Josephson Radiation from Gapless Andreev Bound States in HgTe-Based Topological Junctions

Abstract

Frequency analysis of the rf emission of oscillating Josephson supercurrent is a powerful passive way of probing properties of topological Josephson junctions. In particular, measurements of the Josephson emission enables to detect the expected presence of topological gapless Andreev bound states that give rise to emission at half the Josephson frequency f J , rather than conventional emission at f J . Here we report direct measurement of rf emission spectra on Josephson junctions made of HgTe-based gate-tunable topological weak links. The emission spectra exhibit a clear signal at half the Josephson frequency f J /2. The linewidths of emission lines indicate a coherence time of 0.3−4 ns for the f J /2 line, much shorter than for the f J line (3−4 ns). These observations strongly point towards the presence of topological gapless Andreev bound states, and pave the way for a future HgTe-based platform for topological quantum computation.

Topological transconductance quantization in a four-terminal Josephson junction

“…Josephson junctions are a tool to probe topological properties [9][10][11][12][13], and they may possess interesting topological properties themselves [14][15][16][17][18][19][20]. As some of us have pointed out recently [17], multiterminal Josephson junctions present an alternative to engineering topological materials.…”

Josephson junction dynamics in the presence of 2π - and 4π -periodic supercurrents

“…Additionally to p-wave superconductors like Sr 2 RuO 4 or d + id superconductors on hexagonal lattices [8,9], new platforms to host Majorana bound states based on proximitizing ordinary singlet-spin superconductor to a material with a strong spin-orbit interaction were proposed [10][11][12][13]. In addition to spectroscopic signatures of the Majorana bound states [14][15][16], recent experiments on Josephson junctions (JJs) based on Rashba wires or topological insulators, which could show topologically nontrivial modes, have attracted a lot of attention [17][18][19][20].…”

“…The accuracy and universality of this relation has made the Shapiro steps the basis of the international voltage standard with an accuracy of one part per billion. Alternatively, one can measure the voltage emission spectrum [20]. In this case, the 4π periodicity manifests itself as a resonance line separated by the fractional frequency ω 0 /2 of the junction.…”

Quench dynamics of the Josephson current in a topological Josephson junction

“…Since the 4π Josephson effect is a unique transport property of MQPs, a lot of research has been dedicated towards its realization. Several groups have attempted to build a superconductor-topological * jieliuphy@xjtu.edu.cn insulator-superconductor junction which is also expected to present the 4π Josephson current [23][24][25][26][27][28] . Indeed, Molenkamp's group has showed the signal of 4π-periodic Josephson Effect in such a junction [26][27][28] .…”

“…Motivated by recent advance in experiment 28 , we study the regimes of a constant driving in a semiconductor superconducting wire Josephson junction. We compare the Josephson current under several different conditions: first, we demonstrate that a 4π-periodic …”