Study shows how superconductivity can be switched on and off in superconductors

Ingrid Fadelli is a writer for Phys.org.

Superconductors can enter a state of no electrical resistance through which magnetic fields can't penetrate. Material scientists and engineers have been looking at the potential of these materials for a wide range of electronics applications.

When developing quantum computers, superconductors are particularly useful because of their ability to transport electrical signals while preventing their dissipation. It has so far proved to be difficult to control their states.

A few years ago a study suggested that the superconductivity of materials could be switched on and off. The researchers at IBM Research are trying to explain the switch mechanism unveiled in the previous study. Their findings were outlined in a paper.

Two of the researchers who carried out the study said that metals and metals screen external electric fields very effectively. The authors claimed to have turned on and off the superconductivity in a titanium nanowire via moderate electric fields applied by a nearby gate.

The findings gathered by NEST and SPIN-CNR in Italy would allow the development of entirely new types of electronic and quantum computing devices based on superconductors. When electric fields are present, they set out a few years ago to unveil the physical mechanism occurring in nanometer-sized superconductors.

There are some initial hints about the origin of the suppressed superconductivity in titanium. The new study is a more detailed explanation of the findings gathered by the team at NEST and SPIN-CNR.

The suppression of superconductivity always went hand in hand with small leakage currents flowing from the gate to the nanowire. It was reasonable to assume that such a current would disrupt superconductivity, as the energy of each electron carried by the current was quite large.

The previous study allowed Fuhrer, Nichele and their colleagues to get a sense of the mechanism underpinning the suppression of superconductivity, but it still lacked a number of key ingredients. The paper's main goal was to give a satisfactory explanation for the phenomenon.

Fuhrer and Nichele said that their new experiments are consistent with their first work, that currents leaking from the gates are needed to suppress superconductivity in metallic nanowires.

When high-energy electrons flowed out of the wire and between the two electrodes, the researchers achieved the same results. The suppression of superconductivity is a function of the material's substrate.

The devices used in the experiments are based on a wafer. The currents of high energy electrons flow when high voltages are applied.

Fuhrer and Nichele explained that electrons kick Silicon atoms continuously, transferring their energy to the crystal lattice.

The recent work by Fuhrer, Nichele, and their colleagues shows that phonons act as mediators. The team created a device that has a deep trench etched into it.

Fuhrer and Nichele said that the trench reflects the phonons generated on one side and shields the nanowire. In our devices, the phonons we produce have different energies than those from a temperature increase.

The researchers found that the photon produced had a temperature of over 100 Kelvin when they carried out their experiments. The finding explains why the devices they developed have low power requirements.

The recent work by Fuhrer, Nichele and their colleagues at IBM Research offers a convincing explanation for the experimental results published by the team at NEST and SPIN-CNR. In the future, their explanation could help to understand superconductors further, potentially enabling their use for the development of new types of devices.

Fuhrer and Nichele said that their study contributes to a new generation of devices where a metallic element can be switched from superconducting to resistive in a very fast and power efficient manner.

Fuhrer, Nichele and their colleagues introduced an approach to generate high-energy electrons and phonons on demand. Cosmic rays from outer space can adversely impact the functioning of quantum computers. Their approach could be used to study the effects of high-energy excitations on quantum technology in the future.

The main activity is the realization of quantum bits.

More information: M. F. Ritter et al, Out-of-equilibrium phonons in gated superconducting switches, Nature Electronics (2022). DOI: 10.1038/s41928-022-00721-1

Giorgio De Simoni and his co-workers are working on a metallic supercurrent field-effect transistor. There is a DOI of 10.1038/s41565-018-0190-3.

A switch actuated by injection of high-energy electrons is described in Nature Communications. There is a DOI of 10.1038/s41467-021-21231-2.

The Science X Network will be launched in 2022.

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