Planar Josephson junctions in germanium: Effect of cubic spin-orbit interaction

Luethi, Melina; Laubscher, Katharina; Bosco, Stefano; Loss, Daniel; Klinovaja, Jelena

doi:10.1103/physrevb.107.035435

Cited by 17 publications

(4 citation statements)

References 119 publications

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“…We use the superconducting quantum interference device (SQUID) in Fig. 4a to demonstrate phase control across a Josephson junction, an important ingredient for achieving topological states at low magnetic field 50,[55][56][57] . The device is composed of two Josephson field-effect transistors (JoFETs) with a width of 2 μm and 1 μm for JoFET 1 and JoFET 2 respectively, and equal length of 70 nm.…”

Section: Resultsmentioning

confidence: 99%

“…Although a hard gap is necessary but not sufficient on its own for achieving a topologically protected system, this work positions planar Ge as a promising platform to explore Majorana bound states in phased-biased Josephson junctions 13,61,62 . Calculations with experimentally realistic material parameters 57 show that accessing the topological phase is feasible by careful design of Ge planar Josephson junctions geometries that relaxes magnetic field and spin-orbit constrains. More advanced future experiments should build on our current results to fully assess the readiness of Ge for Majorana bound states experiments, such as increasing the induced superconducting gap and measuring it by non local spectroscopy in multi-terminal devices and demonstrate the twoelectron charging effect in hybrid Ge/PtSiGe islands, a prerequisite for their use in topological quantum computation.…”

Section: Discussionmentioning

confidence: 99%

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Hard superconducting gap in germanium

et al. 2023

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The co-integration of spin, superconducting, and topological systems is emerging as an exciting pathway for scalable and high-fidelity quantum information technology. High-mobility planar germanium is a front-runner semiconductor for building quantum processors with spin-qubits, but progress with hybrid superconductor-semiconductor devices is hindered by the difficulty in obtaining a superconducting hard gap, that is, a gap free of subgap states. Here, we address this challenge by developing a low-disorder, oxide-free interface between high-mobility planar germanium and a germanosilicide parent superconductor. This superconducting contact is formed by the thermally-activated solid phase reaction between a metal, platinum, and the Ge/SiGe semiconductor heterostructure. Electrical characterization reveals near-unity transparency in Josephson junctions and, importantly, a hard induced superconducting gap in quantum point contacts. Furthermore, we demonstrate phase control of a Josephson junction and study transport in a gated two-dimensional superconductor-semiconductor array towards scalable architectures. These results expand the quantum technology toolbox in germanium and provide new avenues for exploring monolithic superconductor-semiconductor quantum circuits towards scalable quantum information processing.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Hard superconducting gap in germanium

et al. 2023

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“…In the dependence, the spontaneous supercurrent and ϕ junction derived from the AMSs formed in the coupled two planar JJs are found. It is predicted that although the topological superconductivity is engineered in single planar JJs with the phase control and the Zeeman field (50)(51)(52), the coherent coupling of two planar JJs engineers the topological superconductivity only with the phase control (53,54). For the realization, it is demanded to elucidate the fundamental physics of the AMSs in the coupled JJs, especially about the symmetry breaking invoked by the phase control.…”

Section: Introductionmentioning

confidence: 99%

Phase engineering of anomalous Josephson effect derived from Andreev molecules

Matsuo,

Imoto,

Yokoyama

et al. 2023

Sci. Adv.

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A Josephson junction (JJ) is a key device for developing superconducting circuits, wherein a supercurrent in the JJ is controlled by the phase difference between the two superconducting electrodes. When two JJs sharing one superconducting electrode are coherently coupled and form the Andreev molecules, a supercurrent of one JJ is expected to be nonlocally controlled by the phase difference of another JJ. Here, we evaluate the supercurrent in one of the coupled two JJs as a function of local and nonlocal phase differences. Consequently, the results exhibit that the nonlocal phase control generates a finite supercurrent even when the local phase difference is zero. In addition, an offset of the local phase difference giving the JJ ground state depends on the nonlocal phase difference. These features demonstrate the anomalous Josephson effect realized by the nonlocal phase control. Our results provide a useful concept for engineering superconducting devices such as phase batteries and dissipationless rectifiers.

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“…The high quality of this material would lead to a weak charge noise influence on quantum devices and therefore guarantees a high performance of the hole spin qubits. 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][19][20] and pioneering work has been conducted on hybridizing Ge quantum wells with superconductors. 5,[21][22][23][24][25] Quantum point contacts (QPCs), as a basic nanostructure, have been widely used in quantum devices, including tunnelling barriers, 26 quantum dots, 27,28 charge sensors 29 and fractional quantum Hall state interferometers.…”

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confidence: 99%