Time:  13:30

Room: in Zaal E, TNW building, Delft 

abstract:

Pumping transport mechanisms have attracted much interest as an alternative means to generate charge and spin currents in the absence of a bias voltage. The pumping current results from periodic modulation of certain system parameters of a nanostructure connected to source and drain leads. Of particular interest has been the quantized regime when the current varies in steps of ef as a function of the system parameters, where e is the electron charge and f is the frequency of modulation.

Much theoretical and experimental work has been devoted to the adiabatic regime, when the time variation of the parameters is slow compared to characteristic relaxation times of the system, and current quantization has been achieved almost 20 years ago [1]. In the non-adiabatic regime the system is driven out of equilibrium and the frequency f becomes another control parameter. Owing to the complex interplay between tunneling rates and frequency experimental realizations have only recently shown quantization [2]. In this work we will present recent developments in non-adiabatic quantized charge pumping in AlGaAs/GaAs nanowire based devices. The wire is crossed by several metallic top gates, set to negative voltages to define a quantum dot (QD). Single parameter non-adiabatic charge pumping [3] is achieved by applying modulation frequencies of f = 0.001 to 3 GHz to one of the outer gates defining the QD, tuning the current into the quantized regime.

Driving a quantized current by a single parameter, is of practical importance in the development of a quantum current standard: up-scaling of the quantized current by parallel operation can be realized immediately [5]. Furthermore the device can serve as a building block for integrated quantized circuits thereby enabling new device functionalities. We will present results on a serial circuit of a single charge pump and a quantum Hall device allowing for the first time the generation of quantized voltages V = (h/e)f by an all semiconductor device [6].

[1] H. Pothier et al., Europhys. Lett. 17, 249 (1992).

[2] M. Blumenthal et al., Nature Physics 3, 343 (2007).

[3] B. Kaestner et al., Phys. Rev. B 77, 153301 (2008); V. Kashcheyevs & B. Kaestner, Phys. Rev. Lett. 104, 186805 (2010).

[4] P. Mirovsky et al., submitted to Apl. Phys. Lett.

[5] B. Kaestner et al., Appl. Phys. Lett. 94, 012106 (2009).

[6] F. Hohls et al., arXiv:1103.1746v1.