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September 12, 2012

Inducing superconductivity in a semi-conductor with Scotch Tape

An international team led by University of Toronto physicists has developed a simple new technique to induce high-temperature superconductivity in a semiconductor for the first time - using Scotch Tape.

The method paves the way for new devices that could be used in quantum computing and to improve energy efficiency.

“Who would have thought simply sticking things together can generate entirely new effects?” said team leader and U of T physicist Ken Burch.

High-temperature superconductors are materials that conduct electricity without heating up or losing energy at liquid nitrogen temperatures. Used to transmit electricity with low loss, these superconductors are also the building blocks of the next generation of devices such as quantum computers.

Nature Communications - Proximity-induced high-temperature superconductivity in the topological insulators Bi2Se3 and Bi2Te3


High-temperature superconductors are materials that conduct electricity without heating up or losing energy at liquid nitrogen temperatures. Used to transmit electricity with low loss, these superconductors are also the building blocks of the next generation of devices such as quantum computers.

However, only certain compounds of iron, copper and oxygen – or cuprates – reveal high-temperature superconducting properties. Cuprates were believed to be impossible to incorporate with semi-conductors, so their use has been severely limited as has the exploration of new effects they may generate.

For example, observing the phenomenon of the proximity effect – wherein the superconductivity in one material generates superconductivity in an otherwise normal semi-conductor – has been difficult because the fundamental quantum mechanics require the materials to be in nearly perfect contact.

That’s where the tape comes in – specifically, Scotch poster tape: a thin, two-sided version of Scotch Tape.

“Typically, junctions between semi-conductors and superconductors were made by complex material growth procedures and fabricating devices with features smaller than a human hair,” explains Burch. “However the cuprates have a completely different structure and complex chemical make-up that simply can’t be incorporated with a normal semiconductor.”

The team used Scotch poster tape and glass slides to place high-temperature superconductors in proximity with a special type of semi-conductor known as a topological insulator. Topological insulators have captured world-wide attention from scientists because they behave like semi-conductors in bulk, but are very metallic at the surface.

The result - induced superconductivity in these novel semi-conductors - was a physics first.

ABSTRACT - Interest in the superconducting proximity effect has been reinvigorated recently by novel optoelectronic applications as well as by the possible emergence of the elusive Majorana fermion at the interface between topological insulators and superconductors. Here we produce high-temperature superconductivity in Bi2Se3 and Bi2Te3 via proximity to Bi2Sr2CaCu2O8+δ, to access higher temperature and energy scales for this phenomenon. This was achieved by a new mechanical bonding technique that we developed, enabling the fabrication of high-quality junctions between materials, unobtainable by conventional approaches. We observe proximity-induced superconductivity in Bi2Se3 and Bi2Te3 persisting up to at least 80 K—a temperature an order of magnitude higher than any previous observations. Moreover, the induced superconducting gap in our devices reaches values of 10 mV, significantly enhancing the relevant energy scales. Our results open new directions for fundamental studies in condensed matter physics and enable a wide range of applications in spintronics and quantum computing.

5 pages of supplemental material

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