Researchers from the SUNY Polytechnic Institute, Stony Brook University and the Brookhaven National Laboratory in the US, along with Aalto University in Finland, have demonstrated a new electronic device that employs the unique ways in which electrons behave in graphene and high-temperature superconductors.
The experiment, led by Sharadh Jois and Ji Ung Lee from SUNY with the support of theoretical work done by Jose Lado, assistant professor at Aalto, demonstrated a new quantum device that combines both graphene and an unconventional high-temperature superconductor.
In particular, the team demonstrated that the electronic transport between graphene and the high-temperature superconductor was dominated by a unique transport process arising from the combination of two intriguing properties: graphene's Klein tunneling and the superconductor's Andreev reflection. The team showed experimentally, for the first time, that this transport process was fully consistent with the existing theoretical predictions concerning hybrid Andreev-Klein electronic transport.
Since graphene electrons behave as if they have no mass, they can move in situations where normal electrons could not. This phenomenon is known as Klein tunneling. In turn, electrons in high-temperature superconductors form so-called Cooper pairs of two electrons. Cooper pairs can have unique mathematical structures, leading to unconventional superconducting states. When a Cooper pair forms exactly at the meeting point of a standard material such a piece of metal and a superconductor, it can result in a phenomenon called Andreev reflection, in which the pair "kicks back" another kind of particle into the metal.
While Andreev reflection involving conventional superconductors and metals is well understood, doing the same with graphene electrons and high-temperature superconductors had not been demonstrated until now. "The demonstration of electronic transport stemming from graphene's Klein tunneling and unconventional superconducting pairing establishes a milestone in graphene-based quantum devices. This observation establishes the starting point to develop a whole new family of graphene-based superconducting quantum circuits that exploit unconventional superconductivity," Lado says.
The unique electronic properties of graphene have made it a promising platform for developing electronics that do not consume a lot of power. Conventional superconductors are key materials in a variety of quantum devices, and they are especially important in one of the strategies to build both qubit and topological quantum computers. By combining the two, the study's results can open new fundamental physics in these materials and ultimately establish a whole new platform for quantum technology devices.