We analyze the superconducting gap in semiconductor/superconductor nanowires under orbital effects of a magnetic field in the weak- and strong-hybridization regime using a universal procedure which guarantees the stationarity of the system, i.e., vanishing of the supercurrent induced by a spatially varying vector potential. We perform minimization of the free energy with respect to the vector potential which allows for taking into account the orbital effects even for systems with intrinsically broken spatial symmetry. For the experimentally relevant scenario of a strongly coupled semiconductor/superconductor system, where the wave function of the charge carriers hybridizes between the two materials, we find that the gap closes due to the orbital effects in a sizable magnetic field in correspondence with the recent experiment [S. M. Albrecht et al., Nature (London) 531, 206 (2016)].

We use both classical magnetotransport and quantum oscillation measurements to study the thickness evolution of the extremely large magnetoresistance (XMR) material and type-II Weyl semimetal candidate $\gamma \text{−}\mathrm{MoT}{\mathrm{e}}_2$, protected from oxidation. We find that the magnetoresistance is systematically suppressed with reduced thickness. This occurs concomitantly with both a decrease in carrier mobility and increase in electron-hole imbalance. We model the two effects separately and conclude that the XMR effect is more sensitive to the former.

Faraday rotation is a fundamental property present in all nonreciprocal optical elements. In the THz range, graphene displays strong Faraday rotation; unfortunately, it is limited to frequencies below the cyclotron resonance. Here, we show experimentally that in specifically designed metasurfaces, magnetoplasmons can be used to circumvent this limitation. We find excellent agreement between theory and experiment and provide physical insights and predictions on these phenomena. Finally, we demonstrate strong tunability in these metasurfaces using electric and magnetic field biasing.

The absorption of a photon and the emission of an electron is not a simple, two-particle process. The complicated many-electron features observed during core photoionization can therefore reveal many of the hidden secrets about the ground and excited-state electronic structures of a material. Careful analysis of the photon-energy dependence of the Ni KLL Auger deexcitation spectra at and above the Ni $1s$ photoionization threshold has identified the satellite structure that appears in both the photoelectron emission and the x-ray absorption spectra of NiO as Ni metal $3d{e}_g\to \mathrm{Ni}$ metal $3d{e}_g$ and O ligand $2p{e}_g\to \mathrm{Ni}$ metal $3d{e}_g$ charge-transfer excitations, respectively. These assignments elucidate the conflicting theoretical predictions of the last five decades in addition to other anomalous effects in the spectroscopy of this unique material.

We describe and implement a first-principles algorithm based on maximally localized Wannier functions for calculating the shift-current response of piezoelectric crystals in the independent-particle approximation. The proposed algorithm presents several advantages over existing ones, including full gauge invariance, low computational cost, and a correct treatment of the optical matrix elements with nonlocal pseudopotentials. Band-truncation errors are avoided by a careful formulation of $k·p$ perturbation theory within the subspace of wannierized bands. The needed ingredients are the matrix elements of the Hamiltonian and of the position operator in the Wannier basis, which are readily available at the end of the wannierization step. If the off-diagonal matrix elements of the position operator are discarded, our expressions reduce to the ones that have been used in recent tight-binding calculations of the shift current. We find that this “diagonal” approximation can introduce sizable errors, highlighting the importance of carefully embedding the tight-binding model in real space for an accurate description of the charge transfer that gives rise to the shift current.

We introduce a family of commuting-projector Hamiltonians whose degrees of freedom involve ${\mathbb{Z}}_3$ parafermion zero modes residing in a parent fractional-quantum-Hall fluid. These commuting-projector models inherit nontrivial Hall conductance from the parent quantum-Hall states in which they are defined, and thus can describe chiral topological phases. The two simplest models in this family emerge from dressing Ising-paramagnet and toric-code spin models with parafermions; we study their edge properties, anyonic excitations, and ground-state degeneracy. We show that the first model realizes a symmetry-enriched topological phase (SET) for which ${\mathbb{Z}}_2$ spin-flip symmetry from the Ising paramagnet permutes the anyons. Interestingly, the interface between this SET and the parent quantum-Hall phase realizes symmetry-enforced ${\mathbb{Z}}_3$ parafermion criticality with no fine-tuning required. The second model exhibits a non-Abelian phase that is consistent with $\text{SU}{\left(2\right)}_4$ topological order, and can be accessed by gauging the ${\mathbb{Z}}_2$ symmetry in the SET. Employing Levin-Wen string-net models with ${\mathbb{Z}}_2$-graded structure, we generalize this picture to construct a large class of commuting-projector models for ${\mathbb{Z}}_2$ SETs and non-Abelian topological orders exhibiting the same relation. Our construction provides the first commuting-projector-Hamiltonian realization of chiral bosonic non-Abelian topological order.

Electron bilayers in a strong magnetic field exhibit insulating behavior for a wide range of interlayer separation $d$ for total Landau level fillings $\nu \le 1/2$, which has been interpreted in terms of a pinned crystal. We study theoretically the competition between many strongly correlated liquid and crystal states and obtain the phase diagram as a function of quantum well width and $d$ for several filling factors of interest. We predict that three crystal structures can be realized: (i) At small $d$, the so-called triangular Ising antiferromagnetic (TIAF) crystal is stabilized, in which the particles overall form a single-layer-like triangular crystal while satisfying the condition that no nearest-neighbor triangle has all three particles in the same layer. (ii) At intermediate $d$, a correlated square (CS) crystal is stabilized, in which particles in each layer form a square lattice, with the particles in one layer located directly across the centers of the squares of the other. (iii) At large $d$, we find a bilayer graphene (BG) crystal in which the A and B sites of the graphene lattice lie in different layers. All crystals that we predict are strongly correlated crystals of composite fermions; a theory incorporating only electron Hartree-Fock crystals does not find any crystals besides the “trivial” ones occurring at large interlayer separations for total filling factor $\nu \le 1/3$ (when layers are uncorrelated and each layer is in the long familiar single-layer crystal phase). The TIAF, CS, and BG crystals come in several varieties, with different flavors of composite fermions and different interlayer correlations. The appearance of these exotic crystal phases adds to the richness of the physics of electron bilayers in a strong magnetic field, and also provides insight into experimentally observed bilayer insulators as well as transitions within the insulating part of the phase diagram.

We investigate a many-body localization transition based on Boltzmann transport theory. Introducing weak-localization corrections into a Boltzmann equation, Hershfield and Ambegaokar rederived the Wolfle-Vollhardt self-consistent equation for the diffusion coefficient [Phys. Rev. B 34, 2147 (1986)]. We generalize this Boltzmann equation framework, introducing electron-electron interactions into the Hershfield-Ambegaokar Boltzmann transport theory based on the study of Zala-Narozhny-Aleiner [Phys. Rev. B 64, 214204 (2001)]. Here, not only Altshuler-Aronov corrections but also dephasing effects are taken into account. As a result, we obtain a self-consistent equation for the diffusion coefficient in terms of the disorder strength and temperature, which extends the Wolfle-Vollhardt self-consistent equation in the presence of electron correlations. Solving our self-consistent equation numerically, we find a many-body localization insulator-metal transition, where a metallic phase appears from dephasing effects dominantly instead of renormalization effects at high temperatures. Although this mechanism is consistent with that of recent seminal papers [Ann. Phys. (NY) 321, 1126 (2006); Phys. Rev. Lett. 95, 206603 (2005)], we find that our three-dimensional metal-insulator transition belongs to the first-order transition, which differs from the Anderson metal-insulator transition described by the Wolfle-Vollhardt self-consistent theory. We speculate that a bimodal distribution function for the diffusion coefficient is responsible for this first-order phase transition.

Spin valve devices, the resistive state of which is controlled by switching the magnetization of a free ferromagnetic layer with respect to a pinned ferromagnetic layer, rely on the scattering of electrons within the active medium to work. Here we demonstrate spin-valve-like effect in the Ni-Mn-In thin films, which consists of a ferromagnetic phase embedded in an antiferromagnetic matrix. Through transport and magnetic measurements, we confirm that scattering at the interfaces between the two phases gives rise to a unidirectional anisotropy and the spin-valve-like effect in this system. The magnitude of the spin-valve-like magnetoresistance (about 0.4% at 10 K) is stable within the temperature range of $10–400$ K. The low- and high-resistance states cannot be destroyed even under a high magnetic field of 100 kOe. This finding opens up a way of realizing the spin valve effect in materials with competing ferromagnetic and antiferromagnetic interactions, where the interface between these phases acts as the active medium.

The electronic phase separation (EPS) of optimally doped ${\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}\mathrm{Mn}{\mathrm{O}}_3$ (LCMO) thin films under various degrees of anisotropic strain is investigated by static magnetotransport and dynamic relaxation measurements. Three LCMO films were grown simultaneously on (001) $\mathrm{NdGa}{\mathrm{O}}_3$ substrates by pulsed laser deposition, and then postgrowth annealed at $780{}^{\circ }\mathrm{C}$ in ${\mathrm{O}}_2$ for different durations of time. With increasing annealing time, the films developed significant strains of opposite signs along the two orthogonal in-plane directions. The static temperature-dependent resistivity, $\rho \left(T\right)$, was measured simultaneously along the two orthogonal directions. With increasing annealing time, both zero-field-cooled and field-cooled $\rho \left(T\right)$ show significant increases, suggesting strain-triggered EPS and appearance of antiferromagnetic insulating (AFI) phases in a ferromagnetic metallic (FMM) ground state. Meanwhile, $\rho \left(T\right)$ along the tensile-strained [010] direction becomes progressively larger than that along the compressive-strained [100]. The enhanced resistivity anisotropy indicates that the EPS is characterized by phase-separated FMM entities with a preferred orientation along [100], possibly due to the cooperative deformation and rotation/tilting of the $\mathrm{Mn}{\mathrm{O}}_6$ octahedra under the enhanced anisotropic strain. The anisotropic EPS can also be tuned by an external magnetic field. During a field cycle at several fixed temperatures, the AFI phases are melted at high fields and recovered at low fields, resulting in sharp resistance changes of ratio as high as ${10}^4$. Furthermore, the resistivity was found to exhibit glasslike behavior, relaxing logarithmically in the phase-separated states. Fitting the data to a phenomenological model, the resulting resistive viscosity and characteristic relaxation time are found to evolve with temperature, showing a close correlation with the static measurements in the EPS states.

Here we study the renormalization group flow of $SU\left(N\right)\times U\left(1\right)$ gauge theory with $M$-fundamental bosons in $4-\epsilon$ dimension by calculating the beta functions. We found a new stable fixed point in the zero mass plane for $M>M_{\mathrm{crit}}$ by expanding up to $O\left(\epsilon \right)$. This indicates a second-order phase transition. We also calculated the critical exponents in both $\epsilon$ expansion and also in the large-$M$ expansion.

The trilayer and pentalayer spin valve structures are revisited to determine the behavior of pair correlations and Josephson current when the magnetic layers are canted at arbitrary angle. The two systems display markedly different behaviors in the center magnetic layer. While the trilayer generates a triplet component that is weakly affected by canting, the pentalayer tunes in singlet pair correlations depending heavily on canting. We also show that a minimum with depleted $m=\pm 1$ triplet components, rather than a $0–\pi$ transition, may be observed in the current profile $I_c\left(d_{\text{F}}\right)$ of a trilayer spin valve. The depleted-triplet minimum is directly attributable to a decrease of $m=\pm 1$ triplet correlations with increased thickness of the central ferromagnet, accompanied by a hidden, simultaneous sign change of the Gor'kov functions contributed from the left and right superconductors. We introduce a toy model for superconducting-magnetic proximity systems to better illuminate the behavior of individual components of the Gor'kov function and compare with a full numerical calculation.

We numerically examine the manipulation of superconducting vortices interacting with a moving trap representing a magnetic force tip translating across a superconducting sample containing a periodic array of pinning sites. As a function of the tip velocity and coupling strength, we find five distinct dynamic phases, including a decoupled regime where the vortices are dragged a short distance within a pinning site, an intermediate coupling regime where vortices in neighboring pinning sites exchange places, an intermediate trapping regime where individual vortices are dragged longer distances and exchange modes of vortices occur in the surrounding pins, an intermittent multiple trapping regime where the trap switches between capturing one or two vortices, and a strong coupling regime in which the trap permanently captures and drags two vortices. In some regimes we observe the counterintuitive behavior that slow moving traps couple less strongly to vortices than faster moving traps; however, the fastest moving traps are generally decoupled. The different phases can be characterized by the distances the vortices are displaced and the force fluctuations exerted on the trap. We find different types of stick-slip motion depending on whether vortices are moving into and out of pinning sites, undergoing exchange, or performing correlated motion induced by vortices outside of the trap. Our results are general to the manipulation of other types of particle-based systems interacting with periodic trap arrays, such as colloidal particles or certain types of frictional systems.

Tempted by the progress in measurements of transport properties of ultracold atomic system and by the experimental methods of creating artificial gauge potentials, we study the Hall conductivity of strongly interacting bosonic particles in a lattice. We use the Haldane-Bose-Hubbard model in the quantum rotor approach to obtain a dependence of the Hall conductivity on the temperature, frequency, and model parameters. We identify two types of excitations contributing to the Hall conductivity, a generation of particle-hole pairs and a coupling of the thermally excited quasiparticles to the external field. We observe a strong influence of the Berry curvature on the transverse transport.

We propose a protocol to locally detect the Berry curvature of the ground state of a three-terminal Josephson junction with a quantum dot based on a synchronic detection of the currents flowing into the reservoir leads when an ac modulation is applied in the device. This local gauge invariant quantity is expressed in terms of the instantaneous Green's function of the Bogoliubov–de Gennes Hamiltonian, and thus correctly accounts for the topological contribution from both the quasiparticle continuum and the Andreev bound states of the junction. We analyze the contribution to the Berry curvature from the latter by introducing an effective low-energy model. In addition, we propose to induce topological properties in the system by breaking time-reversal symmetry with a microwave field in the large frequency nonresonant regime. In the last case, the Floquet-Andreev levels are the ones that determine the topological structure of the junction, which is formally equivalent to a two-dimensional honeycomb Haldane lattice and provides a realization of this celebrated model in a solid state device. A relation between the Floquet Berry curvature and the transconductance of the driven system is derived.

The orthorhombic rare-earth manganate ${\mathrm{Eu}}_{1-x}{\mathrm{Ho}}_x{\mathrm{MnO}}_3$ ($x\ge 0.15$) exhibits multiferroism below $T_{\text{MF}}$ $\sim 25\mathrm{K}$, with a static electric polarization caused by a cycloidal spin order. We observe transient disorder effects in the crystal lattice in a very narrow temperature interval at the onset of the multiferroic ordering. This disorder manifests itself in a distinct transitory violation of the symmetry selection rules for lattice vibration modes in Raman spectroscopy: polarized Raman spectra show a clear increase of the intensity of symmetry-forbidden phonon modes. Possible scenarios of transient disorder in a narrow temperature range are discussed, with special reference to the development of 90° domain walls in ${\mathrm{Eu}}_{1-x}{\mathrm{Ho}}_x{\mathrm{MnO}}_3$, which are associated with the onset of a spontaneous reorientation of the spin cycloids with decreasing temperature.

Lattice thermal conductivities ${\kappa }_{\mathrm{L}}$ of type-I clathrates encapsulating “off-center” guest atoms behave in a way that is sharply different from those of conventional crystals such as on-center type-I clathrates. The latter decreases with increasing temperature according to $1/T$ above a few tens K, while ${\kappa }_{\mathrm{L}}$ of off-center clathrates increase $T$ linearly above a few tens of K. Further increasing temperature above $T\gtrsim 100\mathrm{K}$, ${\kappa }_{\mathrm{L}}$ saturates without exhibiting appreciable $T$ dependence. In this temperature regime, the standard formulation of ${\kappa }_{\mathrm{L}}$ based on the perturbation theory is unfeasible. We herein present a theory of ${\kappa }_{\mathrm{L}}$ based on a “nonperturbative” approach by taking into account the interaction between nonvibrational off-center rattling states of guest atoms and cage shells. It is remarkable that our theory shows excellent agreement with observed ${\kappa }_{\mathrm{L}}\left(T\right)$ for off-center clathrates in magnitudes, the cage volume $\mathrm{\Omega }$ dependence, and $T$ dependence.