A transistor that performs as both topological insulator and superconductor

MIT researchers have demonstrated that a tungsten ditelluride-based transistor combines two different electronic states of matter.

First two-dimensional material that performs as both topological insulator and superconductor
In two-dimensional tungsten ditelluride, two different states of matter — topological insulator and superconductor — can be chosen at will, MIT researchers discovered. Graphic: Sanfeng Wu

A transistor based on the 2-D material tungsten ditelluride (WTe2) sandwiched between boron nitride can switch between two different electronic states — one that conducts current only along its edges, making it a topological insulator, and one that conducts current with no resistance, making it a superconductor — researchers at MIT and colleagues from four other institutions have demonstrated.

Using four-probe measurements, a common quantum electronic transport technique to measure the electronic behavior of materials, the researchers plotted the current carrying capacity and resistance characteristics of the two-dimensional tungsten ditelluride transistor and confirmed their findings across a range of applied voltages and external magnetic fields at extremely low temperatures.

“This is the first time that the exact same material can be tuned either to a topological insulator or to a superconductor,” says Pablo Jarillo-Herrero, the Cecil and Ida Green Professor of Physics at MIT. “We can do this by regular electric field effect using regular, standard dielectrics, so basically the same type of technology you use in standard semiconductor electronics.”

A new class of materials

“This is the first of a new class of materials — topological insulators that can be tuned electrically into superconductors — which opens many possibilities which before there were significant obstacles to realize,” Jarillo-Herrero says. “Having one material where you can do this seamlessly within the same material to transition between this topological insulator and superconductor is something which is potentially very attractive.”

Tungsten ditelluride, which is one of the transition metal dichalcogenide materials, is classified as a semimetal and conducts electricity like metals in bulk form. The new findings detail that in a single-layer crystal form, at temperatures from less than 1 kelvin to liquid nitrogen range (-320.4 degrees Fahrenheit), tungsten ditelluride hosts three distinct phases: topologically insulating, superconducting, and metallic. An applied voltage drives the transition between these phases, which vary with temperature and electron concentration. In superconducting materials, electrons flow without resistance generating no heat.

The new findings have been published online in the journal Science. Valla Fatemi PhD ’18, who is now a postdoc at Yale, and postdoc Sanfeng Wu, who is a Pappalardo Fellow at MIT, are co-first authors of the paper with senior author Jarillo-Herrero. The co-authors are MIT graduate student Yuan Cao; former postdoc Landry Bretheau of the École Polytechnique in France; Quinn D. Gibson of the University of Liverpool in the UK; Kenji Watanabe and Takashi Taniguchi of the National Institute for Materials Science in Japan; and Robert J. Cava, a professor of chemistry at Princeton University.

Read more: First two-dimensional material that performs as both topological insulator and superconductor

Image courtesy of mit.edu

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