We use analytically tractable dielectric response models, which are supported by ab initio calculations for anisotropic two-dimensional (2D) materials and quasi-2D metals that host slow plasmons, to reveal a rich variety of the plasmonic wake patterns in the electric potential induced by a charged particle moving parallel to those materials. Using the method of stationary phase, we discover surprising analogies with Kelvin's ship wakes and atmospheric wakes regarding the asymmetry of the wake, slowing down of the plasmon dispersion, and the onset of Mach-like wake due to nonlocal effects in the dielectric response.

Topological phases have been reported on self-similar structures in the presence of a perpendicular magnetic field. Here, we present an understanding of these phases from a perspective of spectral flow and charge pumping. We study the Harper-Hofstadter model on self-similar structures constructed from the Sierpinski gasket. We numerically investigate the spectral flow and the associated charge pumping when a flux tube is inserted through the structure and the flux through the tube is varied adiabatically. We find that the nature of the spectral flow is qualitatively different from that of translationally invariant noninteracting systems with a perpendicular magnetic field. We show that the instantaneous eigenspectra can be used to understand the quantization of the charge pumped over a cycle, and hence to understand the topological character of the system. We show the correspondence between the local contributions to the Hall conductivity and the spectral flow of the edgelike states. We also show that the edgelike states can be approximated by eigenstates of the discrete angular-momentum operator, their chiral nature being a consequence of this.

Superconducting circuits constitute a promising platform for future implementation of quantum processors and simulators. Arrays of capacitively coupled transmon qubits naturally implement the Bose-Hubbard model with attractive on-site interaction. The spectrum of such many-body systems is characterized by low-energy localized states defining the lattice analog of bright solitons. Here, we demonstrate that these bright solitons can be pinned in the system, and we find that a soliton moves while maintaining its shape. Its velocity obeys a scaling law in terms of the combined interaction and number of constituent bosons. In contrast, the source-to-drain transport of photons through the array occurs through extended states that have higher energy compared to the bright soliton. For weak coupling between the source or drain and the array, the populations of the source and drain oscillate in time; for chains of even length, their population remains low at all times, while it can reach half the number of total bosons in odd chains. Implications of our results for actual experimental realizations are discussed.

The dynamics of a magnetic moment or spin are of high interest to applications in technology. Dissipation in these systems is therefore of importance for improvement of efficiency of devices, such as the ones proposed in spintronics. A large spin in a magnetic field is widely assumed to be described by the Landau-Lifshitz-Gilbert (LLG) equation, which includes a phenomenological Gilbert damping. Here, we couple a large spin to a bath and derive a generic (non-)Ohmic damping term for the low-frequency range using a Caldeira-Leggett model. This leads to a fractional LLG equation, where the first-order derivative Gilbert damping is replaced by a fractional derivative of order $s\in {\mathbb{R}}_{\ge 0}$. We show that the parameter $s$ can be determined from a ferromagnetic resonance experiment, where the resonance frequency and linewidth no longer scale linearly with the effective field strength.

Skutterudites are crystals with a cagelike structure that can be augmented with filler atoms (“rattlers”), usually leading to a reduction in thermal conductivity that can be exploited for thermoelectric applications. Here, we leverage the recently introduced Wigner formulation of thermal transport to elucidate the microscopic physics underlying heat conduction in skutterudites, showing that filler atoms can drive a crossover from the Boltzmann to the Wigner regimes of thermal transport, i.e., from particlelike conduction to wavelike tunneling. At temperatures where the thermoelectric efficiency of skutterudites is largest, wavelike tunneling can become comparable to particlelike propagation. We define a Boltzmann deviation descriptor able to differentiate the two regimes and relate the competition between the two mechanisms to the materials' chemistry, providing a design strategy to select rattlers and identify optimal compositions for thermoelectric applications.

The multiterminal Josephson effect aroused considerable interest recently, in connection with theoretical and experimental evidence for correlations among Cooper pairs, that is, the so-called Cooper quartets. It was further predicted that the spectrum of Andreev bound states in such devices could host Weyl-point singularities. However, the relative phase between the Cooper pair and quartet supercurrents has not yet been addressed experimentally. Here, we propose an experiment involving four-terminal Josephson junctions with two independent orthogonal supercurrents, and calculate the critical current contours (CCCs) from a multiterminal Josephson junction circuit theory. We predict a generically $\pi$-shifted contribution of both the local or nonlocal second-order Josephson harmonics. Furthermore, we show that these lead to marked nonconvex shapes for the CCCs in zero magnetic field where the dissipative state reenters into the superconducting one. Eventually, we discuss distinctive features of the nonlocal Josephson processes in the CCCs. The experimental observation of the latter could allow providing firm evidence of the $\pi$-shifted Cooper quartet current-phase relation.

We perform a systematic analysis of continuously polydisperse hard-sphere fluids as a function of the degree of polydispersity within the framework of the mode-coupling theory of the glass transition (MCT). Our results show that a high degree of polydispersity tends to stabilize the liquid phase against vitrification, the magnitude of which depends on the shape of the polydispersity distribution. Furthermore, we report on a separation between the localization lengths of the smallest and largest particles. A diameter-resolved analysis of the intermediate scattering functions reveals that this separation significantly stretches the relaxation patterns, which we quantitatively study by an analysis of the dynamical exponents predicted by the theory. Our observations have strong implications for our understanding of the nature of dynamical heterogeneities and localization lengths in continuously polydisperse systems with hard-core interactions. These results suggest that the dynamics of the smallest particles is of central importance to understand structural relaxation of such systems, already in the mildly supercooled regime where MCT is usually applicable.

Predicting the phase diagram of interacting quantum many-body systems is a central problem in condensed matter physics and related fields. A variety of quantum many-body systems, ranging from unconventional superconductors to spin liquids, exhibit complex competing phases whose theoretical description has been the focus of intense efforts. Here, we show that neural network quantum states can be combined with a Lee-Yang theory of quantum phase transitions to predict the critical points of strongly correlated spin lattices. Specifically, we implement our approach for quantum phase transitions in the transverse-field Ising model on different lattice geometries in one, two, and three dimensions. We show that the Lee-Yang theory combined with neural network quantum states yields predictions of the critical field, which are consistent with large-scale quantum many-body methods. As such, our results provide a starting point for determining the phase diagram of more complex quantum many-body systems, including frustrated Heisenberg and Hubbard models.

Inelastic neutron scattering is used to study the magnetic excitations of the $S=1$ square-lattice antiferromagnet ${\mathrm{La}}_2{\mathrm{NiO}}_4$. We find that the spin waves cannot be described by a simple classical (harmonic) Heisenberg model with only nearest-neighbor interactions. The spin-wave dispersion measured along the antiferromagnetic Brillouin-zone boundary shows a minimum energy at the $(1/2,0)$ position as is observed in some $S=1/2$ square-lattice antiferromagnets. Thus, our results suggest that the quantum dispersion renormalization effects or longer-range exchange interactions observed in cuprates and other $S=1/2$ square-lattice antiferromagnets are also present in ${\mathrm{La}}_2{\mathrm{NiO}}_4$. We also find that the overall intensity of the spin-wave excitations is suppressed relative to linear spin-wave theory, indicating that covalency is important. Two-magnon scattering is also observed.

We report the direct observation of a commensurate-ordered antiferromagnetic (AFM) state but incommensurate helical spin dynamics in the natural mineral brochantite ${\mathrm{Cu}}_4{\mathrm{SO}}_4{\left(\mathrm{OH}\right)}_6$ through neutron diffraction and neutron spectroscopy measurements. Inelastic neutron scattering measurements reveal magnonlike excitations with considerable dispersion along the $c$ axis and almost flat branches in other principal directions, indicating the strong one-dimensional character of the magnetic correlations. We experimentally observe the effect of the uniform Dzyaloshinskii-Moriya (DM) interaction, which elevates the degeneracy of the spin-wave modes, shifting them in opposite directions in reciprocal space. The system has a commensurate AFM ground state, stabilized by the anisotropic symmetric Heisenberg exchange interactions, and quasi-one-dimensional chiral spin dynamics due to the antisymmetric DM interaction. Employing linear spin-wave theory, we were able to construct an effective Heisenberg Hamiltonian. We quantify both the symmetric exchange parameters and the DM vector components in ${\mathrm{Cu}}_4{\mathrm{SO}}_4{\left(\mathrm{OH}\right)}_6$ and determine the mechanism of the magnetic frustration. Our work provides detailed insights into the complex dynamics of the spin chain in the presence of uniform DM interaction.

After a decade of intense theoretical and experimental efforts, demonstrating braiding of Majorana modes remains an unsolved problem in condensed matter physics due to platform-specific challenges. In this work, we propose topological superconductor–magnetic multilayer heterostructures with on-chip microwave cavity readout as a platform for initializing, braiding, and reading out Majorana modes. Stray fields from a skyrmion in the magnetic layers can nucleate a vortex in the topological superconducting layer. Such a vortex is known to host Majorana bound states at its core. Through analytical calculations within London and Thiele formalisms, and through micromagnetic simulations, we show that our nucleation and braiding scheme can be effectively realized with a variety of existing options for magnetic and superconducting layers. Furthermore, we show that the coupling of the Majorana bound states to the electric field of a resonator leads to an experimentally observable parity-dependent dispersive shift of the resonator frequency. Our work paves the way for realizing Majorana braiding in the near future.

The dynamics triggered by the impact of an ion onto a solid surface has been explored mainly by theoretical modeling or computer simulation to date. Results indicate that the microscopic nonequilibrium relaxation processes triggered by the interaction of the ion with the solid occur on (sub)picosecond time scales. A suitable experimental approach to these dynamics therefore requires a pump-probe method with an appropriate time resolution. Recent experiments have successfully used laser photoionization of noble gas atoms in combination with a Wiley-MacLaren ion buncher to obtain arrival time distributions as narrow as $t_{\mathrm{ion}}=180$ ps. Here, we show that this setup can be significantly improved by replacing the gas at a temperature of $T_{\mathrm{atoms}}\simeq 300$ K with a supersonic beam of cooled noble gas atoms at $T_{\mathrm{atoms}}\simeq 4$ K. The detailed analysis of measured arrival times of individual ${\mathrm{Ne}}^{+}$ ions with a kinetic energy of 4 keV reveals that the arrival time jitter can be reduced by this technique down to $(18\pm 4)$ ps. This opens the door to pump-probe experiments with keV ions with a time resolution in the picosecond range.

The interaction of magnetic dopants with delocalized electron states can result in interesting many-body physics. Here, the magnetic properties of neutral and charged finite silver metal host clusters with a magnetic cobalt atom impurity were investigated experimentally by exploiting the complementary methods of Stern-Gerlach molecular beam deflection and x-ray magnetic circular dichroism spectroscopy and are accompanied by density functional theory calculations and charge transfer multiplet simulations. The influence of the number of valence electrons and the consequences of impurity encapsulation were addressed in free size-selected, singly cobalt-doped silver clusters ${\mathrm{CoAg}}_n^{0,+}$ ($n=2–15$). Encapsulation of the dopant facilitates the formation of delocalized electronic shells with complete hybridization of the impurity $3d$- and the host $5s$-derived orbitals, which results in impurity valence electron delocalization, effective spin relaxation, and a low-spin ground state. In the exohedral size regime, spin pairing in the free electron gas formed by the silver $5s$ electrons is the dominating driving force determining the local $3d$ occupation of the impurity and therefore, adjusting the spin magnetic moment accordingly.

The emergence of quasiparticles is a universal property in integrable systems. String-type quasiparticles, which are characterized by the string solutions of Bethe equations, play fundamental roles in the analysis of their physics. Through an investigation of the Bethe equations in the asymmetric simple exclusion process, we reveal the existence of string solutions in the presence of non-Hermiticity resulting from asymmetrical hopping. Because of the non-Hermiticity, the string solutions exhibit exotic properties such as the complexification of the center of string solutions and the delocalization of Bethe quantum numbers. In addition, we find the picture of string-type quasiparticles collapses in the strong-asymmetry regime. The collapse of string solutions characterizes the transition of eigenstates from bound states to scattering states.

${\mathrm{Ni}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$ is a pyroelectric honeycomb antiferromagnet exhibiting peculiar changes in its electric polarization at magnetic transitions. ${\mathrm{Ni}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$ stands out from isostructural magnetic compounds, showing an anomalously low magnetic transition temperature and unique magnetic anisotropy. We determine the magnetic structure of ${\mathrm{Ni}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$ utilizing high-resolution powder and single-crystal neutron diffraction. A noncollinear stripy antiferromagnetic order is found in the honeycomb planes. The magnetic space group is $P_{C}na{2}_1$. The in-plane magnetic connection is of the stripy type for both the $ab$-plane and $c$-axis spin components. This is a simpler connection than the one proposed previously. The ferromagnetic interlayer order of the $c$-axis spin components in our model is also distinct. The magnetic anisotropy of ${\mathrm{Ni}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$ is characterized by orientation-dependent magnetic susceptibility measurements on a single crystal, consistent with neutron diffraction analysis. The local magnetoelectric tensor analysis using our magnetic models provides insights into its magnetoelectric coupling and polarization. Thus, our results deliver essential information for understanding both the unusual magnetoelectric properties of ${\mathrm{Ni}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$ and the prospects for observing exotic nonreciprocal, Hall, and magnonic effects characteristic of this compound family.

Dissipation-free current transport in type II superconductors requires vortices, the topological defects of the superfluid, to be pinned by defects in the underlying material. The pinning capacity of a defect is quantified by the Labusch parameter $\kappa \sim f_p/\xi \overline{C}$, measuring the pinning force $f_p$ relative to the elasticity $\overline{C}$ of the vortex lattice, with $\xi$ denoting the coherence length (or vortex core size) of the superconductor. The critical value $\kappa =1$ separates weak from strong pinning, with a strong defect at $\kappa >1$ able to pin a vortex on its own. So far, this weak-to-strong pinning transition has been studied for isotropic defect potentials, resulting in a critical exponent $\mu =2$ for the onset of the strong pinning force density $F_{\mathrm{pin}}\sim n_p{f}_p{(\xi /a_0)}^2{(\kappa -1)}^{\mu }$, with $n_p$ denoting the density of defects and $a_0$ the intervortex distance. This result is owed to the special rotational symmetry of the defect producing a finite two-dimensional trapping area $S_{\mathrm{trap}}\sim {\xi }^2$ at the strong pinning onset. The behavior changes dramatically when studying anisotropic defects with no special symmetries: the strong pinning then originates out of isolated points with length scales growing as $\xi {(\kappa -1)}^{1/2}$, resulting in a different force exponent $\mu =5/2$. The strong pinning onset is characterized by the appearance of unstable areas ${\mathcal{U}}_{\tilde{\mathbf{R}}}$ of elliptical shape whose boundaries mark the locations where vortices jump. The associated locations of asymptotic vortex positions define areas ${\mathcal{B}}_{\overline{\mathbf{R}}}$ of bistable vortex states and assume the shape of a crescent. The geometries of unstable and bistable regions are associated with the local differential properties of the Hessian determinant $D\left(\mathbf{R}\right)$ of the pinning potential $e_p\left(\mathbf{R}\right)$, specifically, its minima, maxima, and saddle points. Extending our analysis to the case of a random two-dimensional pinning landscape, a situation describing strong pinning in a thin superconducting film, we discuss the topological properties of unstable and bistable regions as expressed through the Euler characteristic, with the latter related to the local differential properties of $D\left(\mathbf{R}\right)$ through Morse theory.