Luiz Nunes Oliveira
University of São Paulo
luizno@usp.br

THERMAL DEPENDENCE OF THE ZERO-BIAS CONDUCTIANCE OF NANODEVICES

in collaboration with A. C. Seridonio (University of Brasilia) and M. Yoshida (University of the State of São Paulo)

In the late 1980’s, two independent theoretical publications pointed out that the Anderson model for dilute magnetic alloys should describe low-temperature transport in nanodevices. A decade later, the development of the single-electron transistor -a quantum dot bridging two otherwise independent two-dimensional electron gases- rectified those predictions: the universal curve g_univ(T) for the thermal dependence of the impurity contribution to the resistivity of a dilute magnetic alloy was shown to reproduce quantitatively the measured conductances through the quantum dot. More recently, more complex nanostructures such as the side-coupled device, which couples a quantum dot to a quantum wire coupled to two electrodes, were developed. In the side-coupled device, a gate voltage V_g is applied to the quantum dot. Plotted as a function of V_g, the measured current through the electrodes displays Fano antiresonances, instead of the flat plateaus observed in single-electron transistors. The antiresonances are signatures of the interference between the currents through the wire and the dot, which breaks the proportionality between the measured conductance and g_univ(T). This work will show that the thermal dependence of the conductance can nonetheless be mapped onto g_univ(T). The mapping is linear, with coefficients that depend on the low-temperature phase shift in the quantum wire due to its coupling to the dot. As an illustration, a numerical renormalization-group diagonalization of the Anderson Hamiltonian, from which the temperature-dependent conductance of the side-coupled device was computed, will be reported; results for various ratios between the currents through the dot and the wire will be compared with the expected mapping to g_univ(T). In addition, the conductance measurements recently published by Sato et al. [Phys. Rev. Lett. 95, 066801 (2005)] will be discussed. It will be shown that the mapping yields conductance curves in excellent agreement with the experimental data and provides first-principle justification for the authors’ phenomenological interpretation
of their data. Work supported by the CNPq, FAPESP, and IBEM (Brazil).