Josephson Supercurrent through the Topological Surface States of Strained Bulk HgTe

Abstract

Strained bulk HgTe is a three-dimensional topological insulator, whose surface electrons have a high mobility ( $ 30 000 cm 2 =Vs), while its bulk is effectively free of mobile charge carriers. These properties enable a study of transport through its unconventional surface states without being hindered by a parallel bulk conductance. Here, we show transport experiments on HgTe-based Josephson junctions to investigate the appearance of the predicted Majorana states at the interface between a topological insulator and a superconductor. Interestingly, we observe a dissipationless supercurrent flow through the topological surface states of HgTe. The current-voltage characteristics are hysteretic at temperatures below 1 K, with critical supercurrents of several microamperes. Moreover, we observe a magnetic-field-induced Fraunhofer pattern of the critical supercurrent, indicating a dominant 2-periodic Josephson effect in the unconventional surface states. Our results show that strained bulk HgTe is a promising material system to get a better understanding of the Josephson effect in topological surface states, and to search for the manifestation of zero-energy Majorana states in transport experiments.

Majorana Fermion Surface Code for Universal Quantum Computation

“…Proximity-induced superconductivity and supercurrents have been observed in a number of TI materials [46][47][48][49][50][51][52]. Low-temperature scanning tunneling microscopy (STM) experiments have found a proximity-induced superconducting gap on TI surface states, and the tunneling spectrum of Abrikosov vortices shows a zero-bias conductance peak, which is robust in a range of a magnetic field and splits at higher fields [12].…”

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

“…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.…”

“…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].…”

“…To determine whether our experimental results can be described within this framework, we extend the previous model [31] to junctions of finite length (but still technically in the short junction limit), and fit the measured CPRs of the L  200 nm junctions. Our fitting procedure allowed for two free parameters: the induced gap  and the Fermi wavevector kF, which together with the width determines the number of conducting channels, N. The transmission of the weak link was assumed to be one, based on a previous normal state data [20].…”

Buildup of Sn@CNT nanorods by in-situ thermal plasma and the electronic transport behaviors

“…Above T C , the relation of dV/dI vs. bias voltage obeys the normal ohm law and R N ≈0.5 Ω can be obtained. By using the largest I C ≈24 mA at 2 K, the I C R N product [45,46], a characteristic junction parameter, is~12 mV for Sn/CNT/ Sn junction in Sn@CNT NRs.…”