Universal Impurity-Induced Bound State in Topological Superfluids

Hu, Hui; Jiang, Lei; Pu, Han; Chen, Yan; Liu, Xia-Ji

doi:10.1103/physrevlett.110.020401

Cited by 56 publications

(81 citation statements)

References 45 publications

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“…The use of a single impurity is a powerful method to probe the superconducting pairing symmetry [18]. More recently, a universal impurity-induced mid-gap state has also been predicted as a clear signature of topological superfluids [19,20], where the near-zero-energy bound state follows closely follow the symmetry of that of Majorana fermions. Inspired by the observation of a robust zero-bias conductance peak in the STM experiments around an interstitial-Fe-impurity on the surface of the Fe(Te,Se) compound [3], we construct a microscopic model for the local adsorbed impurity within our model.…”

Section: Local Electronic Structure Around An Adsorbed Impuritymentioning

confidence: 99%

Edge states and local electronic structure around an adsorbed impurity in a topological superconductor

et al. 2015

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Recently topological superconducting states has attracted a lot of interest. In this work, we consider a topological superconductor with Z2 topological mirror order [1] and s±-wave superconducting pairing symmetry, within a two-orbital model originally designed for iron-based superconductivity [2]. We predict the existence of gapless edge states. We also study the local electronic structure around an adsorbed interstitial magnetic impurity in the system, and find the existence of low-energy in-gap bound states even with a weak spin polarization on the impurity. We also discuss the relevance of our results to the recent STM experiment on Fe(Te,Se) compound with adsorbed Fe impurity [3], for which our density functional calculations show the Fe impurity is spin polarized. PACS numbers: 73.20.r, 71.70.Ej, 71.10.Pm, 74.20.Pq Topological superconductor (TSC) has been attracted lots of interest on its potential application to the fault-tolerance quantum computation [4] and superconducting spintronics [5]. The TS can be designed through the interface of a topological insulator with the fully gapped superconductor [6] or by engineering through the interface of ferromagneticsuperconducting nanostructure under several special conditions [7][8][9][10][11][12]. Most of these efforts were aimed to look for the edge states and in-gap bound states in a fully gapped superconductor. There are two types of edge states for a twodimensional (2D) TSC. The first type is a chiral edge state in a time-reversal-symmetry-broken superconducting pairing state like [p x + ip y ] ↑↑ [13,14]. The second type is a helical edge state in a time-reversal-symmetry-invariant pairing state like [p x ± ip y ] ↑↓ ) [6,15]. Recently, the crystalline symmetry protected topological phase with mirror Chern number has been studied in a triplet pairing state of Sr 2 RuO 4 [16], for which chiral edge states are obtained [14]. A realization of helical edge state can be established in a junction formed by an s-wave superconductor and a strong topological insulator (TI), mimicking a time-reversal-symmetry-preserved p-wave superconducting pairing state [6].In this work, we propose a feasible scenario to realize a helical topological mirror superconductor (HTMS) based on the coexistence of the interaction-driven Z 2 topological mirror order and s ± -wave pairing symmetry. Our concept is based on the nature of a topological metal, where the superconductivity can be generated through a finite Fermi surface with electron-(hole-) Fermi pockets. The Z 2 mirror topological order creates robust edge states even in the presence of a fully gapped s ± -wave pairing symmetry. We further analyze the local electronic structure of an adsorbed interstitial magnetic impurity (IMI) in the 2D bulk of the HTMS, and identify the different consequence from the topological and non-topological superconductor. It is important to note that, since the superconductivity is intrinsically inherited from the normal-state band structure, our proposal avoids the need to make a TI-SC heterost...

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Section: Local Electronic Structure Around An Adsorbed Impuritymentioning

confidence: 99%

Edge states and local electronic structure around an adsorbed impurity in a topological superconductor

et al. 2015

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“…Similar bound states originated from nonmagnetic impurities in topological superconductors and superfluids have been recently discussed in Refs. [57,58] and can be considered the p-wave counterparts of Yu-Shiba-Rusinov bound states [59][60][61][62] in standard s-wave superconductors with magnetic impurities. A more direct analogy with standard Yu-Shiba-Rusinov magnetic bound states actually applies in the nontopological phase B < B c .…”

Section: Introductionmentioning

confidence: 99%

SNS junctions in nanowires with spin-orbit coupling: Role of confinement and helicity on the subgap spectrum

et al. 2015

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We study normal transport and the subgap spectrum of superconductor-normal-superconductor (SNS) junctions made of semiconducting nanowires with strong Rashba spin-orbit coupling. We focus, in particular, on the role of confinement effects in long ballistic junctions. In the normal regime, scattering at the two contacts gives rise to two distinct features in conductance: Fabry-Perot resonances and Fano dips. The latter arise in the presence of a strong Zeeman field B that removes a spin sector in the leads (helical leads), but not in the central region. Conversely, a helical central region between nonhelical leads exhibits helical gaps of half-quantum conductance, with superimposed helical Fabry-Perot oscillations. These normal features translate into distinct subgap states when the leads become superconducting. In particular, Fabry-Perot resonances within the helical gap become parity-protected zero-energy states (parity crossings), well below the critical field B c at which the superconducting leads become topological. As a function of Zeeman field or Fermi energy, these zero modes oscillate around zero energy, forming characteristic loops, which evolve continuously into Majorana bound states as B exceeds B c . The relation with the physics of parity crossings of Yu-Shiba-Rusinov bound states is discussed.

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“…We remark that to enable the visibility of Efimov signatures in the spectral response of Fermi polarons, the general requirement of l T ∼ d will still hold true. However, depending on the property of underlying Fermi system, for instance, it can be a Fermi superfluid [32,33] or with spin-orbit coupling [34,53], the three-body correlation may manifest itself quite differently in the spectral response, which will be left for future studies.…”

Section: Summary and Discussionmentioning

confidence: 99%

Enhancing the Efimov correlation in Bose polarons with large mass imbalance

Sun

Cui

2017

Phys. Rev. A

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We study the effect of Efimov physics (in the few-body sector) to the spectral response of Bose polaron, a many-body system consisting of an impurity immersed in a bath of bosonic atoms. We find that the Efimov correlation can be greatly enhanced by increasing the mass ratio between the bosons and the impurity, which results in visible signatures in the rf spectrum of the polaron. Using a diagrammatic approach up to the third-order virial expansion, we show how the mass imbalance and the enhanced three-body effect modify the line shape and the width of the polaron spectrum. Moreover, we study the effect of a finite boson-boson interaction to the spectrum. Taking the realistic system of Li impurities immersed in Cs bosons with a positive Cs-Cs scattering length, we find a visible Efimov branch, which is associated with the second lowest Efimov trimer, in the polaron spectrum. In particular, by adjusting the boson density the Efimov branch can greatly hybridize with the attractive polaron branch leading to the spectrum broadening near their avoided level crossing. Our results can be directly probed in the cold atoms experiments on Li-Cs and Li-Rb Bose polarons.

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Universal Impurity-Induced Bound State in Topological Superfluids

Cited by 56 publications

References 45 publications

Edge states and local electronic structure around an adsorbed impurity in a topological superconductor

Edge states and local electronic structure around an adsorbed impurity in a topological superconductor

SNS junctions in nanowires with spin-orbit coupling: Role of confinement and helicity on the subgap spectrum

Enhancing the Efimov correlation in Bose polarons with large mass imbalance

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