We propose a realization of an antisymmetric spin-split band structure through magnetic phase transitions without spin-orbit coupling. It enables us to utilize it for a variety of magnetic-order-driven cross-correlated and nonreciprocal transport phenomena as similar to those in spin-orbit-coupling oriented systems. We unveil its general condition as an emergence of a bond-type magnetic toroidal multipole (polar tensor) in a triangular unit with noncollinear ${120}^{\circ }$ antiferromagnetic structures. By using the concept of augmented multipoles, we systematically analyze the phenomena in terms of an effective multipole coupling. Our multipole description is ubiquitously applied to any trigonal and hexagonal structures including triangular, kagome, and breathing kagome structures, and provides a way to design and engineer materials with a giant antisymmetric spin splitting and its physical responses even without spin-orbit coupling.

Edge roughness in magnetic stripe arrays is an important structural parameter with a sizable impact on magnetic domains, domain correlation, pinning and propagation of domain walls in micro- and nanostripes proposed for data storage and logic devices. We have investigated two different stripe arrays fabricated by lithographic methods from permalloy ${\mathrm{Fe}}_{22}{\mathrm{Ni}}_{78}$, one with rough edges and another one with smooth edges. Performing polarized neutron reflectivity and polarized neutron off-specular scattering both patterns yield specular reflectivity curves with pronounced Kiessig fringes and well resolved Bragg bands in the off-specular regime due to the lateral periodicity. When applying a saturating magnetic field perpendicular to the stripes, a significant diffuse scattering can be detected close to the total reflection edge where it is enhanced by the Yoneda effect. This diffuse magnetic scattering can be attributed to inhomogeneities of the magnetic induction in the empty space between the stripes. In contrast, the sample with much less edge roughness does not exhibit off-specular diffuse scattering. Thus polarized neutron scattering from stripe patterns is a suitable tool for quantitative characterization of inhomogeneous magnetic flux distribution in the interspace between magnetic stripes invoked by their edge roughness.

We present a microscopic calculation of the phase diagram of the Ising superconductor ${\mathrm{NbSe}}_2$ in the presence of both in-plane magnetic field and Rashba spin-orbit coupling (SOC). Repulsive interactions lead to two distinct instabilities, in singlet and triplet interaction channels. While we recover the previously predicted nodal topological superconducting state in the absence of Rashba SOC at large magnetic field with six pairs of nodes along $\mathrm{\Gamma }\text{−}M$ lines, a finite Rashba SOC breaks the symmetry that protects these nodes and therefore generally lifts them, resulting in a topologically trivial phase. There is an exception when the field is applied along one of the three $\mathrm{\Gamma }\text{−}K$ lines, however. In that case, a single mirror symmetry remains that can protect two pairs of nodes out of the original six, resulting in a crystalline topological superconducting phase. Depending on the Cooper pairs' center-of-mass momentum, this superconducting state displays either Bogolyubov Fermi surfaces or point nodes. Moreover, a chiral topological superconducting phase with a Chern number of 6 is realized in the regime of large Rashba SOC and dominant triplet interactions, spontaneously breaking time-reversal symmetry.

Anisotropic multiferroic properties of $\mathrm{SrMnG}{\mathrm{e}}_2{\mathrm{O}}_6$ pyroxene single crystals were systematically investigated by means of magnetization, heat capacity, pyroelectric current measurement, and elastic and inelastic neutron-scattering experiments. Single-crystal neutron diffraction allows us to unambiguously reveal the presence of two incommensurate magnetic orderings: a nonpolar amplitude-modulated collinear sinusoidal magnetic structure emerges at $T_{\mathrm{N}1}=4.36\left(2\right)\mathrm{K}$ followed by a polar elliptical cycloidal spin structure below $T_{\mathrm{N}2}=4.05\left(2\right)\mathrm{K}$. Pyroelectric current measurements on single crystal confirm the appearance of a spontaneous polarization within the ($ac$) plane below $T_{\mathrm{N}2}$ associated with the latter magnetic symmetry through the extended Dzyaloshinskii-Moriya mechanism. The magnetic phase diagram was calculated considering the three isotropic exchange couplings relevant in this system. The magnetic excitations spectra of $\mathrm{SrMnG}{\mathrm{e}}_2{\mathrm{O}}_6$ measured by inelastic neutron scattering were successfully modeled using a set of exchange interactions consistent with this phase diagram.

Layered perovskite ruthenium oxides exhibit a striking series of metal-insulator and magnetic-nonmagnetic phase transitions easily tuned by temperature, pressure, epitaxy, and nonlinear drive. In this work, we combine results from two complementary state-of-the-art many-body methods, auxiliary field quantum Monte Carlo and dynamical mean field theory, to determine the low-temperature phase diagram of ${\mathrm{Ca}}_2{\mathrm{RuO}}_4$. Both methods predict a low-temperature, pressure-driven metal-insulator transition accompanied by a ferromagnetic-antiferromagnetic transition. The properties of the ferromagnetic state vary nonmonotonically with pressure and are dominated by the ruthenium $d_{xy}$ orbital, while the properties of the antiferromagnetic state are dominated by the $d_{xz}$ and $d_{yz}$ orbitals. Differences in the details of the predictions of the two methods are analyzed. This work is theoretically important as it presents the first application of the auxiliary field quantum Monte Carlo method to an orbitally degenerate system with both Mott and Hunds physics and provides an important comparison of the dynamical mean field and auxiliary field quantum Monte Carlo methods.

The electronic band topology of monolayer $\beta -\mathrm{Sb}$ (antimonene) is studied from the flat honeycomb to the equilibrium buckled structure using first-principles calculations and analyzed using a tight-binding model and low-energy Hamiltonians. In flat monolayer Sb, the Fermi level occurs near the intersection of two warped Dirac cones, one associated with the $p_z$ orbitals, and one with the $\{p_x,p_y\}$ orbitals. The differently oriented threefold warping of these two cones leads to an unusually shaped nodal line, which leads to anisotropic in-plane transport properties and goniopolarity. A slight buckling opens a gap along the nodal line except at six remaining Dirac points, protected by symmetry. Under increasing buckling, pairs of Dirac points of opposite winding number annihilate at a critical buckling angle. At a second critical angle, the remaining Dirac points disappear when the band structure opens a gap. Spin-orbit coupling and edge states are discussed.

We studied several aspects of the Mott metal-insulator transition in the disordered case. The model on which we based our analysis is the disordered Hubbard model, which is the simplest model capable of capturing the Mott metal-insulator transition. We investigated this model through statistical dynamical mean-field theory (statDMFT). This theory is a natural extension of dynamical mean-field theory (DMFT), which has been used with relative success in the past several years with the purpose of describing the Mott transition in the clean case. As is the case for the latter theory, statDMFT incorporates the electronic correlation effects only in their local manifestations. Disorder, on the other hand, is treated in such a way as to incorporate Anderson localization effects. With this technique, we analyzed the disordered two-dimensional Mott transition, using the quantum Monte Carlo algorithm to solve the associated single-impurity problems. We found spinodal lines at which the metal and insulator ceased to be metastable. We also studied spatial fluctuations of local quantities, such as self-energy and local Green's function, and showed the appearance of metallic regions within the insulator and vice versa. We carried out an analysis of finite-size effects and showed that, in agreement with the theorems of Imry and Ma [Y. Imry and S. K. Ma, Phys. Rev. Lett. 35, 1399 (1975).], the first-order transition is smeared in the thermodynamic limit. We analyzed transport properties by means of a mapping to a random classical resistor network and calculated both the average current and its distribution across the metal-insulator transition.

We propose a Haldane-like model of dice lattice analogous to graphene and explore its topological properties within the tight-binding formalism. The topological phase boundary of the system is identical to that of Haldane model of graphene but the phase diagram is richer than the latter due to existence of a distorted flat band. The system supports phases which have a “gapped-out” valence (conduction) band and an indirect overlap between the conduction (valence) band and the distorted flat band. The overlap of bands imparts metallic character to the system. These phases may be further divided into topologically trivial and nontrivial ones depending on the Chern number of the “gapped-out” band. The semimetallic phases exist as distinct points that are well separated from each other in the phase diagram and exhibit spin-1 Dirac-Weyl dispersion at low energies. The Chern numbers of the bands in the Chern-insulating phases are 0 and $\pm 2$. This qualifies the system to be candidate for quantum anomalous Hall effect with two chiral channels per edge. Counterpropagating edge states emanate from the flat band in certain topologically trivial phases. The system displays beating pattern in Shubnikov de Haas oscillations for unequal magnitude of mass terms in the two valleys. We show that the chemical potential and ratio of topological parameters of the system viz. Semenoff mass and next-neighbor hopping amplitude may be experimentally determined from the number of oscillations between the beating nodes and the beat frequency, respectively.

This study investigates the transport properties of a chiral elemental semiconductor tellurium (Te) under magnetic fields and pressure. Application of hydrostatic pressure reduces the resistivity of Te, while its temperature dependence remains semiconducting up to 4 GPa, contrary to recent theoretical and experimental studies. Application of higher pressure causes structural as well as semiconductor-metal transitions. The resulting metallic phase above 4 GPa exhibits superconductivity at 2 K along with a noticeable linear magnetoresistance effect. On the other hand, at ambient pressure, we identified metallic surface states on the as-cleaved ($10\overline{1}0$) surfaces of Te. The nature of these metallic surface states has been systematically studied by analyzing quantum oscillations observed in high magnetic fields. We clarify that a well-defined metallic surface state exists not only on chemically etched samples that were previously reported, but also on as-cleaved ones.

We investigate electronic properties of hole-doped cuprates ${\mathrm{Mg}}_{1-x}{\mathrm{Li}}_x{\mathrm{Cu}}_2{\mathrm{O}}_3$ with the quasi-one-dimensional two-leg-ladder structure. We succeeded in extending the solubility limit of Li in ${\mathrm{Mg}}_{1-x}{\mathrm{Li}}_x{\mathrm{Cu}}_2{\mathrm{O}}_3$ from $x=0.12$ to $x=0.60$ by using the high-pressure synthesis technique. The antiferromagnetic transition temperature rapidly decreases with increasing Li content from 94 K at $x=0$ to 7.5 K at $x=0.30$, and takes an almost constant value (3–6 K) at $x\ge 0.35$. The antiferromagnetic order still exists even at $x=0.60$, where the formal valence of Cu is as large as $+2.30$. The temperature dependence of the specific heat suggests the finite contribution of the electronic specific heat at $x=0.20–0.60$, which is consistent with high valence of Cu. Nevertheless, the temperature dependence of resistivity shows a variable range hopping behavior in the whole $x$ ranges, and the insulating behavior survives under the pressure up to 2.9 GPa. This peculiar behavior is owing to the disorder originating from the intersite atom exchanges due to the similar ionic radius of cations in ${\mathrm{Mg}}_{1-x}{\mathrm{Li}}_x{\mathrm{Cu}}_2{\mathrm{O}}_3$. Nonmagnetic ions of ${\mathrm{Mg}}^{2+}$ and ${\mathrm{Li}}^{+}$ are introduced into the ${\mathrm{Cu}}_2{\mathrm{O}}_3$ planes of ${\mathrm{Mg}}_{1-x}{\mathrm{Li}}_x{\mathrm{Cu}}_2{\mathrm{O}}_3$, resulting in the localization of doped hole carriers.

A study of the Fermi surface of the putative topological semimetal ${\mathrm{Pd}}_3\mathrm{Pb}$ has been carried out using Shubnikov–de Haas (SdH) oscillations measured in fields of up to 60 T. ${\mathrm{Pd}}_3\mathrm{Pb}$ has garnered attention in the community due to a peculiar Fermi surface that has been proposed theoretically by Ahn, Pickett, and Lee, Phys. Rev. B 98, 035130 (2018) to host a dispersionless band along $X-\mathrm{\Gamma }$ as well as multiple triply degenerate band crossings that, under the influence of spin-orbit coupling, lead to ten fourfold degenerate Dirac points. Analysis of the SdH oscillation data verifies the calculated multisheet Fermi surface, revealing a $\mathrm{\Gamma }$ centered spheroid that had not been resolved experimentally in prior studies. A comprehensive, angle-dependent analysis of the phase of the SdH oscillations convincingly demonstrates a nontrivial Berry phase for two bands along $\mathrm{\Gamma }-R$, supporting the theoretical predictions, while simultaneously evidencing interference between extremal orbits that mimics a trivial Berry phase at intermediate angles.

Resorting to ordinary GaInAs/AlInAs stepped quantum wells subjected to an external gate, which allows for adjusting the well symmetry and electron occupancy, we demonstrate that the Rashba spin-orbit (SO) strengths of the first (${\alpha }_1$) and second (${\alpha }_2$) subbands exhibit opposite gate dependence, triggered by the inner barrier, of which the structural potential energy for electrons is sandwiched between energy levels of two subbands. This opens a route towards selective and opposite SO control, greatly fascinating for spintronic applications. Moreover, we find that ${\alpha }_1$ and ${\alpha }_2$ may have opposite signs, in favor of hosting topological matter of persistent skymion lattice in conventional semiconductor heterostructures that we recently proposed [J. Y. Fu, P. H. Penteado, M. O. Hachicya, D. Loss, and J. C. Egues, Phys. Rev. Lett. 117, 226401 (2016)]. Finally, while the interband Rashba term ($\eta$) is found to be essentially gate independent, it may lead to the energy dispersion anticrossing or maintaining crossing, depending on intraband Rashba couplings.

Understanding of fundamental physics of plasmonic instabilities is the key issue for the design of a new generation of compact terahertz electronic sources required for numerous terahertz (THz) applications. Variable width plasmonic devices have emerged as potential candidates for such an application. The analysis of the variable width plasmonic devices presented in this paper shows that these structures enable both the Dyakonov-Shur instability (when the electron drift velocity everywhere in the device remains smaller than the plasma velocity) and the “plasmonic boom” instability that requires drift velocity exceeding the plasma velocity in some of the device sections. For symmetrical structures, the driving current could be provided by an rf signal leading to rf to THz and THz to RF frequency conversion using the source and drain antennas and reducing losses associated with ohmic contacts. We show that narrow regions protruding from the channel (“plasmonic stubs”) could control and optimize boundary conditions at the contacts and/or at the interfaces between different device sections. These sections could be combined into plasmonic crystals yielding enhanced power and a better impedance matching. The mathematics of the problems is treated using the transmission line analogy. We show that the combination of the stubs and the variable width channels is required for the instability rise in an optimized plasmonic crystal. Our estimates show that THz plasmonic crystal oscillators could operate at room temperature.

The random dipolar magnet ${\mathrm{LiHo}}_x{\mathrm{Y}}_{1-x}{\mathrm{F}}_4$ enters a strongly frustrated regime for small ${\mathrm{Ho}}^{3+}$ concentrations with $x<0.05$. In this regime, the magnetic moments of the ${\mathrm{Ho}}^{3+}$ ions experience small quantum corrections to the common Ising approximation of ${\mathrm{LiHo}}_x{\mathrm{Y}}_{1-x}{\mathrm{F}}_4$, which lead to a ${\mathbb{Z}}_2$-symmetry breaking and small, degeneracy breaking energy shifts between different eigenstates. Here we show that destructive interference between two almost degenerate excitation pathways burns spectral holes in the magnetic susceptibility of strongly driven magnetic moments in ${\mathrm{LiHo}}_x{\mathrm{Y}}_{1-x}{\mathrm{F}}_4$. Such spectral holes in the susceptibility, microscopically described in terms of Fano resonances, can already occur in setups of only two or three frustrated moments, for which the driven level scheme has the paradigmatic $\mathrm{\Lambda }$ shape. For larger clusters of magnetic moments, the corresponding level schemes separate into almost isolated many-body $\mathrm{\Lambda }$ schemes, in the sense that either the transition matrix elements between them are negligibly small or the energy difference of the transitions is strongly off-resonant to the drive. This enables the observation of Fano resonances, caused by many-body quantum corrections to the common Ising approximation also in the thermodynamic limit. We discuss its dependence on the driving strength and frequency as well as the crucial role that is played by lattice dissipation.

From an application perspective, one of the most important parameters of a ferroelectric is its switching time, and understanding its limiting factors is key to improve device performance. While there is a variety of competing models for switching kinetics in realistic (disordered) ferroelectrics, they are often merely descriptive and provide little insight into the underlying microscopic mechanisms. This holds in particular for the classical Merz law, which describes the commonly observed exponential field dependence of the switching time. Here, we investigate the switching kinetics in the archetypical molecular ferroelectric trialkylbenzene-1,3,5- tricarboxamide using an electrostatic kinetic Monte Carlo model. The simulated field dependence follows the Merz law, which shows that a simple system of interacting dipoles is sufficient to obtain this behavior, even without explicitly considering domain walls or defects that are commonly thought to be involved in the emergence of the Merz law. Through a detailed analysis of the nucleation process, we can relate the macroscopic switching time to the microscopic nucleation energy barrier, which in turn is related to a field-dependent nucleus size. Finally, we use the acquired insight into the nucleation process to derive the Merz law from the theory of thermally activated nucleation-limited switching. This analytical model provides a physically transparent description of the switching kinetics in both experiments and simulations.

We study the all-to-all connected $\mathit{XYZ}$ (anisotropic-Heisenberg) spin model with local and collective dissipations, comparing the results of mean-field (MF) theory with the solution of the Lindblad master equation. Exploiting the weak $\mathcal{PT}$ symmetry of the model (referred to as Liouvillian $\mathbb{PT}$ symmetry), we efficiently calculate the Liouvillian gap, introducing the idea of an antigap, and we demonstrate the presence of a paramagnetic-to-ferromagnetic phase transition. Leveraging the permutational symmetry of the model [N. Shammah et al., Phys Rev. A 98, 063815 (2018)], we characterize criticality, finding exactly (up to numerical precision) the steady state for $N$ up to $N=95$ spins. We demonstrate that the MF theory correctly predicts the results in the thermodynamic limit in all regimes of parameters, and quantitatively describes the finite-size behavior in the small anisotropy regime. However, for an intermediate number of spins and for large anisotropy, we find a significant discrepancy between the results of the MF theory and those of the full quantum simulation. We also study other more experimentally accessible witnesses of the transition, which can be used for finite-size studies, namely, the bimodality coefficient and the angular-averaged susceptibility. In contrast to the bimodality coefficient, the angular-averaged susceptibility fails to capture the onset of the transition, in striking difference with respect to lower-dimensional studies. We also analyze the competition between local dissipative processes (which disentangle the spin system) and collective dissipative ones (generating entanglement). The nature of the phase transition is almost unaffected by the presence of these terms. Our results mark a stark difference with the common intuition that an all-to-all connected system should fall onto the mean-field solution also for intermediate number of spins.

Mineral Herbertsmithite, ${\mathrm{ZnCu}}_3{\left(\mathrm{OH}\right)}_6{\mathrm{Cl}}_2$, is an excellent candidate for S = 1/2 Heisenberg kagome antiferromagnet supporting quantum spin liquid (QSL) ground state at low temperature and ambient pressure. The pressure-induced structural evolution of the kagome lattice in Herbertsmithite has been investigated up to 16 GPa using x-ray diffraction and Raman scattering measurements. The system develops a distorted kagome lattice structure (clinoatacamite-like) beyond 8 GPa. This is accompanied by gradual suppression of the quasi-elastic Raman scattering intensity. Our high pressure magnetic susceptibility measurements indicate the emergence of a weak magnetic ordering in the distorted kagome lattice. Pressure-induced enhancement of the magnetic ordering temperature supports a gapped topological QSL rather than gapless ground state close to a quantum critical point. High-pressure optical absorption measurements support the structural evolution.