1,721,888 research outputs found
Superconductivity and Correlated Insulator in Twisted Bilayer Graphene
Full text linkFu, Liang. (2018). Superconductivity and Correlated Insulator in Twisted Bilayer Graphene. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/197538
Odd-parity topological superconductor with nematic order: Application to Cu[subscript x] Bi[subscript 2] Se[subscript 3]
No full textCu[subscript x] Bi[subscript 2] Se[subscript 3] was recently proposed as a promising candidate for time-reversal-invariant topological superconductors. In this work, we argue that the unusual anisotropy of the Knight shift observed by Zheng and co-workers (unpublished), taken together with specific heat measurements, provides strong support for an unconventional odd-parity pairing in the two-dimensional E[subscript u] representation of the D[subscript 3d] crystal point group, which spontaneously breaks the threefold rotational symmetry of the crystal, leading to a subsidiary nematic order. We predict that the spin-orbit interaction associated with hexagonal warping plays a crucial role in pinning the two-component order parameter and makes the superconducting state generically fully gapped, leading to a topological superconductor. Experimental signatures of the E[subscript u] pairing related to the nematic order are discussed.United States. Dept. of Energy. Division of Materials Sciences and Engineering (Award DE-SC0010526
Parity-Breaking Phases of Spin-Orbit-Coupled Metals with Gyrotropic, Ferroelectric, and Multipolar Orders
Full text linkWe study Fermi liquid instabilities in spin-orbit-coupled metals with inversion symmetry. By introducing a canonical basis for the doubly degenerate Bloch bands in momentum space, we derive the general form of Landau interaction functions. A variety of time-reversal-invariant, parity-breaking phases is found, whose Fermi surface is spontaneously deformed and spin split. In terms of symmetry, these phases possess gyrotropic, ferroelectric, and multipolar orders. The ferroelectric and multipolar phases are accompanied by structural distortions, from which the electronic orders can be identified. The gyrotropic phase exhibits a unique nonlinear optical property. We identify correlated electron materials that exhibit these parity-breaking phases, including LiOsO[subscript 3] and Cd[subscript 2]Re[subscript 2]O[subscript 7].David & Lucile Packard Foundatio
Theory of interacting topological crystalline insulators
Full text linkWe study the effect of electron interactions in topological crystalline insulators (TCIs) protected by mirror symmetry, which are realized in the SnTe material class and host multivalley Dirac fermion surface states. We find that interactions reduce the integer classification of noninteracting TCIs in three dimensions, indexed by the mirror Chern number, to a finite group Z[subscript 8]. In particular, we explicitly construct a microscopic interaction Hamiltonian to gap eight flavors of Dirac fermions on the TCI surface, while preserving the mirror symmetry. Our construction builds on interacting edge states of U(1) × Z[subscript 2] symmetry-protected topological phases of fermions in two dimensions, which we classify. Our work reveals a deep connection between three-dimensional topological phases protected by spatial symmetries and two-dimensional topological phases protected by internal symmetries.David & Lucile Packard Foundatio
Anomalous Crystal Symmetry Fractionalization on the Surface of Topological Crystalline Insulators
Full text linkThe surface of a three-dimensional topological electron system often hosts symmetry-protected gapless surface states. With the effect of electron interactions, these surface states can be gapped out without symmetry breaking by a surface topological order, in which the anyon excitations carry anomalous symmetry fractionalization that cannot be realized in a genuine two-dimensional system. We show that for a mirror-symmetry-protected topological crystalline insulator with mirror Chern number n = 4, its surface can be gapped out by an anomalous Z[subscript 2] topological order, where all anyons carry mirror-symmetry fractionalization M[superscript 2] = -1. The identification of such anomalous crystalline symmetry fractionalization implies that in a two-dimensional Z[subscript 2] spin liquid, the vison excitation cannot carry M[superscript 2] = -1 if the spinon carries M[superscript 2] = -1 or a half-integer spin.United States. Dept. of Energy. Division of Materials Sciences and Engineering (Award DE-SC0010526
Detecting crystal symmetry fractionalization from the ground state: Application to Z[subscript 2] spin liquids on the kagome lattice
No full textIn quantum spin liquid states, the fractionalized spinon excitations can carry fractional crystal symmetry quantum numbers, and this symmetry fractionalization distinguishes different symmetry-enriched spin liquid states with identical intrinsic topological order. In this work we propose a simple way to detect signatures of such crystal symmetry fractionalizations from the crystal symmetry representations of the ground state wave function. We demonstrate our method on projected Z[subscript 2] spin liquid wave functions on the kagome lattice, and show that it can be used to classify generic wave functions. Particularly our method can be used to distinguish several proposed candidates of Z[subscript 2] spin liquid states on the kagome lattice.United States. Dept. of Energy. Division of Materials Sciences and Engineering (Award DE-SC0010526)Perimeter Institute for Theoretical PhysicsCanada. Industry CanadaOntario. Ministry of Research and Innovatio
Topological Crystalline Insulators and Topological Superconductors: From Concepts to Materials
Full text linkIn this review, we discuss recent progress in the explorations of topological materials beyond topological insulators; specifically, we focus on topological crystalline insulators and bulk topological superconductors. The basic concepts, model Hamiltonians, and novel electronic properties of these new topological materials are explained. The key role of the symmetries that underlie their topological properties is elucidated. Key issues in their materials realizations are also discussed.United States. Dept. of Energy. Office of Basic Energy Sciences (DE-SC 0010526
Anomalous supercurrent from Majorana states in topological insulator Josephson junctions
No full textWe propose a Josephson junction setup based on a topological insulator (TI) thin film to detect Majorana states that exploits the unique helical and extended nature of the TI surface state. When the magnetic flux through the junction is close to an integer number of flux quanta, Majorana states, present on both surfaces of the film, give rise to a narrow peak-dip structure in the current-phase relation by hybridizing at the edge of the junction. Remarkably, the maximal Majorana-state contribution to Josephson current takes a (nearly) universal value, approximately equal to the supercurrent capacity of a single quantum channel. These features provide a characteristic signature of Majorana states based entirely on supercurrent.United States. Dept. of Energy. Division of Materials Sciences and Engineering (Award 022090-001
Thermal plasmon resonantly enhances electron scattering in Dirac/Weyl semimetals
Full text linkWe study the inelastic scattering rate due to the Coulomb interaction in three-dimensional Dirac/Weyl semimetals at finite temperature. We show that the perturbation theory diverges because of the long-range nature of the interaction, hence, thermally induced screening must be taken into account. We demonstrate that the scattering rate has a nonmonotonic energy dependence with a sharp peak owing to the resonant decay into thermal plasmons. We also consider the Hubbard interaction for comparison. We show that, in contrast to the Coulomb case, it can be well described by the second-order perturbation theory in a wide energy range.United States. Department of Energy. Office of Basic Energy Sciences (Award DE-SC0010526
Physical implementation of a Majorana fermion surface code for fault-tolerant quantum computation
No full textWe propose a physical realization of a commuting Hamiltonian of interacting Majorana fermions realizing Z2topological order, using an array of Josephson-coupled topological superconductor islands. The required multi-body interaction Hamiltonian is naturally generated by a combination of charging energy induced quantum phase-slips on the superconducting islands and electron tunneling between islands. Our setup improves on a recent proposal for implementing a Majorana fermion surface code (Vijay et al 2015 Phys. Rev. X 5 041038), a 'hybrid' approach to fault-tolerant quantum computation that combines (1) the engineering of a stabilizer Hamiltonian with a topologically ordered ground state with (2) projective stabilizer measurements to implement error correction and a universal set of logical gates. Our hybrid strategy has advantages over the traditional surface code architecture in error suppression and single-step stabilizer measurements, and is widely applicable to implementing stabilizer codes for quantum computation.Packard FoundationUnited States. Department of Energy. Division of Materials Sciences and Engineering (Award No. de-sc0010526
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