1,721,370 research outputs found
Classification of Interacting Topological Floquet Phases in One Dimension
Full text linkPeriodic driving of a quantum system can enable new topological phases with no analog in static systems. In this paper, we systematically classify one-dimensional topological and symmetry-protected topological (SPT) phases in interacting fermionic and bosonic quantum systems subject to periodic driving, which we dub Floquet SPTs (FSPTs). For physical realizations of interacting FSPTs, many-body localization by disorder is a crucial ingredient, required to obtain a stable phase that does not catastrophically heat to infinite temperature. We demonstrate that 1D bosonic and fermionic FSPT phases are classified by the same criteria as equilibrium phases but with an enlarged symmetry group G[over ˜], which now includes discrete time translation symmetry associated with the Floquet evolution. In particular, 1D bosonic FSPTs are classified by projective representations of the enlarged symmetry group H^{2}(G[over ˜],U(1)). We construct explicit lattice models for a variety of systems and then formalize the classification to demonstrate the completeness of this construction. We advocate that a prototypical Z_{2} bosonic FSPT may be realized by very simple Hamiltonians of the type currently available in existing cold atoms and trapped ion experiments
Chiral Floquet Phases of Many-Body Localized Bosons
Full text linkWe construct and classify chiral topological phases in driven (Floquet) systems of strongly interacting bosons, with finite-dimensional site Hilbert spaces, in two spatial dimensions. The construction proceeds by introducing exactly soluble models with chiral edges, which in the presence of many-body localization (MBL) in the bulk are argued to lead to stable chiral phases. These chiral phases do not require any symmetry and in fact owe their existence to the absence of energy conservation in driven systems. Surprisingly, we show that they are classified by a quantized many-body index, which is well defined for any MBL Floquet system. The value of this index, which is always the logarithm of a positive rational number, can be interpreted as the entropy per Floquet cycle pumped along the edge, formalizing the notion of quantum-information flow. We explicitly compute this index for specific models and show that the nontrivial topology leads to edge thermalization, which provides an interesting link between bulk topology and chaos at the edge. We also discuss chiral Floquet phases in interacting fermionic systems and their relation to chiral bosonic phases
Edge Ferromagnetism from Majorana Flat Bands: Application to Split Tunneling-Conductance Peaks in High-T[subscript c] Cuprate Superconductors
No full textIn mean-field descriptions of nodal d-wave superconductors, generic edges exhibit dispersionless Majorana fermion bands at zero energy. These states give rise to an extensive ground-state degeneracy, and are protected by time-reversal symmetry. We argue that the infinite density of states of these flat bands make them inherently unstable to interactions, and show that repulsive interactions lead to edge ferromagnetism which splits the flat bands. This edge ferromagnetism offers an explanation for the observation of the splitting of zero-bias peaks in edge tunneling in high-T[subscript c] cuprate superconductors. We argue that this mechanism for splitting is more likely than previously proposed scenarios and describe its experimental consequences.United States. Dept. of Energy (Grant DEFG0203ER46076
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Classification of Interacting Electronic Topological Insulators in Three Dimensions
Full text linkA fundamental open problem in condensed-matter physics is how the dichotomy between conventional and topological band insulators is modified in the presence of strong electron interactions. We show that there are six interacting electronic topological insulators that have no noninteracting counterpart. Combined with the previously known band insulators, these produce a total of eight topologically distinct phases. Two of the six interacting topological insulators can be described as Mott insulators in which the electron spins form spin analogs of the topological band insulator. The remaining phases are obtained as combinations of these two “topological paramagnets” and the topological band insulator. We prove that these eight phases form a complete list of all possible interacting topological insulators and discuss their experimental signatures.United States. Dept. of Energy (DESC-8739-ER46872)National Science Foundation (U.S.) (Grant ADGE-0801525)Simons Foundation (Award 229736
Gapped symmetry preserving surface state for the electron topological insulator
No full textIt is well known that the three-dimensional (3D) electronic topological insulator (TI) with charge-conservation and time-reversal symmetry cannot have a trivial insulating surface that preserves symmetry. It is often implicitly assumed that if the TI surface preserves both symmetries then it must be gapless. Here we show that it is possible for the TI surface to be both gapped and symmetry preserving, at the expense of having surface-topological order. In contrast to analogous bosonic topological insulators, this symmetric surface topological order is intrinsically non-Abelian. We show that the surface-topological order provides a complete nonperturbative definition of the electron TI that transcends a free-particle band-structure picture, and could provide a useful perspective for studying strongly correlated topological Mott insulators.National Science Foundation (U.S.) (Grant DGE-0801525)United States. Dept. of Energy (DESC-8739-ER46872)Simons Foundation (Award 229736
Topological superconductivity and Majorana fermions in metallic surface states
No full textHeavy metals, such as Au, Ag, and Pb, often have sharp surface states that are split by strong Rashba spin-orbit coupling. The strong spin-orbit coupling and two-dimensional nature of these surface states make them ideal platforms for realizing topological superconductivity and Majorana fermions. In this paper we further develop a proposal to realize Majorana fermions at the ends of quasi-one-dimensional metallic wires. We show how superconductivity can be induced on the metallic surface states by a combination of proximity effect, disorder, and interactions. Applying a magnetic field along the wire can drive the wire into a topologically nontrivial state with Majorana end states. Unlike the case of a perpendicular field, where the chemical potential must be fine-tuned near the Rashba band crossing, the parallel field allows one to realize Majorana fermions for an arbitrarily large chemical potential. We then show that, despite the presence of a large carrier density from the bulk metal, it is still possible to effectively control the chemical potential of the surface states by gating. The simplest version of our proposal, which involves only an Au(111) film deposited on a conventional superconductor, should be readily realizable.United States. Dept. of Energy (Grant No. DEFG0203ER46076)National Science Foundation (U.S.) (Integrative Graduate Education and Research Traineeship Program Grant No. DGE-0801525
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