2,904 research outputs found
Stacking-Induced Symmetry-Protected Topological Phase Transitions
We study symmetry-protected topological (SPT) phase transitions induced by
stacking two gapped one-dimensional subsystems in BDI symmetry class. The
topological invariant of the entire system is a sum of three topological
invariants: two from each subsystem and an emerging topological invariant from
the stacking. We find that any symmetry-preserving stacking of topologically
trivial subsystems can drive the entire system into a topologically nontrivial
phase. We explain this intriguing SPT phase transitions by conditions set by
orbital degrees of freedom and time-reversal symmetry. To exemplify the SPT
transition, we provide a concrete model which consists of an atomic chain and a
spinful nanowire with spin-orbit interaction and -wave superconducting
order. The stacking-induced SPT transition drives this heterostructure into a
zero-field topological superconducting phase.Comment: 7 pages, 4 figure
Spatiotemporal Stochastic Resonance in Fully Frustrated Josephson Ladders
We consider a Josephson-junction ladder in an external magnetic field with
half flux quantum per plaquette. When driven by external currents, periodic in
time and staggered in space, such a fully frustrated system is found to display
spatiotemporal stochastic resonance under the influence of thermal noise. Such
resonance behavior is investigated both numerically and analytically, which
reveals significant effects of anisotropy and yields rich physics.Comment: 8 pages in two columns, 8 figures, to appear in Phys. Rev.
Nonequilibrium Fractional Josephson Effect
Josephson tunnel junctions exhibit a supercurrent typically proportional to
the sine of the superconducting phase difference . In general, a term
proportional to is also present, alongside microscopic electronic
retardation effects. We show that voltage pulses sharply varying in time prompt
a significant impact of the term. Its interplay with the
term results in a nonequilibrium fractional Josephson effect
(NFJE) in the presence of bound states close to zero
frequency. Our microscopic analysis reveals that the interference of
non-equilibrium virtual quasiparticle excitations is responsible for this
phenomenon. We also analyse this phenomenon for topological Josephson junctions
with Majorana bound states. Remarkably, the NFJE is independent of the ground
state fermion parity unlike its equilibrium counterpart
Emergent localized states at the interface of a twofold -symmetric lattice
We consider the role of non-triviality resulting from a non-Hermitian
Hamiltonian that conserves twofold PT-symmetry assembled by interconnections
between a PT-symmetric lattice and its time reversal partner. Twofold
PT-symmetry in the lattice produces additional surface exceptional points that
play the role of new critical points, along with the bulk exceptional point. We
show that there are two distinct regimes possessing symmetry-protected
localized states, of which localization lengths are robust against external
gain and loss. The states are demonstrated by numerical calculation of a
quasi-1D ladder lattice and a 2D bilayered square lattice.Comment: 10 pages, 7 figure
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