Andreev bound states and current-phase relations in three-dimensional topological insulators

Snelder, M.; Veldhorst, Menno; Golubov, Alexandre Avraamovitch; Brinkman, Alexander

doi:10.1103/physrevb.87.104507

Cited by 61 publications

(89 citation statements)

References 57 publications

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“…The measured critical currents are reproducibly observed on different devices and upon multiple cooldowns, and the measurement can be well explained by diffusive transport models and geometric effects. The predicted 4π periodic Josephson effect can only be observed in the future for similar devices with just a single perpendicular mode [60] and when measured faster than the relaxation rate of a quasiparticle inside an Andreev bound state.…”

Section: Discussionmentioning

confidence: 93%

Josephson supercurrent in a topological insulator without a bulk shunt

Snelder¹,

Molenaar²,

Pan³

et al. 2014

Supercond. Sci. Technol.

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Abstract. A Josephson supercurrent has been induced into the three-dimensional topological insulator Bi 1.5 Sb 0.5 Te 1.7 Se 1.3 .We show that the transport in Bi 1.5 Sb 0.5 Te 1.7 Se 1.3 exfoliated flakes is dominated by surface states and that the bulk conductivity can be neglected at the temperatures where we study the proximity induced superconductivity. We prepared Josephson junctions with widths in the order of 40 nm and lengths in the order of 50 to 80 nm on several Bi 1.5 Sb 0.5 Te 1.7 Se 1.3 flakes and measured down to 30 mK. The Fraunhofer patterns unequivocally reveal that the supercurrent is a Josephson supercurrent. The measured critical currents are reproducibly observed on different devices and upon multiple cooldowns, and the critical current dependence on temperature as well as magnetic field can be well explained by diffusive transport models and geometric effects. ‡ Current address:

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Section: Discussionmentioning

confidence: 93%

Josephson supercurrent in a topological insulator without a bulk shunt

Snelder¹,

Molenaar²,

Pan³

et al. 2014

Supercond. Sci. Technol.

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“…the explicit calculations of E n (φ) in Refs. 44,45 . The amplitude of the ABS wave function decreases with increasing wave vector mismatch between SC and TI 45 .…”

Section: B Numerical Calculations Of Abs and Band-bendingmentioning

confidence: 99%

Signature of a topological phase transition in the Josephson supercurrent through a topological insulator

et al. 2016

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Topological insulators (TIs) hold great promise for topological quantum computation in solidstate systems. Recently, several groups reported experimental data suggesting that signatures of Majorana modes have been observed in topological insulator Josephson junctions (TIJJs). A prerequisite for the exploration of Majorana physics is to obtain a good understanding of the properties of low-energy Andreev bound states (ABS) in a material with topologically non-trivial band structure. Here, we present experimental data and a theoretical analysis demonstrating that the band structure inversion close to the surface of a TI has observable consequences for supercurrent transport in TIJJs prepared on surface-doped Bi 2 Se 3 thin films. Electrostatic carrier depletion of the film surface leads to an abrupt drop in the critical current of such devices. The effect can be understood as a relocation of low-energy ABS from a region deeper in the bulk of the material to the more strongly disordered surface which is driven by the topology of the effective band structure in the presence of surface dopants.

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“…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].…”

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confidence: 99%

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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Andreev bound states and current-phase relations in three-dimensional topological insulators

Cited by 61 publications

References 57 publications

Josephson supercurrent in a topological insulator without a bulk shunt

Josephson supercurrent in a topological insulator without a bulk shunt

Signature of a topological phase transition in the Josephson supercurrent through a topological insulator

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

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