scholarly journals Fragility of surface states in topological superfluid 3He

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
P. J. Heikkinen ◽  
A. Casey ◽  
L. V. Levitin ◽  
X. Rojas ◽  
A. Vorontsov ◽  
...  
Keyword(s):  
Momentum Space ◽  
Bound States ◽  
Energy Gap ◽  
Surface States ◽  
Superfluid 3He ◽  
P Wave ◽  
Magnetic Scattering ◽  
Superfluid Transition ◽  
Edge States ◽  
Space Topology

AbstractSuperfluid 3He, with unconventional spin-triplet p-wave pairing, provides a model system for topological superconductors, which have attracted significant interest through potential applications in topologically protected quantum computing. In topological insulators and quantum Hall systems, the surface/edge states, arising from bulk-surface correspondence and the momentum space topology of the band structure, are robust. Here we demonstrate that in topological superfluids and superconductors the surface Andreev bound states, which depend on the momentum space topology of the emergent order parameter, are fragile with respect to the details of surface scattering. We confine superfluid 3He within a cavity of height D comparable to the Cooper pair diameter ξ0. We precisely determine the superfluid transition temperature Tc and the suppression of the superfluid energy gap, for different scattering conditions tuned in situ, and compare to the predictions of quasiclassical theory. We discover that surface magnetic scattering leads to unexpectedly large suppression of Tc, corresponding to an increased density of low energy bound states.

scholarly journals Superconducting topological surface states in the noncentrosymmetric bulk superconductor PbTaSe2

2016 ◽  
Vol 2 (11) ◽  
pp. e1600894 ◽  
Author(s):  
Syu-You Guan ◽  
Peng-Jen Chen ◽  
Ming-Wen Chu ◽  
Raman Sankar ◽  
Fangcheng Chou ◽  
...  
Keyword(s):  
Bound States ◽  
Dirac Point ◽  
Fault Tolerant ◽  
Bulk Material ◽  
Surface States ◽  
Atomic Scale ◽  
Edge States ◽  
Quasi Particle ◽  
Topological Superconductors ◽  
Topological Surface

The search for topological superconductors (TSCs) is one of the most urgent contemporary problems in condensed matter systems. TSCs are characterized by a full superconducting gap in the bulk and topologically protected gapless surface (or edge) states. Within each vortex core of TSCs, there exists the zero-energy Majorana bound states, which are predicted to exhibit non-Abelian statistics and to form the basis of the fault-tolerant quantum computation. To date, no stoichiometric bulk material exhibits the required topological surface states (TSSs) at the Fermi level (EF) combined with fully gapped bulk superconductivity. We report atomic-scale visualization of the TSSs of the noncentrosymmetric fully gapped superconductor PbTaSe2. Using quasi-particle scattering interference imaging, we find two TSSs with a Dirac point atE≅ 1.0 eV, of which the inner TSS and the partial outer TSS crossEF, on the Pb-terminated surface of this fully gapped superconductor. This discovery reveals PbTaSe2as a promising candidate for TSC.

scholarly journals Relation of the runaway avalanche threshold to momentum space topology

2018 ◽  
Vol 60 (2) ◽  
pp. 024004 ◽  
Author(s):  
Christopher J McDevitt ◽  
Zehua Guo ◽  
Xian-Zhu Tang
Keyword(s):  
Momentum Space ◽  
Space Topology

scholarly journals Long-range focusing of magnetic bound states in superconducting lanthanum

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Howon Kim ◽  
Levente Rózsa ◽  
Dominik Schreyer ◽  
Eszter Simon ◽  
Roland Wiesendanger
Keyword(s):  
Long Range ◽  
Bound States ◽  
Theoretical Calculations ◽  
Surface States ◽  
Magnetic Interactions ◽  
Magnetic Impurities ◽  
Natural Choice ◽  
Temperature Scanning ◽  
Quantum Mechanical Systems ◽  
Low Dimensional

Abstract Quantum mechanical systems with long-range interactions between quasiparticles provide a promising platform for coherent quantum information technology. Superconductors are a natural choice for solid-state based quantum devices, while magnetic impurities inside superconductors give rise to quasiparticle excitations of broken Cooper pairs that provide characteristic information about the host superconductor. Here, we reveal that magnetic impurities embedded below a superconducting La(0001) surface interact via quasiparticles extending to very large distances, up to several tens of nanometers. Using low-temperature scanning probe techniques, we observe the corresponding anisotropic and giant oscillations in the LDOS. Theoretical calculations indicate that the quasi-two-dimensional surface states with their strongly anisotropic Fermi surface play a crucial role for the focusing and long-range extension of the magnetic bound states. The quasiparticle focusing mechanism should facilitate the design of versatile magnetic structures with tunable and directed magnetic interactions over large distances, thereby paving the way toward the design of low-dimensional magnet–superconductor hybrid systems exhibiting topologically non-trivial quantum states as possible elements of quantum computation schemes based on Majorana quasiparticles.

scholarly journals Calculation of the annihilation rate of P wave quark-antiquark bound states

1976 ◽  
Vol 60 (2) ◽  
pp. 183-188 ◽  
Author(s):  
R. Barbieri ◽  
R. Gatto ◽  
R. Kögerler
Keyword(s):  
Bound States ◽  
P Wave ◽  
Annihilation Rate

scholarly journals Andreev bound states in superconducting films and confined superfluid 3 He

2018 ◽  
Vol 376 (2125) ◽  
pp. 20150144 ◽  
Author(s):  
Anton B. Vorontsov
Keyword(s):  
Bound States ◽  
Surface States ◽  
Surface Region ◽  
Theme Issue ◽  
Confined Geometry ◽  
Andreev Bound States ◽  
Broken Symmetries ◽  
Parent State ◽  
Open Questions ◽  
Coherence Lengths

This paper reviews confinement-driven phase transitions in superconductors and Bardeen–Cooper–Schrieffer superfluids, and the appearance in thin films of new phases that break the time-reversal or translational symmetry. The origins of the new phases are closely tied to the Andreev scattering processes involving particle-hole conversions that create surface quasiparticle states with energies inside the superconducting gap. Restructuring of the low-energy spectrum in the surface region of several coherence lengths ξ 0 results in large spatial variations of the superconducting order parameter. In confined geometry, such as slabs, films, pores or nano-dots, with one or more physical dimensions D ∼10 ξ 0 , the Andreev bound states can dominate properties of a superconductor, leading to modified experimental signatures. They can significantly change the energy landscape, and drive transitions into new superconducting phases. The new phases are expected in a variety of materials, from singlet d -wave superconductors to multi-component triplet superfluid 3 He, but properties of the new phases will depend on the symmetry of the parent state. I will highlight the connection between the Andreev surface states and confinement-stabilized phases with additional broken symmetries, describe recent progress and open questions in the theoretical and experimental investigation of superfluids in confined geometry. This article is part of the theme issue ‘Andreev bound states’.

scholarly journals Lifshitz scaling effects on the holographic p-wave superconductors coupled to nonlinear electrodynamics

2020 ◽  
Vol 80 (10) ◽  
Author(s):  
Mahya Mohammadi ◽  
Ahmad Sheykhi
Keyword(s):  
Critical Temperature ◽  
Energy Gap ◽  
Mass Parameter ◽  
Delta Function ◽  
P Wave ◽  
Nonlinear Electrodynamics ◽  
Model Parameters ◽  
Scaling Effects ◽  
Low Frequencies ◽  
The Real

AbstractWe employ gauge/gravity duality to study the effects of Lifshitz scaling on the holographic p-wave superconductors in the presence of Born–Infeld nonlinear electrodynamics. By using the shooting method in the probe limit, we calculate the relation between critical temperature $$T_\mathrm{{c}}$$ T c and $$\rho ^{z/d}$$ ρ z / d numerically for different values of mass, nonlinear parameter b and Lifshitz critical exponent z in various dimensions. We observe that critical temperature decreases by increasing b, z or the mass parameter m which makes conductor/superconductor phase transition harder to form. In addition, we analyze the electrical conductivity and find the behavior of the real and the imaginary parts as a function of frequency, which depend on the model parameters. However, some universal behaviors are seen. For instance at low frequencies, the real part of conductivity shows a delta function behavior, while the imaginary part has a pole, which means that these two parts are connected to each other through the Kramers–Kronig relation. The behavior of the real part of the conductivity in the large frequency regime can be achieved by $$\mathrm{{Re}}[\sigma ]=\omega ^{D-4}$$ Re [ σ ] = ω D - 4 . Furthermore, with increasing the Lifshitz scaling z, the energy gap and the minimum values of the real and imaginary parts become unclear.

scholarly journals Effects of A Magnetic Field on the Transport and Noise Properties of a Graphene Ribbon with Antidots

Nanomaterials ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 2098
Author(s):  
Paolo Marconcini ◽  
Massimo Macucci
Keyword(s):  
Magnetic Field ◽  
Numerical Simulation ◽  
Charge Transport ◽  
Shot Noise ◽  
Energy Gap ◽  
Mass Term ◽  
Edge States ◽  
Graphene Ribbon ◽  
The Magnetic Field ◽  
Armchair Graphene

We perform a numerical simulation of the effects of an orthogonal magnetic field on charge transport and shot noise in an armchair graphene ribbon with a lattice of antidots. This study relies on our envelope-function based code, in which the presence of antidots is simulated through a nonzero mass term and the magnetic field is introduced with a proper choice of gauge for the vector potential. We observe that by increasing the magnetic field, the energy gap present with no magnetic field progressively disappears, together with features related to commensurability and quantum effects. In particular, we focus on the behavior for high values of the magnetic field: we notice that when it is sufficiently large, the effect of the antidots vanishes and shot noise disappears, as a consequence of the formation of edge states crawling along the boundaries of the structure without experiencing any interaction with the antidots.

ELECTRICAL CONDUCTANCE OF ZIGZAG NANOGRAPHITE RIBBONS WITH LOCALLY APPLIED GATE VOLTAGE

2002 ◽  
Vol 16 (32) ◽  
pp. 4897-4909 ◽  
Author(s):  
KATSUNORI WAKABAYASHI ◽  
TAKASHI AOKI
Keyword(s):  
Gate Voltage ◽  
Chemical Potential ◽  
Single Channel ◽  
Energy Gap ◽  
Electrical Conductance ◽  
Transmission Probability ◽  
Edge States ◽  
Transport Channel ◽  
Electric Conductance ◽  
Voltage Bias

The electric conductance of the graphite ribbon with locally applied gate voltage has been studied in terms of the Landauer approach. In the low-energy region, nano-graphite ribbon with zigzag boundaries exhibits the single electronic transport channel due to the edge states. The chemical potential dependence of the electric conductance shows qualitatively different behavior, depending on whether the magnitude of the potential barrier (gate voltage bias) Vg is larger than the energy gap Δ of the single channel region of the zigzag ribbon. For positive Vg with Vg < Δ, the zero-conductance resonances appear for 0 ≤ E ≤ Vg, and average transmission probability is quite small in this region. However the transmission probability is almost one, i.e. perfect transmission, for E > Vg. This step-function-like behavior of the conductance shows that it is possible to fabricate a nano-graphite-based switching device by the application of weak gate voltage bias.

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