Tailoring spin-orbit interactions and Coulomb repulsion are the key features to observe exotic physical phenomena such as magnetic anisotropy and topological spin texture at oxide interfaces. Our study proposes a platform for engineering magnetism and spin-orbit coupling at the ${\mathrm{LaMnO}}_3/{\mathrm{SrIrO}}_3$ $\left(3d\text{−}5d\right)$ oxide interface by tuning the ${\mathrm{LaMnO}}_3$ growth conditions, which controls the lattice displacement and spin-correlated interfacial coupling through charge transfer. We report a tunable and enhanced interface-induced Rashba spin-orbit coupling where the spin relaxation mechanism varies with magnetic behavior of the underlying ${\mathrm{LaMnO}}_3$ layer. The x-ray spectroscopy measurements reveal the quantitative valence states of Mn and their impact on charge transfer. Our angle-dependent magnetoresistance measurements also reflects the signature of magnetic proximity effect in ${\mathrm{SrIrO}}_3$ and can be tuned with the magnetic nature of ${\mathrm{LaMnO}}_3$ in a ${\mathrm{LaMnO}}_3/{\mathrm{SrIrO}}_3$ bilayer. Our work demonstrates a route to engineer the interface-induced Rashba spin-orbit coupling and magnetic proximity effect at the $3d\text{−}5d$ oxide interface for spintronics applications.

The correlated electron material ${\mathrm{CePd}}_2{\mathrm{P}}_2$ crystallizes in the ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$ structure and orders ferromagnetically at 29 K. Prior work by Lai et al. [Phys. Rev. B 97, 224406 (2018)] found evidence for a ferromagnetic quantum critical point induced by chemical compression via substitution of Ni for Pd. However, disorder effects due to the chemical substitution interfere with a simple analysis of the possible critical behavior. In the present paper, we examine the temperature—pressure—magnetic-field phase diagram of single crystalline ${\mathrm{CePd}}_2{\mathrm{P}}_2$ to 25 GPa using a combination of resistivity, magnetic susceptibility, and x-ray diffraction measurements. We find that the ferromagnetism appears to be destroyed near 12 GPa, without any change in the crystal structure.

We derive a closed equation of motion for the one particle density matrix of a quantum system coupled to multiple baths using the Redfield master equation combined with a mean-field approximation. The steady-state solution may be found analytically with perturbation theory. Application of the method to a one-dimensional noninteracting quantum wire yields an expression for the current that reproduces the celebrated Landauer's formula. Nonlinear rectification is found for the case of a mesoscopic three-dimensional semiconductor $p-n$ junction. The results are in good agreement with numerical simulations obtained using nonequilibrium Green's functions, supporting the validity of the Redfield equations for the description of transport.

Unlike conventional Weyl nodes, unconventional ones carry a quantized monopole charge $\mathcal{C}>1$, and their existence needs the protection of crystalline symmetries in addition to translation symmetry. There have been many studies on unconventional Weyl nodes, yet we have so far missed one, which is the twofold Weyl node with $\mathcal{C}=4$. In this paper, we study the relationship between the winding number and pseudospin texture in all twofold Weyl nodes, and offer an intuitive way to understand the complex pseudospin texture of the twofold quadruple Weyl node. We not only list all the possible space groups and corresponding momenta, where the twofold quadruple Weyl node can be stabilized, but also propose a series of LaIrSi-type materials that have the Weyl node with $\mathcal{C}=4$ in both the electronic band structure and the phonon spectra. In the electronic band structure, the twofold quadruple Weyl node will evolve into a fourfold quadruple Weyl node and change both the chirality and the monopole charge after considering spin-orbit coupling, which is uncommon in the known Weyl semimetals. In the phonon spectra, we propose a platform having a Weyl node with $\mathcal{C}=4$.

Magnetic impurities with sufficient anisotropy could account for the observed strong deviation of the edge conductance of 2D topological insulators from the anticipated quantized value. In this work we consider such a helical edge coupled to dilute impurities with an arbitrary spin $S$ and a general form of the exchange matrix. We calculate the backscattering current noise at finite frequencies as a function of the temperature and applied voltage bias. We find that, in addition to the Lorentzian resonance at zero frequency, the backscattering current noise features Fano-type resonances at nonzero frequencies. The widths of the resonances are controlled by the spectrum of corresponding Korringa rates. At a fixed frequency the backscattering current noise has nonmonotonic behavior as a function of the bias voltage.

A first-principles density functional method along with the direct solution of linearized Boltzmann transport equations are employed to systematically analyze the low-temperature thermal transport in crystalline GeTe. The extensive thermal transport simulations, ranging from room temperature to cryogenic temperatures, reveal the emergence of a phonon hydrodynamic regime in GeTe at low temperature. The reduction of grain boundary scattering is found to play a crucial role along with the divergent trend of umklapp and normal scattering at low temperatures in accommodating the hydrodynamic regime. Average scattering rates for normal, umklapp, and other resistive processes are distinguished for a wide range (4–300 K) of temperatures and used for identifying various phonon transport regimes. Therefore, the variations of lattice thermal conductivity, phonon propagation length, and thermal diffusivity with temperature, related to these transport regimes (ballistic, hydrodynamic, and kinetic), have been thoroughly investigated. The modewise decomposition of lattice thermal conductivity and the distinction of thermal diffusivity according to different scattering processes reveal rich information on the dominant phonon modes and phonon scattering processes in GeTe at low temperature. Further, the kinetic-collective model is used to elucidate the hydrodynamic behavior of phonon scattering through the relative study of collective and kinetic contributions to the thermal transport properties. In this context, the Knudsen number is estimated through the characteristic nonlocal length and the grain size, which further quantifies the consistent hydrodynamic behavior of phonon thermal transport for GeTe. Finally, phonon-vacancy scattering for GeTe is realized, and vacancies are found strongly to influence the hydrodynamic window while incorporating the other resistive scattering mechanisms.

The lacunar spinel compound ${\mathrm{GaV}}_4{\mathrm{S}}_8$ exhibits a Néel-type skyrmion, which holds great promise for future spintronics and ultrahigh-density magnetic memory devices. To gain more insight into the magnetic interactions, the critical behavior of ${\mathrm{GaV}}_4{\mathrm{S}}_8$ is studied by dc magnetization measurement around the Curie temperature $\left(T_{\mathrm{C}}\right)$. A set of reliable critical exponents ($\beta =0.220\pm 0.024$, $\gamma =0.909\pm 0.005$, and $\delta =5.161\pm 0.003$) is obtained by the modified Arrott plot technique, the Kouvel-Fisher method, and critical isothermal analysis. The generated critical exponents fulfill the universality class of tricritical mean-field theory, which suggests a field-induced tricritical phenomenon. Based on the scaling equations, boundaries between the skyrmion and ferromagnetic phases can be distinguished. A tricritical point is revealed at the temperature of $T_{\mathrm{Tr}}=12\mathrm{K}$ and field of $H_{\mathrm{Tr}}=60\mathrm{mT}$, which is located at the intersection point among the skyrmion, ferromagnetic, and paramagnetic phases. It is suggested that the origin of the tricritical behavior in ${\mathrm{GaV}}_4{\mathrm{S}}_8$ is related to the skyrmion state near the magnetic transition temperature $T_{\mathrm{C}}$.

In recent experiments, high Curie temperatures $T_c$ above room temperature were reported in ferromagnetic semiconductors Fe-doped GaSb and InSb, while low $T_c$ between 20 K to 90 K were observed in some other semiconductors with the same crystal structure, including Fe-doped InAs and Mn-doped GaSb, InSb, and InAs. Here we study systematically the origin of high temperature ferromagnetism in Fe, Mn, Cr-doped GaSb, InSb, and InAs magnetic semiconductors by combining the methods of density functional theory and quantum Monte Carlo. In the diluted impurity limit, the calculations show that the impurities Fe, Mn, and Cr have similar magnetic correlations in the same semiconductors. Our results suggest that high (low) $T_c$ obtained in these experiments mainly comes from high (low) impurity concentrations. In addition, our calculations predict the ferromagnetic semiconductors of Cr-doped InSb, InAs, and GaSb that may have possibly high $T_c$. Our results show that the origin of high $T_c$ in (Ga,Fe)Sb and (In,Fe)Sb is not due to the carrier induced mechanism because ${\mathrm{Fe}}^{3+}$ does not introduce carriers.

Topologically protected gapless edge/surface states are phases of quantum matter which behave as massless Dirac fermions and are immune to disorders and continuous perturbations. Recently, a new class of topological insulators (TIs) with gapped edge states and in-gap corner states has been theoretically predicted in electronic systems and experimentally realized in two-dimensional (2D) mechanical and electromagnetic systems, electrical circuits, optical and sonic crystals, and elastic phononic plates. Here we elaborately design a three-dimensional topological acoustic system by arranging acoustic meta-atoms in a simple cubic lattice. Under the direct field measurements, besides the 2D surface propagations on all of the six surfaces, the one-dimensional hinge propagations behaving as acoustic fibers along the 12 hinges, and the zero-dimensional corner modes working as localized resonances at the eight corners are experimentally confirmed. As these multidimensional topological states are activated in different frequencies and independent spaces, our works may provide a new pathway for designing high-performance integrated acoustic devices that can manipulate the propagation of sound waves in multiple dimensions.

Controlling interfaces is highly relevant from a technological point of view. However, their rich and complex behavior makes them very difficult to describe theoretically, and hence to predict. In this work, we establish a procedure to connect two levels of descriptions of interfaces: for a bulk description, we consider a two-dimensional Ginzburg-Landau model evolving with a Langevin equation, and boundary conditions imposing the formation of a rectilinear domain wall. At this level of description no assumptions need to be done over the interface, but analytical calculations are very difficult to handle, especially for disordered systems. On a different level of description, we consider a one-dimensional elastic line model evolving according to the Edwards-Wilkinson equation, which only allows one to study continuous and univalued interfaces, but which was up to now one of the most successful tools to treat interfaces analytically. To establish the connection between the bulk description and the interface description, we propose a simple method which has the advantage to be readily applicable to disordered systems. We probe the connection by numerical simulations at both levels for clean and disordered systems, and our simulations, in addition to making contact with experiments, allow us to test and provide insight to develop new analytical approaches to treat interfaces.

Close to the quantum critical point of the transverse-field Ising spin-chain model, an exotic dynamic spectrum was predicted to emerge upon a perturbative longitudinal field. The dynamic spectrum consists of eight particles and is governed by the symmetry of the $E_8$ Lie algebra. Here we report on high-resolution terahertz spectroscopy of quantum spin dynamics in the ferromagnetic Ising-chain material ${\mathrm{CoNb}}_2{\mathrm{O}}_6$. At 0.25 K in the magnetically ordered phase we identify characteristics of the first six $E_8$ particles, ${\mathrm{m}}_1$ to ${\mathrm{m}}_6$, and the two-particle $({\mathrm{m}}_1+{\mathrm{m}}_2)$ continuum in an applied transverse magnetic field of $B_c^{\text{1D}}=4.75 \mathrm{T}$, before the three-dimensional magnetic order is suppressed above $B_c^{\text{3D}}\approx 5.3 \mathrm{T}$. The observation of the higher-energy particles $({\mathrm{m}}_3 \mathrm{to} {\mathrm{m}}_6)$ above the low-energy two-particle continua features quantum many-body effects in the exotic dynamic spectrum.

The Hubbard model and its strong-coupling version, the Heisenberg one, have been widely studied on the triangular lattice to capture the essential low-temperature properties of different materials. One example is given by transition metal dichalcogenides, as $1\mathrm{T}-{\mathrm{TaS}}_2$, where a large unit cell with 13 Ta atoms forms weakly coupled layers with an isotropic triangular lattice. By using accurate variational Monte Carlo calculations, we report the phase diagram of the $t-t^{\prime }$ Hubbard model on the triangular lattice, highlighting the differences between positive and negative values of $t^{\prime }/t$; this result can be captured only by including the charge fluctuations that are always present for a finite electron-electron repulsion. Two spin-liquid regions are detected: one for $t^{\prime }/t<0$, which persists down to intermediate values of the electron-electron repulsion, and a narrower one for $t^{\prime }/t>0$. The spin-liquid phase appears to be gapless, though the variational wave function has a nematic character, in contrast to the Heisenberg limit. We do not find any evidence for nonmagnetic Mott phases in the proximity of the metal-insulator transition, at variance with the predictions (mainly based upon strong-coupling expansions in $t/U$) that suggest the existence of a weak-Mott phase that intrudes between the metal and the magnetically ordered insulator.

Efficient generation of magnons is highly desirable for magnonics. Here we theoretically investigate the charge-magnon conversion at the interface of topological insulator/antiferromagnetic insulator (AFMI), where the Dirac electrons and the antiferromagnetic magnons are coupled by the fluctuation of s-d exchange field. Our model reveals that the charge-magnon conversion efficiency for uncompensated interface is 2–3 orders higher than that for compensated interface. The conversion is more efficient with smaller magnon gap and larger s-d exchange coupling. We find a significant efficiency enhancement when the thickness of the AFMI is in the two-dimensional regime, where the magnons experience a quantum confinement effect. $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_3/\alpha -\mathrm{MnTe}$ bilayers are then proposed to be a promising system to realize strong charge-magnon conversion. Our work provides the principles of manipulating charge-magnon conversion and designing efficient charge-magnon conversion structure, which would help to improve the performance of antiferromagnetic magnonics, such as magnon transistor and magnon torque memories.

The electronic band structure of the phosphorus-doped high-quality high-pressure and high-temperature–grown single crystal diamond was studied by infrared absorption, magneto- and electron paramagnetic resonance spectroscopy, and first-principles calculations. The complete picture of the $1s\to n{p}_{\pm }$ and $1s\to n{p}_0$ ($n=2$, 3, 4) donor transitions with new $1s\to 3p{}_0,4p{}_0$ and $1s\to 4p{}_{\pm }$ transitions allowed us to refine the energy levels of ground and exited states with those obtained from effective mass approximation calculation. For the first time, as far as we know, we have observed the fine doublet structures of the $1s$(${\mathrm{B}}_2,\mathrm{E})\to 2p_{\pm }, 1s$(${\mathrm{B}}_2,\mathrm{E})\to 4p{}_0, 1s$(${\mathrm{B}}_2,\mathrm{E})\to 3p{}_{\pm }$, and $1s$(${\mathrm{B}}_2,\mathrm{E})\to 4p{}_{\pm }$ donor transitions with the splitting value of 1.05 meV. These doublet structures arise from the dynamic Jahn-Teller (JT) distortion which splits the energy level of the $1s$(${\mathrm{T}}_2$) state in the ${\mathrm{T}}_d$ configuration into those of the $1s$(${\mathrm{B}}_2$) ground state and the $1s$(E) state in the ${\mathrm{D}}_{2d}$ configuration. The dynamic JT distortion of the tetrahedral donor ground state has been proved by following facts: the observation of vibronic energy levels and temperature behavior of doublet bands in the IR spectrum, the absence of P-donor-related electron paramagnetic resonance signals, and first-principles calculations. We believe that the dramatic broadening of the $2p{}_0$ band attributed to the $1s$(${\mathrm{B}}_2,\mathrm{E})\to 2p_0$ donor transition at 524 meV is caused by the resonant interaction of this 524 meV energy level with that of ∼517 meV formed due to the dynamic JT coupling of the $1s$(E) energy level equal to 387 meV with the longitudinal acoustic phonon of $\sim 130$ meV.

The Levin-Wen model of string-net condensation explains how topological phases emerge from the microscopic degrees of freedom of a physical system. However, the original construction is not applicable to all unitary fusion categories since some additional symmetries for the $F$-symbols are imposed. In particular, the so-called tetrahedral symmetry is not fulfilled by many interesting unitary fusion categories. In this paper, we present a generalized construction of the Levin-Wen model for arbitrary multiplicity-free unitary fusion categories that works without requiring these additional symmetries. We explicitly calculate the matrix elements of the Hamiltonian and, furthermore, show that it has the same properties as the original one.

We use the Wick-rotated time-dependent supersymmetry to construct models of two-dimensional Dirac fermions in the presence of an electrostatic grating. We show that there appears omnidirectional perfect transmission through the grating at specific energy. Additionally to being transparent for incoming fermions, the grating hosts strongly localized states.

We present an experimental study on microwave illuminated high mobility MgZnO/ZnO based two-dimensional electron systems with different electron densities and, hence, varying Coulomb interaction strength. The photoresponse of the low-temperature dc resistance in perpendicular magnetic field is examined in low and high density samples over a broad range of illumination frequencies. In low density samples a response due to cyclotron resonance (CR) absorption dominates, while high-density samples exhibit pronounced microwave-induced resistance oscillations (MIRO). Microwave transmission experiments serve as a complementary means of detecting the CR over the entire range of electron densities and as a reference for the band mass unrenormalized by interactions. Both CR and MIRO-associated features in the resistance permit extraction of the effective mass of electrons but yield two distinct values. The conventional cyclotron mass representing center-of-mass dynamics exhibits no change with density and coincides with the band electron mass of bulk ZnO, while MIRO mass reveals a systematic increase with lowering electron density consistent with renormalization expected in interacting Fermi liquids.

In a joint experimental and theoretical study on metallic $\mathrm{Tb}{\mathrm{Si}}_2$ nanowires, we observe a continuous crossover from a two-dimensional (2D) to a quasi-one-dimensional (1D) electronic structure by reduction of the nanowire width. The nanowires were grown by self-organization on vicinal Si(111) substrates denoted by the Miller indices $\left(hhk\right)$. Their electronic structure was analyzed by angle-resolved photoemission spectroscopy (ARPES) and calculated using density functional theory (DFT). In ARPES, the $\mathrm{Tb}{\mathrm{Si}}_2$ nanowires show basically the 2D electronic structure of the $\mathrm{Tb}{\mathrm{Si}}_2$ film on planar Si(111) with an increasing momentum broadening for decreasing nanowire widths, consistent with Heisenberg's uncertainty principle. In contrast, DFT calculations predict a purely 1D electronic structure for $\mathrm{Tb}{\mathrm{Si}}_2$ nanowires. Unfolding this 1D electronic structure onto the Brillouin zone of the $\mathrm{Tb}{\mathrm{Si}}_2$ film leads to a Fermi surface appearing similar to the one of the 2D $\mathrm{Tb}{\mathrm{Si}}_2$ film, but with an additional 1D contribution from nanowire edges. Such an additional 1D signature is also observed in ARPES for narrow nanowires. These results indicate a continuous transition to a 1D electronic structure for decreasing nanowire widths.