We report low-temperature transport measurements on Coulomb blockaded double quantum dots in coaxial Ge/Si nanowires [1]. Carriers in our wires are known to be holes in the valence band of the Ge core [1]: in such a confined system it is expected that the g-factor will be strongly dependent on the angular momentum of the hole states in the nanowire as a consequence of the mixing between light holes and heavy holes [2]. Multiple quantum dots reported here are obtained by the fabrication of local nanofinger gates patterned on top of the wire [3,4]. These allow defining either a single big quantum dot or two coupled dots with a selectively controllable population of the individual islands. The inter-dot coupling can be fully tuned and Coulomb blockade measurements at low-temperature attest the evolution between different coupling regimes ranging from a single big dot to two smaller decoupled dots. In addition to this we present Coulomb blockade spectroscopy data of a single dot in different orientations of the external magnetic field. We discuss the evolution of the Coulomb blockade peaks and of peaks spacing and we provide limits for the value of the g-factor in our devices.
[1] "Ge/Si nanowire heterostructures as high-performance field-effect transistors", J. Xiang, W. Lu, Y. Hu, Y. Wu, H. Yan and C.M. Lieber, Nature 441, 489 (2006).
[2] "Zeeman splitting in cylindrical hole quantum wires", U. Zulicke and C. Csontos, in publication on Current Applied Physics.
[3] "Tunable Double Quantum Dots in InAs Nanowires Defined by Local Gate Electrodes", C. Fast, A. Fuhrer, M. T. Björk, L. Samuelson, NanoLetters 5, 1487 (2005).
[4] "Top-gate defined double quantum dots in InAs nanowires", A. Pfund, I. Shorubalko, R. Leturcq, K. Ensslin, Appl. Phys. Lett. 89, 252106 (2006). |