Spin blockade in ground state resonance of a quantum dot

– We present measurements on spin blockade in a laterally integrated quantum dot. The dot is tuned into the regime of strong Coulomb blockade, confining ∼ 50 electrons. At certain electronic states we find an additional mechanism suppressing electron transport. This we identify as spin blockade at zero bias, possibly accompanied by a change in orbital momentum in subsequent dot ground states. We support this by probing the bias, magnetic field and temperature dependence of the transport spectrum. Weak violation of the blockade is modelled by detailed calculations of non-linear transport taking into account forbidden transitions. Conventional electronics relies on controlling charge in semiconductor transistors. The ultimate limit of integration is reached when these transistors, termed quantum dots, are operated by exchanging single electrons only. The mechanism governing electron transport through dots is known as Coulomb blockade (CB) [1, 2]. Apart from this, electrons naturally possess a spin degree of freedom, which recently attracted considerable interest regarding the combination of spintronics and quantum information processing [3]. Hence, studies on the interplay of spin and charge quantum states in quantum dots form an integral contribution for defining and controlling electron spin quantum bits. One of the key techniques applied to study electronic structure in quantum dots is transport spectroscopy: Defining the dots by locally depleting a two-dimensional electron gas enables this direct monitoring of ground and excited states of the artificial atoms [4]. In contrast to Kondo physics [5] in the limit of transparent tunneling barriers between the quantum dot and the reservoirs, we are focusing on the regime of opaque barriers and Coulomb blockade. In other words the strong hybridization with electronic reservoir states found for the dot electrons in Kondo physics is suppressed and both electron spin and orbital quantum numbers remain well-defined.