Coulomb-Blockade Oscillations in the Thermopower of a Quantum Dot

Abstract

PACS. 73.60 -Electronic properties of thin films. PACS. 72.20P -Thermoelectric effects. PACS. 73.40G -Tunnelling: general.Abstract. -The thermopower of a quantum dot, defmed in the two-dimensional electron gas in a GaAs-Alj-Ga! _ ^As heterostructure, is investigated using a current heating technique. At lattice temperatures k^T much smaller than the charging energy e 2 /C, and at small heating currents, sawtoohlike thermopower oscillations are observed äs a function of gate voltage, in agreement with a recent theory. In addition, a remarkable sign reversal of the amplitude of the thermopower oscillations is found in the non-linear regime at large heating currents.Single-electron tunnelling [1] is the dominant mechanism governing the transport properties of a quantum dot that is weakly coupled to reservoirs by tunnel barriers. At temperatures T such that k B T«e 2 /C, with C the capacitance of the dot, it leads the Coulomb-blockade oscillations in the conductance äs a function of the voltage applied to a capacitively coupled gate electrode [2]. Whereas the conductance has been studied extensively, the thermo-electric properties of a quantum dot remain essentially unexplored. Amman et al. have studied theoretically the role of Coulomb interactions on thermo-electric effects in a single mesoscopic tunnel junction, and have used their results to Interpret the thermopower of granulär thin bismuth films [3]. Recently, a theory was developed for the thermopower of a quantum dot in the Coulomb-blockade regime [4]. This theory predicts sawtoothlike oscillations in the thermopower äs a function of the Fermi energy in the reservoirs, with an amplitude that is determined by the charging energy and temperature only.Here, we present an experimental study of the thermo-electric properties of a quantum dot, using the current-heating technique applied previously to study the thermovoltage across a quantum point-contact [5]. At low lattice temperatures and small heating currents,

Extracting net current from an upstream neutral mode in the fractional quantum Hall regime

“…3a). However, the thermo-electric current I te , driven solely by a temperature gradient across the dot, will strongly depend on the position of the dot's relevant energy level (E D ) with respect to the Fermi energy (e F ) 20,21 . When E D oe F electrons will flow from the cold to the hot lead, whereas when E D 4e F they will run in the opposite direction (Fig.…”

Theory of the thermopower of a quantum dot

“…This is the regime of single-electron tunneling through a quantum dot of small capacitance. The measured thermopower 15 shows pronounced oscillations äs a function of gate voltage (i.e., essentially äs a function of Fermi energy). The thermopower oscillations have the same periodicity äs the oscillations in the conductance of the same structure.…”

“…Electron-electron interactions do not play a dominant role in these two regimes. Very recently, thermoelectric experiments 15 have been performed in a transport regime, where the interactions are of crucial importance. This is the regime of single-electron tunneling through a quantum dot of small capacitance.…”

Fate of the spin- 12 Kondo effect in the presence of temperature gradients

“…By combining Eqs. (16) and (17) in a single complex equation and resorting to the Fourier space one gets …”

“…In the nonlinear regime of transport, Ref. [16] observed a sign change in the thermovoltage V th with the applied thermal bias θ. More recently, Svensson et al [17] found analogous nonlinear effects in V th for nanowire QDs.…”