Spin droplets and the 5/2 state in confined quantum Hall systems

Esa Räsänen

Freie Universität Berlin, Germany

We have studied semiconductor quantum dots in the filling-factor range 2 - 3. In this regime, our theoretical and experimental results give evidence of a collective spin polarization on the highest occupied Landau level [1]. The effect appears as a formation of an energetically stable spin droplet in the core of the quantum dot, requiring that the total number of electrons in the dot is sufficiently large (~> 30). The spin-droplet formation corresponds to particular characteristics in the spin-blockade transport data. Interestingly, the filling factor 5/2 state is found to correspond to the maximum spin droplet. In contrast with the case of the 2D electron gas, the 5/2 state in quantum dots has a small overlap with the Pfaffian wave function, indicating the absence of electron pairing in confined geometries [2].
[1] E. Räsänen et al., Phys. Rev. B 77, 041302(R) (2008).
[2] A. Harju, H. Saarikoski, and E. Räsänen, Phys. Rev. Lett. 96, 126805 (2006).