Majorana fermions in semiconductor nanostructures with two wires connected through a ring

Sun, Bo; Wu, M. W.

doi:10.1088/1367-2630/16/7/073045

Cited by 5 publications

(9 citation statements)

References 58 publications

(102 reference statements)

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“…This is in strong contrast to the case of effective p-wave superconductors where the excitation gap is always smaller than the superconducting gap. [9][10][11][12][13][14][15][16][17][18] As the large topologically nontrivial gap has been shown to be probably most important for applications in topological insulators, 4,5 topological crystalline insulators, 38 and QAH insulators, 38-40 our finding, i.e., reporting a large bulk excitation gap in the TSC is crucial to the field of TSCs and Majorana modes. This paves a way to obtain robust TSCs and Majorana modes using the QAH states.…”

Section: 34mentioning

confidence: 59%

Topological superconductor with a large Chern number and a large bulk excitation gap in single-layer graphene

Wang¹,

Wu²

2016

Phys. Rev. B

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We show that a two-dimensional topological superconductor (TSC) can be realized in a hybrid system with a conventional s-wave superconductor proximity-coupled to a quantum anomalous Hall (QAH) state from the Rashba and exchange effects in single layer graphene. With very low or even zero doping near the Dirac points, i.e., two inequivalent valleys, this TSC has a Chern number as large as four, which supports four Majorana edge modes. More importantly, we show that this TSC has a robust topologically nontrivial bulk excitation gap, which can be larger or even one order of magnitude larger than the proximity-induced superconducting gap. This unique property paves a way for the application of QAH insulators as seed materials to realize robust TSCs and Majorana modes.

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Section: 34mentioning

confidence: 59%

Topological superconductor with a large Chern number and a large bulk excitation gap in single-layer graphene

Wang¹,

Wu²

2016

Phys. Rev. B

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“…Most proposals to detect Majorana modes in a condensed matter context usually involve conductance orin the case of rings-interference measurements. 62,63,66,95 The signature of Majorana modes in these measurements is typically a zero-bias conductance peak or conductance peaks close to zero. However, these zero-bias conductance peaks can also originate from phenomena other than Majorana modes (such as the Kondo effect 73 ), which in turn makes it difficult to identify Majorana modes conclusively.…”

Section: Magnetic Field Penetrating Into the Superconducting Regionmentioning

confidence: 99%

“…89 In contrast to these wire structures, we investigate the quasiparticle excitations, including possible Majorana modes, in quantum dots (QDs) and quantum rings (QRs) with (possibly induced) p-wave pairing. While there are several works on the ring geometry for the chiral p-wave superconductor and related models, 17,62,63,[90][91][92][93] our focus is on providing an in-depth analysis of the system and of the effects of finite size or magnetic fields penetrating into the superconducting region.…”

Section: Introductionmentioning

confidence: 99%

“…Potential signatures of Majorana modes in the above systems are usually centered on the fact that Majorana modes can also affect transport and thermodynamic properties of the (induced) topological superconductors. [50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65] Of all these proposals, the setup based on hybrid superconductor-semiconductor wire structures with Rashba spin-orbit coupling and Zeeman splitting 31,32 has been the most prevalent until now, with experiments conducted in InSb [66][67][68] and InAs 69,70 semiconductor wires as well as ferromagnetic atomic chains. 71,72 In these experiments, a zero-bias peak in the tunneling conductance has been observed, which potentially points to the presence of Majorana zero-energy modes.…”

Section: Introductionmentioning

confidence: 99%

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Probing Majorana-like states in quantum dots and quantum rings

Scharf

Žutić

2015

Phys. Rev. B

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Engineering chiral p-wave superconductivity in semiconductor structures offers fascinating ways to obtain and study Majorana modes in a condensed matter context. Here, we theoretically investigate chiral p-wave superconductivity in quantum dots and quantum rings. Using both analytical as well as numerical methods, we calculate the quasiparticle excitation spectra in these structures and the corresponding excitation amplitudes and charge densities. In the topological regime, we can observe the chiral edge modes localized at the boundaries and possessing finite energy in quantum dots and quantum rings. By applying a magnetic field which is expelled from the quantum ring, but which creates a flux that is an odd integer multiple of Φ0/2 = π /e, Majorana modes, that is, (approximately) degenerate edge modes with zero energy and zero charge density, become possible in the topological regime. Furthermore, we investigate finite-size effects that split these degenerate edge modes as well as the effect of a magnetic field penetrating into the superconducting region that can under certain circumstances still support edge modes with approximately zero energy and charge.

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“…This progress motivates further experiments that would be more conclusive than the 'local' Majorana features seen in tunneling spectroscopy so far. Theoretical proposals for probing their nonlocal properties range from interference experiments [24][25][26][27][28][29][30][31], teleportation [32], fusion-rule tests [33], coherence measurement of topological qubits [33], and ultimately to braiding [33][34][35][36][37][38][39][40][41][42][43]. The latter would unambiguously demonstrate non-Abelian exchange statistics.…”

mentioning

confidence: 99%

Coupling and braiding Majorana bound states in networks defined in two-dimensional electron gases with proximity-induced superconductivity

2017

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Two-dimensional electron gases with strong spin-orbit coupling covered by a superconducting layer offer a flexible and potentially scalable platform for Majorana networks. We predict Majorana bound states (MBSs) to appear for experimentally achievable parameters and realistic gate potentials in two designs: either underneath a narrow stripe of a superconducting layer (S-stripes) or where a narrow stripe has been removed from a uniform layer (N-stripes). The coupling of the MBSs can be tuned for both types in a wide range (< 1 neV to > 10 µeV) using gates placed adjacent to the stripes. For both types, we numerically compute the local density of states for two parallel Majorana-stripe ends as well as Majorana trijunctions formed in a tuning-fork geometry. The MBS coupling between parallel Majorana stripes can be suppressed below 1 neV for potential barriers in the meV range for separations of about 200 nm. We further show that the MBS couplings in a trijunction can be gate-controlled in a range similar to the intra-stripe coupling while maintaining a sizable gap to the excited states (tens of µeV). Altogether, this suggests that braiding can carried out on a time scale of 10-100 ns.PACS numbers: 71.10. Pm, 74.50.+r, Majorana bound states (MBSs) are quasiparticles in superconductors that are their own 'self-adjoints' [1][2][3][4]. This requires them to be an equal superposition of particles and holes and ties their energy to the middle of the superconducting gap. MBSs can appear in spatially separate pairs as, for example, at the opposite edges of a topological superconductor. This nonlocality may be utilized for storage and manipulation of quantum information in a topologically protected way [5][6][7]. However, the realization of MBSs requires superconducting p-wave pairing, which appears intrinsically only in exotic materials. Fortunately, p-wave pairing can also be engineered by combining s-wave superconductors with strong spin-orbit materials [8][9][10][11]. Based on this, experiments looked so far for evidence of MBSs in, for example, semiconducting nanowires [12][13][14][15][16][17][18][19], topological insulators [20], magnetic atom chains [21,22], and recently also twodimensional electron gases [23].This progress motivates further experiments that would be more conclusive than the 'local' Majorana features seen in tunneling spectroscopy so far. Theoretical proposals for probing their nonlocal properties range from interference experiments [24-31], teleportation [32], fusion-rule tests [33], coherence measurement of topological qubits [33], and ultimately to braiding [33][34][35][36][37][38][39][40][41][42][43]. The latter would unambiguously demonstrate non-Abelian exchange statistics. Realizing these proposals calls for a flexible platform for building complex and controllable Majorana devices. Such a Majorana platform should preferably also be scalable to build large-scale MBS networks later on as a central part of a topological quantum computer.A potential platform granting such flexibility and sca-FIG. ...

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Majorana fermions in semiconductor nanostructures with two wires connected through a ring

Cited by 5 publications

References 58 publications

Topological superconductor with a large Chern number and a large bulk excitation gap in single-layer graphene

Topological superconductor with a large Chern number and a large bulk excitation gap in single-layer graphene

Probing Majorana-like states in quantum dots and quantum rings

Coupling and braiding Majorana bound states in networks defined in two-dimensional electron gases with proximity-induced superconductivity

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