The thermopower of a Kondo-correlated gate-defined quantum dot is studied using a current heating technique. In the presence of spin correlations the thermopower shows a clear deviation from the semiclassical Mott relation between thermopower and conductivity. The strong thermopower signal indicates a significant asymmetry in the spectral density of states of the Kondo resonance with respect to the Fermi energies of the reservoirs. The observed behavior can be explained within the framework of an Anderson-impurity model.Keywords: Thermoelectric and thermomagnetic effects, Coulomb blockade, single electron tunneling, 73.23.Hk The Kondo effect due to magnetic impurity scattering in metals is a well known and widely studied phenomenon [1]. The effect has recently received much renewed attention since it was demonstrated [2,3] that the Kondo effect can significantly influence transport through a semiconductor quantum dot (QD). In a gate defined QD, the electronic states can be controlled externally, which allows experimenters to address many questions concerning Kondo physics [4] that were previously inaccessible. As yet unexplored are the thermoelectric properties of a QD in the presence of Kondo correlations. This is unfortunate, since these properties often yield valuable additional information concerning transport phenomena. For example, the thermopower (TP) S is related to the average energy E with respect to the Fermi energy E F of the particles contributing to the transport by [5,6] where V T is the thermovoltage, ∆T the applied temperature difference, and e the elementary charge. S is therefore a direct measure of the weighted spectral density of states in a correlated system with respect to the Fermi energy E F . Moreover, the TP can be used to determine the spin-entropy flux accompanying electron transport, which sets boundaries on the operating regime of spinbased quantum computers [7]. Spin entropy was recently shown to be the origin of the giant thermoelectric power of layered cobalt oxides [8], and one may anticipate similarly large effects for single quantum dots. where k B is Boltzmann's constant, and G(E) is the energy-dependent conductance of the QD. Figure 1 shows an SEM-photograph of the sample structure. This structure is fabricated by electron-beam lithography on a (Al,Ga)As/GaAs heterostructure containing a two dimensional electron gas (2DEG) with carrier density n s = 2.3 × 10 15 m −2 and mobility µ = 100 m 2 /(Vs). Gates A, D, E, and F form the QD and gates A, B, C, and D are the boundaries of the electronheating channel, which is 20 µm long and 2 µm wide. The QD has a lithographical diameter of approximately 250 nm and has a design [9] that allows great flexibility in the number of electron on the dot. For the present experiment, the barriers are adjusted such that the number of electrons can be varied conveniently (i.e., by changing only the voltage V E applied to plunger gate E) between 20 and 40, as can be deduced from the magnetic-field evolution of the CB peaks. The sample is mount...

We report the observation of thermal rectification in a semiconductor quantum dot, as inferred from the asymmetric line shape of the thermopower oscillations. The asymmetry is observed at high in-plane magnetic fields and caused by the presence of a high orbital momentum state in the dot.

We have studied the temperature dependent thermopower of gate-defined, lateral quantum dots in the Coulomb blockade regime using an electron heating technique. The line shape of the thermopower oscillations depends strongly on the contributing tunneling processes. Between 1.5 K and 40 mK a crossover from a pure sawtooth-to an intermitted sawtooth-like line shape is observed. The latter is attributed to the increasing dominance of cotunneling processes in the Coulomb blockade regime at low temperatures.

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Within a very few years, InAs/GaSb superlattice technology has proven its suitability for high-performance infrared imaging detector arrays. At the Fraunhofer Institute for Applied Solid State Physics (IAF) and AIM InfrarotModule GmbH, efforts have been focused on developing mature fabrication technology for dual-color InAs/GaSb superlattice focal-plane arrays for simultaneous, colocated detection at 3 lm to 4 lm and 4 lm to 5 lm in the mid-wavelength infrared atmospheric transmission window. Integrated into a wide-field-of-view missile approach warning system for an airborne platform, a very low number of pixel outages and cluster defects is mandatory for bispectral detector arrays. Process refinements, intense root-cause analysis, and specific test methodologies employed at various stages during the process have proven to be the key for yield enhancements.