Physics

Factoring in Noise

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Science  12 Feb 2010:
Vol. 327, Issue 5967, pp. 762
DOI: 10.1126/science.327.5967.762-b

Quantum dots are semiconducting nanostructures often referred to as “artificial atoms” because of the discreteness of their energy levels. However, unlike real atoms, quantum dots of a given elemental formula are not all created equal: A typical manufacturing process inevitably results in dots that vary in shape and size, leading to differences in energy levels and other properties. Thus, the full ensemble of quantum dots must be carefully characterized before the potential use of its constituents in spintronics and quantum information applications. One of the most important properties in these contexts is the current carriers' response to external magnetic fields, quantified by the so-called Landé or g factor. The g factor is usually measured through optical pump-probe studies. Now, Crooker et al. have analyzed the weak spin noise signature in (In,Ga)As/GaAs quantum dots using sophisticated power spectral averaging to extract the response of both negative (electron) and positive (hole) carriers. The applied magnetic field causes the carriers' spins to precess and centers the spin fluctuation spectrum at the associated Larmor frequency, proportional to the g factor. The study reveals that the hole g factor is highly anisotropic and that within the sample this anisotropy varies monotonically with the quantum dot confining energy.

Phys. Rev. Lett. 104, 36601 (2010).

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