The magnetization process of the spin-$1/2$ antiferromagnetic Heisenberg model on two-dimensional square-kagome lattice is studied theoretically. The metamagnetic jumps exist in the magnetization process at the higher edge of the $1/3$ and $2/3$ plateaus. The parameter-dependencies of the critical field and the magnitude of the magnetization jump at the higher edge of the $1/3$ plateau are obtained by using the approximated state in the unit cell and compared with the numerical results of the exact diagonalization of 42 sites.

Ultrafast spin dynamics in magnetic materials is generally associated with ultrafast heating of the electronic system by a near infrared femtosecond laser pulse, thus offering only an indirect and nonselective access to the spin order. Here we explore spin dynamics in ferromagnets by means of extremely intense THz pulses, as at these low frequencies the magnetic field provides a direct and selective route to coherently control the magnetization. We find that, at low fields, the observed off-resonantly excited spin precession is phase locked to the THz magnetic field. At extreme THz fields, the coherent spin dynamics become convoluted with an ultrafast incoherent magnetic quenching due to the absorbed energy. This demagnetization takes place upon a single shot exposure. The magnetic properties are found to be permanently modified above a THz pump fluence of $\approx 100\mathrm{mJ}/{\mathrm{cm}}^2$. We conclude that magnetization switching cannot be reached. Our atomistic spin-dynamics simulations excellently explain the measured magnetization response. We find that demagnetization driven by THz laser-field coupling to electron charges occurs, suggesting nonconducting materials for achieving coherent THz-magnetization reversal.

The superfluid state in bulk liquid ${}^3\mathrm{He}$ is realized in the form of A or B phases. Uniaxially anisotropic aerogel (nafen) stabilizes the transition from the normal to the polar superfluid state which on further cooling transitions to the axipolar orbital glass state [Dmitriev, Senin, Soldatov, and Yudin, Phys. Rev. Lett. 115, 165304 (2015)]. This is the case in nafen aerogel preplated by several atomic layers of ${}^4\mathrm{He}$. When pure liquid ${}^3\mathrm{He}$ fills the same nafen aerogel a solid-like layer of ${}^3\mathrm{He}$ atoms coats the aerogel structure. The polar state is not formed anymore and a phase transition occurs directly to the axipolar phase [Dmitriev, Soldatov, and Yudin, Phys. Rev. Lett. 120, 075301 (2018)]. The substitution of ${}^4\mathrm{He}$ by ${}^3\mathrm{He}$ atoms at the aerogel surface changes the potential and adds the exchange scattering of quasiparticles on the aerogel strands. A calculation shows that both of these effects can decrease the degree of anisotropy of scattering and suppress the polar phase formation. The derived anisotropy of the spin diffusion coefficient in globally anisotropic aerogel is determined by the same parameter which controls the polar state emergence, which allows one to check the effect of anisotropy change for different types of covering.

We consider a Josephson junction consisting of superconductor/ferromagnetic insulator (S/FI) bilayers as electrodes which proximizes a nearby two-dimensional (2D) electron gas. By starting from a generic Josephson hybrid planar setup, we present an exhaustive analysis of the interplay between the superconducting and magnetic proximity effects and the conditions under which the structure undergoes transitions to a nontrivial topological phase. We address the 2D bound-state problem by using a general transfer-matrix approach that reduces the problem to an effective 1D Hamiltonian. This allows for a straightforward study of the topological properties in different symmetry classes. As an example we consider a narrow channel coupled with multiple ferromagnetic superconducting fingers, and discuss how the Majorana bound states can be spatially controlled by tuning the superconducting phases. Following our approach, we also show the energy spectrum, the free energy, and finally the multiterminal Josephson current of the setup.

Iron phonon partial densities of states of ${{\mathrm{Pd}}_3}^{57}\mathrm{Fe}$ were measured from room temperature through the Curie transition at 500 K using nuclear resonant inelastic x-ray scattering. The experimental results were compared to ab initio spin-polarized calculations that model the finite-temperature thermodynamic properties of $L{1}_2$-ordered ${\mathrm{Pd}}_3\mathrm{Fe}$ with stochastically generated atomic displacements, coupled with magnetic special quasirandom structures of noncollinear magnetic moments. The scattering measurements and first-principles calculations show that the Fe partial vibrational entropy is close to what is predicted by the quasiharmonic approximation owing to a cancellation of effects. Anharmonicity and a magnon-phonon interaction approximately cancel a ferromagnetic optical phonon stiffening.

Understanding the evolution of spin-orbit torque (SOT) with increasing heavy-metal thickness in ferromagnet/normal metal (FM/NM) bilayers is critical for the development of magnetic memory based on SOT. However, several experiments have revealed an apparent discrepancy between damping enhancement and dampinglike SOT regarding their dependence on NM thickness. Here, using linewidth and phase-resolved amplitude analysis of vector network analyzer ferromagnetic resonance (VNA-FMR) measurements, we simultaneously extract damping enhancement and both fieldlike and dampinglike inverse SOT in ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$/Pt bilayers as a function of Pt thickness. By enforcing an interpretation of the data which satisfies Onsager reciprocity, we find that both the damping enhancement and dampinglike inverse SOT can be described by a single spin diffusion length $\left(\approx 4\mathrm{nm}\right)$, and that we can separate the spin pumping and spin-memory loss contributions to the total damping. This analysis indicates that less than 40% of the angular momentum pumped by FMR through the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$/Pt interface is transported as spin current into the Pt. On account of the spin-memory loss and corresponding reduction in total spin current available for spin-charge transduction in the Pt, we determine the Pt spin Hall conductivity $[{\sigma }_{\mathrm{SH}}=(2.36\pm 0.04)\times {10}^6{\omega }^{-1}{\mathrm{m}}^{-1}]$ and bulk spin Hall angle $\left({\theta }_{\mathrm{SH}}=0.387\pm 0.008\right)$ to be larger than commonly cited values. These results suggest that Pt can be an extremely useful source of SOT if the FM/NM interface can be engineered to minimize spin loss. Lastly, we find that self-consistent fitting of the damping and SOT data is best achieved by a model with Elliott-Yafet spin relaxation and extrinsic inverse spin Hall effect, such that both the spin diffusion length and spin Hall conductivity are proportional to the Pt charge conductivity.

Since it was first discussed by Baxter in 1970, the three coloring model has been studied in several contexts, from frustrated magnetism to superconducting devices and glassiness. In presence of interactions, when the model is no longer exactly soluble, it was already observed that the phase diagram is highly nontrivial. Here we discuss the generic case of “color-dependent” nearest-neighbor interactions between the vertex chiralities. We uncover different critical regimes merging into one another: $c=1/2$ free fermions combining into $c=1$ free bosons; $c=1$ free bosons combining into $c=2$ critical loop models; as well as three separate $c=1/2$ critical lines merging at a supersymmetric $c=3/2$ critical point. When the three coupling constants are tuned to equal one another, transfer-matrix calculations highlight a puzzling regime where the central charge appears to vary continuously from $3/2$ to 2.

We propose a generalization of the concept of superconducting fitness, which allows us to make statements analogous to Anderson's theorems concerning the stability of different superconducting states. This concept can be applied to complex materials with several orbital, layer, sublattice, or valley degrees of freedom. The superconducting fitness functions $F_A\left(\mathbf{k}\right)$ and $F_C\left(\mathbf{k}\right)$ give a direct measure of the robustness of the weak-coupling instability and of the presence of detrimental terms in the Hamiltonian, respectively. These two functions can be employed as a guide to engineer normal state Hamiltonians in order to favor or suppress superconducting order parameters with different symmetries and topological properties. To illustrate the applicability and power of this concept we study three cases: the noncentrosymmetric heavy fermion ${\mathrm{CePt}}_3\mathrm{Si}$, the hole-doped iron pnictide ${\mathrm{KFe}}_2{\mathrm{As}}_2$, and the doped topological insulator ${\mathrm{Cu}}_x{\mathrm{Bi}}_2{\mathrm{Se}}_3$.

The imaginary-time Green's function is a building block of various numerical methods for correlated electron systems. Recently, it was shown that a model-independent compact orthogonal representation of the Green's function can be constructed by decomposing its spectral representation. We investigate the performance of this so-called intermediate representation (IR) from several points of view. First, we develop an efficient algorithm for computing the IR basis functions of arbitrary high degree. Second, for two simple models, we study the number of coefficients required to represent the Green's function within a given tolerance. We show that the number of coefficients grows only as $O(ln\beta )$ for fermions and converges to a constant for bosons as temperature $T=1/\beta$ decreases. Third, we show that this remarkable feature is ascribed to the properties of the physically constructed basis functions. The fermionic basis functions on the real-frequency axis have features whose width is scaled as $O\left(T\right)$, which is consistent with the low-$T$ properties of quasiparticles in a Fermi liquid state. On the other hand, the properties of the bosonic basis functions are consistent with those of spin/orbital susceptibilities at low $T$. These results demonstrate the potential wide applications of the IR to calculations of correlated systems.

Charge transport in disordered inorganic semiconductors is governed by the multiple trapping (MT) of carriers from delocalized states in the conduction band into localized traps in the band tail. Although it is well known that carrier mobility in these materials strongly depends on electric field, a consistent description of this effect in the MT regime is still missing. We analyze experimental data obtained in a series of disordered inorganic semiconductors and show that the combined effects of temperature and of the electric field on the carrier mobility can be described by a single parameter, the field-dependent effective temperature. This conclusion is supported by the theoretical analysis of the MT transport, which takes into account the field-assisted release of carriers from the traps into the conduction band.

We present a scheme for correcting for crosstalk- and noise-induced errors in exchange-coupled singlet-triplet semiconductor double quantum dot qubits. While exchange coupling allows the coupling strength to be controlled independently of the intraqubit exchange couplings, there is also the problem of leakage, which must be addressed. We show that, if a large magnetic field difference is present between the two qubits, leakage is suppressed. We then develop pulse sequences that correct for crosstalk- and noise-induced errors and present parameters describing them for the 24 Clifford gates. We determine the infidelity for both the uncorrected and corrected gates as a function of the error-inducing terms and show that our corrected pulse sequences reduce the error by several orders of magnitude.

We analyze the dynamical response of a two-dimensional system of itinerant fermions coupled to a scalar boson $\varphi$, which undergoes a continuous transition towards nematic order with a $d$-wave form factor. We consider two cases: (a) when $\varphi$ is a soft collective mode of fermions near a Pomeranchuk instability, and (b) when it is an independent critical degree of freedom, such as a composite spin order parameter. In both cases, the order parameter is not a conserved quantity and the $d$-wave fermionic polarization $\mathrm{\Pi }(q,\mathrm{\Omega })$ remains finite even at $q=0$. The polarization $\mathrm{\Pi }(0,\mathrm{\Omega })$ has similar behavior in the two cases, but the relations between $\mathrm{\Pi }(0,\mathrm{\Omega })$ and the bosonic susceptibility $\chi (0,\mathrm{\Omega })$ are different, leading to different forms of ${\chi }^{\prime \prime }(0,\mathrm{\Omega })$, as measured by Raman scattering. We compare our results with polarization-resolved Raman data for the Fe-based superconductors ${\mathrm{FeSe}}_{1-x}{\mathrm{S}}_x,{\mathrm{NaFe}}_{1-x}{\mathrm{Co}}_x\mathrm{As}$, and ${\mathrm{BaFe}}_2{\mathrm{As}}_2$.

Spontaneous discrete symmetry breaking can be described in the framework of projected entangled pair states (PEPS) by linearly superposing local tensors belonging to two (or more) symmetry classes of tensors. This is illustrated in the case of a frustrated spin-1 Heisenberg model on the square lattice, which hosts a nematic spin liquid spontaneously breaking lattice $\pi /2$-rotation symmetry. A superposition of SU(2)-symmetric PEPS tensors belonging to two irreducible representations of the lattice point group is shown to capture accurately the properties of the nematic phase, as shown from a comparison to exact diagonalizations and density matrix renormalization group results.

We have studied the properties of the prototype hybrid organic-inorganic perovskite ${\text{CH}}_3{\text{NH}}_3{\text{PbI}}_3$ using relativistic density functional theory (DFT). For our analysis we introduce the concept of ${\text{CH}}_3{\text{NH}}_3^{+}$ “pair modes,” that is, characteristic relative orientations of two neighboring ${\text{CH}}_3{\text{NH}}_3^{+}$ cations. In our previous work [Li and Rinke, Phys. Rev. B 94, 045201 (2016)] we identified two preferential orientations that a single ${\text{CH}}_3{\text{NH}}_3^{+}$ cation adopts in a unit cell. The total number of relevant pairs can be reduced from the resulting 196 combinations to only 25 by applying symmetry operations. DFT results of several $2\times 2\times 2$ supercell models reveal the dependence of the total energy, band gap, and band structure on the distribution of ${\text{CH}}_3{\text{NH}}_3^{+}$ cations and the pair modes. We have then analyzed the pair-mode distribution of a series of $4\times 4\times 4$ supercell models with disordered ${\text{CH}}_3{\text{NH}}_3^{+}$ cations. Our results show that diagonally oriented ${\text{CH}}_3{\text{NH}}_3^{+}$ cations are rare in optimized ${\text{CH}}_3{\text{NH}}_3{\text{PbI}}_3$ supercell structures. In the prevailing pair modes, the $\mathrm{C}\text{–}\mathrm{N}$ bonds of the two neighboring ${\text{CH}}_3{\text{NH}}_3^{+}$ cations are aligned approximately vertically. Furthermore, we fit the coefficients of a pair-mode expansion to our supercell DFT reference structures. The pair-mode model can then be used to quickly estimate the energies of disordered perovskite structures. Our pair-mode concept provides combined atomistic-statistical insight into disordered structures in bulk hybrid perovskite materials.

We report on nonlocal transport in large-scale epitaxial graphene on silicon carbide under an applied external magnetic field. The nonlocality is related to the emergence of the quantum Hall regime and persists up to the millimeter scale. The nonlocal resistance reaches values comparable to the local (Hall and longitudinal) resistances. At moderate magnetic fields, it is almost independent on the in-plane component of the magnetic field, which suggests that spin currents are not at play. The nonlocality cannot be explained by thermoelectric effects without assuming extraordinary large Nernst and Ettingshausen coefficients. A model based on counterpropagating edge states backscattered by the bulk reproduces quite well the experimental data.

In this paper we study Maxwell lattices with nonrectilinear constraints, where the elastic energy is determined by the collective motion of three or more particles, in contrast to a rectilinear spring whose elastic energy only relies on the displacement of two particles attached to the two ends of the spring. Utilizing polygon-shaped constraints, we found that the Maxwell counting argument and the topological construction, based on the compatibility matrix and the equilibrium matrix, can be generalized in our models, and our elastic systems follow the same topological classification. In addition, we also found that nonrectilinear constraints offers a natural pass towards topological states with higher topological indices and multiple edge states, which can be achieved even for a simple unit cell with one degree of freedom per unit cell without enlarging the unit cell in the bulk or at the edge.

We report a giant spin-torque generation originated from the ferromagnet/heavily oxidized Pt interface. The heavily oxidized Pt was fabricated by magnetron sputtering in a mixture of oxygen and argon gases with different oxygen flow rate $Q$ from $50\%$ to $100\%$. The dominant structure of the oxidized Pt is confirmed to be ${\mathrm{PtO}}_2$ in this $Q$ range. We show that even in this heavily oxidized range, robust dampinglike and fieldlike spin torques can still be generated from the ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$/oxidized Pt interface. By increasing the oxidation level of the oxidized Pt, the generation efficiencies of both dampinglike and fieldlike torques increase drastically, and noticeably, a maximum generation efficiency of 0.92 for the dampinglike torque is obtained. Our study further demonstrates that the generation efficiency of the dampinglike torque has a much larger value than that of the fieldlike torque, which indicates a dominant generation of the dampinglike torque from the interface. Since no energy dissipation occurs in the bulk of the spin-torque generator, this study provides a piece of information for the development of the energy-efficient spin-orbit devices based on insulating metallic oxides.

Temperature modulation due to a pure spin current has been investigated in bilayer metallic films consisting of a paramagnetic metal (PM; Pt, W, or Ta) and a ferromagnetic metal (FM; CoFeB or permalloy). When a charge current is applied to the PM/FM bilayer film, a spin current is generated across the PM/FM interface owing to the spin Hall effect in PM. The spin current was found to exhibit cooling and heating features depending on the sign of the spin Hall angle of PM; the spin-current-induced temperature modulation is estimated by subtracting the contribution of the anomalous Ettingshausen effect in FM monolayer films, and attributed to the conduction-electron-driven spin-dependent Peltier effect and magnon-driven spin Peltier effect in FM. To reveal the origin of the spin-current-induced contribution in the PM/FM films, we compared the experimental results with the phenomenological calculations based on the spin and magnon diffusion models. We found that the spin-current-induced temperature modulation is greater than that expected from the spin-dependent Peltier coefficients reported in earlier studies and its characteristic length is around 10 nm, possibly larger than typical spin-diffusion lengths of conduction electrons in FM. These facts indicate that the signals in the PM/FM films contain the substantial contribution from the magnon-driven spin Peltier effect.

The curvature of a magnetic membrane was presented as a means of inducing nonreciprocities in the spin-wave (SW) dispersion relation [see Otálora et al. Phys. Rev. Lett. 117, 227203 (2017) and Otálora et al. Phys. Rev. B 95, 184415 (2017)], thereby expanding the toolbox for controlling SWs. In this paper, we further complement this toolbox by analytically showing that the membrane curvature is also manifested in the absorption of SWs, leading to a difference in the frequency linewidth (or lifetime) of counterpropagating magnons. Herein, we studied the nanotubular case, predicting changes of approximately greater than 10% and up to 20% in the frequency linewidth of counterpropagating SWs for a wide range of nanotube radii ranging from $30\mathrm{nm}$ to $260\mathrm{nm}$ and with a thickness of $10\mathrm{nm}$. These percentages are comparable to those that can be extracted from experiments on heavy metal/magnetic metal sandwiches, wherein linewidth asymmetry results from an interfacial Dzyaloshinskii-Moriya interaction (DMI). We also show that the interplay between the frequency linewidth and group velocity leads to asymmetries in the SW decay length, presenting changes between 10% and 22% for counterpropagating SWs in the frequency range of 2–10 GHz. For the case of the SW dispersion relation, the predicted effects are identified as the classical dipole-dipole interaction, and the analytical expression of the frequency linewidth has the same mathematical form as in thin films with the DMI. Furthermore, we present limiting cases of a tubular geometry with negligible curvature such that our analytical model converges to the case of a planar thin film known from the literature. Our findings represent a step forward toward the realization of three-dimensional curvilinear magnonic devices.