We investigate the light-matter interaction between the edge state of a 2D topological insulator and quantum electromagnetic field. The interaction originates from the Zeeman term between the spin of the edge electrons and the magnetic field, and also through the Peierls substitution. The continuous U(1) symmetry of the system in the absence of the vector potential reduces into discrete time reversal symmetry in the presence of the vector potential. Due to light-matter interaction, a superradiant ground state emerges with spontaneously broken time reversal symmetry, accompanied by a net photocurrent along the edge, generated by the vector potential of the quantum light. The spectral function of the photon field reveals polariton continuum excitations above a threshold energy, corresponding to a Higgs mode and another low energy collective mode due to the phase fluctuations of the ground state. This collective mode is a zero energy Goldstone mode that arises from the broken continuous U(1) symmetry in the absence of the vector potential and acquires finite a gap in the presence of the vector potential. The optical conductivity of the edge electrons is calculated using the random phase approximation by taking the fluctuation of the order parameter into account. It contains the collective modes as a Drude peak with renormalized effective mass, which moves to finite frequencies as the symmetry of the system is lowered by the inclusion of the vector potential.

We construct a family of two-dimensional non-Abelian topological phases from coupled wires using a non-Abelian bosonization approach. We then demonstrate how to determine the nature of the non-Abelian topological order (in particular, the anyonic excitations and the topological degeneracy on the torus) realized in the resulting gapped phases of matter. This paper focuses on the detailed case study of a coupled-wire realization of the bosonic $su{\left(2\right)}_2^{}$ Moore-Read state, but the approach we outline here can be extended to general bosonic $su{\left(2\right)}_k^{}$ topological phases described by non-Abelian Chern-Simons theories. We also discuss possible generalizations of this approach to the construction of three-dimensional non-Abelian topological phases.

We show the significant impact of weak disorder on the Mott transition by investigating electronic transport in a systematically x-ray-irradiated layered organic conductor under continuous pressure control. The critical end point of the first-order Mott transition is dramatically suppressed by such weak disorder that causes only a minor reduction in the transition temperature of disorder-sensitive nodal superconductivity. Instead, quantum critical scaling of resistance holds at lower temperatures and Fermi-liquid coherence temperature on the metallic side is lowered. Introducing disorder unveils the interaction-induced quantum criticality hidden behind the first-order transition.

The generalized pseudopotential theory (GPT) is a powerful method for deriving real-space transferable interatomic potentials. Using a coarse-grained electronic structure, one can explicitly calculate the pair ion-ion and multi-ion interactions in simple and transition metals. While successful in determining bulk properties, in central force metals the GPT fails to describe crystal defects for which there is a significant local volume change. A previous paper [J. A. Moriarty and R. Phillips, Phys. Rev. Lett. 66, 3036 (1991)] found that by allowing the GPT total energy to depend upon some spatially averaged local electron density, the energetics of vacancies and surfaces could be calculated within experimental ranges. In this paper, we develop the formalism further by explicitly calculating the forces and stress tensor associated with this total energy. We call this scheme the adaptive GPT (aGPT) and it is capable of both molecular dynamics (MD) and molecular statics. We apply the aGPT to vacancy formation, divacancy binding, and stacking faults in hcp Mg. We also calculate the local electron density corrections to the bulk elastic constants and phonon dispersion for which there is refinement over the baseline GPT treatment. In addition, we demonstrate aGPT-MD simulation through the calculation of thermal expansion in magnesium to 700 K.

We investigate phase-coherent thermal transport in Josephson junctions made from unconventional superconductors or superfluids. The thermal conductance is evaluated for one- and two-dimensional junctions within the Bogoliubov–de Gennes formalism. We analyze three different scenarios of junctions between two triplet superconductors with (i) helical pairing, (ii) unitary chiral pairing, and (iii) nonunitary chiral pairing. We find that the phase-dependent thermal conductance allows us to distinguish the different pairings and provides insight into the formation of topologically nontrivial Andreev bound states in the junction.

The anharmonic lattice dynamics of MgO has been studied at ambient conditions and at high temperatures by infrared spectroscopy and inelastic x-ray scattering measurements combined with density functional perturbation theory calculations. The agreement between the measured phonon energies and widths with ab initio calculated values provides a direct and pertinent test of the validity of advanced theoretical methods. Long observed anharmonic features in the infrared reflectivity find a clear explanation in terms of well-defined multiphonon scattering processes and lattice dynamics peculiarities, also responsible for a significant and sharp reduction of the longitudinal optical phonon lifetime at critical finite wave vectors. Our work highlights the importance of multiphonon scattering processes on the collective dynamics and related material properties.

We present the full phase diagram of the dumbbell model of spin ice as a function of temperature, chemical potential and staggered chemical potential which breaks the point group symmetry of the underlying diamond lattice in favor of a magnetic charge crystal. We observe a double winged structure with five possible phases, monopole fluid (spin ice), fragmented single monopole crystal phases, and double monopole crystal, the zinc-blende structure. Our model provides a skeleton for liquid-liquid phase transitions and for the winged structures observed for itinerant magnets under pressure and external field. We relate our results to recent experiments on ${\mathrm{Ho}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ and propose a wide ranging set of new experiments that exploit the phase diagram, including high-pressure protocols, dynamical scaling of Kibble-Zurek form, and universal violations of the fluctuation-dissipation theorem.

Disorder is generically anticipated to suppress long range charge density wave (CDW) order. We report transport, thermodynamic, and scattering experiments on ${\mathrm{Pd}}_x{\mathrm{ErTe}}_3$, a model CDW system with disorder induced by intercalation. The pristine parent compound ($x=0$) shows two separate, mutually perpendicular, incommensurate unidirectional CDW phases setting in at 270 K and 165 K. In this work we present measurements on a finely-spaced series of single crystal samples, in which we track the suppression of signatures corresponding to these two parent transitions as the Pd concentration increases. At the largest values of $x$, we observe complete suppression of long range CDW order in favor of superconductivity. We also report evidence from electron and x-ray diffraction which suggests a tendency toward short-range ordering along both wave vectors which persists even well above the crossover temperature and comment on the origin and consequences of this effect. Based on this work, ${\mathrm{Pd}}_x{\mathrm{ErTe}}_3$ appears to provide a promising model system for the study of the interrelation of charge order and superconductivity in the presence of quenched disorder, for pseudotetragonal materials.

We propose a quantum nondemolition Majorana qubit readout protocol based on parametric modulation of a longitudinal interaction between a pair of Majorana bound states and a resonator. The interaction can be modulated through microwave-frequency gate voltage or flux control of a tunable tunnel barrier. The qubit-resonator coupling is quantum nondemolition to exponential accuracy, a property inherited from the topological nature of the Majorana zero modes. The same mechanism as used for single-qubit readout can also be extended to perform multiqubit measurements and be used to enact long-range entangling gates.

An explanation is proposed for the recently observed in optical spectra of monolayer graphene giant increase in the Drude-peak width under applied uniaxial strain. We argue that the underlying mechanism of this increase can be based on resonant scattering of carriers from inevitably present impurities such as adsorbed atoms that can be described by the Fano-Anderson model. We demonstrate that the often neglected scalar deformation potential plays the essential role in this process. The conditions necessary for the maximum effect of the giant Drude-peak broadening are determined. It is stressed that the effect is strongly enhanced when the Fermi level gets closer to the Dirac point. Our theoretical analysis provides guidelines for functionalizing graphene samples in a way that would allow to modulate efficiently the Drude-peak width by the applied strain.

The Read-Rezayi (RR) parafermion states form a series of exotic non-Abelian fractional quantum Hall (FQH) states at filling $\nu =k/(k+2)$. Computationally, the wave functions of these states are prohibitively expensive to generate for large systems. We introduce a series of parton states, denoted ${\overline{2}}^k{1}^{k+1}$, and show that they lie in the same universality classes as the particle-hole-conjugate RR (“anti-RR”) states. Our analytical results imply that a $[U{\left(1\right)}_{k+1}\times U{\left(2k\right)}_{-1}]/[SU{\left(k\right)}_{-2}\times U{\left(1\right)}_{-1}]$ coset conformal field theory describes the edge excitations of the ${\overline{2}}^k{1}^{k+1}$ state, suggesting nontrivial dualities with respect to previously known descriptions. The parton construction allows wave functions in anti-RR phases to be generated for hundreds of particles. We further propose the parton sequence $\overline{n}{\overline{2}}^2{1}^4$, with $n=1,2,3$, to describe the FQH states observed at $\nu =2+1/2$, $2+2/5$, and $2+3/8$.

A stripe-type magnetic structure and related orbital ordering are universally observed in iron-based superconductors. As an exception, the quasi-one-dimensional ladder material ${\mathrm{BaFe}}_2{\mathrm{Se}}_3$, which shows pressure-induced superconductivity, exhibits a block-type antiferromagnetic ordering. The research of the electronic and structural properties in ${\mathrm{BaFe}}_2{\mathrm{Se}}_3$ at ambient conditions is important to reveal the origin of multiorbital superconductivity. Here, we report the temperature-dependent crystal structure of ${\mathrm{BaFe}}_2{\mathrm{Se}}_3$, combining optical second harmonic generation experiments and neutron diffraction measurements. We elucidate the crystal structure with the $Pmn{2}_1$ space group in the low-temperature phase below $T_{s2}=400$ K, further above the Néel temperature. This low-temperature phase loses spatial inversion symmetry, where a resultant macroscopic polarization emerges along the rung direction. The transition is characterized by block-type lattice distortions possibly accompanied by polar orbital ordering.

We studied the effect of external pressure on the optical response of the nodal-line semimetal candidate ZrSiTe by reflectivity measurements. At pressures of a few GPa, the reflectivity, optical conductivity, and loss function are strongly affected in the whole measured frequency range ($200–16500{\mathrm{cm}}^{-1}$), indicating drastic changes in the electronic band structure. The pressure-induced shift of the electronic bands affects both the intraband and interband transitions. We find anomalies in the pressure dependence of several optical parameters at the pressures $P_{c1}\approx 4.1\mathrm{GPa}$ and $P_{c2}\approx 6.5\mathrm{GPa}$, suggesting the occurrence of two phase transitions of either structural or electronic type.

We propose and analyze a mechanism for rectification of spin transport through a small junction between two spin baths or leads. For interacting baths, we show that transport is conditioned on the spacial asymmetry of the quantum junction mediating the transport, and attribute this behavior to a gapped spectral structure of the lead-system-lead configuration. For noninteracting leads, a minimal quantum model that allows for spin rectification requires an interface of only two interacting two-level systems. In our paper, we have performed a thorough study of the current, including its time dependence and steady-state value. We obtain approximate results with a weak-coupling Born master equation in excellent agreement with matrix-product-state calculations that are extrapolated in time by mimicking absorbing boundary conditions. These results should be observable in controlled spin systems realized with cold atoms, trapped ions, or in electrons in quantum dot arrays.

We investigate two-dimensional compactifications of three-dimensional fractonic stabilizer models. We find the two-dimensional topological phases produced as a function of compactification radius for the $X$-cube model and Haah's cubic code. Furthermore, we uncover translation symmetry enrichment in the compactified cubic code that leads to twisted boundary conditions.

The competition between the Ruderman-Kittel-Kasuya-Yosida effect and Kondo effect is a central subject of the periodic Anderson model. By using the density matrix embedding theory, we study a three-orbital periodic Anderson model, in which the effects of degenerate conduction orbitals, via the local magnetic moments, number of electrons, and spin-spin correlation functions, are investigated. From the phase diagram at half filling, we find there exist two different antiferromagnetic phases and one paramagnetic phase. To explore the difference between the two antiferromagnetic phases, the topology of the Fermi surface and the connection with the standard periodic Anderson model are considered. The spin-spin correlation functions yield insight into the competition between Ruderman-Kittel-Kasuya-Yosida interaction and Kondo interaction. We further find there exist “scaling transformations,” and by applying them to the data with different hybridization strength, all the data collapses. Our calculations agree with previous studies on the standard periodic Anderson model.

We study the topological phase diagram of a setup composed of two nanowires with strong Rashba spin-orbit interaction subjected to an external magnetic field and brought into the proximity to a bulk $s$-wave superconductor in the presence of a supercurrent flowing through it. The supercurrent reduces the critical values of the Zeeman energy and crossed Andreev superconducting pairing required to reach the topological phase characterized by the presence of one Majorana bound state localized at each system end. We demonstrate that, even in the regime of the crossed Andreev pairing being smaller than the direct pairing, a relatively weak magnetic field drives the system into the topological phase due to the presence of the supercurrent.