We study the far-from-equilibrium properties of nanoscopic classical spin systems. In particular, we focus on the interplay between lattice vibrations and magnetic frustrations induced by surface effects in antiferromagnets. We use an extended Monte Carlo simulations which treats both the ionic degrees of freedom and spin variables on the same footing via a Heisenberg-Lennard-Jones Hamiltonian with a spin-lattice coupling. The interplay of the local ordered magnetic moments and the lattice dynamics provides, at zero temperature, a structural phase diagram characterizing the magnetic order in two different antiferromagnetic nanoclusters. At nonzero temperature, the competition between spins and the ionic vibrations considerably affects the magnetization of these systems. Next, we explore the dynamical response of the antiferromagnetic structures subjected to an initial ferromagnetic quench by solving the stochastic Landau-Lifshitz-Gilbert equation at finite temperature. The dynamics reveals a nontrivial structure-induced behavior in the spin relaxation with a concomitant memory of the initially applied ferromagnetic quench. These observations of long-lived nonthermal states could open new avenues in nanotechnology.

Topological phase transitions can be described by the theory of critical phenomena and identified by critical exponents that define their universality classes. This is a consequence of the existence of a diverging length at the transition that has been identified as the penetration depth of the surface modes in the nontrivial topological phase. In this paper we characterize different universality classes of topological transitions by determining their correlation length exponents directly from numerical calculations of the penetration length of the edge modes as a function of the distance to the topological transition. We consider generalizations of the topological nontrivial Su-Schriefer-Heeger (SSH) model, for the case of next next nearest neighbors hopping terms and in the presence of a synthetic potential. The latter allows the system to transit between two universality classes with different correlation length and dynamic critical exponents. It presents a line of multicritical point in its phase diagram since the behavior of the Berry connection depends on the path it is approached. We compare our results with those obtained from a scaling approach to the Berry connection.

We study the de Haas-van Alphen (dHvA) oscillations in the two-dimensional compensated metal with overtilted Dirac cones near the Lifshitz transition. We employ the tight-binding model of $\alpha -{(\mathrm{BEDT}-\mathrm{TTF})}_2{\mathrm{I}}_3$, in which the massless Dirac fermions are realized. When a uniaxial pressure $\left(P\right)$ along the $y$ axis is applied above $P\simeq 0.2$ kbar in $\alpha -{(\mathrm{BEDT}-\mathrm{TTF})}_2{\mathrm{I}}_3$, one electron pocket, which encloses the overtilted Dirac points, is changed to two electron pockets, i.e., Lifshitz transition happens, while a hole pocket does not change a topology. We show that the Fourier components corresponding to the $\frac{3}{2}$ and $\frac{5}{2}$ areas of the hole pocket are anomalously enhanced in the region of pressure where the Lifshitz transition occurs. This phenomenon will be observed in the two-dimensional overtilted Dirac fermions near the Lifshitz transition.

We present experimental evidence of an intriguing phase transition between distinct topological states in the type-II Weyl semimetal ${\mathrm{MoTe}}_2$. We observe anomalies in the Raman phonon frequencies and linewidths as well as electronic quasielastic peaks around 70 K, which, together with structural, thermodynamic measurements, and electron-phonon coupling calculations, demonstrate a temperature-induced transition between two topological phases previously identified by contrasting spectroscopic measurements. An analysis of experimental data suggests electron-phonon coupling as the main driving mechanism for the change of key topological characters in the electronic structure of ${\mathrm{MoTe}}_2$. We also find the phase transition to be sensitive to sample conditions distinguished by synthesis methods. These discoveries of temperature and material condition-dependent topological phase evolutions and transitions in ${\mathrm{MoTe}}_2$ advance the fundamental understanding of the underlying physics and enable an effective approach to tuning Weyl semimetal states for technological applications.

Recent theoretical studies have extended the Berry phase framework to account for higher electric multipole moments; quadrupole and octupole topological phases have been proposed. Although the two-dimensional quantized quadrupole insulators have been demonstrated experimentally, octupole topological phases have not previously been observed experimentally. Here we report on the experimental realization of a classical analog of the octupole topological insulator in the electric circuit system. Three-dimensional topolectrical circuits for realizing such topological phases are constructed experimentally. We observe octupole topological states protected by the topology of the bulk, which are localized at the corners. Our results provide conclusive evidence of a form of robustness against disorder and deformation, which is characteristic of octupole topological insulators. Our study opens a route toward higher-order topological phenomena in three dimensions and paves the way for employing topolectrical circuitry to study complex topological phenomena.

A high-dimensional potential energy surface (PES) for CO interaction with the Au(111) surface is developed using a machine-learning algorithm. Including both molecular and surface coordinates, this PES enables the simulations of the recent experiment on scattering of vibrationally excited CO from Au(111). Trapping in a physisorption well is observed to increase with decreasing incidence energy. While the energy dissipation of physisorbed CO is slow, due to weak coupling with both the phonons and electron-hole pairs, the access of the impinging CO to the chemisorption well facilitates its fast vibrational relaxation through nonadiabatic coupling with surface electron-hole pairs. The latter is proposed as a mechanism for the experimentally observed fast as well as slow components of the $\mathrm{CO}\left(\nu =1\right)$ product.

${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ is characterized by a large spin-orbit coupling, which gives rise to bands with strongly entangled spin and orbital characters, called ${\mathrm{J}}_{1/2}$ and ${\mathrm{J}}_{3/2}$. We use light-polarization dependent ARPES to study directly the orbital character of these bands and fully map out their dispersion. We observe bands in very good agreement with our cluster dynamical mean-field theory calculations. We show that the ${\mathrm{J}}_{1/2}$ band, the closest to the Fermi level $E_F$, is dominated by $d_{xz}$ character along $k_x$ and $d_{yz}$ along $k_y$. This is actually in agreement with an isotropic ${\mathrm{J}}_{1/2}$ character on average, but this large orbital dependence in $\mathbf{k}$ space was mostly overlooked before. It gives rise to strong modulations of the ARPES intensity that we explain and carefully take into account to compare dispersions in equivalent directions of the Brillouin zone. Although the latter dispersions look different at first, suggesting possible symmetry breakings, they are found essentially similar, once corrected for these intensity variations. In particular, the pseudogaplike features close to the $X$ point appearing in the nearly metallic 15% Rh-doped ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ strongly depend on experimental conditions. We reveal that there is nevertheless an energy scale of 30 meV below which spectral weight is suppressed, independent of the experimental conditions, which gives a reliable basis to analyze this behavior. We suggest it is caused by disorder.

We report on the design and the numerical and experimental characterization of an all-dielectric reflecting focusing metasurface (metamirror) which does not have a back reflector, but effectively reflects incident waves with the desired reflection phase gradient. The profile of the reflection phase can be tuned independently for both sides of the single-layer subwavelength-thick metamirror by properly selecting dimensions of its dielectric inclusions. Such a feature stems from the bianisotropic omega properties of the inclusions. To demonstrate independent control of the reflection phase, we have designed a metamirror focusing normally incident plane waves at different focal distances being illuminated from the opposite sides. The proposed two-sided metamirror can find applications in antennas, diffraction gratings, and complex holograms. The absence of conducting elements makes it a perfect candidate for optical applications requiring asymmetric wave-front control.

The origin of the metal-to-insulator transition (MIT) in $R{\mathrm{NiO}}_3$ perovskites with $R$ = trivalent $4f$ ion has challenged the condensed matter research community for almost three decades. A drawback for progress in this direction has been the lack of studies combining physical properties and accurate structural data covering the full nickelate phase diagram. Here we focus on a small region close to the itinerant limit $(R$ = Pr, $1.5\text{K}<T<300$ K), where we investigate the gap opening and the simultaneous emergence of charge order in ${\mathrm{PrNiO}}_3$. We combine electrical resistivity, magnetization, and heat capacity measurements with high-resolution neutron and synchrotron x-ray powder diffraction data that, in contrast to previous studies, we analyze in terms of symmetry-adapted distortion modes. Such analysis allow us to identify the contribution of the different modes to the global distortion in a broad temperature range. Moreover, it shows that the structural changes at the MIT, traditionally described in terms of the evolution of the interatomic distances and angles, appear as abrupt increases of $all$ nonzero mode amplitudes at $T_{\mathrm{MIT}}=T_N\sim 130$ K accompanied by the appearance of new modes below this temperature. A further interesting observation is the existence of a nearly perfect linear correlation between the amplitude of the breathing mode associated to the charge order and the staggered magnetization below the MIT. Our data also uncover a previously unnoticed anomaly at $T^{*}\sim 60$ K $\left(\sim 0.4\times T_{\mathrm{MIT}}\right)$, clearly visible in the electrical resistivity, lattice parameters and some mode amplitudes. Since phase coexistence is only observed in a small temperature region around $T_{\mathrm{MIT}}(\sim \pm 10$ K), these observations suggest the existence of a hidden symmetry in the insulating phase. We discuss some possible origins, among them the theoretically predicted existence of polar distortions induced by the noncentrosymmetric magnetic order [Perez-Mato et al., J. Phys.: Condens. Matter 28, 286001 (2016); Giovanetti et al., Phys. Rev. Lett. 103, 156401 (2009)].

The behavior of the spin relaxation time of electrons bound to donors immersed in the middle of a CdTe quantum well was measured in the range of temperatures 10–80 K, by using picosecond pump-probe Kerr rotation. Different doping concentrations spanning from isolated donors up to a concentration beyond the metal-insulator transition were considered at a fixed magnetic field; at very low temperature, in insulating regime all electrons are bound to donors but for one high concentration we had to consider that a fraction of electrons is in conduction states. By increasing the temperature, the number of conduction electrons increases. The experimental temperature dependences were explained by invoking spin exchange between electron spins localized on donors and the spin of electrons promoted to conduction states. A good agreement between experiment and theory was found and allowed us to conclude that, while the spin of localized electrons undergoes the effect of both hyperfine and anisotropic exchange interactions, the D’yakonov-Perel’ mechanism governs the spin relaxation of the conduction electrons for the whole range of the studied doping concentrations. Moreover, we identified the scattering mechanisms possibly undergone by the conduction electrons at low temperature.

The nature of the fractional quantum Hall state at quarter filling in a wide quantum well is still under debate. Both one-component non-Abelian and two-component Abelian orders have been proposed to describe the system. Interestingly, these candidates received support from different experiments under disparate conditions. In this article, we focus on non-Abelian orders from Cooper pairing between composite fermions and the Abelian Halperin-(5,5,3) order. We discuss and predict systematically different experimental signatures to identify them in future experiments. In particular, we address the Mach-Zehnder interferometry experiment and show that it can identify the recently proposed 22111 parton order.

Parafermions are non-Abelian anyons which generalize Majorana fermions and hold great promise for topological quantum computation. We study the braiding of ${\mathbb{Z}}_{2n}$ parafermions which have been predicted to emerge as localized zero modes in fractional quantum Hall systems at filling factor $\nu =1/n$ ($n$ odd). Using a combination of bosonization and refermionization, we calculate the energy splitting as a function of distance and chemical potential for a pair of parafermions separated by a gapped region. Braiding of parafermions in quantum Hall edge states can be implemented by repeated fusion and nucleation of parafermion pairs. We simulate the conventional braiding protocol of parafermions numerically, taking into account the finite separation and finite chemical potential. We show that a nonzero chemical potential poses challenges for the adiabaticity of the braiding process because it leads to accidental crossings in the spectrum. To remedy this, we propose an improved braiding protocol which avoids those degeneracies.

The implementation of quantum technologies in electronics leads naturally to the concept of coherent single-electron circuits, in which a single charge is used coherently to provide enhanced performance. In this work, we propose a coherent single-electron device that operates as an electrically-tunable capacitor. This system exhibits an oscillating dependence of the capacitance with voltage, in which the amplitude of the capacitance changes and the voltage period can be tuned by electric means. The device concept is based on double-passage Landau-Zener-Stückelberg-Majorana interferometry of a coupled two-level system that is further tunnel coupled to an electron reservoir. We test this model experimentally by performing Landau-Zener-Stückelberg-Majorana interferometry in a single-electron double quantum dot coupled to an electron reservoir and show that the voltage period of the capacitance oscillations is directly proportional to the excitation frequency and that the amplitude of the oscillations depends on the dynamical parameters of the system: intrinsic relaxation and coherence times, as well as the tunneling rate to the reservoir. Our work opens up an opportunity to use the nonlinear capacitance of double quantum dots to obtain enhanced device functionalities.

We present a theoretical and numerical study of a dual-metasurface superlens dedicated to the near-field optical imaging of submicron objects. Compared to the previous studies of dual-metasurface plasmonic superlenses, we suggest a more adequate theoretical model of their operation. The new model allows us to obtain twice better operational characteristics of the redesigned superlens. For the first time, we describe the operation of such the superlens using full-wave numerical simulations, taking into account the interfaces of the host medium slab and proving the nanoimaging for scattering objects instead of radiating sources. We discuss and address both application and fabrication issues for this superlens.

We observe magnetic effects in ultrahigh-quality factor crystalline quartz bulk acoustic wave resonators at milli-Kelvin temperature. The study reveals the existence of hysteresis loops, jumps, and memory effects of acoustical resonance frequencies. These loops arise as a response to the external magnetic field, and they span a few Hertz for modes with linewidths of about $25\mathrm{mHz}$, which constitute a frequency shift of order 60 linewidths. The effects are broadband but get stronger toward higher frequencies where both nonlinear effects and losses are limited by two-level systems. This suggests that the observed effects are due to the ferromagnet-like phase of a spin ensemble coupled to mechanical modes. The observed coupling between mechanical and spin degrees of freedom in the ultralow-loss regime brings about new possibilities for the emerging class of quantum hybrid systems.

We report magnetocrystalline anisotropy (MCA) calculations of Fe, Co, and Ni slabs of various thicknesses and crystallographic orientations from two density functional theory codes based either on a plane wave or a local atomic basis set expansion and a magnetic tight-binding method. We analyze the evolution of the MCA with the number of layers of the slabs. The decomposition of MCA into contributions of atomic sites helps understanding the oscillatory behavior of the MCA with the slab thickness and highlights the role of finite size effects. We also identify some specific systems with enhanced MCA. A $k$ space as well as a band-filling analysis show very rich features of the MCA that could be used to tailor systems with enhanced magnetic properties. Finally, this work can serve as a benchmark for MCA calculations.

Magneto-optical spectroscopy in fields up to 30 T reveals anomalies in the equilibrium and ultrafast magnetic properties of the ferrimagnetic rare-earth–transition-metal alloy TbFeCo. In particular, near the magnetization compensation temperature, each of the magnetizations of the antiferromagnetically coupled Tb and FeCo sublattices show triple hysteresis loops. Contrary to state-of-the-art theory, which explains such loops by sample inhomogeneities, here we show that they are an intrinsic property of the rare-earth ferrimagnets. Assuming that the rare-earth ions are paramagnetic and have a nonzero orbital momentum in the ground state and, therefore, a large magnetic anisotropy, we are able to reproduce the experimentally observed behavior in equilibrium. The same theory is also able to describe the experimentally observed critical slowdown of the spin dynamics near the magnetization compensation temperature, emphasizing the role played by the orbital momentum in static and ultrafast magnetism of ferrimagnets.

Noncentrosymmetric molybdenum nitride $\mathrm{R}{\mathrm{h}}_2\mathrm{M}{\mathrm{o}}_3\mathrm{N}$ is a conventional $s$-wave superconductor at ambient pressure. Here we report the evolution of structural and electronic properties of $\mathrm{R}{\mathrm{h}}_2\mathrm{M}{\mathrm{o}}_3\mathrm{N}$ under high pressure. X-ray diffraction measurements reveal the stability of pristine β-Mn-type cubic structure up to 47.9 GPa, accompanied by the continuously enhanced distortion of $\mathrm{M}{\mathrm{o}}_6\mathrm{N}$ octahedra. Electronic transport experiments show the robustness of superconductivity under pressure, i.e., the superconducting transition temperature $T_{\mathrm{c}}$ varies only ∼0.7 K upon compression up to 38.5 GPa. Meanwhile, detailed analyses of both structural and transport results consistently reveal a critical pressure of ∼14.0 GPa. In agreement with the enhancement of octahedral distortion, the temperature dependence of upper critical magnetic field accords with a $p$-wave model at 22.0 GPa and an $s$-wave model at 6.0 GPa. These results suggest the emergence of novel superconductivity in the distorted $\mathrm{R}{\mathrm{h}}_2\mathrm{M}{\mathrm{o}}_3\mathrm{N}$ cubic phase under pressure, which could be attributed to the enhanced strength of antisymmetric spin-orbit coupling (ASOC) via pressure-modified local octahedral distortion. Our findings may shed light on the searching and understanding of unique triplet-pairing superconductivity in other inversion-broken superconductors with strong ASOC.

In this paper, we investigate the realization of topological Anderson insulators in electric circuits. A disordered Haldane model is constructed through electric circuit networks composed of capacitors and inductors, where the disorder is introduced through the random induction of the grounding inductors. Based on the noncommutative geometry method and transport calculations, we confirm that such kind of disorder can drive a phase transition from a normal insulator to a topological Anderson insulator. Besides, such a disorder also possesses unique characteristics which are absent for the usual Anderson disorder. Therefore distinct features are exhibited by the topological Anderson transition in electric circuits. Finally, the topological Anderson insulator in circuits holds additional advantages for microelectronic technology that can be easily detected by measuring the quantized transmission coefficients and the edge state wave functions.