Parity-conserving Cooper-pair transport and ideal superconducting diode in planar germanium

Abstract

Superconductor/semiconductor hybrid devices have attracted increasing interest in the past years. Superconducting electronics aims to complement semiconductor technology, while hybrid architectures are at the forefront of new ideas such as topological superconductivity and protected qubits. In this work, we engineer the induced superconductivity in two-dimensional germanium hole gas by varying the distance between the quantum well and the aluminum. We demonstrate a hard superconducting gap and realize an electrically and flux tunable superconducting diode using a superconducting quantum interference device (SQUID). This allows to tune the current phase relation (CPR), to a regime where single Cooper pair tunneling is suppressed, creating a $$\sin \left(2\varphi \right)$$ sin 2 φ CPR. Shapiro experiments complement this interpretation and the microwave drive allows to create a diode with ≈ 100% efficiency. The reported results open up the path towards integration of spin qubit devices, microwave resonators and (protected) superconducting qubits on the same silicon technology compatible platform.

Proximity-induced gapless superconductivity in two-dimensional Rashba semiconductor in magnetic field

“…In addition, to make the model of 2DEG more realistic, one may incorporate the Dresselhaus spin-orbit coupling along with Rashba spin-orbit considered here, and take into account more realistic band structure of 2DEG. These ingredients may be particularly important for treatment of heterostructures beyond Al-InAs, such as Al-Ge [39], Al-InSbAs [65], and other materials.…”

“…More broadly, our theoretical model with some modifications will be applicable to a much broader family of materials, such as hybrid semiconductor [36] and topological insulator [37,38] nanowires or proximitized surface states [25], Germanium based 2DEGs [39], ferromagnetic hybrids [11], and two-dimensional materials with strong spin orbit coupling such as transition metal dichalcogenides. Also, it can be extended to predict the dissipative electromagnetic response, spin susceptibility and other characteristics accessible in the future experiments.…”

Flux-Tunable Josephson Diode Effect in a Hybrid Four-Terminal Josephson Junction

“…29,30 Such CPRs, containing contributions from higher harmonics than the conventional 2π-periodic component, are routinely attained in high-quality superconductor−semiconductor planar materials, 31−33 where hybrid JJs host Andreev bound states (ABSs) characterized by high transmission. Key ingredients for the JDE to occur in this system are the different harmonic content between the two JJs and a magnetic flux threading the SQUID loop, 29 (2D) electron 34,35 and hole 36 systems, obtaining large diode efficiencies at equilibrium up to approximately 30%. Multiterminal JJs are emerging as a promising platform to investigate supercurrent nonreciprocities.…”

“…Since its observation in superconducting multilayers, the SDE has been the subject of thorough experimental and theoretical investigation, both in junction-free thin films − and JJs based on semiconductors with spin–orbit coupling, − finite-momentum superconductors, − or multilayered materials, realizing sizable asymmetries even without external magnetic fields. − An alternative platform proposed to achieve the SDE in Josephson deviceswhere it is usually referred to as the Josephson diode effect (JDE)relies on a supercurrent interferometer, where two JJs with nonsinusoidal current–phase relations (CPRs) are combined in a SQUID. , Such CPRs, containing contributions from higher harmonics than the conventional 2π-periodic component, are routinely attained in high-quality superconductor–semiconductor planar materials, − where hybrid JJs host Andreev bound states (ABSs) characterized by high transmission. Key ingredients for the JDE to occur in this system are the different harmonic content between the two JJs and a magnetic flux threading the SQUID loop, as recently demonstrated in two-dimensional (2D) electron , and hole systems, obtaining large diode efficiencies at equilibrium up to approximately 30%.…”

Gate-defined quantum point contacts in a germanium quantum well

“…8,9 Aside from spin qubits, high-mobility Ge quantum wells are also considered as a competing platform for non-Abelian Majorana zero modes 18–20 and pioneering work has been conducted on hybridizing Ge quantum wells with superconductors. 5,21–25…”