591 research outputs found
Topological pumping in class-D superconducting wires
We study adiabatic pumping at a normal metal/class-D superconductor hybrid
interface when superconductivity is induced through the proximity effect in a
spin-orbit coupled nanowire in the presence of a tilted Zeeman field. When the
induced order parameter in the nanowire is non-uniform, the phase diagram has
isolated trivial regions surrounded by topological ones. We show that in this
case the pumped charge is quantized in units of the elementary charge and
has a topological nature.Comment: 7 pages, 6 figures. Published versio
Emergent Finite Frequency Criticality of Driven-Dissipative Correlated Lattice Bosons
Critical points and phase transitions are characterized by diverging
susceptibilities, reflecting the tendency of the system toward spontaneous
symmetry breaking. Equilibrium statistical mechanics bounds these instabilities
to occur at zero frequency, giving rise to static order parameters. In this
work we introduce a new class of dynamical transitions in a quantum many body
system far from thermal equilibrium, characterized by a susceptibility
diverging at a finite non-zero frequency, an emerging scale set by interactions
and non-equilibrium effects. In the broken-symmetry phase the corresponding
macroscopic order parameter becomes non-stationary and oscillates in time
without damping, thus breaking continuous time-translational symmetry. Our
results, obtained for a paradigmatic model of bosons interacting on lattice in
prensence of drive and dissipation, are relevant for the upcoming generation of
circuit QED arrays experiments and outline a generic framework to study
time-domain instabilities in non-equilibrium quantum systems, including Floquet
time crystals and quantum synchronization.Comment: 10 pages, 8 figure
Persistent spin oscillations in a spin-orbit-coupled superconductor
Quasi-two-dimensional superconductors with tunable spin-orbit coupling are
very interesting systems with properties that are also potentially useful for
applications. In this manuscript we demonstrate that these systems exhibit
undamped collective spin oscillations that can be excited by the application of
a supercurrent. We propose to use these collective excitations to realize
persistent spin oscillators operating in the frequency range of 10 GHz - 1 THz.Comment: 10 pages, 4 figures, published versio
Local density of states in metal - topological superconductor hybrid systems
We study by means of the recursive Green's function technique the local
density-of-states of (finite and semi-infinite) multi-band spin-orbit coupled
semiconducting nanowires in proximity to an s-wave superconductor and attached
to normal-metal electrodes. When the nanowire is coupled to a normal electrode,
the zero-energy peak, corresponding to the Majorana state in the topological
phase, broadens with increasing transmission between the wire and the leads,
eventually disappearing for ideal interfaces. Interestingly, for a finite
transmission a peak is present also in the normal electrode, even though it has
a smaller amplitude and broadens more rapidly with the strength of the
coupling. Unpaired Majorana states can survive close to a topological phase
transition even when the number of open channels (defined in the absence of
superconductivity) is even. We finally study the Andreev-bound-state spectrum
in superconductor-normal metal-superconductor junctions and find that in
multi-band nanowires the distinction between topologically trivial and
non-trivial systems based on the number of zero-energy crossings is preserved.Comment: 11 pages, 12 figures, published versio
Josephson-Majorana cycle in topological single-electron hybrid transistors
Charge transport through a small topological superconducting island in
contact with a normal and a superconducting electrode occurs through a cycle
that involves coherent oscillations of Cooper pairs and tunneling in/out the
normal electrode through a Majorana bound state, the Josephson-Majorana cycle.
We illustrate this mechanism by studying the current-voltage characteristics of
a superconductor-topological superconductor-normal metal single-electron
transistor. At low bias and temperature the Josephson-Majorana cycle is the
dominant mechanism for transport. We discuss a three-terminal configuration
where the non-local character of the Majorana bound states is emergent.Comment: 6 pages, 4 figure
The XYZ chain with Dzyaloshinsky-Moriya interactions: from spin-orbit-coupled lattice bosons to interacting Kitaev chains
Using the density-matrix renormalization-group algorithm (DMRG) and a
finite-size scaling analysis, we study the properties of the one-dimensional
completely-anisotropic spin-1/2 XYZ model with Dzyaloshinsky-Moriya (DM)
interactions. The model shows a rich phase diagram: depending on the value of
the coupling constants, the system can display different kinds of ferromagnetic
order and Luttinger-liquid behavior. Transitions from ferromagnetic to
Luttinger-liquid phases are first order. We thoroughly discuss the transition
between different ferromagnetic phases, which, in the absence of DM
interactions, belongs to the XX universality class. We provide evidence that
the DM exchange term turns out to split this critical line into two separated
Ising-like transitions and that in between a disordered phase may appear. Our
study sheds light on the general problem of strongly-interacting
spin-orbit-coupled bosonic gases trapped in an optical lattice and can be used
to characterize the topological properties of superconducting nanowires in the
presence of an imposed supercurrent and of interactions.Comment: 18 pages, 8 figure
Photoemission spectra of massless Dirac fermions on the verge of exciton condensation
Angle-resolved photoemission spectroscopy (ARPES) is a powerful probe of
electron correlations in two-dimensional layered materials. In this Letter we
demonstrate that ARPES can be used to probe the onset of exciton condensation
in spatially-separated systems of electrons and holes created by gating
techniques in either double-layer graphene or topological-insulator thin films.Comment: 5 pages, 3 figure
Theory of integer quantum Hall polaritons in graphene
We present a theory of the cavity quantum electrodynamics of the graphene
cyclotron resonance. By employing a canonical transformation, we derive an
effective Hamiltonian for the system comprised of two neighboring Landau levels
dressed by the cavity electromagnetic field (integer quantum Hall polaritons).
This generalized Dicke Hamiltonian, which contains terms that are quadratic in
the electromagnetic field and respects gauge invariance, is then used to
calculate thermodynamic properties of the quantum Hall polariton system.
Finally, we demonstrate that the generalized Dicke description fails when the
graphene sheet is heavily doped, i.e. when the Landau level spectrum of 2D
massless Dirac fermions is approximately harmonic. In this case we `integrate
out' the Landau levels in valence band and obtain an effective Hamiltonian for
the entire stack of Landau levels in conduction band, as dressed by strong
light-matter interactions.Comment: 20 pages, 7 figure
Fully Frustrated Cold Atoms
Fully frustrated Josephson Junction arrays (FF-JJA's) exhibit a subtle
compound phase transition in which an Ising transition associated with discrete
broken translational symmetry and a Berezinskii-Kosterlitz-Thouless (BKT)
transition associated with quasi-long-range phase coherence occur nearly
simultaneously. In this Letter we discuss a cold atom realization of the FF-JJA
system. We demonstrate that both orders can be studied by standard
momentum-distribution-function measurements and present numerical results,
based on a successful self-consistent spin-wave approximation, that illustrate
the expected behavior of observables.Comment: 5 pages, 3 figures, submitte
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