We analyze the micromagnetics of short longitudinal modulations of a high-magnetization material in cylindrical nanowires made of a soft-magnetic material of lower magnetization such as permalloy, combining magnetic microscopy, analytical modeling, and micromagnetic simulations. The mismatch of magnetization induces curling of magnetization around the axis in the modulations, in an attempt to screen the interfacial magnetic charges. The curling angle increases with modulation length, until a plateau is reached with nearly full charge screening for a specific length scale ${\mathrm{\Delta }}_{\mathrm{mod}}$, larger than the dipolar exchange length of any of the two materials. The curling circulation can be switched by the Oersted field arising from a charge current with typical magnitude ${10}^{12}\mathrm{A}/{\mathrm{m}}^2$ for a diameter of $\sim 100$ nm, and reaching a maximum for ${\mathrm{\Delta }}_{\mathrm{mod}}$.

A noncollinear magnet consists of the magnetic moments forming a noncollinear spin structure. Because of this structure, the Hamiltonian of magnons acquires the cubic terms. Although the cubic terms are the magnon-magnon interactions characteristic of noncollinear magnets, their effects on magnon transport have not been clarified yet. Here we show that in a canted antiferromagnet the cubic terms cause a magnon drag that magnons drag magnon spin current and heat current, which can be used to enhance these currents by tuning a magnetic field. For a strong magnetic field, we find that the cubic terms induce low-temperature peaks of a spin-Seebeck coefficient, a magnon conductivity, and a magnon thermal conductivity, and that each value is one order of magnitude larger than the noninteracting value. This enhancement is mainly due to the magnetic field dependence of the coupling constant of the cubic terms through the magnetic-field dependent canting angle. Our magnon drag offers a way for controlling the magnon currents of noncollinear magnets via the many-body effect.

We performed a systematic study of the nonmagnetic skutterudite-related ${\mathrm{Y}}_5{\mathrm{Rh}}_6{\mathrm{Sn}}_{18}$ superconductor, where the lattice disorder on the coherence length scale $\xi$ additionally generates a nonhomogeneous, high-temperature superconducting phase with disorder-enhanced critical temperature $T_c^{★}$. We have previously discussed various possibilities of local atomic disorder; one of the possibilities is doping. Our present studies focus on the series of ${\mathrm{Y}}_{5-\delta }\left({\mathrm{Rh}}_{5.5}{M}_{0.5}\right){\mathrm{Sn}}_{18}$ compounds ($\delta \ll 1$), where the dopants $M=$ Co, Ir, Ru, and Pd, when they are smaller (Co) or larger (Pd) than Rh, generate the peak effect in fields smaller than the critical field $H_{c2}$. This phenomenon manifests itself as a weak peak in the real and imaginary parts of ac susceptibility and is more distinct in magnetoresistance. Using a simple theoretical model, we demonstrate that the effectiveness of this mechanism depends not only on the magnitude of the difference between the size of the dopant and the host atom, but also on whether the dopant is smaller or larger. The agreement between this prediction and our experimental data strongly supports the impurity-based scenario of the observed peak effect. Magnetoresistance isotherms of the remaining samples ($M=$ Ir and Ru) with the radius of $M$ being very similar to that of Rh show, however, a weak peak-effect-like behavior, which is mainly due to vacancies $\delta$ at Y sites, while the corresponding ac susceptibility isotherms exhibit a distinct peak at $H\sim H_{c2}$. This field-dependent ${\chi }_{\mathrm{ac}}$ anomaly appears to be similar in nature to the peak effect; however, it cannot be attributed to pinning and appears to be an equilibrium property of the system. We also report the coexistence of spin fluctuations and superconductivity for ${\mathrm{Y}}_5{\mathrm{Rh}}_6{\mathrm{Sn}}_{18}$ doped with Pd and Co.

We investigate the impact of dilution by setting the on-site repulsion strength $U$ to zero at a fraction of sites in the half filled Hubbard model on a simple cubic lattice. We employ a semiclassical Monte Carlo approach first to recover the zero dilution (undiluted $x=1$) properties, including $U$ dependence of insulator to metal crossover temperature scale $T^{*}$ and long-range staggered antiferromagnetic ordering temperature $T_N$. For the nonperturbative regime of $U\approx$ bandwidth, we find a rapid suppression of $T^{*}$ with reducing $x$ from 1 to 0.7. However, $T_N$ remains unchanged in this dilution range, showing a weakening of the insulating state but not of the magnetic order. At $x\le 0.7, T^{*}$ and $T_N$ coincide and are suppressed together with decrease in $x$. Within the Monte Carlo study we show that the long-range magnetic order vanishes at $x=0.15$ at $T=0.01$ much below the classical percolation threshold. The magnetic order below the classical percolation threshold is in line with the expected fragile long-range magnetic order at vanishingly small $x$ at $T=0$. We exhibit that the induced moments on $U=0$ sites drive the magnetic order below the classical percolation limit by studying local moment systematics and finite-size analysis of magnetic order. At the end, we show that either increasing $U$ to large values or raising temperature beyond a $U$ dependent critical value, suppresses the induced local moments of the $U=0$ sites and recovers the classical percolation threshold.

In Phys. Rev. Lett. 128, 176402 (2022), we argued that the chiral central charge—a topologically protected quantity characterizing the edge theory of a gapped $(2+1)$-dimensional system—can be extracted from the bulk by using an order parameter called the modular commutator. In this paper, we reveal general properties of the modular commutator and strengthen its relationship with the chiral central charge. First, we identify connections between the modular commutator and conditional mutual information, time reversal, and modular flow. Second, we prove, within the framework of the entanglement bootstrap program, that two topologically ordered media connected by a gapped domain wall must have the same modular commutator in their respective bulk. Third, we numerically calculate the value of the modular commutator for a bosonic lattice Laughlin state for finite sizes and extrapolate to the infinite-volume limit. The result of this extrapolation is consistent with the proposed formula up to an error of about $0.7\%$.

We present an angle-resolved photoemission study of the electronic band structure of the excitonic insulator ${\mathrm{Ta}}_2{\mathrm{NiSe}}_5$, as well as its evolution upon sulfur doping. Our experimental data show that while the excitonic insulating phase is still preserved at a sulfur-doping level of $25\%$, such a phase is heavily suppressed when there is a substantial amount, $\sim 50\%$, of S-doping at liquid nitrogen temperatures. Moreover, our photon energy-dependent measurements reveal a clear three-dimensionality of the electronic structure, both in ${\mathrm{Ta}}_2{\mathrm{NiSe}}_5$ and ${\mathrm{Ta}}_2\mathrm{Ni}{\left({\mathrm{Se}}_{1-x}{\mathrm{S}}_x\right)}_5$ ($x=0.25,0.50$) compounds. This suggests a reduction of electrical and thermal conductivities, which might make these compounds less suitable for electronic transport applications.

We study theoretically nonlinear optical properties of graphene quantum dots placed in a field of a short and strong linearly polarized optical pulse. We address the problem of high harmonic generation in quantum dots and how such nonlinear effect is affected by dephasing processes in a quantum dot. The dephasing makes the ultrafast electron dynamics more irreversible with a large residual population of the excited quantum dot levels. In relation to the high-harmonic spectrum, with increasing the dephasing time, the intensities of the low-frequency harmonics increase while the cutoff energy decreases. The dependence of the cutoff energy on the amplitude of the optical pulse is also sensitive to the frequency of the pulse. When the frequency of the optical pulse is much less than the quantum dot band gap, this dependence is almost linear, but when the frequency of the pulse is comparable to the band gap, the cutoff energy shows saturation behavior at large field amplitude, $>0.4$ V/Å.

Long-range interactions (LRIs) are ubiquitous in nature. Higher-order topological (HOT) insulators represent a new phase of matter. A critical issue is how LRI dictates the HOT phases. In this work, we discover four topologically distinct phases, i.e., HOT phase, bound state in the continuum, Dirac semimetal (DSM) phase, and trivial insulator phase in a breathing kagome circuit with tunable LRIs. We find an emerging type-III corner state in the HOT phase, which splits from the edge state continuum and originates from the strong coupling between nodes at different edges. We experimentally detect this novel state by impedance and voltage measurements. In the DSM phase, the Dirac cone exhibits an itinerant feature with a tunable position that depends on the LRI strength. Our findings provide a deeper understanding of the LRI effect on exotic topological states and pave the way for regulating interactions in topolectrical circuits.

Tungsten ditelluride $\left({\mathrm{WTe}}_2\right)$ is a transition metal dichalcogenide with novel electronic structures and unique properties for application to next-generation devices. Defects in ${\mathrm{WTe}}_2$ can impact its properties in both positive and negative ways. Therefore, it urgently requires a precise classification to help understand the possible impacts. Here we report on both geometric and electronic characteristics of the defects in ${\mathrm{WTe}}_2$ identified by the combination of scanning tunneling microscopy (STM) and density functional theory (DFT) calculation. We found four types of defects derived from a missing Te atom; two of them are located at the topmost surface while the others are under the surface. The former are imaged topographically and are ascribed to point vacancies of surface Te atoms. The DFT calculations reveal the noncentrosymmetric displacements of atoms around the defects and reasonably reproduce the STM images. Interestingly, the latter defects are hardly observed but they are dressed with the noncentrosymmetric quasiparticle interference (QPI) fringes which enable us to identify them. These findings demonstrate that STM-QPI can be a feasible method to characterize the defects in layered materials.

We study photoexcitations in small Hubbard clusters of up to 12 sites. After the electric field pulse some of these clusters show an increase of the double occupation through impact ionization. We treat the time-dependent electromagnetic field classically and calculate time evolution by exact diagonalization. As a tool for better analyzing the out-of-equilibrium dynamics, we generalize the Loschmidt amplitude. In this way we are able to resolve which many-body energy eigenstates are responsible for impact ionization and which ones show pronounced changes in the double occupation and spin energy. Our analysis reveals that the increase of spin energy is of little importance for impact ionization. We further demonstrate that, for one-dimensional chains, the optical conductivity has a characteristic peak structure originating solely from vertex corrections.

Real-space entanglement spectra (RSES) capture characteristic features of the topological order encoded in the fractional quantum Hall (FQH) states. In this work, we numerically compute, using Monte Carlo methods, the RSES and the counting of edge excitations of non-Abelian FQH states constructed using the parton theory. Efficient numerical computation of RSES of parton states is possible, thanks to their product-of-Slater-determinant structure, allowing us to compute the spectra in systems of up to 80 particles. Specifically, we compute the RSES of the parton states ${\varphi }_2^2, {\varphi }_2^3$, and ${\varphi }_3^2$, where ${\varphi }_n$ is the wave function of $n$-filled Landau levels, in the ground state as well as in the presence of bulk quasihole states. We then explicitly demonstrate a one-to-one correspondence of RSES of the parton states with representations of the Kac-Moody algebras satisfied by their edge currents. We also show that for the lowest Landau level projected version of these parton states, the spectra match with that obtained from the edge current algebra. We also perform a computation of spectra of the overlap matrices corresponding to the edge excitations of the parton states with a constrained number of particles in the different parton Landau levels. Counting in these match the individual branches present in RSES, providing insight about how different branches are formed.

We consider a neutral exciton localized on a model $p-i-n$ junction defined in a two-dimensional crystal, ${\mathrm{MoSe}}_2$ and phosphorene, using a variational approach to the effective mass Hamiltonian. The variational solution to the problem with nonseparable center of mass provides the exciton density in the real space and accounts for the kinetic energy due to the exciton localization. For low values of the potential step across the junction, the exciton occupies an area which is much larger than the nominal width of the junction. Localization of the exciton within the junction area is accompanied by the appearance of the dipole moment induced by the local electric field. The induced dipole moment becomes a linear function of the potential step only when the step is sufficiently large. In consequence, the energy dependence on the step value is nonparabolic. We demonstrate that the exciton gets localized not exactly at the center of the junction but on the side which is more energetically favorable for the heavier carrier: electron or hole.

The electronic dynamics in ${\mathrm{Nb}}_{2n+1}{\mathrm{Si}}_n{\mathrm{Te}}_{4n+2}$ with varying component $n$ are systematically investigated by low-temperature scanning tunneling microscopy/spectroscopy (STM/STS). Our quasiparticle interferences reveal a nondecay standing wave at the Fermi level, proving the one-dimensional (1D) nature of the charge carriers (holes) in the materials. The energy and component dependence of phase relaxation length $l_{\varphi }$ and lifetime $\tau$ of 1D holes are unveiled and found to be consistent with the Tomonaga-Luttinger liquid theory. Our work demonstrates ${\mathrm{Nb}}_{2n+1}{\mathrm{Si}}_n{\mathrm{Te}}_{4n+2}$ as a platform to manipulate 1D physics and offers an alternative perspective for studying electronic dynamics of non-Fermi liquids through STM experiments.

The properties of glasses can change significantly as they evolve toward equilibrium. Mechanical deformation appears to influence this physical aging process in conflicting ways, with experiments and simulations showing both effects associated with rejuvenation away from and overaging toward the equilibrium state. Here we report a significant densification effect in a polymer undergoing shear flow under high pressure. We used the high-aspect ratio geometry of the layer compression test to measure the uniform and homogeneous accumulation of plastic strain during isothermal confined compression of a deeply quenched film of polystyrene glass. Combined scanning transmission x-ray microscopy (STXM) and atomic force microscopy confirmed defect-free deformation leaving up to 1.2% residual densification under conditions of confined uniaxial strain. At higher peak strain, plastic shear flow extruded glass from below the compressing punch under conditions of a high background pressure. A further density increase of 2% was observed by STXM for a highly thinned residual thickness of polymer that nevertheless showed no signs of crystallization or internal strain localization. While the confined uniaxial densification can be accounted for by a simple elastic–plastic constitutive model, the high-pressure extrusion densification cannot.

Disorder-free localization has been proposed as a mechanism for ergodicity breaking in lattice gauge theories (LGTs) which can even occur in two spatial dimensions (2D). It has been shown that the U(1) quantum link model (QLM) can localize due to an emergent classical percolation transition fragmenting the system into disconnected real-space clusters. While the nature of the quantum localization transition (QLT) is still debated for conventional many-body localization, here we provide a comprehensive characterization of the QLT for the QLM in 2D for a disorder-free case. In this Letter we find compelling evidence that the QLT in the 2D QLM is continuous and we determine its universality class. We base our considerations on a spectral analysis of finite-size clusters in the percolation problem which exhibits two regimes—one in which large clusters effectively behave nonergodically, a result naturally accounted for as an interference phenomenon in configuration space, and the other in which all large clusters behave ergodically. Our analysis can also be applied to other 2D U(1) LGTs potentially including also matter degrees of freedom.

Considering theoretically the transition between hydrodynamic and ballistic regimes in 2D semiconductors, we show that electrons in high-mobility 2D GaAs are by far the best system for the direct observation of collective hydrodynamic effects even in bulk transport properties independent of complicated transport features in narrow constrictions and small systems where Gurzhi phenomena are typically studied experimentally. We predict a strong hydrodynamics-induced generic violation of the Wiedeman-Franz law in bulk 2D GaAs systems for mobilities as modest as ${10}^6{\mathrm{cm}}^2/\text{Vs}$ and densities $1–5\times {10}^{11}{\mathrm{cm}}^{-2}$ in the temperature range of $T=1–40\text{K}$.

We devise a framework to compute accurate phonons in molecular crystals even in case of strong quantum anharmonicity. Our approach is based on the calculation of the static limit of the phononic Matsubara Green's function from path integral molecular dynamics simulations. Our method enjoys a remarkably low variance, which allows one to compute accurate phonon frequencies after a few picoseconds of nuclear dynamics, and it is further stabilized by the use of appropriate constrained displacement operators. We applied it to solid hydrogen at high pressure. For phase III, our predicted infrared (IR) and Raman active vibrons agree very well with experiments. We then characterize the crystalline symmetry of phase IV by direct comparison with vibrational data and we determine the character and isotopic shift of its Raman and IR vibron peaks.

A pure spin current is predicted to occur when an external magnetic field and a linearly inhomogeneous spin-only field are appropriately aligned. Under these conditions (such as originate from nuclear contact hyperfine fields that do not affect orbital motion) a linear, spin-dependent dispersion for free electrons emerges from the Landau Hamiltonian. The result is that spins of opposite orientation flow in opposite directions giving rise to a pure spin current. A classical model of the spin and charge dynamics reveals intuitive aspects of the full quantum mechanical solution. We propose optical orientation or electrical polarization experiments to demonstrate this outcome.

We study the combined effect of quasiperiodic disorder, driven, and interaction in the periodically kicked Aubry-André model. In the noninteracting limit, by analyzing the quasienergy spectrum statistics, we verify the existence of a dynamical localization transition in the high-frequency region, whereas the spectrum statistics becomes intricate in the low-frequency region due to the emergence of the extended/localized-to-multifractal edges in the quasienergy spectrum, which separate the multifractal states from the extended (localized) states. When the interaction is introduced, we find the periodically kicked incommensurate potential can lead to a transition from the ergodic to many-body-localization phase in the high-frequency region. However, the many-body localization phase vanishes in the low-frequency region even for the strong quasiperiodic disorder. Our studies demonstrate that the periodically kicked Aubry-André model displays rich dynamical phenomena and the driving frequency plays an important role in the formation of many-body localization in addition to the disorder strength.

We applied the self-consistent harmonic approximation (SCHA), combined with coherent states formalism, to study the ferromagnetic resonance (FMR) in a ferromagentic/normal metal junction. Due to the interface interaction, the FMR-generated spin current is injected from the magnetic insulator to the normal metal, the so-called spin pumping. Ordinarily, ferromagnetic models are described by bosonic representation or phenomenological theories; however, in a coherent magnetization state, the SCHA is the more natural choice to treat FMR problems. Over the years, the SCHA has successfully applied to investigate ferro- and antiferromagnetism in a wide range of scenarios. The main point of the SCHA formalism involves the adoption of a quadratic model for which corrections are included through temperature-dependent renormalization parameters. Therefore the SCHA is an efficient method for determining the properties of magnetically ordered phases. Using the SCHA, we obtained the temperature dependence of FMR-driven spin pumping. In addition, we found the spin-mix conductance, the additional damping from the angular momentum injection into the normal metal side, and the magnetic susceptibility. The SCHA outcomes are in remarkable agreement with the results of the literature.