We examine models for the quantum-interference correction to the magnetoconductivity in two-dimensional electron gases (2DEGs) with both Rashba and Dresselhaus spin-orbit coupling for their applicability to experimental data fitting. In particular, we compare the Landau-quantized Cooperon approach, which is mostly only numerically treatable, and the quasiclassical approximation that was recently employed to obtain an explicit solution for arbitrary Rashba and Dresselhaus spin-orbit couplings [Marinescu et al., Phys. Rev. Lett. 112, 156601 (2019)]. It is found that the quasiclassical approximation yields significantly different results even to the lowest order in the magnetic field and appears unsuitable for reliable parameter fitting. The discrepancy emerges when a sum over Landau levels is replaced by an integral over wave vectors. Substantial improvement is achieved by supplementing the quasiclassical model with the first two corrections given by the Euler-MacLaurin formula for approximating a sum by an integral. Corresponding modifications are, however, only feasible in special spin-orbit parameter configurations where the mixing of Landau bands is negligible and a closed-form solution that accounts for Landau quantization is also available. Such a scenario appears in a parameter regime where a persistent spin helix emerges and a transition between weak localization and weak antilocalization takes place. Combining recent findings, we derive a generalized closed-form expression for the magnetoconductivity correction applicable to generic 2DEGs that are grown along a crystal direction with at least two growth-direction Miller indices equal in modulus. The result is a function of spin lifetimes of the long-lived spin textures and valid close to the persistent-spin-helix regime. The accuracy of the derived formula is validated by comparing with results from numerical diagonalization of the multiband Cooperon as well as a recently established Monte Carlo-based real-space simulation in exemplary (001)-, (113)-, and (110)-2DEGs.

Acoustic phonons with long mean free paths have long been believed to control the lattice thermal conductivity ${\kappa }_{\mathrm{L}}$ in solids dominantly. In this study, however, we demonstrate an optical phonon dominated ${\kappa }_{\mathrm{L}}$ in ${\mathrm{BaSnS}}_2$. By solving the Peierls-Boltzmann transport equation, we predict a low diagonal lattice thermal conductivity ${\kappa }_{\mathrm{L}}\left(\mathrm{D}\right)$ of $0.34\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ at 850 K, which is less than half the ${\kappa }_{\mathrm{L}}\left(\mathrm{D}\right)$ of SnS at the same temperature. Further calculations following the Allen-Feldman model suggest the additional off-diagonal lattice thermal conductivity ${\kappa }_{\mathrm{L}}\left(\mathrm{OD}\right)$ contributed by wavelike tunneling phonons. The ${\kappa }_{\mathrm{L}}\left(\mathrm{OD}\right)$ becomes pronounced at the high temperature ($0.17\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ at 850 K) and leads to a deviation of the temperature dependence of ${\kappa }_{\mathrm{L}}$ from $T^{\text{–}1}$ to $T^{\text{–}0.76}$, suggesting the potential lattice anharmonicity in ${\mathrm{BaSnS}}_2$. Further analyses indicate ${\mathrm{BaSnS}}_2$ has over 68% of ${\kappa }_{\mathrm{L}}$ contributed by optical phonons. We show this uncommon optical phonon dominated ${\kappa }_{\mathrm{L}}$ is due to the relatively high group velocities of optical phonons in ${\mathrm{BaSnS}}_2$. The phonon mode visualization suggests these relatively high-velocity optical phonons correspond to the antiphase vibrations in ${\mathrm{BaSnS}}_2$ monolayers, which is originated from the unique permutation of ${\mathrm{SnS}}_3$ tetrahedra. Finally, by investigating the mode-resolved group velocity, relaxation time, and Grüneisen parameter, we attribute the intrinsic low ${\kappa }_{\mathrm{L}}$ of ${\mathrm{BaSnS}}_2$ to the soft lattice and the relatively high lattice anharmonicity induced by the Ba-S weak bonding and Sn(II) lone-pair electrons. Our study explicitly analyzes the microscopic mechanism of optical phonon dominated heat transport in ${\mathrm{BaSnS}}_2$ and suggests it worthy of further experimental studies as an intrinsic low-${\kappa }_{\mathrm{L}}$ material.

While the large paramagnetic response measured in certain ensembles of metallic nanoparticles has been assigned to orbital effects of conduction electrons, the spin-orbit coupling has been pointed out as a possible origin of the anomalously large diamagnetic response observed in other cases. Such a relativistic effect, arising from the inhomogeneous electrostatic potential seen by the conduction electrons, might originate from the host ionic lattice, impurities, or the self-consistent confining potential. Here we theoretically investigate the effect of the spin-orbit coupling arising from the confining potential, quantifying its contribution to the zero-field magnetic susceptibility and gauging it against the ones generated by other weakly-relativistic corrections. Two ideal geometries are considered in detail, the sphere and the half sphere, focusing on the expected increased role of the spin-orbit coupling upon a symmetry reduction, and the application of these results to actual metallic nanoparticles is discussed. The matrix elements of the different weakly-relativistic corrections are obtained and incorporated in a perturbative treatment of the magnetic field, leading to tractable semi-analytical and semiclassical expressions for the case of the sphere, while a numerical treatment becomes necessary for the half sphere. The correction to the zero-field susceptibility arising from the spin-orbit coupling in a single sphere is quite small, and it is dominated by the weakly-relativistic kinetic energy correction, which in turn remains considerably smaller than the typical values of the nonrelativistic zero-field susceptibility. Moreover, the spin-orbit contribution to the average response for ensembles of nanoparticles with a large size dispersion is shown to vanish. The symmetry reduction in going from the single sphere to the half sphere does not translate into a significant increase of the spin-orbit contribution to the zero-field susceptibility.

Metasurfaces have been employed to control the electromagnetic and acoustic waves. We suggest that the quantum particles can be manipulated with a de Broglie wave metasurface. The effect was achieved by using the dielectric films milled with subwavelength slits, which behave as the quantum meta-atoms with an effective potential energy. The calculations show that ∼100% transmission of de Broglie waves may appear in certain conditions. Moreover, by tuning the effective potential of the slits, a full 360° coverage of transmission phase is attainable. With a carefully designed annular metasurface, highly efficient and subwavelength focusing of de Broglie waves has been theoretically demonstrated. Our work may render a way to manipulate quantum particles.

We consider an electrostatically induced square lattice of quantum dots and study the role of electron-electron correlations in the resulting electronic features of the system. We utilize the Wannier functions methodology to construct a Hamiltonian for interacting fermions, and find that the change of the depth of the quantum dot confining potential results in a transition from a moderately, to strongly correlated regime of the system. We obtain the approximate ground state by means of the variational Monte Carlo method for a wide range of dopings. The values of microscopic parameters, charge gap, as well as spin- and pair-correlation functions obtained in the strongly correlated regime signify the presence of antiferromagnetic spin ordering and the realization of the Mott insulator phase. Moreover, we report on a two-dome structure of the emerging $d$-wave paired state residing on both sides of the half-filled case. The obtained results are discussed in view of the well-known family of unconventional superconducting materials, such as copper-based compounds.

The experimental observation of the Dirac fermion states in ${\beta }_{12}$-borophene sheets and the discovery of their novel topological properties have made them a promising candidate for spintronic applications. Here, by combining the nonequilibrium Green's function (NEGF) and tight-binding (TB) approximations, we study the charge and spin transport properties through a ${\beta }_{12}$-borophene nanoribbon (BNR) with different edge shapes. We show that for BNR exposed to a nonlocal exchange magnetic field, the spin filtering occurs so that the spin direction of transmitted electrons could be controlled by adjusting the energy of incoming electrons with the help of an external backgate voltage. It is found that an armchair BNR (ABNR) in the simultaneous presence of a transverse electric field and a nonlocal exchange field acquires half-metallic properties. The influence of local exchange fields is evaluated by exposing the edges of BNRs to ferromagnetic strips with parallel and antiparallel configurations. Our findings show that the edge manipulations in BNRs lead to the emergence of giant magnetoresistance and a perfect spin filter. Finally, we study the effects of edge vacancies and Anderson disorder on the spin-dependent conductance of an ABNR and find that the perfect spin polarization is not destroyed in the presence of Anderson disorder and various single vacancies. Our results reveal the outstanding spin transport properties of ABNRs for future spintronic devices.

We demonstrate that all-anisotropic transition metal dichalcogenide (TMDC) nanostructures can support advanced optical nanoantenna functionalities, such as high end-fire directivity and directionality inversion. The designed chain structures, driven by a dipole emitter, are composed of negative uniaxial anisotropic tungsten disulfide $\left({\mathrm{WS}}_2\right)$ TMDC nanoparticles featuring ordinary/extraordinary refractive indices. The ordinary index, whose values are much higher than those of Si (Si is typically used in all-dielectric nanostructures), is also much higher than the extraordinary index, thus allowing for a strong material birefringence. We find that anisotropy of this type makes it possible to achieve high end-fire directivity, and also offers an extra degree of freedom that allows for an orientation-based coupling between a free-to-rotate dipole emitter and fixed ${\mathrm{WS}}_2$ elements. Furthermore, appropriately rotating half the array elements achieves end-fire directional inversion (at a fixed operating wavelength) simply by adjusting the emitter orientation. This unique feature is characteristic of the high anisotropy exhibited by ${\mathrm{WS}}_2$ in the optical-near infrared regime, and cannot be readily realized with isotropic all-dielectric or plasmonic spherical structures due to their material symmetry. The presented material-anisotropy-based designs comprise a nanophotonics platform that allows for unique functionalities at the nanoscale, as well as for the implementation of tunable nanophotonic devices.

We propose a series of scaling theories for Kosterlitz-Thouless (KT) phase transitions on the basis of the hallmark exponential growth of their correlation length. Finite-size scaling, finite-entanglement scaling, short-time critical dynamics, and finite-time scaling, as well as some of their interplay, are considered. Relaxation times of both a normal power-law and an anomalous power-law with a logarithmic factor are studied. Finite-size and finite-entanglement scaling forms somehow similar to but different from a frequently employed ansatz are presented. The Kibble-Zurek scaling of topological defect density for a linear driving across the KT transition point is investigated in detail. An implicit equation for a rate exponent in the theory is derived, and the exponent varies with the distance from the critical point and the driving rate consistent with relevant experiments. To verify the theories, we utilize the KT phase transition of a one-dimensional Bose-Hubbard model. The infinite time-evolving-block-decimation algorithm is employed to solve numerically the model for finite bond dimensions. Both a correlation length and an entanglement entropy in imaginary time and only the entanglement entropy in real-time driving are computed. Both the short-time critical dynamics in imaginary time and the finite-time scaling in real-time driving, both including the finite bond dimension, for the measured quantities are found to describe the numerical results quite well via surface collapses. The critical point is also estimated and confirmed to be 0.302(1) at the infinite bond dimension on the basis of the scaling theories.

Experimental platforms based on trapped ions, cold molecules, and Rydberg atoms have made possible the investigation of highly nonlocal spin-$1/2$ Hamiltonians with long-range couplings. Here, we study the effects of such nonlocal couplings in the long-range spin-$1/2$ XXZ Heisenberg Hamiltonian. We calculate explicitly the two-spin energy spectrum, which describes all possible energetic configurations of two spins pointing in a specific direction embedded in a background of spins with opposite orientation. For fast decay of the spin-spin couplings, we find that the two-spin energy spectrum is characterized by well-defined discrete values, corresponding to bound states, separated by a set of continuum states describing the scattering region. In the deep long-range regime instead, the bound states disappear as they get incorporated by the scattering region. The presence of two-spin bound states results to be crucial to determine both two- and many-spin dynamics. On one hand, radically different two-spin spreadings can be observed by tuning the decay of the spin couplings. On the other hand, two-spin bound states enable the dynamical stabilization of effective antiferromagnetic states in the presence of ferromagnetic couplings. Finally, we propose a novel scheme based on a trapped-ion quantum simulator to experimentally realize the long-range XXZ model and to study its out-of-equilibrium properties.

We report on the magnetic structures of ${\mathrm{Tb}}_3{\mathrm{RuO}}_7$ and ${\mathrm{Nd}}_3{\mathrm{RuO}}_7$ determined from powder neutron-diffraction experiments. In ${\mathrm{Tb}}_3{\mathrm{RuO}}_7$, alternating-bond spin-$\frac{3}{2}$ Ru1-Ru2 chains are formed. The Ru1 and Ru2 moments are ordered and disordered (paramagnetic), respectively, below 15 K. This result indicates the appearance of a partially disordered (PD) state, although the two Ru sites are very similar to each other. In ${\mathrm{Nd}}_3{\mathrm{RuO}}_7$, the Ru1 and Ru2 ions form independent uniform chains. Both the Ru1 and Ru2 moments are ordered below 17.5 K. Probably, the main source of the PD state in ${\mathrm{Tb}}_3{\mathrm{RuO}}_7$ is the magnetic frustration in the exchange interactions. The internal magnetic field generated by the Tb ordered moments at the Ru1 sites is different from that at the Ru2 sites. We speculate that the different (nonuniform) internal magnetic field enhances the difference in the properties between the Ru1 and Ru2 moments. We also report on the magnetic entropy changes of ${\mathrm{Tb}}_3{\mathrm{RuO}}_7$ and ${\mathrm{Gd}}_3{\mathrm{RuO}}_7$.

We discuss the theory of linear and nonlinear spectroscopy of an rf superconducting quantum interference device (rf-SQUID) coupled to a Josephson spectrometer. Recent experimental measurements on this system have shown a strongly nonlinear absorption line shape, whose current peak maximum undergoes a forward-backward bending transition depending on the value of the rf-SQUID phase. We show that this transition can be qualitatively understood by mapping the dynamics of the driven rf-SQUID onto a generalized Duffing oscillator, with tunable drive and nonlinearity, undergoing a bifurcation. Finally we show that in order to quantitatively reproduce the experimental data reported by Griesmar et al. [Phys. Rev. Research 3, 043078 (2021)], it is crucial to include the feedback from the load line, leading to an additional source of nonlinearity.

The search for optimal materials to be used in superconductor/ferromagnet hybrids is fundamental to the development of superconducting spintronic devices. One of the main issues which should be tackled is the optimum ferromagnetic material that should be used in these systems, i.e., a ballistic ferromagnet with a large value of the exchange energy or a weak ferromagnet with diffusive transport. Here, we investigate the proximity effect between Nb and amorphous ${\mathrm{NdNi}}_5$. We observe that the electrical transport is influenced by the strong disorder in the ferromagnetic layers. For small values of the ferromagnetic layer thickness, the depression of the superconducting critical temperature is stronger than as observed in metallic ferromagnetic layers with comparable values of the exchange energy. On the contrary, for a large thickness of the ferromagnet the interface transparency is very small and the effect of the ferromagnet on the superconductor becomes negligible. The results are in line with recent observations and confirm the prominent role played by the structural and morphological properties of the ferromagnet on the physics of superconductor/ferromagnet bilayers.

We study a non-Hermitian AA model with long-range hopping, $1/r^a$, and different choices of quasiperiodic parameters $\beta$ to be a member of the metallic mean family. We find that when the power-law exponent is in the $a<1$ regime, the system displays a delocalized-to-multifractal (DM) edge in its eigenstate spectrum. For the $a>1$ case, a delocalized-to-localized (DL) edge exists, also called the mobility edge. While a striking feature of the Hermitian AA model with long-range hopping is that the fraction of delocalized states can be obtained from a general sequence manifesting a mathematical feature of the metallic mean family, we find that the DM or DL edge for the non-Hermitian cases is independent of the mathematical feature of the metallic mean family. To understand this difference, we consider a specific case of the non-Hermitian long-range AA model with $a=2$, for which we can apply the Sarnak method to analytically derive its localization transition points and the exact expression of the DL edge. Our analytical result clearly demonstrates that the mobility edge is independent of the quasiperiodic parameter $\beta$, which confirms our numerical result. Finally, an optical setup is proposed to realize the non-Hermitian long-range AA model.

We experimentally and analytically investigate laser excitation of picosecond longitudinal and shear acoustic pulses in highly magnetostrictive terfenol-${\mathrm{TbFe}}_2$-epitaxial thin films. We report a magnetoelastic mechanism for picosecond longitudinal and shear acoustic strain excitation, so-called direct transient demagnetostriction, which denotes the ultrafast laser-induced demagnetization and release of static magnetostrictive built-in strains. From analytical considerations and numerical modeling, we demonstrate that the efficiency of ultrashort longitudinal and shear acoustic strains generation strongly depends on the magnetization orientation with respect to the lattice crystallographic directions. Overall, our study provides insight into ultrafast acoustic waves excitation and detection in all sorts of magnetic materials from laser-based mechanisms.

We develop two numerical schemes to study the conductance of the two-wire junction of inequivalent Tomonaga-Luttinger liquids. In the first scheme we use the static current-current correlation function across the junction to extract the linear conductance through a relation that is derived via the bosonization method. In the second scheme we apply a voltage bias and evaluate the time-dependent current across the junction to obtain the current-voltage characteristic. The conductance is then extracted from the small bias result within the linear response regime. Both schemes are based on the infinite-size matrix product state to minimize the finite-size effects. Due to the lack of the translational invariance, we focus on a finite-size window containing the junction. For time-independent calculations, we use infinite boundary conditions to evaluate the correlations within the window. For time-dependent calculations, we use the window technique to evaluate the local currents within the window. The numerical results obtained by both schemes show excellent agreement with the analytical predictions.

Motivated by the increasing number of systems featuring multiple bands at low energy, we address the Boltzmann approach to transport in a multiband weakly disordered noninteracting crystal subject to a small electric field. In general, the multiband structure leads to a considerable complication of the Boltzmann equation. Indeed, even in the presence of elastic impurity scattering, one needs to compute for each band and momentum the dressed velocities, which account for scattering events. Here we provide a semianalytical solution to the Boltzmann equation that reduces such a challenging numerical task to the much simpler numerical computation of a small tensor whose dimension is set by the number of bands at the Fermi level. This approach further allows us to discuss the interplay of symmetry and disorder for different impurity types, including those originating from random-matrix Wigner ensembles. As an example of application, we consider the 2D isotropic Rashba metal and we discuss, in a full analytical fashion, how different types of disorders may break the exactness of the relaxation-time approximation and induce transport anisotropy, and may allow one to identify the presence of spin-orbit coupling as deviations of the conductivity from the Drude behavior.

Based on first-principles calculations, we study the electron-phonon scattering effect on the resistivity in the zirconium dichalcogenides, ${\text{Zr}}_{}{\text{S}}_2$ and ${\text{Zr}}_{}{\text{Se}}_2$, whose electronic band structures possess multiple valleys at the conduction band minimum. The computed resistivity exhibits nonlinear temperature dependence, especially for ${\text{Zr}}_{}{\text{S}}_2$, which is also experimentally observed on some transition metal dichalcogenides such as ${\text{Ti}}_{}{\text{S}}_2$ and ${\text{Zr}}_{}{\text{Se}}_2$. By performing the decomposition of the contributions of scattering processes, we find that the intravalley scattering by acoustic phonons mainly contributes to the resistivity around 50 K. Moreover, the contribution of the intravalley scattering by optical phonons becomes dominant even above 80 K, which is a sufficiently low temperature compared with their frequencies. By contrast, the effect of the intervalley scattering is found to be not significant. Our study identifies the characteristic scattering channels in the resistivity of the zirconium dichalcogenides, which provides critical knowledge to microscopically understand electron transport in systems with multivalley band structure.

Periodic optical pumping of semiconductor systems like gallium arsenide grants insight into the spin dynamics and coupling of electrons and nuclei. Nuclear-induced frequency focusing occurs when spin-polarized nuclei alter the Larmor spin precession frequency of the electrons to approach discrete values. These discrete values are integer or half-integer multiples of a quantity that is proportional to the repetition rate of the optical pulses. In earlier work, we presented a numerical model based on the optical Stark effect that captures the interplay of electron and nuclear spins in bulk gallium arsenide. In this paper, we report the observation of nuclear-induced frequency focusing in our material and show that this behavior can help to explain the peak deformations that we observe to persist in subsequent peaks in a magnetic-field scan measurement of Kerr rotation when the field scan is paused for an extended time interval. We demonstrate that extending our model to account for a distribution of electron spins with different Overhauser fields allows us to reproduce these observations as well as additional phenomena, including changes in Kerr rotation amplitude, from our previous work.