Available online at www.sciencedirect.com Physica E 17 (2003) 584–588 www.elsevier.com/locate/physe Capacitively coupled quantum dots as a single-electron switch I.H. Chan a , P. Fallahi a , R.M. Westervelt a ; * , K.D. Maranowski b , A.C. Gossard b a Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA b Materials Department, University of California at Santa Barbara, Santa Barbara, CA 93106, USA Abstract A double quantum dot in a GaAs/AlGaAs heterostructure with strong interdot capacitance but no interdot tunneling can be constructed using a oating metal gate that covers both dots and an etched trench between the dots that prevents tunneling. The interdot capacitance CINT =0:34C between Dots 1 and 2, measured using the Coulomb blockade, was signicantly larger than that measured for similar dots without a oating gate. When a single electron is added to Dot 1 the charge couples to Dot 2, and vice versa, causing the Coulomb blockade peaks to split. The change in dot conductance from peak splitting can be as large as two orders of magnitude, allowing the double dot to be used as a single-electron switch. The split conductance peaks observed for weak tunneling from each dot to its leads were t by a thermally broadened line shape, and good agreement with the data was found. Charge uctuations induced by stronger tunneling from Dot 2 to its leads softened the splitting transition on Dot 1 that was maintained in the weak tunneling regime. Under the same conditions the splitting for Dot 2 remained sharp. ? 2002 Elsevier Science B.V. All rights reserved. Keywords: Quantum dots; Coulomb blockade; Single-electronics; Switch 1. Introduction Quantum dots have been studied extensively [1–3] and the eect of tunneling on the Coulomb blockade behavior in a double-dot system is well understood [4–9]. We turn to explore the Coulomb blockade behavior of a capacitively coupled double quantum dot system in which there is no tunneling between the dots [10]. While there have been experiments that used capacitively coupled dots to measure the charge of a device [11], they were operated in the linear regime where the conductance of the dot was * Corresponding author. Tel.: +1-617-495-3296; fax: +1-617-495-9837. E-mail address: westervelt@deas.harvard.edu (R.M. Westervelt). essentially a linear function of the charge being mea- sured. This paper describes the Coulomb blockade behavior of a strongly capacitively coupled quantum dot system, and shows how its non-linear conduc- tance versus charge behavior can be employed as a single-electron switch. Single-electron switches may be used in logic circuits and possible implementations of quantum information processing. 2. Device The device used in this experiment is shown in Fig. 1(a) together with a schematic of the coupled dots in perspective (Fig. 1(b)). The device was made in a two-dimensional electron gas (2DEG) inside a GaAs/AlGaAs heterostructure using electron-beam 1386-9477/03/$ - see front matter ? 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S1386-9477(02)00876-7