Research Associate, University of Cambridge
I'm investigating a new material which is a potential platform to build a quantum computer
Futuristic computers are expected to be built not from ordinary bits, but so-called 'quantum bits' (or qubits) which rely on the striking and counterintuitive quantum effects that appear in matter at very low temperatures. In contrast to bits which assume on of two discrete values (0 or 1), qubits can be 0 and 1 simultaneously! This property stems directly from the quantum mechanical phenomenon known as superposition. The principle advantage qubits have on offer, therefore, is that one can simultaneously operate on the entire spectrum of possible values rather than doing so serially using bits. That, however, is still some distance in the future. Currently the scientific community is working towards identifying the most suitable material from which stable and robust qubits can be built. Theory predicts that a special class of superconductors are ideally suited for this and can maintain this superposition property with minimal error. Unfortunately, however, to date it appears that such superconductors do not occur naturally and thus several groups have resorted to engineering such a superconductor through a combination of different materials. My recent research challenges this notion in that I have shown that germanium telluride is a material which may naturally harbour this kind of superconductivity. This remarkable materials is semiconducting, which means its electrical characteristics can be tuned, it is superconducting at low temperatures, and most importantly, it has an enormous ‘spin-orbit field’ – an inherent magnetic field that depends on the velocity/direction of mobile charges within in. These are precisely the ingredients that theory predicts are necessary to induce the special superconductivity which has come to be known as ‘topological superconductivity’. My results thus far show that the superconducting state in germanium telluride has clear signatures of topological superconductivity, most notably in its energy spectrum. Conventional superconductors have a gap in the energy spectrum whereas germanium telluride does not. Furthermore, and once again in contrast to conventional superconductors, superconductivity in germanium telluride appears to be stabilised by a small magnetic field. The discovery of a naturally occurring topological superconductor is a major breakthrough and will greatly facilitate future technological endeavours based on the wonderful manifestations of quantum mechanics.
Abstract: There is much current interest in combining superconductivity and spin–orbit coupling in order to induce the topological superconductor phase and associated Majorana‐like quasiparticles which hold great promise towards fault‐tolerant quantum computing. Experimentally these effects have been combined by the proximity‐coupling of super‐conducting leads and high spin–orbit materials such as InSb and InAs, or by controlled Cu‐doping of topological insu‐lators such as Bi2Se3. However, for practical purposes, a single‐phase material which intrinsically displays both these effects is highly desirable. Here we demonstrate coexisting superconducting correlations and spin–orbit coupling in molecular‐beam‐epitaxy‐grown thin films of GeTe. The former is evidenced by a precipitous low‐temperature drop in the electrical resistivity which is quelled by a magnetic field, and the latter manifests as a weak antilocalisation (WAL) cusp in the magnetotransport. Our studies reveal several other intriguing features such as the presence of two‐dimensional rather than bulk transport channels below 2 K, possible signatures of topological superconductivity, and unexpected hysteresis in the magnetotransport. Our work demonstrates GeTe to be a potential host of topological SC and Majorana‐like excitations, and to be a versatile platform to develop quantum information device architectures. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)
Pub.: 18 Jan '16, Pinned: 30 Jun '17
Abstract: Majorana fermions are particles identical to their own antiparticles. They have been theoretically predicted to exist in topological superconductors. Here, we report electrical measurements on indium antimonide nanowires contacted with one normal (gold) and one superconducting (niobium titanium nitride) electrode. Gate voltages vary electron density and define a tunnel barrier between normal and superconducting contacts. In the presence of magnetic fields on the order of 100 millitesla, we observe bound, midgap states at zero bias voltage. These bound states remain fixed to zero bias, even when magnetic fields and gate voltages are changed over considerable ranges. Our observations support the hypothesis of Majorana fermions in nanowires coupled to superconductors.
Pub.: 14 Apr '12, Pinned: 30 Jun '17
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