We investigate the absorption of a spin current at a ferromagnetic-metal/Pt-oxide interface by measuring ferromagnetic resonance. The spin absorption was characterized by the magnetic damping of the heterostructure. We show that the magnetic damping of a ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ film is clearly enhanced by attaching Pt oxide on the ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ film. The damping enhancement disappears by inserting an ultrathin Cu layer between the ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ and Pt-oxide layers. These results demonstrate an essential role of the direct contact between the ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ and Pt oxide to induce sizable interface spin-orbit coupling. Furthermore, the spin-absorption parameter of the ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$/Pt-oxide interface is comparable to that of intensively studied heterostructures with strong spin-orbit coupling, such as an oxide interface, topological insulators, and metallic junctions with Rashba spin-orbit coupling. This result illustrates strong spin-orbit coupling at the ferromagnetic-metal/Pt-oxide interface, providing an important piece of information for quantitative understanding of the spin absorption and spin-charge conversion at the ferromagnetic-metal/metallic-oxide interface.

Iridates are often viewed as an equivalent of cuprates with strong spin-orbit coupling. As such, they offer a new way to study the physics of Mott insulators. The hybridization with oxygen is, of course, essential in both compounds and may play a crucial role in the doping process. It could be quite different in the two families, iridates being $5d$ transition metals with different orbital geometries. But this difference has not been studied in detail so far. We present a combined angle-resolved photoemission spectrescopy and O $K$-edge resonant inelastic x-ray scattering study to document this aspect in ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$, pure and doped with 4% La and 15% Rh. We evidence different charge transfer excitations and distinguish those associated with apical or in-plane oxygens. We observe a specific evolution of one excitation upon Rh doping, which suggests a more itinerant nature of the holes related to the apical oxygen. This gives information on the way doping proceeds in iridates.

The notion of topological (Thouless) pumping in topological phases is traditionally associated with Laughlin's pump argument for the quantization of the Hall conductance in two-dimensional (2D) quantum Hall systems. It relies on magnetic flux variations that thread the system of interest without penetrating its bulk, in the spirit of Aharonov-Bohm effects. Here we explore a different paradigm for topological pumping induced, instead, by magnetic flux variations $\delta \chi$ inserted through the bulk of topological phases. We show that $\delta \chi$ generically controls the analog of a topological pump, accompanied by robust physical phenomena. We demonstrate this concept of bulk pumping in two paradigmatic types of 2D topological phases: integer and fractional quantum Hall systems and topological superconductors. We show that bulk pumping provides a unifying connection between seemingly distinct physical effects such as density variations described by Streda's formula in quantum Hall phases and fractional Josephson currents in topological superconductors. More importantly, we argue that bulk pumping provides a generic tool for probing topological phases and inducing robust physical effects, similar in spirit yet crucially different from Laughlin's pump. We discuss its generalizations in other topological phases.

A complete understanding of a material requires both knowledge of the excited states as well as of the ground state. In particular, the low energy excitations are of utmost importance while studying the electronic, magnetic, dynamical, and thermodynamical properties of the material. Time-dependent density functional theory (TDDFT), within the linear regime, is a successful ab initio method to assess the electronic charge and spin excitations. However, it requires an approximation to the exchange-correlation (XC) kernel which encapsulates the effect of electron-electron interactions in the many-body system. In this work we derive and implement the spin-polarized XC kernel for semilocal approximation, the so-called adiabatic generalized gradient approximation (AGGA). This kernel has a quadratic dependence on the wave vector $\mathbf{q}$ of the perturbation, however the impact of this on the electron energy loss spectra (EELS) is small. We show that the AGGA generally worsens the spin-excitation spectra by overestimating the magnon energies and suppressing the intensity of spin waves.

A discrete time crystal is a recently discovered nonequilibrium phase of matter that has been shown to exist in disordered, periodically driven Ising spin chains. In this phase, if the system is initially prepared in one of a certain class of pure multispin product states, it periodically returns to this state over very long timescales despite the presence of interactions, disorder, and pulse imperfections. Here, we show that this phase occurs in GaAs quantum dot spin arrays containing as few as three quantum dots, each confining one electron spin, for naturally occurring levels of nuclear spin noise and charge noise. Although the physical interaction in these arrays is a nearest-neighbor Heisenberg exchange interaction, we show that this can be effectively converted into an Ising interaction by applying additional pulses during each drive period. We show that by changing the rotation axis of these pulses, we can select the direction of the Ising interaction and, consequently, the quantization axis of the stabilized multispin states. Moreover, we demonstrate that it is possible to perform coherent rotations of the stabilized states while remaining in the time-crystal phase. These findings open up the intriguing possibility of using time-crystal phases to extend the lifetime of quantum states for information applications.

Scanning tunneling microscopy, low-energy electron diffraction, and helium atom scattering show a transition to a dimerizationlike reconstruction in the one-dimensional atomic chains on Bi(114) at low temperatures. One-dimensional metals are generally unstable against such a Peierls-like distortion, but neither the shape nor the spin texture of the Bi(114) Fermi contour favors the transition: Although the Fermi contour is one dimensional and thus perfectly nested, the very short nesting vector $2k_F$ is inconsistent with the periodicity of the distortion. Moreover, the nesting occurs between two Fermi contour branches of opposite spin, which is also expected to prevent the formation of a Peierls phase. Indeed, angle-resolved photoemission spectroscopy does not reveal any change in the electronic structure near the Fermi energy around the phase transition. On the other hand, distinct changes at higher binding energies are found to accompany the structural phase transition. This suggests that the transition of a strong-coupling type and that it is driven by phonon entropy rather than electronic entropy. This picture is supported by the observed short correlation length of the pairing distortion, the second-order-like character of the phase transition, and pronounced differences between the surface phonon spectra of the high- and low-temperature phases.

We investigate parity-odd nondissipative transport in an anisotropic Dirac semimetal in two spatial dimensions. The analysis is relevant for interacting electronic systems with merging Dirac points at charge neutrality. For such systems the dispersion relation is relativistic in one direction and nonrelativistic in the other. We give a proposal of how to calculate the Berry curvature for this system and use it to derive more than one odd viscosities, in contrast to rotationally invariant systems. We observe that in such a model the odd part of viscosity tensor is parametrized by two independent transport coefficients and one that is identically zero.

Thermalization is a probabilistic process. As such, it is generally expected that when we increase the temperature of a system, its classical behavior dominates its quantum coherences. By employing the Gibbs state of a translationally invariant quantum spin liquid—Kitaev's honeycomb lattice model—we demonstrate that an insulating phase at $T=0$ becomes metallic purely by increasing temperature. In particular, we compute the finite-temperature distribution of energies and show that it diverges logarithmically, as we move to small energies. The corresponding wave functions become critical like at Anderson transitions. These characteristics are obtained within an exact Monte Carlo method that simulates the finite-temperature behavior of the Kitaev model. In particular, we take into account the projection onto the physical parity sectors, required for identifying the topological degeneracy of the model. Our work opens the possibility to detect thermal metal behavior in spin liquid experiments.

We report the systematic measurement of the magnetoresistance (MR) properties and Hall resistivity of the topological nodal-line semimetal $\mathrm{SrA}{\mathrm{s}}_3$ single crystals. We observed large unsaturated MR accompanied by pronounced Shubnikov-de Hass (SdH) oscillations. Analysis of the SdH oscillations reveals two small frequencies of 1.6 T ($\alpha$ pocket) and 5.8 T ($\beta$ pocket). The $\alpha$ pocket has a nontrivial Berry phase and a small effective mass of $\sim 0.034m_0$, while the $\beta$ pocket has a trivial Berry phase with an effective mass of $\sim 0.11m_0$. Hall resistivity measurement reveals the coexistence of a low-concentration hole $(n_h=6.45\times {10}^{16}\mathrm{c}{\mathrm{m}}^{-3}$) with high mobility ($1.68\times {10}^5$ $\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$) and a high-concentration electron $(n_e=2.34\times {10}^{17}\mathrm{c}{\mathrm{m}}^{-3}$) with lower mobility ($9.50\times {10}^3$ $\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$) at 2 K. Furthermore, we observed robust large negative MR in the presence of parallel magnetic and electric fields induced by the chiral magnetic effect.

We predict the occurrence of triply degenerate nodal points (TP) in the band structure of a series of quaternary Heusler alloys using first principle electronic structure calculation and appropriate point group symmetry analysis. TPs are usually formed due to the interplay of threefold rotational, mirror, and time reversal symmetries in the momentum space. We projected these TPs onto the (111) and (100) surfaces that lead to the formation of topological Fermi arcs, which may further be detected by scanning tunneling spectroscopy and angle resolved photoemission spectroscopy. These Fermi arcs arise due to the symmetry protected band degeneracies, which are robust and cannot be avoided due to the nontrivial band topology. A great advantage of the currently studied systems over other existing compounds is that the TPs in this class of systems are located far away from the $\mathrm{\Gamma }$ point along ${\mathrm{C}}_3$ axes. This helps to overcome the experimental difficulties over previously studied hexagonal and HgTe-type compounds.

The kinetic energy of a system made from normal ${}^3\mathrm{He}$ liquid is estimated and shows that progress has been made in resolving a long-standing disagreement with most experimental values of this quantity. In general, in the investigation of systems formed from strongly correlated fermions, the disagreement between experimental and “exact” theoretical values of the kinetic energy is a matter of concern. For these systems, difficulties are not only due to the Fermi-Dirac statistics they must obey, but also are due to the configurations that are used in estimations of quantities that do not commute with the Hamiltonian. We are able to improve the sampling of configurations and to avoid most of the bias from variational theories. Bias analysis and unbiased estimates of quantities that do not commute with the system Hamiltonian are also easily made.

We investigate the electronic structure of a two-dimensional electron gas created at the surface of the multivalley semimetal $1\mathrm{T}-{\mathrm{PtSe}}_2$. Using angle-resolved photoemission and first-principles-based surface space-charge calculations, we show how the induced quantum well sub-band states form multiple Fermi surfaces, which exhibit highly anisotropic Rashba-like spin splittings. We further show how the presence of both electronlike and holelike bulk carriers causes the near-surface band bending potential to develop an unusual nonmonotonic form, with spatially segregated electron accumulation and hole accumulation regions, which in turn amplifies the induced spin splitting. Our results thus demonstrate the novel environment that semimetals provide for tailoring electrostatically induced potential profiles and their corresponding quantum sub-band states.

We present an alignment-resolved ${\mathrm{O}}_2$ scattering experiment showing that the alignment of an incident homonuclear diatomic molecule strongly influences the angular distribution of scattered molecule, the energy loss during the collision, and the trapping probability. Clear surface rainbow scattering has been observed on LiF(001) when ${\mathrm{O}}_2$ is scattered along the [110] azimuth with its axis perpendicular to the scattering plane. The results can be understood based on the alignment dependence of the surface corrugation felt by an incident molecule. The fact that ${\mathrm{O}}_2$ trapping probability on a highly oriented pyrolytic graphite surface is higher for end-on collision has been associated with the observed larger energy loss for this geometry.

Pressure-induced glass-glass transition (GGT) has been reported in a few rare-earth based and main-group metallic glasses (MGs), a process during which the compressibility decreases with the transformation from a low-density to a high-density amorphous state. Herein, we report an unexpected GGT behavior in Pd-based MGs under pressure, which is characterized by an anomalous increase in the compressibility with the pressure. State-of-the-art high-energy synchrotron technique, coupled with theoretical simulations, reveals that this unique GGT behavior is primarily caused by the change in bonding characteristics, i.e., some covalentlike atomic bonds in the as-prepared state change to metallic ones under high pressure, which also leads to the increase in the compressibility. Our current findings shed light on the understanding of the nature of polyamorphic transitions in MGs.

It is well known that for ordinary one-dimensional (1D) disordered systems, the Anderson localization length $\xi$ diverges as ${\lambda }^m$ in the long-wavelength limit ($\lambda \to \infty$) with a universal exponent $m=2$, independent of the type of disorder. Here, we show rigorously that pseudospin-1 systems exhibit nonuniversal critical behavior when they are subjected to 1D random potentials. In such systems, we find that $\xi \propto {\lambda }^m$ with $m$ depending on the type of disorder. For binary disorder, $m=6$ and the fast divergence is due to a super-Klein-tunneling effect. When we add additional potential fluctuations to the binary disorder, the critical exponent $m$ crosses over from 6 to 4 as the wavelength increases. Moreover, for disordered superlattices, in which the random potential layers are separated by layers of background medium, the exponent $m$ is further reduced to 2 due to the multiple reflections inside the background layer. To obtain the above results, we developed an analytic method based on a stack recursion equation. Our analytical results are in excellent agreement with the numerical results obtained by the transfer-matrix method. For pseudospin-1/2 systems, we find both numerically and analytically that $\xi \propto {\lambda }^2$ for all types of disorder, same as ordinary 1D disordered systems. Our analytical method provides a convenient way to obtain easily the critical exponent $m$ for general 1D Anderson localization problems.

We investigate numerically and experimentally the near-field response of disordered arrays comprising asymmetrically split ring resonators that exhibit a strong cooperative response. Our simulations treat the unit cell split-ring resonators as discrete pointlike oscillators with associated electric and magnetic point dipole radiation, while the strong cooperative radiative coupling between the different split rings is fully included at all orders. The methods allow us to calculate local field and Purcell factor enhancement arising from the collective electric and magnetic excitations. We find substantially increased standard deviation of the Purcell enhancement with disorder, making it increasingly likely to find collective excitation eigenmodes with very high Purcell factors that are also stronger for magnetic than electric excitations. We show that disorder can dramatically modify the cooperative response of the metamaterial even in the presence of strong dissipation losses, as is the case for plasmonic systems. Our analysis in terms of collective eigenmodes paves the way for controlled engineering of electromagnetic device functionalities based on strongly interacting metamaterial arrays.

We report the systematic dependence of spin pumping in tungsten (W)/CoFeB heterostructures on the structural phase of W, which is intricately related to argon gas pressure ($p_{\mathrm{Ar}}$) maintained during the sputter deposition. We found that with increasing $p_{\mathrm{Ar}}$ the structural phase of W changes from mixed ($\alpha +\beta$) phase to pure $\beta$ phase. The $\beta$-W is stabilized in films for the high thickness of 40 nm which is desirable for spin devices. Using ferromagnetic resonance measurement of W($p_{\mathrm{Ar}}$)/CoFeB heterostructures, it is shown that enhancement of magnetic damping (${\alpha }_{\mathrm{eff}}$) from spin pumping is more in $\beta$-W compared to ($\alpha +\beta$)-W. The effective spin mixing conductance ($g_{\mathrm{eff}}^{\uparrow \downarrow }$) is estimated for different phases of W from the linear evolution of ${\alpha }_{\mathrm{eff}}$ with the inverse thickness of the CoFeB layer. For $\beta$-W, the $g_{\mathrm{eff}}^{\uparrow \downarrow }$ is found to be larger than that of ($\alpha +\beta$)-W and it is attributed to different interface structure. Thus, effective tuning of spin pumping efficiency can be achieved using different W crystal phases. We also studied the dependence of ${\alpha }_{\mathrm{eff}}$ on $\beta$-W film thickness to calculate the value of spin-diffusion length (${\lambda }_{\mathrm{SD}}$) and intrinsic spin mixing conductance ($g_{\beta \text{−}W}^{\uparrow \downarrow }$) using both the ballistic and diffusive spin transport models.

We study an integrable system that is reducible to free fermions by a Jordan-Wigner transformation which is subjected to a Fibonacci driving protocol based on two noncommuting Hamiltonians. In the high-frequency limit $\omega \to \infty$, we show that the system reaches a nonequilibrium steady state, up to some small fluctuations which can be quantified. For each momentum $k$, the trajectory of the stroboscopically observed state lies between two concentric circles on the Bloch sphere; the circles represent the boundaries of the small fluctuations. The residual energy is found to oscillate in a quasiperiodic way between two values which correspond to the two Hamiltonians that define the Fibonacci protocol. These results can be understood in terms of an effective Hamiltonian which simulates the dynamics of the system in the high-frequency limit.