Nonlocal compensation of magnetic damping by spin injection has been theoretically shown to establish dynamic, noncollinear magnetization states that carry spin currents over micrometer distances. Such states can be generically referred to as dissipative exchange flows (DEFs) because spatially diffusing spin currents are established by the mutual exchange torque exerted by neighboring spins. Analytical studies to date have been limited to the weak spin injection assumption whereby the equation of motion for the magnetization is mapped to hydrodynamic equations describing spin flow and then linearized. Here, we analytically and numerically study easy-plane ferromagnetic channels subject to spin injection of arbitrary strength at one extremum under a unified hydrodynamic framework. We find that DEFs generally exhibit a nonlinear profile along the channel accompanied by a nonlinear frequency tunability. At large injection strengths, we fully characterize a magnetization state we call a contact-soliton DEF (CS-DEF) composed of a stationary soliton at the injection site, which smoothly transitions into a DEF and exhibits a negative frequency tunability. The transition between a DEF and a CS-DEF occurs at the maximum precessional frequency and coincides with the Landau criterion: a subsonic to supersonic flow transition. Leveraging the hydraulic-electrical analogy, the current-voltage characteristics of a nonlinear DEF circuit are presented. Micromagnetic simulations of nanowires that include magnetocrystalline anisotropy and nonlocal dipole fields are in qualitative agreement with the analytical results. The magnetization states found here along with their characteristic profile and spectral features provide quantitative guidelines to pursue an experimental demonstration of DEFs in ferromagnetic materials and establish a unified description for long-distance spin transport.

We present a general graph-based projected entangled-pair state (gPEPS) algorithm to approximate ground states of nearest-neighbor local Hamiltonians on any lattice or graph of infinite size. By introducing the structural matrix, which codifies the details of tensor networks on any graphs in any dimension $d$, we are able to produce a code that can be essentially launched to simulate any lattice. We further introduce an optimized algorithm to compute simple tensor updates as well as expectation values and correlators with a mean-field-like effective environments. Though not being variational, this strategy allows to cope with PEPS of very large bond dimension (e.g., $D=100$) and produces remarkably accurate results in the thermodynamic limit in many situations, and specially when the correlation length is small and the connectivity of the lattice is large. We prove the validity of our approach by benchmarking the algorithm against known results for several models, i.e., the antiferromagnetic Heisenberg model on a chain, star and cubic lattices, the hardcore Bose-Hubbard model on square lattice, the ferromagnetic Heisenberg model in a field on the pyrochlore lattice, as well as the three-state quantum Potts model in field on the kagome lattice and the spin-1 bilinear-biquadratic Heisenberg model on the triangular lattice. We further demonstrate the performance of gPEPS by studying the quantum phase transition of the $2d$ quantum Ising model in transverse magnetic field on the square lattice, and the phase diagram of the Kitaev-Heisenberg model on the hyperhoneycomb lattice. Our results are in excellent agreement with previous studies.

Using high-resolution angle-resolved photoemission spectroscopy and ab initio calculation, we have studied the bulk and surface electronic structure of metallic rutile $5d$ transition metal oxide ${\mathrm{IrO}}_2$ that harbors both edge and corner sharing Ir-O octahedrons. We observe strong modulation of the band structure by spin-orbit coupling (SOC). The measured band structure is well reproduced by our ab initio calculation without band renormalization, suggesting the absence of the SOC-enhanced correlation effect in ${\mathrm{IrO}}_2$. In accordance with the calculation, we visualize two types of Dirac nodal lines (DNLs) protected by mirror symmetry and nonsymmorphic crystal symmetry, respectively. SOC gaps the first type of DNLs, which may contribute largely to the strong spin Hall effect. The second type of DNLs at the edges of Brillouin zone, however, remain intact against SOC. Our results not only provide important insights into the exotic transport properties of ${\mathrm{IrO}}_2$, but also shed light on the understanding of the role of SOC in the iridate family.

We report investigations of gold single crystals carried out with the help of an original apparatus combining ultrahigh vacuum scanning tunneling microscopy and a compression device for in situ observations. It is demonstrated that the herringbone reconstruction on Au(111) is highly influenced by the appearance of slip traces that result from the emergence at the free surface of moving dislocations in the bulk. A reorganization of the herringbones in a $\mathsf{U}$-shaped pattern is directly observed but only on the lower terrace associated with the slip trace. In addition, kinks have been experimentally evidenced along the slip traces at the atomic scale. Molecular dynamics simulations using a modified embedded atom method potential have demonstrated that the kinks are related to the evolution of the Au(111) reconstruction. In particular, a linear relation between the size of the kinks and the period of the $\mathsf{U}$-shaped pattern is determined.

We investigate the electronic structure of realistic partial dislocation networks in bilayer graphene that feature annihilating, wandering, and intersecting partial lines. We find charge accumulation states at partials that are sensitive to Fermi energy and partial Burgers vector but not to the screw versus edge character of the partial. These states are shown to be current carrying, with the current density executing a spiral motion along the dislocation line with a strong interlayer component to the current. Close to the Dirac point, localization on partials switches to localization on intersections of partials, with a corresponding complex current flow around the nodes.

A simple and reliable finite-difference approach is presented for solution of the Dirac equation eigenproblem for states confined in rotationally symmetric systems. The method sets the boundary condition for the spinor wave function components at the external edge of the system and then sweeps the radial mesh in search for the energies for which the boundary conditions are met inside the flake. The sweep that is performed from the edge of the system towards the origin allows for application of a two-point finite-difference quotient of the first derivative, which prevents the fermion doubling problem appearing with spurious solutions and rapidly oscillating wave functions.

We present magnetotransport measurements of a strongly hybridized inverted InAs/GaSb double quantum well. We find that the spin-orbit interaction leads to an appreciable spin-splitting of hole-like states, which form distinct Landau levels in a perpendicular magnetic field. The resulting quantum Hall state is governed by a periodic even and odd total filling arising due to the simultaneous occupation of electron-like and hole-like Landau levels of differing degeneracy. Furthermore, oscillatory charge transfer between all involved subbands leads to discrete phase slips in the usual sequential filling of Landau levels, and coincidentally the phase slips are close to $\pi$. These results shed light on the Landau level structure in composite systems and have consequences for interpreting intercepts obtained from index plots, which are routinely employed to investigate the presence of Berry's phase.

It was well known that pressure can have profound effects on the structural, magnetic, and electronic properties of transition metal oxides. However, it is a challenge both experimentally and theoretically to determine the exact structural and magnetic order of a complicated oxide system under pressure. To this end, we develop a global optimization approach based on the genetic algorithm by taking into account explicitly both structural and magnetic degrees of freedom. With this approach, we investigate the effect of pressure on the structure, magnetism, and charge ordering of the recently synthesized perovskite oxide $\mathrm{PbCo}{\mathrm{O}}_3$, which is an interesting system since both Pb and Co sites can change the valence states. At low pressure, we predict that $\mathrm{PbCo}{\mathrm{O}}_3$ can order in two multiferroic phases (i.e., $R3c$ and $Pna{2}_1$). Both phases are ferroelectric with a large electric polarization due to unusual coupling between the ferroelectric mode and other antipolar modes. Both phases display weak ferromagnetism. The ferroelectric polarization and weak ferromagnetism in these two phases are coupled to each other, suggesting that they may be used to realize the electric field control of magnetism. At higher pressure, the valence transition takes place from $\mathrm{P}{\mathrm{b}}^{4+}\mathrm{C}{\mathrm{o}}^{2+}{\mathrm{O}}_3$ to the $A$-site and $B$-site charge-ordering state $\mathrm{P}{\mathrm{b}}^{2+}{\mathrm{Pb}}_3^{4+}{\mathrm{Co}}_2^{2+}{\mathrm{Co}}_2^{3+}{\mathrm{O}}_{12}$ accompanied with an unusual enhancement of the band gap. In this work, we not only provide a general powerful method to determine the spin-orbital-charge ordering of intriguing correlated systems, but also predict that $\mathrm{PbCo}{\mathrm{O}}_3$ may be a multiferroic material under low pressure.

Orbital degrees of freedom play a fundamental role in condensed matter physics and can be studied controllably in artificial lattices. Recently, a new kind of artificial electron lattice was realized in experiments by confining the metal surface electrons with an adsorbed molecular lattice. This enables the study of novel two-dimensional lattice structures. The Lieb lattice is one example which is of special interest due to its flat-band physics [M. R. Slot et al., Nat. Phys. 13, 672 (2017)]. Here, by first-principles simulation, muffin-tin potential, and tight-binding calculations, we demonstrate that the high-energy states observed in the experiment actually correspond to the artificial $p$ orbitals of the electron lattice. Our numerical results, together with the experimental observation, show that the long-pursued artificial $p$-orbital fermionic lattice has already been realized in a solid-state system. This opens a new avenue to investigate the orbital degrees of freedom in a controllable way.

The chirality of magnetostatic Damon-Eshbach (DE) magnons affects the transport of energy and angular momentum at the surface of magnetic films and spheres. We calculate the surface-disorder-limited dephasing and transport lifetimes of surface modes of sufficiently thick high-quality ferromagnetic films such as yttrium iron garnet. Surface magnons are not protected by chirality, but interact strongly with smooth surface roughness. Nevertheless, for long-range disorder, the transport is much less affected by the suppressed backscattering (vertex correction). Moreover, in the presence of roughness, ferromagnetic resonance under a uniform microwave field can generate a considerable number of surface magnons.

We study a robust topological transport carried by vortices in a thin film of an easy-plane magnetic insulator between two metal contacts. A vortex, which is a nonlocal topological spin texture in two-dimensional magnets, exhibits some beneficial features as compared to skyrmions, which are local topological defects. In particular, the total topological charge carried by vorticity is robust against local fluctuations of the spin order-parameter magnitude. We show that an electric current in one of the magnetized metal contacts can pump vortices into the insulating bulk. Diffusion and two-dimensional nonlocal Coulomb-like interaction between these vortices will establish a steady-state vortex flow. Vortices leaving the bulk produce an electromotive force at another contact, which is related to the current-induced vorticity pumping by the Onsager reciprocity. The voltage signal decays algebraically with the separation between two contacts, similarly to a superfluid spin transport. Finally, the vorticity and closely related skyrmion-type topological hydrodynamics are generalized to arbitrary dimensions, in terms of nonsingular order-parameter vector fields.

The ultrafast deterministic thermally induced magnetization switching (TIMS) under the excitation by a one-shot femtosecond laser pulse has been widely achieved in disordered ferrimagnetic alloys such as GdFeCo. Among multiple factors influencing the occurrence of this phenomenon, the role of the exchange parameters is poorly understood. Here, using atomistic spin simulations based on the spin Hamiltonian parameterized through ab initio calculations for ordered stoichiometric ${\text{GdFe}}_2$ and ${\text{TbFe}}_2$ Laves phases $C15$, we investigate the conditions for the occurrence of deterministic TIMS. Our simulations show that both inter- and intrasublattice exchange interactions are too strong in ordered alloys and the switching is not produced for any excitation. By varying the exchange parameters, we find their regions for which the deterministic TIMS takes place in some interval of laser fluence. Consequently, neither weakly nor strongly antiferromagnetically coupled materials would switch. This explains the success of disordered alloys to produce this phenomenon since the average strength of the exchange interactions is mediated by the rare-earth-metal concentration in this case. Our simulations also show that in the ordered lattice case only materials possessing the magnetization compensation point are switched by this mechanism.

Harmonic measurements of the longitudinal and transverse voltages in Bi-Sb/Co bilayers are presented. A large second harmonic voltage signal due to the ordinary Nernst effect is observed. In experiments where a magnetic field is rotated in the film plane, the ordinary Nernst effect shows the same angular dependence in the transverse voltage as the dampinglike spin-orbit torque and in the longitudinal voltage as the unidirectional spin-Hall magnetoresistance, respectively. Therefore, the ordinary Nernst effect can be a spurious signal in spin-orbit torque measurements, leading to an overestimation of the spin-Hall angle and spin-Hall conductivity in topological insulators or semimetals.

In the framework of real-time time-dependent density functional theory we unravel the layer-resolved dynamics of excited carriers in a ${\left(\mathrm{Fe}\right)}_1/{\left(\mathrm{MgO}\right)}_3$(001) multilayer after an optical excitation with a frequency below the band gap of bulk MgO. Substantial transient changes to the electronic structure, which persist after the duration of the pulse, are mainly observed for in-plane polarized electric fields, corresponding to a laser pulse arriving perpendicular to the interface. While the strongest charge redistribution takes place in the Fe layer, a time-dependent change in the occupation numbers is visible in all layers, mediated by the presence of interface states. The time evolution of the layer-resolved time-dependent occupation numbers indicates a strong orbital dependence with the depletion from in-plane orbitals (e.g., $d_{x^2-y^2}$ of Fe) and accumulation in out-of-plane orbitals ($d_{3z^2-r^2}$ of Fe and $p_z$ of apical oxygen). We also observe a small net charge transfer of less than one percent of an electron away from oxygen towards the Mg sites, even for MgO layers which are not directly in contact with the metallic Fe.

We present low-temperature transport measurements of a gate-tunable thin-film topological insulator system that features high mobility and low carrier density. Upon gate tuning to a regime around the charge neutrality point, we infer an absence of strong localization even at conductivities well below $e^2/h$, where two-dimensional electron systems should conventionally scale to an insulating state. Oddly, in this regime the localization coherence peak lacks conventional temperature broadening, though its tails do change dramatically with temperature. Using a model with electron-impurity scattering, we extract values for the disorder potential and the hybridization of the top and bottom surface states.

Many unconventional superconductors, such as cuprates and iron-based materials, display spin-glass states in the underdoped regime, which usually coexist and/or compete with unconventional superconductivity. Here, we performed zero-field (ZF) and longitudinal-field (LF) muon spin-rotation experiments ($\mu \mathrm{SR}$) on quasi-one-dimensional ${\mathrm{KCr}}_3{\mathrm{As}}_3$. Our ZF $\mu \mathrm{SR}$ measurements reveal a large decrease (about 1/3) in the initial asymmetry below 10 K, indicating the presence of a magnetic phase transition. The analysis of the LF $\mu \mathrm{SR}$ results illustrates this transition at the same temperature, and points it to a spin-glassy state. These results would, potentially, confirm unconventional superconductivity in K-Cr-As and related compounds.

Polycrystalline samples of ${\mathrm{NaYbO}}_2$ are investigated by bulk magnetization and specific-heat measurements, as well as by nuclear magnetic resonance (NMR) and electron spin resonance (ESR) as local probes. No signatures of long-range magnetic order are found down to 0.3 K, evidencing a highly frustrated spin-liquid-like ground state in zero field. Above 2 T, signatures of magnetic order are observed in thermodynamic measurements, suggesting the possibility of a field-induced quantum phase transition. The ${}^{23}\mathrm{Na}$ NMR relaxation rates reveal the absence of magnetic order and persistent fluctuations down to 0.3 K at very low fields and confirm the bulk magnetic order above 2 T. The $H-T$ phase diagram is obtained and discussed along with the existing theoretical concepts for layered spin-$\frac{1}{2}$ triangular-lattice antiferromagnets.

At a superconductor interface with a ferromagnetic insulator (FI), the FI acts to induce a local exchange field within the S layer, which in the presence of spin-orbit interaction promotes a phase- modulated superconducting state. Here we demonstrate that within a thin superconducting loop that is partially proximitized by a FI, spontaneous currents form with a magnetization-orientation-dependent chirality with sizable shifts in Little-Parks oscillations. Furthermore, the critical temperature of the loop is also magnetization-orientation-dependent and conversely, the superconducting transition itself may influence the magnetization direction. More generally, the superconducting region above the FI serves as a “phase battery” and so offers a new device concept for superconducting spintronics.

Topologically ordered states are fundamentally important in theoretical physics, which are also suggested as promising candidates to build fault-tolerant quantum devices. However, it is still elusive how topological orders can be affected or detected under noises. In this work, we find a quantity, termed as the ring degeneracy $\mathcal{D}$, which is robust under pure noise to detect both trivial and intrinsic topological orders. The ring degeneracy is defined as the degeneracy of the solutions of the self-consistent equations that encode the contraction of the corresponding tensor network (TN). For the $Z_N$ orders, we find that the ring degeneracy satisfies a simple relation $\mathcal{D}=(N+1)/2+d$, with $d=0$ for odd $N$ and $d=1/2$ for even $N$. Simulations on several nontrivial states (two-dimensional Ising model, $Z_N$ topological states, and resonating valence bond states) show that the ring degeneracy can tolerate noises up to a strength associated to the gap of the TN boundary theory.