Structural behavior of $\mathrm{Pb}{\mathrm{Mn}}_7{\mathrm{O}}_{12}$ has been studied by high resolution synchrotron x-ray powder diffraction. This material belongs to a family of quadruple perovskite manganites that exhibit an incommensurate structural modulation associated with an orbital density wave. It has been found that the structural modulation in $\mathrm{Pb}{\mathrm{Mn}}_7{\mathrm{O}}_{12}$ onsets at 294 K with the incommensurate propagation vector ${\mathbf{k}}_s=(0,0,\sim 2.08)$. At 110 K another structural transition takes place where the propagation vector suddenly drops down to a quasicommensurate value ${\mathbf{k}}_s=(0,0,2.0060\left(6\right))$. The quasicommensurate phase is stable in the temperature range of 40–110 K, and below 40 K the propagation vector jumps back to the incommensurate value ${\mathbf{k}}_s=(0,0,\sim 2.06)$. Both low temperature structural transitions are strongly first order with large thermal hysteresis. The orbital density wave in the quasicommensurate phase has been found to be substantially suppressed in comparison with the incommensurate phases, which naturally explains unusual magnetic behavior recently reported for this perovskite. Analysis of the refined structural parameters revealed that that the presence of the quasicommensurate phase is likely to be associated with a competition between the ${\mathrm{Pb}}^{2+}$ lone electron pair and ${\mathrm{Mn}}^{3+}$ Jahn-Teller instabilities.

We report the experimental results of magnetotransport on the single crystal ${\mathrm{MoGe}}_2$, which was theoretically predicated to be a topological insulator. The resistivity of ${\mathrm{MoGe}}_2$ exhibits a metallic behavior at zero field, while with magnetic fields applied along the $z$ axis and perpendicular to current, ${\mathrm{MoGe}}_2$ presents an upturn resistivity behavior and unsaturated quadratic large magnetoresistance (MR). The analysis of Hall effect shows that ${\mathrm{MoGe}}_2$ is a compensated semimetal with high mobilities at low temperatures, which is the origin of resistivity upturn and unsaturated large MR. As magnetic fields parallel to current, ${\mathrm{MoGe}}_2$ shows a weak antilocalization effect at low fields and a pronounced negative MR at higher fields, which is analogous to the picture of the Adler-Bell-Jackiw axial anomaly. Our results indicate that ${\mathrm{MoGe}}_2$ is a topological semimetal rather than a topological insulator, and will encourage further theoretical and experimental investigations on this compound.

Angle-dispersive x-ray powder diffraction experiments have been performed on neodymium metal to a pressure of 302 GPa. Up to 70 GPa we observe the $hP4\to cF4\to hR24\to oI16\to hP3$ transition sequence reported previously. At 71(2) GPa we find a transition to a phase which has an orthorhombic structure ($oF8$) with eight atoms in the unit cell, space group $Fddd$. This structure is the same as that recently observed in samarium above 93 GPa, and is isostructural with high-pressure structures found in the actinides Am, Cf, and Cm. We see a further phase transition at 98(1) GPa to a phase with the orthorhombic $\alpha$-U ($oC4$) structure, which remains stable up to 302 GPa, the highest pressure reached in this study. Electronic structure calculations find the same structural sequence, with calculated transition pressures of 66 and 88 GPa, respectively, for the $hP3\to F8$ and $oF8\to oC4$ transitions. The calculations further predict that $oC4$-Nd loses its magnetism at 100 GPa, in agreement with previous experimental results, and it is the accompanying decrease in enthalpy and volume that results in the transition to this phase. Comparison calculations on the $oF8$ and $oC4$ phases of Sm show that they both retain their magnetism to at least 240 GPa, with the result that $oC4$-Sm is calculated to have the lowest enthalpy over a narrow pressure region near 200 GPa at 0 K.

We study many-body localization (MBL) in a pair-hopping model exhibiting strong fragmentation of the Hilbert space. We show that several Krylov subspaces have both ergodic statistics in the thermodynamic limit and a dimension that scales much slower than the full Hilbert space but still exponentially. Such a property allows us to study the MBL phase transition in systems including up to 64 spins. The different Krylov spaces that we consider show clear signatures of a many-body localization transition, both in the Kullback-Leibler divergence of the distribution of their level spacing ratio and their entanglement properties. However, they also present distinct scalings with the system size. Depending on the subspace, the critical disorder strength can be nearly independent of the system size or conversely show an approximately linear increase with the number of spins.

We take account of normal currents that emerge when vortices move. Abrikosov vortices in the bulk and Pearl vortices in thin films are considered. Velocity-dependent distributions of both normal and persistent currents are studied in the frame of time-dependent London equations. In thin films near the Pearl vortex core, these distributions are intriguing in particular.

Single-photon detectors have typically consisted of macroscopic materials where both the photon absorption and transduction to an electrical signal happen. Newly proposed designs suggest that large arrays of nanoscale detectors could provide improved performance in addition to decoupling the absorption and transduction processes. Here we study the properties of such a detector consisting of a nanoscale superconducting (SC) transport channel functionalized by a photon absorber. We explore two detection mechanisms based on photoinduced electrostatic gating and magnetic effects. To this end we model the narrow channel as a one-dimensional atomic chain and use a self-consistent Keldysh-Nambu Green's function formalism to describe nonequilibrium effects and SC phenomena. We consider cases where the photon creates electrostatic and magnetic changes in the absorber, as well as devices with strong and weak coupling to the metal leads. Our results indicate that the most promising case is when the SC channel is weakly coupled to the leads and in the presence of a background magnetic field, where photoexcitation of a magnetic molecule can trigger a SC-to-normal transition in the channel that leads to a change in the device current several times larger than in the case of a normal-phase channel device.

The first-order liquid-liquid phase transition (LLPT) describes the counterintuitive nature between two distinct liquids in a single system. However, the physical understanding of LLPT in simple liquid mixtures has remained elusive. Here, a first-order LLPT for nitrogen-oxygen (N-O) mixtures is investigated via extensive ab initio molecular dynamics simulations. The first-order LLPT is characterized by discontinuities of a short-range order and transport properties, occurring at the transition pressures identified by looking at isotherms. The LLPT in N-O mixtures is dominated primarily by the molecular-to-polymeric transformation. The resulting phase boundaries and further structural analysis show the crucial influence of oxygen on weakening the LLPT of N-O mixtures by promoting chemical reactions with nitrogen and crippling polymerizations. Furthermore, noncovalent interactions of short- to long-range van der Waals have evident impacts on the LLPT boundary. The introduction of the strongly constrained and appropriately normed functional with revised Vydrov–van Voorhis nonlocal correlation (SCAN-$r\mathrm{VV}10$) functional to describe the phase-transition behaviors improves the agreement with experimental data. The results highlight the characteristic features of the complex interplay in binary mixtures and revisit the first-order phase transition of dense nitrogen.

We show that a one-dimensional disordered conductor with correlated disorder has an extended state and a Landauer resistance that is nonzero in the limit of infinite system size in contrast to the predictions of the scaling theory of Anderson localization. The delocalization transition is not related to any underlying symmetry of the model such as particle-hole symmetry. Moreover, the form of correlated disorder considered here is distinct from other models with delocalization transitions that have been considered in the literature. For a wire of finite length the effect manifests as a sharp transmission resonance that narrows as the length of the wire is increased. Experimental realizations and applications are discussed including the possibility of constructing a narrow-band light filter.

The nonequilibrium dynamics of two-dimensional Su-Schrieffer-Heeger model, in the presence of staggered chemical potential, is investigated using the notion of dynamical quantum phase transition. We contribute to expanding the systematic understanding of the interrelation between the equilibrium quantum phase transition and the dynamical quantum phase transition (DQPT). Specifically, we find that dynamical quantum phase transition relies on the existence of massless propagating quasiparticles as signaled by their impact on the Loschmidt overlap. These massless excitations are a subset of all gapless modes, which leads to quantum phase transitions. The underlying two-dimensional model reveals gapless modes, which do not couple to the dynamical quantum phase transitions, while relevant massless quasiparticles present periodic nonanalytic signatures on the Loschmidt amplitude. The topological nature of DQPT is verified by the quantized integer values of the topological order parameter, which gets even values. Moreover, we have shown that the dynamical topological order parameter truly captures the topological phase transition on the zero Berry curvature line, where the Chern number is zero and the two-dimensional Zak phase is not the proper indicator.

Effects of interfacial Dzyaloshinskii-Moriya interaction (IDMI) on current-driven dynamics of ${180}^{\circ }$ domain walls (180DWs) in long and narrow spin valves (LNSVs) with heavy-metal cap layers are investigated. We focus on LNSVs with in-plane magnetic anisotropy in their free layers. For planar-transverse polarizers (pinned layers of LNSVs), the Walker breakdown is postponed considerably (practical infinity) by IDMI. More interestingly, the originally unstable traveling mode is stabilized by IDMI regardless of the polarization magnitude while bearing a high saturated velocity and thus can serve as a fast carrier of information. For parallel polarizers, the Walker limit is increased, and the corresponding modifications of IDMI to wall velocity in both steady and precessional flows of 180DWs are provided. As for perpendicular polarizers, precessional flow of 180DWs is absent due to the stability of the stationary mode beyond the modified Walker limit. Similar results are obtained for LNSVs with perpendicular magnetic anisotropy in their free layers. Our findings open possibilities for developing magnetic nanodevices based on 180DW propagation with low energy consumption and high robustness.

In recent years several experimental observations and theoretical predictions of unique phenomena involving the interplay between spin currents and the coupled magnetization-elastic dynamics have invigorated the field of spintronics. One important experiment reported several years ago showed that elastic waves can produce spin pumping, that is, generation of spin currents in a metallic film in contact with a ferromagnetic material. Very recently the Onsager reciprocal of this effect has been observed in samples made of a film of the insulating ferrimagnet yttrium iron garnet in contact with a platinum strip with nanoscopic silver particles that is known to exhibit a giant spin Hall effect. By passing an electric current through the metallic strip, the spin current generated by the spin Hall effect produces a large magnonic spin current that excites phonons with microwave frequency, observed by Brillouin light scattering. Here we show that these experiments are explained by a theory based on a process in which one magnon in the spin current creates one phonon and another magnon, with conservation of energy and momentum. The theoretical value of the critical charge current in the metallic strip necessary to drive phonons and the values of the phonon frequencies are in good agreement with the values measured experimentally.

We show that the general low-energy Bogoliubov–de Gennes Hamiltonian in a multiband superconductor with broken time-reversal and preserved inversion symmetry is a generator of a real four-dimensional representation of $SO\left(4\right)$. In the particular representation such an effective Hamiltonian is a purely imaginary matrix, and it is proportional to the antisymmetric tensor of a fictitious electromagnetic field which one can define in the momentum space. The quantum time evolution of the low-energy quasiparticle state becomes this way closely related to the classical relativistic motion of a charged particle in the presence of the Lorentz force that would be derived from such an electromagnetic field configuration. The condition for the emergence of a Bogoliubov-Fermi surface can then be understood as orthogonality of the fictitious electric and magnetic fields, which would allow zero Lorentz force. The corresponding zero-energy eigenstates are identified as the physical timelike and the unphysical spacelike solutions of the Lorentz force equation. We study the looming instability of the inversion-symmetric Bogoliubov-Fermi surface in the presence of electron-electron interaction by formulating a concrete interacting model on the Lieb lattice that features the requisite $SO\left(4\right)$ kinetic energy term together with nearest-neighbor two-body repulsion. The latter is shown to favor dynamical breaking of the inversion symmetry. The inversion symmetry in our lattice model indeed becomes spontaneously broken at zero temperature at infinitesimal repulsion, with the original Bogoliubov-Fermi surface deformed and reduced in size. General features of this symmetry-breaking phenomenon are discussed and a comparison with other works in the literature is presented.

We describe a construction of topological orders from coupled lower-dimensional symmetry-protected topological orders, which is closely related to gauging a subsystem symmetry. Our construction yields both conventional topological orders and exotic fracton topological orders of type-I and type-II. In particular, we find a coupled spin-chain construction of Haah's cubic code, and a coupled-layer construction of Yoshida's fractal spin liquids.

Moiré superlattices of transition metal dichalcogenide (TMD) bilayers have been shown to host correlated electronic states, which arise from the interplay of long wavelength moiré potential and long-range Coulomb interaction. Here, we theoretically investigate structural relaxation and single-particle electronic structure of twisted TMD homobilayer. From the large-scale density functional theory calculation and continuum model with layer degrees of freedom, we find that the out-of-plane gating field creates a tunable charge transfer gap at the Dirac point between the first and second moiré valence bands. We further study the charge orders at the fractional band fillings. In the flat band limit, we find from Monte Carlo simulations a series of charge-ordered insulating states at various fillings $n=\frac{1}{4},\frac{1}{3},\frac{1}{2},\frac{2}{3},1$. We predict that gating field induces a phase transition between different electron crystals at fixed filling $n=\frac{1}{2}$ or $\frac{2}{3}$. At half-filling $n=1$, the ground state is a Mott insulator with electronically driven ferroelectricity. This work demonstrates that TMD homobilayer provides a powerful platform for the investigation of tunable charge transfer insulator and charge orders.

We continue recent efforts to discover examples of deconfined quantum criticality in one-dimensional models. In this work we investigate the transition between a ${\mathbb{Z}}_3$ ferromagnet and a phase with valence bond solid (VBS) order in a spin chain with ${\mathbb{Z}}_3\times {\mathbb{Z}}_3$ global symmetry. We study a model with alternating projective representations on the sites of the two sublattices, allowing the Hamiltonian to connect to an exactly solvable point having VBS order with the character of $SU(3)$-invariant singlets. Such a model does not admit a Lieb-Schultz-Mattis theorem typical of systems realizing deconfined critical points. Nevertheless, we find evidence for a direct transition from the VBS phase to a ${\mathbb{Z}}_3$ ferromagnet. Finite-entanglement scaling data are consistent with a second-order or weakly first-order transition. We find in our parameter space an integrable lattice model apparently describing the phase transition, with a very long, finite, correlation length of 190878 lattice spacings. Based on exact results for this model, we propose that the transition is extremely weakly first order and is part of a family of deconfined quantum critical points described by walking of renormalization group flows.

We present a theory of conducting quantum networks that accounts for Abelian and non-Abelian fields acting on spin carriers. We apply this approach to model the conductance of mesoscopic spin interferometers of different geometry (such as squares and rings), reproducing recent experimental findings in nanostructured InAsGa quantum wells subject to Rashba spin-orbit and Zeeman fields (as, e.g., the manipulation of Aharonov-Casher interference patterns by geometric means). Moreover, by introducing an additional field-texture engineering, we manage to single out a previously unnoticed spin-phase suppression mechanism. We notice that our approach can also be used for the study of complex networks and the spectral properties of closed systems.

In this paper, we study gapless fermionic and bosonic systems in $d$-dimensional continuum space with $U\left(1\right)$ particle-number-conservation and ${\mathbb{R}}^d$ translation symmetry. We present low-energy effective field theories for several gapless phases with the $U\left(1\right)\times {\mathbb{R}}^d$ symmetry. The $U\left(1\right)\times {\mathbb{R}}^d$ symmetry has a property that a $U\left(1\right)$ symmetry twist will induce a nonzero momentum proportional to the $U\left(1\right)$ charge density $\overline{\rho }$, which will be referred to as a mixed anomaly. The different effective field theories for different phases of the same system must have the same mixed anomaly. As a result, all the low-energy effective field theories must have fields with nonzero momenta of the order of ${\overline{\rho }}^{1/d}$. In particular, we present a low-energy effective field theory with infinite number of fields for Fermi liquid. We also present the Fermi-liquid effective field theory in the presence of a real space magnetic field and $\mathit{k}$-space “magnetic” field, as well as in the presence of interaction described by Landau parameters. Our effective field theory correctly captures the mixed anomaly, which constrains the low-energy dynamics, such as determines the volume of the Fermi surface in terms of the mixed anomaly [i.e., in terms of the $U\left(1\right)$ charge density]. This is another formulation of the Luttinger-Ward-Oshikawa theorem.

Friedel oscillation is a well-known wave phenomenon which represents the oscillatory response of electron waves to imperfection. By utilizing the pseudospin-momentum locking in gapless graphene, two recent experiments demonstrate the measurement of the topological Berry phase by corresponding to the unique number of wavefront dislocations in Friedel oscillations. Here, we study the Friedel oscillations in gapped graphene, in which the pseudospin-momentum locking is broken. Unusually, the wavefront dislocations do occur like that in gapless graphene, which requires immediate verification in the current experimental condition. The number of wavefront dislocations is ascribed to the invariant pseudospin winding number in gapped and gapless graphene. This study deepens the understanding of the correspondence between topological quantity and wavefront dislocations in Friedel oscillations and implies the possibility to observe the wavefront dislocations of Friedel oscillations in intrinsic gapped two-dimensional materials, e.g., transition metal dichalcogenides.

For broad nanoscale applications, it is crucial to implement more functional properties, especially ferroic orders, into two-dimensional materials. Here, ${\mathrm{GdI}}_3$ is theoretically identified as a honeycomb antiferromagnet with a large $4f$ magnetic moment. The intercalation of metal atoms can dope electrons into Gd's $5d$ orbitals, which alters its magnetic state and leads to a Peierls transition. Due to strong electron-phonon coupling, the Peierls transition induces prominent ferroelasticity, making it a multiferroic system. The strain from unidirectional stretching can be self-relaxed via the resizing of triple ferroelastic domains, which can protect the magnet against mechanical breaking in flexible applications.

Recent studies revealed that the electric multipole moments of insulators result in fractional electric charges localized to the hinges and corners of the sample. We here explore the magnetic analog of this relation. We show that a collinear antiferromagnet with spin $S$ defined on a $d$-dimensional cubic lattice features fractionally quantized magnetization $M_{\text{c}}^z=S/2^d$ at the corners. We find that the quantization is robust even in the presence of gapless excitations originating from the spontaneous formation of the Néel order, although the localization length diverges, suggesting a power-law localization of the corner magnetization. When the spin rotational symmetry about the $z$ axis is explicitly broken, the corner magnetization is no longer sharply quantized. Even in this case, we numerically find that the deviation from the quantized value is negligibly small based on quantum Monte Carlo simulations.