Helical Andreev bound states and superconducting Klein tunneling in topological insulator Josephson junctions

Tkachov, G.; Hankiewicz, Ewelina M.

doi:10.1103/physrevb.88.075401

Cited by 77 publications

(100 citation statements)

References 49 publications

(78 reference statements)

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“…Moreover, the involved surface states are known to be of a topological origin [20,42]. Both the observed skewness and the amplitude of the CPR agree with the model of ballistic quasiparticle transport through helical Andreev bound states [31]. Detailed descriptions of the induced gap and number of channels inferred from the fits are given in the Supplementary Information, together with the fit confidence range.…”

supporting

confidence: 70%

Nonsinusoidal Current-Phase Relationship in Josephson Junctions from the 3D Topological Insulator HgTe

et al. 2015

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We use Superconducting QUantum Interference Device (SQUID) microscopy to characterize the current-phase relation (CPR) of Josephson Junctions from 3-dimentional topological insulator HgTe (3D-HgTe). We find clear skewness in the CPRs of HgTe junctions ranging in length from 200 nm to 600 nm. The skewness indicates that the Josephson current is predominantly carried by Andreev bound states with high transmittance, and the fact that the skewness persists in junctions that are longer than the mean free path suggests that the effect may be related to the helical nature of the Andreev bound states in the surface of HgTe.Topological insulators (TI) have a special band structure with important consequences for proximity-induced superconductivity. In 3-dimentional topological insulators (3D-TI), the inversion of the conduction and valence bands leads to conducting 2D surface states with energies that are linearly proportional to their momenta [1][2][3][4][5]. Spinmomentum locking protects the charge carriers at the surface against elastic backscattering [6,7]. These special properties are reflected in the superconducting proximity effect in an S/3D-TI bilayer or an S/TI/S junction, which may host Majorana fermions in a quasi-1D channel or vortex core [8][9][10]. Most previous works characterized current-voltage characteristics to determine the critical current's dependence on temperature, gate voltage, or magnetic field [11][12][13][14][15][16][17][18][19][20][21][22], while a few studies characterized the CPR [23,24].Here, we use a scanning SQUID microscope to perform contactless measurements of the diamagnetic response of Nb/HgTe bilayers and of the CPR of Nb/HgTe/Nb junctions. In contrast to previous CPR results [23,24], we find no evidence for bulk states, 2 and we observe that the CPRs of many junctions of different sizes consistently exhibit forward skewness.The CPR in an S/TI/S junction is a key diagnostic [8,[25][26][27][28][29][30][31][32]. Weak disorder in the TI far from the superconducting contacts theoretically does not affect the induced superconducting state [33,34]; therefore, Andreev bound states should form in hightransmittance surface channels [8,26,27,29,31]. A CPR with forward skewness -that is, a deviation from a perfect sinusoidal form -is a signature of such high-transmittance Andreev bound states [35][36][37].To our knowledge, there have not been direct observations of forward skewed CPRs in topological insulators [23,24], although the skewness has been indirectly inferred [24] from the Fraunhofer interference pattern. Previous CPR experiments in topological insulators [23,24] were complicated in part by bulk states, self-inductance effects, and bias voltage, factors that are eliminated in this work.Moreover, a skewed CPR can also result from ballistic transport [35]. Measurements in metallic break junctions showed that the CPR approaches the predictions for quantum point contacts in the ballistic limit [38]. In metallic atomic point contacts, the CPR was significantly skewed only in contacts wi...

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confidence: 70%

Nonsinusoidal Current-Phase Relationship in Josephson Junctions from the 3D Topological Insulator HgTe

et al. 2015

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“…This result is similar to the result found by Tkachov in Ref. [141,142] for a topological insulator. In Ref.…”

Section: Regime |M | =supporting

confidence: 82%

“…For example, it is shown by Tkachov and Hankiewicz [141,142] that the p-wave and s-wave pairing correlations have different spatial dependencies so that it depends on the channel length of the normal part which superconducting pairing correlation is dominant. We have also seen in Chap.…”

Section: Suppression Of Ldosmentioning

confidence: 99%

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Non-triviality matters

Snelder¹

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“…In the first case, the topological phase diagram and the prediction of Majorana states at the boundaries are analyzed upon changing the experimental conditions (geometry, spin-orbit coupling, gate potential, disorder, symmetry of the order parameter) 7,29,[33][34][35] and criteria for the recognition of MBSs are proposed 36,37 . In the second case, most of papers adopt an analytical model for the self-energy to represent the proximityinduced superconductivity 30,32,[38][39][40][41] . In this paper we present a detailed study of the physics of semiconductor nanowires in the presence of Rashba spin-orbit coupling 42 , such as InAs or InSb in proximity to a cuprate high critical temperature d x 2 −y 2 superconductor (such as YBCO), employing both a microscopic self-consistent approach based onto a tight-binding Bogolubov De Gennes (TBBDG) scheme and a semianalytical formulation, based on a path-integral scheme, allowing us to calculate explicitly the exact proximity self-energy.…”

Section: Introductionmentioning

confidence: 99%

High critical temperature nodal superconductors as building block for time-reversal invariant topological superconductivity

Trani¹,

Campagnano²,

Tagliacozzo³

et al. 2016

Phys. Rev. B

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We study possible applications of high critical temperature nodal superconductors for the search for Majorana bound states in the DIII class. We propose a microscopic analysis of the proximity effect induced by d-wave superconductors on a semiconductor wire with strong spin-orbit coupling. We characterize the induced superconductivity on the wire employing a numerical self-consistent tight-binding Bogoliubov-De-Gennes approach, and analytical considerations on the Green's funtion. The order parameter induced on the wire, the pair correlation function and the renormalization of the Fermi points are analyzed in detail, as well as the topological phase diagram in the case of weak coupling. We highlight optimal Hamiltonian parameters to access the non trivial topological phase which could display time-reversal invariant Majorana doublets at the boundaries of the wire.

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Helical Andreev bound states and superconducting Klein tunneling in topological insulator Josephson junctions

Cited by 77 publications

References 49 publications

Nonsinusoidal Current-Phase Relationship in Josephson Junctions from the 3D Topological Insulator HgTe

Nonsinusoidal Current-Phase Relationship in Josephson Junctions from the 3D Topological Insulator HgTe

Non-triviality matters

High critical temperature nodal superconductors as building block for time-reversal invariant topological superconductivity

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