We predict magnon-polariton states circulating unidirectionally in a microwave cavity when loaded by a number of magnets on special lines. Realistic finite-element numerical simulations, including dielectric, time-dependent, and nonlinear effects, confirm the validity of the approximations of a fully analytical input-output model. We find that a phased antenna array can focus all power into a coherent microwave beam with controlled direction and an intensity that scales with the number of magnets.

In the field of frustrated magnetism, Kitaev models provide a unique framework to study the phenomena of spin fractionalization and emergent lattice gauge theories in two and three spatial dimensions. Their ground states are quantum spin liquids, which can typically be described in terms of a Majorana band structure and an ordering of the underlying ${\mathbb{Z}}_2$ gauge structure. Here we provide a comprehensive classification of the “gauge physics” of a family of elementary three-dimensional Kitaev models, discussing how their thermodynamics and ground state order depends on the underlying lattice geometry. Using large-scale, sign-free quantum Monte Carlo simulations we show that the ground-state gauge order can generally be understood in terms of the length of elementary plaquettes—a result which extends the applicability of Lieb's theorem to lattice geometries beyond its original scope. At finite temperatures, the proliferation of (gapped) vison excitations destroys the gauge order at a critical temperature scale, which we show to correlate with the size of vison gap for the family of three-dimensional Kitaev models. We also discuss two notable exceptions where the lattice structure gives rise to “gauge frustration” or intertwines the gauge ordering with time-reversal symmetry breaking. In a more general context, the thermodynamic gauge transitions in such 3D Kitaev models are one of the most natural settings for phase transitions beyond the standard Landau-Ginzburg-Wilson paradigm.

When a magnetic field is applied to a single crystal of magnetite at $124\mathrm{K}>T>50\mathrm{K}$, the monoclinic $c_M$ axis, which is the easy magnetization axis, switches to one of the ⟨100⟩ cubic directions, nearest to the direction of the magnetic field, and the phenomenon known as an axis switching (AS) occurs. A global symmetry probe, resonant x-ray scattering, and a local probe, Mössbauer spectroscopy, are used to better understand the mechanism of axis switching. The behavior of three subsystems ordered below the Verwey transition temperature $T_V$, i.e., lattice distortion, an orbital, and charge orderings, was observed via resonant x-ray scattering as a function of an external magnetic field. This was preceded by calculation of selected peak intensities using the fdmnes code. The Mössbauer spectroscopy studies confirmed that the magnetic field triggers electronic rearrangements and atomic displacements. The structure observed after the process of axis switching is very similar to the one obtained after cooling below $T_V$ with the magnetic field applied along one of the initial ⟨100⟩ cubic directions and distinct from the cooling in the absence of a magnetic field. From all the experimental observations of the phenomenon done so far, it is clear that AS starts from the fluctuations between octahedral iron orbitals that ultimately lead to the Verwey transition, but also to the higher-temperature trimeron dynamics. Therefore, further observation of the axis switching may be a key point to the understanding of a majority of strongly correlated electronic behavior in magnetite as well as in other transition metal oxides.

Two-dimensional materials and their mechanical properties are known to be profoundly affected by rippling deformations. However, although ripples are fairly well understood, less is known about their origin and controlled modification. Here, motivated by recent reports of laser-controlled creation of line defects in graphene, we investigate how line defects could be used to control rippling in graphene and other two-dimensional materials. By sequential multiscale coupling of density-functional tight-binding and continuum elasticity simulations, we quantify the amount of rippling when the number and the cumulative length of the line defects increase. Simulations show that elastic sheets with networks of line defects create rippling that induces considerable out-of-plane rigidification and in-plane softening with nonlinear elastic behavior. We hope that these insights help to guide experimental attempts to modify the mechanical properties of graphene and other two-dimensional materials.

Recently, it has been shown how shift and ballistic currents in piezoelectric sillenite crystals ${\mathrm{Bi}}_{12}\mathrm{Ge}{\mathrm{O}}_{20}$ and ${\mathrm{Bi}}_{12}\mathrm{Si}{\mathrm{O}}_{20}$ can be separated experimentally under the assumption that the shift component of the circular current is small. However, it has been claimed that the shift and ballistic currents cannot be quantified by this method, due to the magnetophotovoltaic effect caused either by the change of the crystal's spatial symmetry in the magnetic field or by the breaking of time-reversal symmetry. Presently, we report observations of photovoltaic currents in ${\mathrm{Bi}}_{12}\mathrm{Si}{\mathrm{O}}_{20}$, excited by linearly and circularly polarized light under weak external magnetic field, as well as measurements of the corresponding photo-Hall signals. We demonstrate that the magnetophotovoltaic current constitutes a significant fraction of the measured current in the Hall direction for ${\mathrm{Bi}}_{12}\mathrm{Si}{\mathrm{O}}_{20}$ under specific experimental conditions.

In compensated two-component systems in confined, two-dimensional geometries, nonlocal response may appear due to an external magnetic field. Within a phenomenological two-fluid framework, we demonstrate the evolution of charge flow profiles and the emergence of a giant nonlocal pattern dominating charge transport in a magnetic field. Applying our approach to the specific case of intrinsic graphene, we suggest a simple physical explanation for the experimental observation of giant nonlocality. Our results provide an intuitive way to predict the outcome of future experiments exploring the rich physics of many-body electron systems in confined geometries as well as to design possible applications.

The magnetotransport of an electron gas in a two-dimensional, random arrangement of overlapping retroreflective crosses is studied using a combination of experiment and classical event-driven molecular dynamics simulation. The experimentally measured magnetoconductivity ${\sigma }_{xx}$ as a function of the magnetic field $B$ displays an anomalous behavior at low $B$ fields, accompanied with an increase of ${\sigma }_{xx}$ with increasing temperature at $B=0$. The simulations show that at $B=0$ the magnetoconductivity does not exist and is associated with anomalous diffusion in the asymptotic long-time limit that depends on the orientational order of the obstacles. At any finite $B$ field, the motion of the tracer particle is asymptotically diffusive but the diffusion coefficient vanishes with a power law in the limit $B\to 0$.

We propose a new idea to generate pure spin current with photogalvanic effect (PGE) by designing devices with spatial inversion symmetry based on two-dimensional spin semiconducting materials. Due to the preservation of spatial inversion symmetry, the electric current generated by the PGE must be zero. However, finite spin-dependent current $I_{\uparrow /\downarrow }$ may still be produced. Once an amount of spin-up electrons flow into the device region from lead $\alpha$ and flow out from lead $\beta$ under light irradiation, the same amount of spin-down electrons will flow into the device region from lead $\beta$ and flow out from lead $\alpha$, which results in $I_c^{\alpha /\beta }=I_{\uparrow }^{\alpha /\beta }+I_{\downarrow }^{\alpha /\beta }=0$ and $I_s^{\alpha /\beta }=I_{\uparrow }^{\alpha /\beta }-I_{\downarrow }^{\alpha /\beta }\ne 0$ simultaneously for each lead and thus finite pure spin current arises. As a concrete example, this idea is demonstrated by calculating the PGE in a photoelectric device constructed with an armchair-edged graphene nanoribbon which is divided into two semi-infinite ribbons. The two semi-infinite ribbons are then periodically and symmetrically patterned with ferromagnetic triangle antidots in the form of “$▹◃$” to achieve spatial inversion symmetry of the device. We find that the pure spin current can be robustly generated, neither dependent on the photon energy and polarization/helicity angle, nor dependent on whether it is linearly, circularly, or elliptically polarized.

We compute the Lyapunov exponent characterizing quantum scrambling in a family of generalized Sachdev-Ye-Kitaev models, which can be tuned between different low temperature states from Fermi liquids, through non-Fermi liquids, to fast scramblers. The analytic calculation, controlled by a small coupling constant and large $N$, allows us to clarify the relations between the quasiparticle relaxation rate $1/\tau$ and the Lyapunov exponent ${\lambda }_L$ characterizing scrambling. In the Fermi liquid states we find that the quasiparticle relaxation rate dictates the Lyapunov exponent. In non-Fermi liquids, where $1/\tau \gg T$, we find that ${\lambda }_L$ is always $T$ linear with a prefactor that is independent of the coupling constant in the limit of weak coupling. Instead it is determined by a scaling exponent that characterizes the relaxation rate. ${\lambda }_L$ approaches the general upper bound $2\pi T$ at the transition to a fast scrambling state. Finally, in a marginal Fermi liquid state the exponent is linear in temperature with a prefactor that vanishes as a nonanalytic function $\sim gln(1/g)$ of the coupling constant $g$.

We investigate the possibility of spontaneous loop currents in the two-leg ladder cuprate ${\mathrm{Sr}}_{14-x}{\mathrm{Ca}}_x{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ by applying cluster dynamical mean field theory (CDMFT) to a seven-band Hubbard model for that compound, with an exact diagonalization solver. We sample several values of the local interaction $U_d$ and of the Cu-O energy difference $E_{pd}$, by applying an external field that induces loop currents. We find no instance of spontaneous loop currents once the external field is brought to zero.

The two-dimensional electron gas (2DEG) at the ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ interface exhibits gate-tunable superconductivity with a domelike shape of $T_{\mathrm{C}}$ as a function of electron concentration. Here, we propose that the experimentally observed behavior can be explained as a direct effect of the dominant $extended s-wave$ symmetry of the superconducting gap. Our results agree very well with the experimental data. As shown, neither the correlation effects nor the spin-orbit coupling significantly influence the physical picture of the paired state stemming from our analysis.

The single-site Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) ignores short-range ordering present in disordered metallic systems. In this paper, we establish a technique to fix this shortcoming by embedding an averaged cluster that displays chemical short-range order (SRO). The degree of SRO can be tuned by externally defined order parameters. This averaged cluster can be embedded in the single-site CPA medium or a self-consistently obtained effective medium that contains SRO information. The validity of this method is demonstrated by applying it to two alloy systems—the CuZn body-centered cubic (BCC) solid solution, and AlCrTiV, a four-element BCC high entropy alloy. A comparison between the non-self-consistent and self-consistent modes is also provided for the two above-mentioned systems. We make the code available on the internet. Planned extensions to this paper are discussed.

We investigate entanglement phase transitions from volume-law to area-law entanglement in a quantum many-body state under continuous position measurement on the basis of the quantum trajectory approach. We find the signatures of the transitions as peak structures in the mutual information as a function of measurement strength, as previously reported for random unitary circuits with projective measurements. At the transition points, the entanglement entropy scales logarithmically and various physical quantities scale algebraically, implying emergent conformal criticality, for both integrable and nonintegrable one-dimensional interacting Hamiltonians; however, such transitions have been argued to be absent in noninteracting regimes in some previous studies. With the aid of $U\left(1\right)$ symmetry in our model, the measurement-induced criticality exhibits a spectral signature resembling a Tomonaga-Luttinger liquid theory from symmetry-resolved entanglement. These intriguing critical phenomena are unique to steady-state regimes of the conditional dynamics at the single-trajectory level and are absent in the unconditional dynamics obeying the Lindblad master equation, in which the system ends up with the featureless, infinite-temperature mixed state. We also propose a possible experimental setup to test the predicted entanglement transition based on the subsystem particle-number fluctuations. This quantity should readily be measured by the current techniques of quantum gas microscopy and is in practice easier to obtain than the entanglement entropy itself.

Auto-oscillations of magnetization driven by direct spin current have been previously observed in multiple quasi-zero-dimensional (0D) ferromagnetic systems such as nanomagnets and nanocontacts. Recently, it was shown that pure spin Hall current can excite coherent auto-oscillatory dynamics in quasi-one-dimensional (1D) ferromagnetic nanowires but not in quasi-two-dimensional (2D) ferromagnetic films. Here we study the 1D to 2D dimensional crossover of current-driven magnetization dynamics in wire-based Pt/${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ bilayer spin Hall oscillators via varying the wire width. We find that increasing the wire width results in an increase of the number of excited auto-oscillatory modes accompanied by a decrease of the amplitude and coherence of each mode. We also observe a crossover from a hard to a soft onset of the auto-oscillations with increasing wire width. The amplitude of auto-oscillations rapidly decreases with increasing temperature suggesting that interactions of the phase-coherent auto-oscillatory modes with incoherent thermal magnons play an important role in suppression of the auto-oscillatory dynamics. Our measurements set the upper limit on the dimensions of an individual spin Hall oscillator and elucidate the mechanisms leading to suppression of coherent auto-oscillations with increasing oscillator size.

The nickelate $\mathrm{P}{\mathrm{r}}_4\mathrm{N}{\mathrm{i}}_3{\mathrm{O}}_8$ features quasi-two-dimensional layers consisting of three stacked square-planar $\mathrm{Ni}{\mathrm{O}}_2$ planes, in a similar way to the well-known cuprate superconductors. The mixed-valent nature of Ni and its metallic properties makes it a candidate for potentially unconventional superconductivity. We have synthesized $\mathrm{P}{\mathrm{r}}_4\mathrm{N}{\mathrm{i}}_3{\mathrm{O}}_8$ by topotactic reduction of $\mathrm{P}{\mathrm{r}}_4\mathrm{N}{\mathrm{i}}_3{\mathrm{O}}_{10}$ in 10% hydrogen gas, and report on measurements of powder-neutron diffraction, magnetization, and muon-spin rotation (µSR). We find that $\mathrm{P}{\mathrm{r}}_4\mathrm{N}{\mathrm{i}}_3{\mathrm{O}}_8$ shows complicated spin-glass behavior with a distinct magnetic memory effect in the temperature range from 2 to 300 K and a freezing temperature $T_s\approx 68\mathrm{K}$. Moreover, the analysis of µSR spectra indicates two magnetic processes characterized by remarkably different relaxation rates: a slowly relaxing signal, resulting from paramagnetic fluctuations of Pr/Ni ions, and a fast-relaxing signal, whose relaxation rate increases substantially below $\approx 70\mathrm{K}$ which can be ascribed to the presence of short-range correlated regions. We conclude that the complex spin-freezing process in $\mathrm{P}{\mathrm{r}}_4\mathrm{N}{\mathrm{i}}_3{\mathrm{O}}_8$ is governed by these multiple magnetic interactions. It is possible that the complex magnetism in $\mathrm{P}{\mathrm{r}}_4\mathrm{N}{\mathrm{i}}_3{\mathrm{O}}_8$ is detrimental to the occurrence of superconductivity.

We report resistance and elastoresistance measurements on $\left({\mathrm{Ba}}_{0.5}{\mathrm{K}}_{0.5}\right){\mathrm{Fe}}_2{\mathrm{As}}_2$, ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$, and ${\mathrm{KCa}}_2{\mathrm{Fe}}_4{\mathrm{As}}_4{\mathrm{F}}_2$. The Fe-site symmetry is $D_{2d}$ in the first compound but $C_{2v}$ in the latter two, which lifts the degeneracy of the Fe $d_{xz}$ and $d_{yz}$ orbitals. The temperature dependence of the resistance and elastoresistance is similar between the three compounds. Especially, the [110] elastoresistance is enhanced with decreasing temperature irrespective of the Fe-site symmetry. This appears to be in conflict with recent Raman scattering studies on ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$, which suggest the absence of nematic fluctuations. We consider possible ways of reconciliation and suggest that the present result is important in elucidating the origin of in-plane resistivity anisotropy in iron-based superconductors.

The antiferromagnetic system on a rare-earth pyrochlore has been focused as a strong candidate of U(1) quantum spin liquid. Here, we study the phase transitions driven by external magnetic field and discuss the thermal Hall effect due to emergent spinon excitations with staggered gauge fields. Despite the spinons, the charge excitations of the effective action that carry spin-1/2 quantum number, do not couple to the external field, the emergent U(1) gauge field is influenced in the presence of external magnetic field. In particular, along the [111] and [110] directions, we discuss the possible phase transitions between U(1) spin liquids with different gauge fluxes are stabilized in fields. Beyond the cases where the gauge flux per plaquette is fixed to be either 0 or $\pi$, there exists a regime where the staggered gauge fluxes are stabilized without time-reversal symmetry. In such a phase, the thermal Hall conductivity ${\kappa }_{xy}/T\sim 4.6\times {10}^{-3}\text{W}/\left({\text{K}}^2\text{m}\right)$ is expected to be measurable below 1 K.

X-ray synchrotron diffraction (XRD) measurements of single-crystal and powder molybdenum disulfide $\mathrm{Mo}{\mathrm{S}}_2$ are performed at pressures (P) up to 78 GPa and temperatures (T) of 20 to 298 K in diamond-anvil cells. The results on single crystals demonstrate a sharp pressure induced isosymmetric phase transition of $2H_c$ to $2H_a$ modification at 23 GPa at 40 and 300 K. The structure of the high-pressure $2H_a$ phase previously inferred theoretically and from powder XRD data is confirmed by our single-crystal XRD data solution, which also definitively determines the atomic potions as a function of pressure. No additional periodicity (commensurate or incommensurate) or distortion is found in the whole P-T range of this study. These results suggest that a previously proposed hypothetic charge-density-wave phase does not host pressure induced superconductivity experimentally found above 90 GPa.

We investigate the temperature dependences of the magnetic properties, electrical resistivity, magnetoresistance, and Hall effect resistivity, ${\rho }_H\left(H\right)$, in thin films of the Heusler-type ${\mathrm{Ni}}_{47.3}{\mathrm{Mn}}_{30.6}{\mathrm{Ga}}_{22.1}$ (at.%) magnetic shape memory alloys epitaxially grown onto a MgO(001) substrate. The results reveal martensitic transformation at about 230 K, premartensitic transition around 285 K, and the Curie temperature of austenite around 380 K. We obtained the coefficients of normal Hall effect (NHE), $R_0$, and anomalous Hall effect (AHE), $R_s$, by fitting the total Hall resistivity curves ${\rho }_H=R_0{B}_z+4\pi R_s{M}_z$ in several magnetic field ranges (0.1–1, 0–5, 8–16, and 0–16 kOe), using experimental magnetization data. Both coefficients $R_0$ and $R_s$ strongly depend on the magnetic field. We also fit the Hall effect resistivity with the expression ${\rho }_H=R_0{B}_z+4\pi R_s{M}_z+\mathrm{\Delta }{\rho }_H$ using the coefficients $R_0$ and $R_s$ obtained from the high-field interval (8–16 kOe), where the last term, $\mathrm{\Delta }{\rho }_H$, was considered to correspond either to the topological Hall effect or to the antiferromagnetic Hall effect. The obtained temperature dependence and magnitude of $\mathrm{\Delta }{\rho }_H$ discard the presence of the skyrmions or antiskyrmions. We conclude that unconventional field dependences of the NHE and AHE coefficients are produced by the antiferromagnetic correlations and the influence of the magnetic field on the electronic structure.

The mixed-spin Ising-Heisenberg and Heisenberg branched chains whose magnetic backbone consists of regularly alternating spins 1/2 and 5/2, the latter of which are additionally coupled to an extra spin 1/2 providing lateral branching, are investigated using exact analytical and density matrix renormalization group (DMRG) methods. The proposed spin-chain models capture some relevant aspects of the heterotrimetallic coordination polymer $\left[\mathrm{Cu}\mathrm{Mn}\left(\mathrm{L}\right)\right]\left[\mathrm{Fe}\left(\mathrm{bpb}\right){\left(\mathrm{CN}\right)}_2\right]·\mathrm{Cl}{\mathrm{O}}_4·{\mathrm{H}}_2\mathrm{O}$. The mixed spin-$(1/2,5/2,1/2)$ Ising-Heisenberg branched chain is exactly solvable under the assumption of an Ising-like exchange coupling along the chain, while the lateral branching is treated as an anisotropic $XXZ$ Heisenberg exchange interaction. We determine the ground-state phase diagram and quantify a bipartite quantum entanglement between dimers at lateral branching. It is shown that the studied mixed-spin Ising-Heisenberg branched chain accurately fits available experimental data for temperature dependence of the magnetic susceptibility. The ground-state phase diagram of the analogous mixed spin-$(1/2,5/2,1/2)$ Heisenberg branched chain is obtained within the DMRG method. The ground-state phase diagrams of the Ising-Heisenberg and its full Heisenberg counterpart are contrasted. In particular, the ground-state phase diagram of the mixed-spin Heisenberg branched chain involves a special Gaussian critical point, for which a proper finite-size scaling analysis is provided to accurately estimate its location and the correlation length critical exponent.