Dynamical detection of quantum phases and phase transitions (QPTs) in quenched systems with experimentally convenient initial states is a topic of interest from both theoretical and experimental perspectives. Quenched from polarized states, longitudinal magnetization decays exponentially to zero in time for the short-range transverse-field Ising model and hence has a featureless steady state regime, which prevents it from exhibiting dynamical phase transitions of type I. In this paper, we ask whether the transient regimes of such nonequilibrium processes probed by single-site observables, that is magnetization per site, could encode information about the underlying QPT. The decay rates of time-dependent and single-site observables exhibit a dynamical crossover that separates two dynamical regions, ordered and disordered, both of which have distinct nonequilibrium responses. We construct a dynamical order parameterlike quantity that exhibits a scaling law in the vicinity of the crossover. Our results reveal that scaling law exponent in short times in the close vicinity of the dynamical crossover is significantly different than the one predicted by analytical theory for long times. When integrability is strongly broken, the crossover boundary turns into a region that separates two other dynamical regions that act like dynamically ordered and disordered regimes.

The hidden order phase in $\mathrm{U}{\mathrm{Ru}}_2{\mathrm{Si}}_2$ is highly sensitive to electronic doping. A special interest in silicon-to-phosphorus substitution is due to the fact that it may allow one, in part, to isolate the effects of tuning the chemical potential from the complexity of the correlated $f$ and $d$ electronic states. We investigate the new antiferromagnetic phase that is induced in $\mathrm{U}{\mathrm{Ru}}_2{\mathrm{Si}}_{2-x}{\mathrm{P}}_x$ at $x\gtrsim 0.27$. Time-of-flight neutron diffraction of a single crystal ($x=0.28$) reveals $c$-axis collinear ${\mathbf{q}}_{\mathrm{m}}=(\frac{1}{2},\frac{1}{2},\frac{1}{2})$ magnetic order with localized magnetic moments ($\sim 2.1$–$2.6{\mu }_{\mathrm{B}}$). This points to an unexpected analogy between the (Si,P) and (Ru,Rh) substitution series. Through further comparisons with other tuning studies of ${\mathrm{URu}}_2{\mathrm{Si}}_2$, we are able to delineate the mechanisms by which silicon-to-phosphorus substitution affects the system. In particular, both the localization of itinerant $5f$ electrons as well as the choice of ${\mathbf{q}}_m$ appear to be consequences of the increase in chemical potential. Further, enhanced exchange interactions are induced by chemical pressure and lead to magnetic order, in which an increase in interlayer spacing may play a special role.

We study phase transitions in the two-dimensional Heisenberg model with Dzyaloshinskii-Moriya interaction, Ising anisotropy $\eta$, and dipolar interaction under zero and finite magnetic fields $H$. For three typical strengths (zero, weak, and strong) of the dipolar interaction, we present the $H\text{−}\eta$ phase diagrams by estimating order parameters for skyrmion-lattice and helical phases and in-plane magnetization using a Monte Carlo method with an $O\left(N\right)$ algorithm. We find in the phase diagrams three types of skyrmion-lattice phases, i.e., two square lattices and a triangular lattice, helical phases with diagonal and vertical (or horizontal) stripes, a canted ferromagnetic phase, and a polarized ferromagnetic phase. The effect of the dipolar interaction varies the types of the skyrmion and helical phases in a complex manner. The dipolar interaction also expands the regions of the ordered phases accompanying shifts of the phase boundaries to the positive $H$ and $\eta$ directions and causes an increase of the density of skyrmions and shortening of the pitch length (stripe width) of helical structures. We discuss the details of the features of the phase transitions.

${\mathrm{Ag}}_3\mathrm{Li}{\mathrm{Ir}}_2{\mathrm{O}}_6$ is a Kitaev spin-liquid candidate material synthesized from $\alpha \text{−}{\mathrm{Li}}_2\mathrm{Ir}{\mathrm{O}}_3$ through a topotactic reaction. We investigate the structural and magnetic properties of two samples of ${\mathrm{Ag}}_3\mathrm{Li}{\mathrm{Ir}}_2{\mathrm{O}}_6$ based on the ${}^7\mathrm{Li}$ nuclear magnetic resonance line shape, Knight shift, and spin-lattice relaxation rate $1/T_1$. The first sample A shows signatures of magnetically ordered spins, and exhibits one sharp ${}^7\mathrm{Li}$ peak with the full width at half maximum increasing significantly below 14 K. $1/T_1^{\text{stretch}}$ of this sample displays a broad local maximum at 40 K, followed by a very sharp peak at $T_N=9\pm 1\mathrm{K}$ due to a critical slowing down of Ir spin fluctuations, a typical signature of magnetic long-range order. In order to shed light on the position-by-position variation of $1/T_1$ throughout the sample, we use a numerical inverse Laplace transform $T_1$ analysis based on Tikhonov regularization to deduce the density distribution function $P(1/T_1)$. We demonstrate that $\sim 60\%$ of Ir spins are statically ordered at the NMR measurement timescale but the rest of the sample volume remains paramagnetic even at 4.2 K, presumably because of structural disorder induced primarily by stacking faults. In order to further investigate the influence of structural disorder, we compare these NMR results with those of a second sample B, which has been shown by transmission electron microscopy to have domains with unwanted Ag inclusion at the Li and Ir sites within the Ir honeycomb planes. Sample B displays an additional NMR peak with a relative intensity of $\sim 17\%$. The small Knight shift and $1/T_1$ of these defect-induced ${}^7\mathrm{Li}$ sites and the enhancement of bulk susceptibility at low temperatures suggest that these defects generate domains of only weakly magnetic Ir spins accompanied by free spins, leading to a lack of clear signatures of long-range order. The apparent lack of long-range order could be easily misinterpreted as evidence for the realization of a spin-liquid ground state in highly disordered Kitaev lattices.

We report the synthesis and physical properties of a full Heusler compound, $\mathrm{Mg}{\mathrm{Pd}}_2\mathrm{Sb}$, which we found to show superconductivity below $T_c=2.2\mathrm{K}$. $\mathrm{Mg}{\mathrm{Pd}}_2\mathrm{Sb}$ was obtained by a two-step solid-state reaction method and its purity and cubic crystal structure [$Fm\text{−}3m, a=6.4523\left(1\right)\AA$] were confirmed by powder x-ray diffraction. Normal and superconducting states were studied by electrical resistivity, magnetic susceptibility, and heat capacity measurements. The results show that $\mathrm{Mg}{\mathrm{Pd}}_2\mathrm{Sb}$ is a type-II, weak coupling superconductor (${\lambda }_{e\text{−}p}=0.53$). The observed pressure dependence of $T_c$ ($\mathrm{\Delta }{T}_c/p\approx –0.23\mathrm{K}/\mathrm{GPa}$) is one of the strongest reported for a superconducting Heusler compound. The electronic structure, phonons, and electron-phonon coupling in $\mathrm{Mg}{\mathrm{Pd}}_2\mathrm{Sb}$ were theoretically investigated. The obtained results are in agreement with the experiment, confirming the electron-phonon coupling mechanism of superconductivity. We compare the superconducting parameters to those of all reported Heusler-type superconductors.

Majorana zero modes can appear at the wire ends of a one-dimensional topological superconductor and manifest themselves as a quantized zero-bias conductance peak in the tunneling spectroscopy of normal-superconductor junctions. However, in superconductor-semiconductor hybrid nanowires, zero-bias conductance peaks may arise owing to topologically trivial mechanisms as well, mimicking the Majorana-induced topological peak in many aspects. In this work, we systematically investigate the characteristics of zero-bias conductance peaks for topological Majorana bound states, trivial quasi-Majorana bound states and low-energy Andreev bound states arising from smooth potential variations and disorder-induced subgap bound states. Our focus is on the conductance peak value (i.e., equal to, greater than, or less than $2e^2/h$), as well as the robustness (plateau- or spike-like) against the tuning parameters (e.g., the magnetic field and tunneling gate voltage) for zero-bias peaks arising from the different mechanisms. We find that for Majoranas and quasi-Majoranas, the zero-bias peak values are no more than $2e^2/h$, and a quantized conductance plateau forms generically as a function of parameters. By contrast, for conductance peaks due to low-energy Andreev bound states or disorder-induced bound states, the peak values may exceed $2e^2/h$, and a conductance plateau is rarely observed unless through careful postselection and fine-tuning. Our findings should shed light on the interpretation of experimental measurements on the tunneling spectroscopy of normal-superconductor junctions of hybrid Majorana nanowires.

We evaluate the spin-wave spectrum and dynamic susceptibility in a layered superconductor with helical interlayer magnetic structure. We especially focus on the structure in which the moments rotate ${90}^{\circ }$ from layer to layer realized in the iron pnictide ${\mathrm{RbEuFe}}_4{\mathrm{As}}_4$. While in nonmagnetic superconductors low-frequency magnetic field decays on the distance of the order of the London penetration depth, spin waves mediate its propagation to much larger distances limited by external dissipation mechanisms. The spin-wave spectrum in superconductors is strongly renormalized due to the long-range electromagnetic interactions between the oscillating magnetic moments. This leads to strong enhancement of the frequency of the mode coupled with uniform field and this enhancement exists only within a narrow range of the $c$-axis wave vectors of the order of the inverse London penetration depth. The key feature of materials like ${\mathrm{RbEuFe}}_4{\mathrm{As}}_4$ is that this uniform mode corresponds to the maximum frequency of the spin-wave spectrum with respect to the $c$-axis wave vector. As a consequence, the high-frequency surface resistance acquires a very distinct asymmetric feature spreading between the bare and renormalized frequencies. We also consider excitation of spin waves with the Josephson effect in a tunneling contact between helical-magnetic and conventional superconductors and study the interplay between the spin-wave features and geometrical cavity resonances in the current-voltage characteristics.

We identify the ground state structure of the phase KBaBi using ab initio evolutionary structure search methods and demonstrate that the bonding of this compound leads to a combination of very low thermal conductivity and electronic properties that are favorable for thermoelectric performance. The structure is the hexagonal ZrBeSi-type structure, with the cubic half-Heusler structure as a higher-energy competing phase. The bonding of the hexagonal structure leads to strongly anharmonic vibrational properties, which underlie the low thermal conductivity. The calculated figure of merit is approximately $ZT=3$ at 1000 K with optimized doping. This work underscores the use of chemical control of bonding to obtain low thermal conductivity and identifies a chemistry that achieves this.

Hyperuniform many-body systems in $d$-dimensional Euclidean space $R^d$ are characterized by completely suppressed (normalized) infinite-wavelength density fluctuations, and appear to be endowed with novel exotic physical properties. Recently, hyperuniform systems of disordered varieties have been observed in the context of various atomic-scale two-dimensional (2D) materials. In this work, we analyze the effects of localized defects on the density fluctuations across length scales and on the hyperuniformity property of experimental samples of 2D transition metal dichalcogenides. In particular, we extract atomic coordinates from time series annular dark field-scanning transmission electron microscopy imaging data of 2D tungsten chalcogenides with the 2H structure (Te-doped 2H-${\mathrm{WSe}}_2$) showing continuous development and evolution of electron-beam-induced defects, and construct the corresponding chemical-bonding informed coordination networks between the atoms. We then compute a variety of pair statistics and bond-orientational statistics to characterize the samples. At low defect concentrations, the corresponding materials are nearly hyperuniform, characterized by significantly suppressed scattering at the zero wave-number limit (omitting forward/ballistic scattering). As more defects are introduced, the (approximate) hyperuniformity of the materials is gradually destroyed, and the system becomes nonhyperuniform even when the material still contains a significant amount of crystalline regions. At high defect concentrations, the structures become antihyperuniform with diverging (normalized) large-scale density fluctuations, mimicking those typically observed at the thermal critical points associated with phase transitions. Overall, the defected materials possess varying degrees of orientation order, and there is apparently no intermediate hexatic phase emerging. To understand the observed nearly hyperuniform density fluctuations in the slightly defected materials, we construct a minimalist structural model and demonstrate that the experimental samples can be essentially viewed as perturbed honeycomb crystals with small correlated displacements and double chalcogen vacancies. Moreover, the small correlated displacements alone can significantly degrade hyperuniformity of the perfect honeycomb structure. Therefore, even a small amount of vacancies, when coupled with correlated displacements, can completely destroy hyperuniformity of the system.

In this study, the level statistics of the three-dimensional tight-binding model with non-Hermitian disorder, introduced by Tzortzakakis, Makris, and Economou (TME), and its variants were analyzed. The shift-and-invert Arnoldi method was used to analyze the eigenvalues of the TME model up to a $48\times 48\times 48$ cubic lattice, which was larger than those used in previous studies. The results showed that the magnitude of critical disorders in the isotropic TME model was larger than that reported in previous numerical studies for smaller systems. The localization-delocalization transition in an anisotropic model was also investigated. The computational method adopted in this study was shown to be quite effective for large-scale analysis of the calculation of all eigenvalues of sparse non-Hermitian matrices.

We investigate the structural and spectral properties of deterministic aperiodic arrays designed from statistically isotropic pinwheel tiling. By studying the scaling of the cumulative integral of its structure factor in combination with a higher-order structural correlation analysis we conclude that pinwheel arrays belong to the weakly hyperuniformity class. Moreover, by solving the multiple scattering problem for electric point dipoles using the rigorous Green's matrix theory, we demonstrate a clear transition from diffusive transport to localization behavior. This is shown by studying the Thouless number as a function of the scattering strength and the spectral statistics of the scattering resonances. Surprisingly, despite the absence of sharp diffraction peaks, clear spectral gaps are discovered in the density of states of pinwheel arrays that manifest a distinctive long-range order. Furthermore, the level-spacing statistics at large optical density exhibits a sharp transition from level repulsion to the Poisson behavior, consistently with the onset of the wave localization regime. Our findings reveal the importance of hyperuniform aperiodic structures with statistically isotropic $k$ space for the engineering of enhanced light-matter interactions and localization properties.

We study the characterization and realization of higher-order topological Anderson insulator (HOTAI) in non-Hermitian systems, where the non-Hermitian mechanism ensures extra symmetries as well as gain and loss disorder. We illuminate that the quadrupole moment $Q_{xy}$ can be used as the real space topological invariant of non-Hermitian higher-order topological insulator (HOTI). Based on the biorthogonal bases and non-Hermitian symmetries, we prove that $Q_{xy}$ can be quantized to 0 or 0.5. Considering the disorder effect, we find the disorder-induced phase transition from normal insulator to non-Hermitian HOTAI. Furthermore, to clarify the universality of real-space topological invariant in non-Hermitian systems, we elucidate that $Q_{xy}$ is also applicable for samples with the non-Hermitian skin effect. Our work enlightens the study of the combination of disorder and non-Hermitian HOTI.

We map the infinite-range coupled quantum kicked rotors over an infinite-range coupled interacting bosonic model. In this way we can apply exact diagonalization up to quite large system sizes and confirm that the system tends to ergodicity in the large-size limit. In the thermodynamic limit the system is described by a set of coupled Gross-Pitaevskii equations equivalent to an effective nonlinear single-rotor Hamiltonian. These equations give rise to a power-law increase in time of the energy with exponent $\gamma \sim 2/3$ in a wide range of parameters. We explain this finding by means of a master-equation approach based on the noisy behavior of the effective nonlinear single-rotor Hamiltonian and on the Anderson localization of the single-rotor Floquet states. Furthermore, we study chaos by means of the largest Lyapunov exponent and find that it decreases towards zero for portions of the phase space with increasing momentum. Finally, we show that some stroboscopic Floquet integrals of motion of the noninteracting dynamics deviate from their initial values over a timescale related to the interaction strength according to the Nekhoroshev theorem.

The prospect of a system possessing two or more stable states for a given excitation condition is of topical interest with applications in information processing networks. In this work, we establish the remote transfer of bistability from a nonlinear resource in a dissipatively coupled two-mode system. As a clear advantage over coherently coupled settings, the dissipative nature of interaction is found to support a lower pumping threshold for bistable signals. For comparable parameters, the bistability threshold for dissipatively coupled systems is lower by a factor of about 5. The resulting hysteresis can be studied spectroscopically by applying a probe field through the waveguide and examining the polariton character of the transmitted field. Our model is generic, apropos of an extensive set of quantum systems, and we demonstrate our results in the context of magnonics where experimental interest has flourished of late. As a consequence of dissipative coupling and the nonlinearity, a long-lived mode emerges, which is responsible for heightened transmission levels and pronounced sensitivity in signal propagation through the fiber.

We study the spin dynamics of a classical Heisenberg antiferromagnet with nearest-neighbor interactions on a quasi-two-dimensional kagome bilayer. This geometrically frustrated lattice consists of two kagome layers connected by a triangular-lattice linking layer. By combining Monte Carlo with precessional spin dynamics simulations, we compute the dynamical structure factor of the classical spin liquid in the kagome bilayer and investigate the thermal and dilution effects. While the low-frequency and long-wavelength dynamics of the cooperative paramagnetic phase is dominated by spin diffusion, weak magnon excitations persist at higher energies, giving rise to the half-moon pattern in the dynamical structure factor. In the presence of spin vacancies, the dynamical properties of the diluted system can be understood within the two-population picture. The spin diffusion of the “correlated” spin clusters is mainly driven by the zero-energy weather-vane modes, giving rise to an autocorrelation function that decays exponentially with time. On the other hand, the diffusive dynamics of the quasifree “orphan” spins leads to a distinctive longer-time power-law tail in the autocorrelation function. We discuss the implications of our work for the glassy behaviors observed in the archetypal frustrated magnet $\mathrm{Sr}{\mathrm{Cr}}_{9p}{\mathrm{Ga}}_{12-9p}{\mathrm{O}}_{19}$ (SCGO).

We present a broadband ferromagnetic resonance study of the Gilbert damping enhancement $\left(\mathrm{\Delta }\alpha \right)$ due to spin pumping in NiFe/Pt bilayers. The bilayers, which have negligible interfacial spin memory loss, are studied as a function of the Pt layer thickness $\left(t_{\text{Pt}}\right)$ and temperature (100–293 K). Within the framework of diffusive spin pumping theory, we demonstrate that Dyakonov-Perel (DP) or Elliot-Yaffet (EY) spin relaxation mechanisms acting alone are incompatible with our observations. In contrast, if we consider that the relation between spin relaxation characteristic time $\left({\tau }_{\text{s}}\right)$ and momentum relaxation characteristic time $\left({\tau }_{\text{p}}\right)$ is determined by a superposition of DP and EY mechanisms, the qualitative and quantitative agreement with experimental results is excellent. Remarkably, we found that ${\tau }_{\text{p}}$ must be determined by the out-of-plane electrical resistivity $\left(\rho \right)$ of the Pt film and hence its spin diffusion length $\left({\lambda }_{\text{Pt}}\right)$ is independent of $t_{\text{Pt}}$. Our work settles the controversy regarding the $t_{\text{Pt}}$ dependence of ${\lambda }_{\text{Pt}}$ by demonstrating its fundamental connection with $\rho$ considered along the same direction of spin current flow.

The interlayer coupling in two-dimensional (2D) magnetic materials is significantly important in determining the properties of 2D materials and applications of related devices. However, the mechanism that determines the interlayer magnetic coupling has only been comprehensively studied in $\mathrm{Cr}{\mathrm{I}}_3$ and that of transition metal dichalcogenides is still blurred. In this work, through first-principle calculations, we find in 2D magnetic bilayer that the interlayer magnetic coupling is determined by the stacking order of interlayer nonmagnetic atoms, accompanied by the transition between half metal and semiconductor in $\mathrm{Mn}{\mathrm{S}}_2$. The nonmagnetic atoms bridge the interlayer coupling and the stacking order of nonmagnetic atoms determines the interlayer coupling by altering the interlayer $p_z$-orbital bonding. Adjusting the structure of interlayer nomagnetic atoms by biaxial strain can also tune the interlayer coupling. The perspective proposed in our work, from the stacking order of nonmagnetic atoms, to understand the interlayer magnetic coupling is also applicable in other 2D materials.

The low-temperature linear-in-T resistivity of “strange metals,” such as the metallic state of the cuprate high-temperature superconductors, has long been thought to be associated with a quantum critical point. However, recent transport studies of the cuprates have found this behavior persists over a finite range of overdoping. In this work, we report magnetoresistance and Hall effect results for electron-doped films of the cuprate superconductor ${\mathrm{La}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$ (LCCO) for temperatures from 0.7 to 45 K and magnetic fields up to 65 T. For $x=0.12$ and 0.13, just below the Fermi surface reconstruction (FSR) at $x=0.14$, the normal state in-plane resistivity exhibits a well-known upturn at low temperature. Our new results show that this resistivity upturn is eliminated at high magnetic field and the resistivity becomes linear-in-temperature from ∼40 K down to 0.7 K. The magnitude of the linear coefficient scales with Tc and doping, as found previously [K. Jin, Nature(London) 476, 73 (2011), T. Sarkar, Sci. Adv. 5, eaav6753 (2019)] for dopings above the FSR. This striking observation suggests that the strange metal is not confined to a single “critical point” in the phase diagram, but rather is a robust universal feature of the metallic ground state of the cuprates.

Layered platinum tellurium $\left(\mathrm{Pt}{\mathrm{Te}}_2\right)$ was recently synthesized with controllable layer numbers down to a monolayer limit. Using ab initio calculations based on anisotropic Midgal-Eliashberg formalism, we show that by rubidium (Rb) intercalation, weak superconductivity in bilayer $\mathrm{Pt}{\mathrm{Te}}_2$ can be significantly boosted with superconducting $T_{\text{c}}=8$ K in the presence of spin-orbit coupling (SOC). The intercalant on one hand mediates the interlayer coupling and serves as an electron donor, leading to large density of states at Fermi energy. On the other hand, it increases the mass-enhancement parameter with electron-phonon coupling strength comparable to that of Pt. The potassium intercalated bilayer $\mathrm{Pt}{\mathrm{Te}}_2$ has a comparable $T_{\text{c}}$ to the case of Rb intercalation. The relatively high $T_{\text{c}}$ with SOC combined with experimental accessible crystal structures suggest that these superconductors are promising platforms to study the novel quantum physics associated with two-dimensional superconductivity, such as the recently proposed type-II Ising superconductivity.

We investigate whether there could exist topological invariants of gapped two-dimensional materials related to dissipationless thermoelectric transport at low temperatures. We give both macroscopic and microscopic arguments showing that thermoelectric transport coefficients vanish in the limit of zero temperature, and thus topological invariants arise only from the electric Hall conductance and the thermal Hall conductance. Our arguments apply to systems with arbitrarily strong interactions. We also show that there is no analog of the Thouless pump for entropy.