4π-periodic Josephson supercurrent in HgTe-based topological Josephson junctions

Wiedenmann, Jonas; Bocquillon, Erwann; Deacon, Russell; Hartinger, Simon; Herrmann, Oliver; Klapwijk, T. M.; Maier, Luis; Ames, Christopher P.; Brüne, C.; Gould, C.; Oiwa, A.; Ishibashi, Koji; Tarucha, Seigo; Buhmann, H.; Molenkamp, Laurens W.

doi:10.1038/ncomms10303

Cited by 383 publications

(452 citation statements)

References 53 publications

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“…Proximity induced superconductivity has been demonstrated in 3D TIs based on Bi [11][12][13][14][15][16][17] and HgTe 18,19 with the reported values of the induced gap on the order of a few 100 µeV. Similar gap values were recently observed via Andreev spectroscopy 20 in quaternary BiSbTeSe compound, established as a 3D TI with negligible contribution of the bulk conduction 21,22 .…”

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confidence: 75%

Andreev Reflection in ans-Type Superconductor Proximized 3D Topological Insulator

et al. 2016

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We investigate transport and shot noise in lateral N-TI-S contacts, where N is a normal metal, TI is a Bi-based three dimensional topological insulator (3D TI), and S is an s-type superconductor. In the normal state, the devices are in the elastic diffusive transport regime, as demonstrated by a nearly universal value of the shot noise Fano factor FN ≈ 1/3 in magnetic field and in a reference normal metal contact. In the absence of magnetic field, we identify the Andreev reflection (AR) regime, which gives rise to the effective charge doubling in shot noise measurements. Surprisingly, the Fano factor FAR ≈ 0.22 ± 0.02 is considerably reduced in the AR regime compared to FN, in contrast to previous AR experiments in normal metals and semiconductors. We suggest that this effect is related to a finite thermal conduction of the proximized, superconducting TI owing to a residual density of states at low energies.A surface state of a three-dimensional topological insulator (3D TI) is a unique example of a spin-orbit coupled and symmetry protected conductor 1 . Similar to graphene, in 3D TI the surface electronic states are massless Dirac fermions. Unlike in graphene, however, a single Dirac cone is lacking spin and valley degeneracies. That makes a 3D TI an intriguing candidate for the realization of a solid state two-dimensional topological superconductor 2 . As originally proposed by Fu and Kane 3 , p-wave like superconducting correlations are expected to emerge via proximity coupling the 3D TI to a conventional stype superconductor (S). This gives rise to symmetry protected Majorana zero modes bound at vortices or at the boundaries of various hybrid structures 4,5 . Emerging zero modes are predicted to have a strong impact on the low energy physics, modifying Andreev reflection (AR) at the interface with a normal metal 6 , affecting the edge conductance distribution 7 , noise 8 and thermal transport 9,10 .Proximity induced superconductivity has been demonstrated in 3D TIs based on Bi 11-17 and HgTe 18,19 with the reported values of the induced gap on the order of a few 100 µeV. Similar gap values were recently observed via Andreev spectroscopy 20 in quaternary BiSbTeSe compound, established as a 3D TI with negligible contribution of the bulk conduction 21,22 . In spite of these advances, the microscopic nature of the proximity induced gap in Bi-based 3D TIs remains largely unexplored. This particularly concerns the statistics of the transmission eigenvalue distribution in short junctions and the role of possible in-gap states. On this route, valuable information, often hidden in transport, can be obtained via measurements of the non-equilibrium current fluctuationsthe shot noise 23 . Relevant for the AR, prominent examples include unusual shot noise behavior at the interface between a normal metal and superconductors with other than s-type order parameter symmetry 24,25 and, more recently, shot noise detection of the thermal and charge transport via Majorana zero modes 9,10,26 .Here, we investigate the AR in latera...

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supporting

confidence: 75%

Andreev Reflection in ans-Type Superconductor Proximized 3D Topological Insulator

et al. 2016

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“…Topological superconductors (TSCs) supporting Majorana modes have been shown to demonstrate a 4π-periodic Josephson effect 4-10 , which is doubled period compared to the conventional Josephson effect. This phenomenon, which is known as the fractional Josephson effect, has been observed in quite a few devices 11,12 including the quantum spin Hall edge 13,14 . At first this is quite counter-intuitive given that the Hamiltonian itself is 2π-periodic.…”

Section: Introductionmentioning

confidence: 95%

8π -periodic dissipationless ac Josephson effect on a quantum spin Hall edge via a quantum magnetic impurity

Hui

2017

Phys. Rev. B

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Time-reversal invariance places strong constraints on the properties of the quantum spin Hall edge. One such restriction is the inevitability of dissipation in a Josephson junction between two superconductors formed on such an edge without the presence of interaction. Interactions and spinconservation breaking are key ingredients for the realization of dissipationless ac Josephson effect on such quantum spin Hall edges. We present a simple quantum impurity model that allows to create a dissipationless fractional Josephson effect on a quantum spin Hall edge. We then use this model to substantiate a general argument that shows that any such non-dissipative Josephson effect must necessarily be 8π-periodic.

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“…In proximity to a bulk s-wave superconductor and subjected to a magnetic field perpendicular to the Rashba axis, the wire is expected to have a completely gapped spectrum, except for a single Majorana bound state at each end. [1][2][3] There have been several suggestive experimental signatures of Majorana physics, including zero-bias peaks [4][5][6][7] and an unconventional 4π Josephson effect, 8 but there is not yet any completely conclusive measurement which would rule out all alternative explanations of the observed features. In this respect, it is necessary to independently characterize the RSOC strength of nanowires.…”

Section: Introductionmentioning

confidence: 99%

Dynamic response functions and helical gaps in interacting Rashba nanowires with and without magnetic fields

et al. 2016

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A partially gapped spectrum due to the application of a magnetic field is one of the main probes of Rashba spin-orbit coupling in nanowires. Such a "helical gap" manifests itself in the linear conductance, as well as in dynamic response functions such as the spectral function, the structure factor, or the tunnelling density of states. In this paper, we investigate theoretically the signature of the helical gap in these observables with a particular focus on the interplay between Rashba spin-orbit coupling and electron-electron interactions. We show that in a quasi-one-dimensional wire, interactions can open a helical gap even without magnetic field. We calculate the dynamic response functions using bosonization, a renormalization group analysis, and the exact form factors of the emerging sine-Gordon model. For special interaction strengths, we verify our results by refermionization. We show how the two types of helical gaps, caused by magnetic fields or interactions, can be distinguished in experiments.

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4π-periodic Josephson supercurrent in HgTe-based topological Josephson junctions

Cited by 383 publications

References 53 publications

Andreev Reflection in ans-Type Superconductor Proximized 3D Topological Insulator

Andreev Reflection in ans-Type Superconductor Proximized 3D Topological Insulator

8π -periodic dissipationless ac Josephson effect on a quantum spin Hall edge via a quantum magnetic impurity

Dynamic response functions and helical gaps in interacting Rashba nanowires with and without magnetic fields

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