Effect of Coulomb correlation on electron transport through concentric quantum ring-quantum dot structure

We theoretically study the single electron transfer through two-terminal quantum ring capacitively coupled to charged dot placed in its center. For this purpose we solve time-dependent Schrodinger equation for fully correlated two-particle system constituted by the transferred electron and the second particle confined in the dot. Analysis of transmission probability dependence on magnetic field in Ahronov-Bohm effect indicates that the maxima of transmission probability may be enhanced as well as reduced for attractive or repulsive Coulomb interaction respectively. The existence of Coulomb correlation in the system may also lead to inelastic scattering of the transferred electron. In such case, transmission of electron thorugh the ring is not completely blocked for (n+1/2) magnetic flux quanta

Thermoelectric performance of n-type Mg2Ge

Magnesium-based thermoelectric materials (Mg2X, X = Si, Ge, Sn) have received considerable attention due to their availability, low toxicity, and reasonably good thermoelectric performance. The synthesis of these materials with high purity is challenging, however, due to the reactive nature and high vapour pressure of magnesium. In the current study, high purity single phase n-type Mg2Ge has been fabricated through a one-step reaction of MgH2 and elemental Ge, using spark plasma sintering (SPS) to reduce the formation of magnesium oxides due to the liberation of hydrogen. We have found that Bi has a very limited solubility in Mg2Ge and results in the precipitation of Mg2Bi3. Bismuth doping increases the electrical conductivity of Mg2Ge up to its solubility limit, beyond which the variation is minimal. The main improvement in the thermoelectric performance is originated from the significant phonon scattering achieved by the Mg2Bi3 precipitates located mainly at grain boundaries. This reduces the lattice thermal conductivity by ~50% and increases the maximum zT for n-type Mg2Ge to 0.32, compared to previously reported maximum value of 0.2 for Sb-doped Mg2Ge

Electronic band structure, magnetic, transport and thermodynamic properties of In-filled skutterudites InxCo4Sb12

International audienceThe thermoelectric and thermodynamic properties of polycrystalline InxCo4Sb12 (0.0 <= x <= 0.26) skutterudites were investigated and analysed between 2 and 800K by means of electrical resistivity, thermopower, thermal conductivity and specific heat measurements. Hall effect, sound velocity and thermal expansion measurements were also made in order to gain insights into the transport and elastic properties of these compounds. The impact of the In filling on the crystal structure as well as the thermal dynamics of the In atoms were tracked down to 4K using powder neutron diffraction experiments. Analyses of the transport data were compared with the evolution of the electronic band structure with x determined theoretically within the Korringa-Kohn-Rostoker method with the coherent potential approximation. These calculations indicate that In gives rise to a remarkably large p-like density of states located at the conduction band edge. The electrical properties show typical trends of heavily doped semiconductors regardless of the In content. The thermal transport in CoSb3 is strongly influenced by the presence of In in the voids of the crystal structure resulting in a drop in the lattice thermal conductivity values in the whole temperature range. The low value of the Gruneisen parameter suggests that this decrease mainly originates from enhanced mass-fluctuations and point-defect scattering mechanisms. The highest thermoelectric figure of merit ZT similar to 1.0 at 750K was achieved at the maximum In filling fraction, i.e. for x = 0.26