6 research outputs found
Quartet Tomography in Multiterminal Josephson Junctions
We investigate the detection of quartets in hybrid multiterminal Josephson
junctions. Using simple models of quantum dots coupled to superconducting
leads, we find that quartets are ubiquitous and show how to rigorously extract
their contribution to the current-phase relation (CPR). We also demonstrate
that quartets are closely related to the hybridization of Andreev bound states
(ABSs) in these systems and propose a method to identify quartets directly in
ABS spectra. We illustrate our method by analyzing the spectroscopic
measurements of the ABS spectrum in a three-terminal Josephson junction
realized in an InAs/Al heterostructure. Our analysis strongly suggests the
existence of quartets in the studied hybrid system.Comment: 6 pages, 2 figure
Zeeman- and Orbital-Driven Phase Shifts in Planar Josephson Junctions
We perform supercurrent and tunneling spectroscopy measurements on gate-tunable InAs/Al Josephson junctions (JJs) in an in-plane magnetic field and report on phase shifts in the current–phase relation measured with respect to an absolute phase reference. The impact of orbital effects is investigated by studying multiple devices with different superconducting lead sizes. At low fields, we observe gate-dependent phase shifts of up to φ0 = 0.5π, which are consistent with a Zeeman field coupling to highly transmissive Andreev bound states via Rashba spin–orbit interaction. A distinct phase shift emerges at larger fields, concomitant with a switching current minimum and the closing and reopening of the superconducting gap. These signatures of an induced phase transition, which might resemble a topological transition, scale with the superconducting lead size, demonstrating the crucial role of orbital effects. Our results elucidate the interplay of Zeeman, spin–orbit, and orbital effects in InAs/Al JJs, giving improved understanding of phase transitions in hybrid JJs and their applications in quantum computing and superconducting electronics.ISSN:1936-0851ISSN:1936-086
Microwave-induced conductance replicas in hybrid Josephson junctions without Floquet—Andreev states
Light–matter coupling allows control and engineering of complex quantum states. Here we investigate a hybrid superconducting–semiconducting Josephson junction subject to microwave irradiation by means of tunnelling spectroscopy of the Andreev bound state spectrum and measurements of the current–phase relation. For increasing microwave power, discrete levels in the tunnelling conductance develop into a series of equally spaced replicas, while the current–phase relation changes amplitude and skewness, and develops dips. Quantitative analysis of our results indicates that conductance replicas originate from photon assisted tunnelling of quasiparticles into Andreev bound states through the tunnelling barrier. Despite strong qualitative similarities with proposed signatures of Floquet–Andreev states, our study rules out this scenario. The distortion of the current–phase relation is explained by the interaction of Andreev bound states with microwave photons, including a non-equilibrium Andreev bound state occupation. The techniques outlined here establish a baseline to study light–matter coupling in hybrid nanostructures and distinguish photon assisted tunnelling from Floquet–Andreev states in mesoscopic devices.ISSN:2041-172
Demonstration of the Nonlocal Josephson Effect in Andreev Molecules
We perform switching current measurements of planar Josephson junctions (JJs) coupled by a common superconducting electrode with independent control over the two superconducting phase differences. We observe an anomalous phase shift in the current–phase relation of a JJ as a function of gate voltage or phase difference in the second JJ. This demonstrates the nonlocal Josephson effect, and the implementation of a φ0-junction which is tunable both electrostatically and magnetically. The anomalous phase shift is larger for shorter distances between the JJs and vanishes for distances much longer than the superconducting coherence length. Results are consistent with the hybridization of Andreev bound states, leading to the formation of an Andreev molecule. Our devices constitute a realization of a tunable superconducting phase source and could enable new coupling schemes for hybrid quantum devices.ISSN:1530-6984ISSN:1530-699
Control over epitaxy and the role of the InAs/Al interface in hybrid two-dimensional electron gas systems
In situ synthesized semiconductor/superconductor hybrid structures became an important material platform in condensed matter physics. Their development enabled a plethora of novel quantum transport experiments with focus on Andreev and Majorana physics. The combination of InAs and Al has become the workhorse material and has been successfully implemented in the form of one-dimensional structures and two-dimensional electron gases. In contrast to the well-developed semiconductor parts of the hybrid materials, the direct effect of the crystal nanotexture of Al films on the electron transport still remains unclear. This is mainly due to the complex epitaxial relation between Al and the semiconductor. Here, we present characterization of Al thin films grown on shallow InAs two-dimensional electron gas systems by molecular beam epitaxy. Using a growth approach based on an intentional roughening of the epitaxial interface, we demonstrate growth of grain-boundary-free Al. We show that the implemented roughening does not negatively impact either the electron mobility of the two-dimensional electron gas or the basic superconducting properties of the proximitized system. This is an important step in understanding the role of properties of the InAs/Al interface in hybrid devices. Ultimately, our results provide a growth approach to achieve a high-degree of epitaxy in lattice-mismatched materials.ISSN:2475-995
Phase-engineering the Andreev band structure of a three-terminal Josephson junction
Data and code upload for publication of the same name. Folder 'Data' contains raw, processed and simulated data for all figures of Main Text and Supplementary Information. Folder 'Code' contains the MATLAB scripts used to generate the simulated data. In each folder, a description complementing the information available in the manuscript is provided in the 'readme.txt' file.Additional funding: Deutsche Forschungsgemeinschaft (DFG) via SFD 1432, ID 425217212 and BE 3803/14-1, ID 467596333; Spanish Ministry of Science and Innovation, PID2020-114880GB-I00