CNR NANO - Istituto Nanoscienze Consiglio Nazionale delle Ricerche

- 05.03.2019 - NEST Seminar Liliana Arrachea
Date and Time: Tuesday March 5, 2019 - 11:00
Venue: NEST Seminar Room

Speaker: prof. Liliana Arrachea
International Center for Advanced Studies, Universidad Nacional de San Martín, Argentina

Title: Thermoelectric effects in structures of the quantum Hall effect and the quantum spin Hall

Abstract: Boosting the efficiency for the conversion of electrical and thermal energy at finite power is motivating an intense research activity, not only in the areas of material science and applied physics but also in experimental and theoretical areas of statistical mechanics and condensed matter physics. Efforts are concentrated in developing new materials and devices as well as on analyzing different operational conditions.
In the latter direction, taking advantage of the quantum effects is one of the most interesting avenues. Nanostructured devices operating at low temperatures are particularly appealing quantum devices, since they offer the conditions for coherent transport, where “parasitic” heat currents by phonons are strongly suppressed.
A two-dimensional electron gas in the quantum Hall regime is one of the most paradigmatic examples of quantum coherent transport. In the first part of the talk, I will present recent results on the thermoelectric response of a quantum dot embedded in a constriction of a quantum Hall bar with fractional filling factors ? = 1/m within Laughlin series. The “figure of merit” ZT for the maximum efficiency at a fixed temperature difference and the thermopower show a significant enhancement in the fractional filling in relation to the integer-filling case, which is a direct consequence of the fractionalization of the electron in the fractional quantum Hall states.
In the second part of the talk I will present results on the thermoelectric response of a device containing a pair of helical edge states of the quantum spin Hall effect, connected to an external reservoir with different chemical potential and temperature through a side quantum dot. Different operational modes can be induced by applying a magnetic field B and a gate voltage Vg at the quantum dot.
At finite B, the quantum dot acts simultaneously as a charge and a spin filter.
Charge and spin currents are induced, not only through the quantum dot, but also along the edge states. We focus on linear response and analyze the regimes, which we identify as charge heat engines or refrigerator, spin heat engine and spin refrigerator.
Finally, I will briefly comment on recent experimental and theoretical results of thermoelectricity in Corbino structures of the quantum Hall effect.