First superconducting transistor at practical voltage and temperature

A team of physicists from the University of Groningen led by Associate Professor Justin Ye has constructed a superconducting transistor that operates at a few K elvin. The back gate which switches the molybdenum disulphide transistor from the metallic to the superconducting phase operates at a continuous low voltage. This type of transistor could be used in quantum logic circuits. The results were published on 28 May in the journal Advanced Materials.

Switching the properties of quantum electronic systems, such as the superconducting phase, is challenging. Superconducting transistor-like devices have been constructed, but these prototypes still have major drawbacks, explains University of Groningen Associate Professor of Quantum Interfaces and Device Physics Justin Ye. ‘Most of these systems can perform continuous switching, but they need to be cooled down or warmed up to do so. Furthermore, for exceptions that can be tuned continuously, a high voltage is needed to switch between states, as well as temperatures below 1.5 Kelvin.’ Cooling to these temperatures requires complex equipment and the very rare Helium-3.

Tipping point

By contrast, Ye has now developed a dual gate device that can switch between the metallic and superconducting phases with a low voltage back gate of 20 Volts at ~10 Kelvin. The device, which is based on molybdenum disulphide, operates like a field effect transistor. Ye uses an ionic liquid gate to add charge carriers to the material. This is tuned to the tipping point between the metallic and superconducting phases, so a back gate of hafnium oxide operating below 20 volts can switch the device between states.

‘As far as I know, we are the first to make a superconducting transistor with continuous switching at an easily accessible temperature of a few Kelvin’, says Ye. This means that his transistor operates in a relatively simple cooling device that uses Helium-4. Ye’s group first showed that molybdenum disulphide – a semiconductor but also a common dry lubricant – becomes a superconductor at low temperatures in 2012. ‘We used the same type of device in this new experiment, but we improved the dielectric properties of the back gate to obtain a bigger range of tuning carriers.’

This process took several years, but the result is rewarding. ‘We can now switch a quantum state. Eventually, this could lead to the construction of superconducting logic circuits.’ But although the current device shows all the functionality of a real transistor, such an application is still a long way off. ‘The next step is to show the frequency response’, says Ye. However, building applications is just one of the aims of his group. ‘We are into scientific exploration; we make devices with the aim of finding both new physical phenomena and new functionalities.’

Reference: Qihong Chen, Jianming Lu, Lei Liang, Oleksandr Zheliuk, Abdurrahman Ali El Yumin and Jianting Ye: Continuous Low‐Bias Switching of Superconductivity in a MoS2 Transistor. Advanced Materials, online 28 mei 2018

DOI: 10.1002/adma.201800399