining potential at the edge. Shot-noise measurements suggest that phase averaging (due to phase randomization), rather than single-particle decoherence, is likely to be the cause of the dephasing in the fractional regime.

We first provide a formula to calculate the probability of occurrence of different configurations (formation probabilities) in a generic free fermion system. We then study the scaling of these probabilities with respect to the size in the case of the critical transverse-field XY chain in the ${\sigma }^z$ bases. In the case of the transverse field Ising model, we show that all the “crystal” configurations follow the formulas expected from conformal field theory (CFT). In the case of the critical XX chain, we show that the only configurations that follow the formulas of the CFT are the ones which respect the filling factor of the system. By repeating all the calculations in the presence of open and periodic boundary conditions we find further support for our classification of different configurations. Using the developed technique, we also study Shannon information of a subregion in our system. In this respect we distinguish particular configurations that are more important in the study of the scaling limit of the Shannon information of the subsystem. Finally, we study the evolution of formation probabilities, Shannon information, and Shannon mutual information after a quantum quench in free fermion system. In particular, for the initial state considered in this paper, we demonstrate that the Shannon information after quantum quench first increases with the time and then saturates at time $t^{*}=\frac{l}{2}$, where $l$ is the size of the subsystem.

The impact of variable Ti self-doping on the $1T-{\mathrm{TiSe}}_2$ charge density wave (CDW) is studied by scanning tunneling microscopy. Supported by density functional theory, we show that agglomeration of intercalated-Ti atoms acts as preferential nucleation centers for the CDW that breaks up in phase-shifted CDW domains whose size directly depends on the intercalated-Ti concentration and which are separated by atomically sharp phase boundaries. The close relationship between the diminution of the CDW domain size and the disappearance of the anomalous peak in the temperature-dependent resistivity allows to draw a coherent picture of the $1T-{\mathrm{TiSe}}_2$ CDW phase transition and its relation to excitons.

The Stokes and anti-Stokes components in the inelastic scattering of light are related to phonon statistics and have been broadly used to measure temperature and phonon lifetimes in different materials. However, correlation between the components is expected to change the Stokes/anti-Stokes intensity ratio, imposing corrections to the broadly used Bose-Einstein statistics. In this work the excitation power dependence of these scattering processes is theoretically described by an effective Hamiltonian that includes correlation between the Stokes and the anti-Stokes events. The model is used to fit available experimental results in three-dimensional diamond and two-dimensional graphene, showing that the phenomenon can significantly increase in the low-dimensional system under specific resonance conditions. By setting the scientific basis for the Stokes–anti-Stokes correlated phenomenon, the use of the Bose-Einstein population function to determine the inelastic scattering is generalized, providing a model to predict the conversion of optical phonons into heat or light, according to coupling constants and decay rates. The model applies to inelastic scattering in general.

The $GW$ approximation is a well-known method to improve electronic structure predictions calculated within density functional theory. In this work, we have implemented a computationally efficient $GW$ approach that calculates central properties within the Matsubara-time domain using the modified version of elk, the full-potential linearized augmented plane wave (FP-LAPW) package. Continuous-pole expansion (CPE), a recently proposed analytic continuation method, has been incorporated and compared to the widely used Padé approximation. Full crystal symmetry has been employed for computational speedup. We have applied our approach to 18 well-studied semiconductors/insulators that cover a wide range of band gaps computed at the levels of single-shot $G_0{W}_0$, partially self-consistent $G{W}_0$, and fully self-consistent $GW$ (full-$GW$), in conjunction with the diagonal approximation. Our calculations show that $G_0{W}_0$ leads to band gaps that agree well with experiment for the case of simple $s-p$ electron systems, whereas full-$GW$ is required for improving the band gaps in $3d$ electron systems. In addition, $G{W}_0$ almost always predicts larger band gap values compared to full-$GW$, likely due to the substantial underestimation of screening effects as well as the diagonal approximation. Both the CPE method and Padé approximation lead to similar band gaps for most systems except strontium titantate, suggesting that further investigation into the latter approximation is necessary for strongly correlated systems. Moreover, the calculated cation $d$ band energies suggest that both full-$GW$ and $G{W}_0$ lead to results in good agreement with experiment. Our computed band gaps serve as important benchmarks for the accuracy of the Matsubara-time $GW$ approach.