Al-Ge-Al Nanowire Heterostructure: From Single-Hole Quantum Dot to Josephson Effect

Area of Science:

• Quantum physics
• Condensed matter physics
• Materials science

Background:

• Superconductor-semiconductor heterostructures are crucial for fundamental quantum studies and low-power nanoelectronic devices.
• Hybrid systems offer unique properties for advanced quantum technologies.

Purpose of the Study:

• To investigate low-temperature transport in intrinsic germanium (i-Ge) quantum dots within ultrascaled monolithic Al-Ge-Al nanowire heterostructures.
• To demonstrate the tunable behavior of these heterostructures, from insulating to supercurrent regimes.

Main Methods:

• Fabrication of ultrascaled monolithic Al-Ge-Al nanowire heterostructures with monocrystalline Al leads and abrupt interfaces.
• Low-temperature electrical transport measurements of intrinsic Ge quantum dots.

Main Results:

• Demonstrated tunable quantum dot behavior, transitioning from insulating to single-hole filling and finally to a supercurrent regime.
• Achieved a Josephson field-effect transistor with a maximum critical current of 10 nA at 390 mK.
• Realized high junction transparency, enabling the study of sub-gap transport via Andreev states.

Conclusions:

• The intrinsic Ge-based architecture is promising for hybrid superconductor-semiconductor devices.
• This architecture facilitates the study of Majorana zero modes and components for quantum computing, such as gatemons and tunable superconducting quantum interference devices.