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Register a new userReentrant topological transitions with Majorana end states in 1D superconductors by lattice modulation
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The possibility to observe and manipulate Majorana fermions as end states of one-dimensional topological superconductors has been actively discussed recently. In a quantum wire with strong spin-orbit coupling placed in proximity to a bulk superconductor, a topological superconductor has been expected to be realized when the band energy is split by the application of a magnetic field. When a periodic lattice modulation is applied multiple topological superconductor phases appear in the phase diagram. Some of them occur for higher filling factors compared to the case without the modulation. We study the effects of phase jumps and argue that the topologically nontrivial state of the whole system is retained even if they are present. We also study the effect of the spatial modulation in the hopping parameter.
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Topological superconductors have been discovered with recent advances in understanding the topological properties of condensed matters. These states have a full pairing gap in the bulk and gapless counter-propagating Majorana states at the boundary. A pair of Majorana zero modes is associated with each vortex. This understanding had a great influence on the theory of superconductivity and their following experiments, but its relevantce to organic compounds was not closely observed. Here, we analyze the topological states of various polyaromatic hydrocarbons (PAHs), including benzene, and reveal that they are topological superconductors. We have analyzed the momentum vectors of benzene and other PAHs through a semi-classical approach to confirm their non-trivial state. Their unique properties might be originated from the odd number of Kramers doublets in PAHs. The Huckel rule describing aromaticity can be reinterpreted with a topological viewpoint. It suggests that the (4n+2) rule can be split into two pairs of (2n+1) electrons each, namely, electrons and holes with spin up and down. Therefore, it always forms an odd number of Kramers` doublet. Moreover, n in the Huckel rule can be interpreted as the winding number in global next-nearest-neighbor(NNN) hopping. This work will re-establish the definition of aromaticity that has been known so far and extend the use of aromatic compounds as topological superconductors to quantum computers.
We classify discrete-rotation symmetric topological crystalline superconductors (TCS) in two dimensions and provide the criteria for a zero energy Majorana bound state (MBS) to be present at composite defects made from magnetic flux, dislocations, and disclinations. In addition to the Chern number that encodes chirality, discrete rotation symmetry further divides TCS into distinct stable topological classes according to the rotation eigenspectrum of Bogoliubov-de Gennes quasi-particles. Conical crystalline defects are shown to be able to accommodate robust MBS when a certain combination of these bulk topological invariants is non-trivial as dictated by the index theorems proved within. The number parity of MBS is counted by a $mathbb{Z}_2$-valued index that solely depends on the disclination and the topological class of the TCS. We also discuss the implications for corner-bound Majorana modes on the boundary of topological crystalline superconductors.
We find that quasiperiodicity-induced localization-delocalization transitions in generic 1D systems are associated with hidden dualities that generalize the well-known duality of the Aubry-Andre model. For a given energy window, such duality is locally defined near the transition and can be explicitly determined by considering commensurate approximants. This relies on the construction of an auxiliary 2D Fermi surface of the commensurate approximants as a function of the phase-twisting boundary condition and of the phase-shifting real-space structure. Considering widely different families of quasiperiodic 1D models, we show that, around the critical point of the limiting quasiperiodic system, the auxiliary Fermi surface of a high-enough-order approximant converges to a universal form. This allows us to devise a highly-accurate method to compute mobility edges and duality transformations for generic 1D quasiperiodic systems through their commensurate approximants. To illustrate the power of this approach, we consider several previously studied systems, including generalized Aubry-Andre models and coupled Moire chains. Our findings bring a new perspective to examine quasiperiodicity-induced localization-delocalization transitions in 1D, provide a working criterion for the appearance of mobility edges, and an explicit way to understand the properties of eigenstates close and at the transition.
Chains of magnetic atoms with either strong spin-orbit coupling or spiral magnetic order which are proximity-coupled to superconducting substrates can host topologically non-trivial Majorana bound states. The experimental signature of these states consists of spectral weight at the Fermi energy and spatially localized near the ends of the chain. However, topologically trivial Yu-Shiba-Rusinov in-gap states localized near the ends of the chain can lead to similar spectra. Here, we explore a protocol to disentangle these contributions by artificially augmenting a candidate Majorana spin chain with orbitally-compatible nonmagnetic atoms. Combining scanning tunneling spectroscopy with ab-initio and tight-binding calculations, we realize a sharp spatial transition between the proximity-coupled spiral magnetic order and the non-magnetic superconducting wire termination, with persistent zero-energy spectral weight localized at either end of the magnetic spiral. Our findings open a new path towards the control of the spatial position of in-gap end states, trivial or Majorana, via different chain terminations, and the realization of designer Majorana chain networks for demonstrating topological quantum computation.
We study theoretically the effects of long-range and on-site Coulomb interactions on the topological phases and transport properties of spin-orbit-coupled quasi-one-dimensional quantum wires imposed on an s-wave superconductor. The electrostatic potential and charge density distributions are computed self-consistently within the Hartree approximation. Due to the finite width of the wires and the charge repulsion, the potential and density distribute inhomogeneously in the transverse direction and tend to accumulate along the lateral edges where the hard-wall confinement is assumed. This result has profound effects on the topological phases and the differential conductance of the interacting quantum wires and their hybrid junctions with superconductors. Coulomb interactions renormalize the chemical potential, and alter the topological phases strongly by enhancing the topological regimes and producing jagged boundaries. Moreover, the multicritical points connecting different topological phases from high-index subbands are modified remarkably in striking contrast to the predictions of the two-band model. We further suggest the possible non-magnetic topological phase transitions manipulated externally with the aid of long-range interactions. Finally, the transport properties of normal-superconductor junctions are also examined and interaction impacts on the emergence of Majorana fermions and the strength of Majorana zero-bias peaks are revealed.
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