Reversal of thermoelectric current in tubular nanowires
Sept. 4, 2017
An international team of researchers, including an IFISC (CSIC-UIB) member, predicts an inversed current in nanowires subjected to strong thermal gradients.
The thermoelectric effect arises when the sides of a conductive material are held at different temperatures. The resulting energy difference drives an electric current. Usually, this flow of charge moves from the hot to the cold side. The effect can be exploited in different applications, such as the construction of high precision temperature-determining devices dubbed thermocouples. However, when the size of the system is reduced to the nanometric scale, special features show up.
An international team of researchers including a member of IFISC (UIB-CSIC) has shown using numerical simulations that in the case of nanometric tubular conductors (nanowires) the generated electric current can travel from the cold to the hot end, which may seem counter-intuitive. This surprising phenomenon has been observed in two types of nanowires, the so-called topological insulators and the core / shell nanowires. In both cases, a tubular conductive material with bulk insulating properties is required, so that the electrons are confined to move on the nanowire shell.
To obtain a reversal of the expected current, the system must be under the influence of a magnetic field perpendicular to the axis of the nanowire. The magnetic strength along with the temperature difference between the ends of the system allows to manipulate the sign of the current. This anomalous current can be observed even with nanowires with a certain level of impurities, although the magnitude of the anomalous current is reduced as the disorder degree increases.
The reversed current phenomenon had already been predicted and tested experimentally in the case of quantum dots; however, for the case of nanowires this paper predicts a much stronger current, which would ease its future technological applications.
Sigurdur I. Erlingsson, Andrei Manolescu, George Alexandru Nemnes, Jens H. Bardarson, and David Sanchez. Reversal of Thermoelectric Current in Tubular Nanowires. Physical Review Letters. DOI: 10.1103/PhysRevLett.119.036804
