2007/05/31 by Rogerio de Sousa · 1 citation
Physics and Astronomy · #cond-mat.mes-hall #cond-mat.mtrl-sci
paper · pdf · doi:10.1103/physrevb.76.245306
published as Phys. Rev. B 76, 245306 (2007) · Final published version
arxiv created 2008/01/19 · arxiv updated 2009/12/01
We propose a model for magnetic noise based on spin-flips (not electron-trapping) of paramagnetic dangling-bonds at the amorphous-semiconductor/oxide interface. A wide distribution of spin-flip times is derived from the single-phonon cross-relaxation mechanism for a dangling-bond interacting with the tunneling two-level systems of the amorphous interface. The temperature and frequency dependence is sensitive to three energy scales: The dangling-bond spin Zeeman energy delta, as well as the minimum (Emin) and maximum (Emax) values for the energy splittings of the tunneling two-level systems. We compare and fit our model parameters to a recent experiment probing spin coherence of antimony donors implanted in nuclear-spin-free silicon [T. Schenkel \it et al., Appl. Phys. Lett. 88, 112101 (2006)], and conclude that a dangling-bond area density of the order of 1014cm-2 is consistent with the data. This enables the prediction of single spin qubit coherence times as a function of the distance from the interface and the dangling-bond area density in a real device structure. We apply our theory to calculations of magnetic flux noise affecting SQUID devices due to their Si/SiO2 substrate. Our explicit estimates of flux noise in SQUIDs lead to a noise spectral density of the order of 10-12Phi02 Hz-1 at f=1Hz. This value might explain the origin of flux noise in some SQUID devices. Finally, we consider the suppression of these effects using surface passivation with hydrogen, and the residual nuclear-spin noise resulting from a perfect silicon-hydride surface.