Signature of the Overhauser field on the coherent spin dynamics of donor-bound electron in a single CdTe quantum well

We have studied the coherent spin dynamics in an oblique magnetic field of electrons localized on donors and placed in the middle of a single CdTe quantum well, by using a time-resolved optical technique: the photo-induced Faraday rotation. We showed that this dynamics is affected by a weak Overhauser field created via the hyperfine interaction of optically spin-polarized donor-bound electrons with the surrounding nuclear isotopes carrying non-zero spins. We have measured this nuclear field, which is on the order of a few mT and can reach a maximum experimental value of 9.4 mT. This value represents 13 % of the maximal nuclear polarization, and corresponds also to 13 % of maximal electronic polarization.Comment: 15 pages, 4 figure

Hole spin dephasing time associated to hyperfine interaction in quantum dots

The spin interaction of a hole confined in a quantum dot with the surrounding nuclei is described in terms of an effective magnetic field. We show that, in contrast to the Fermi contact hyperfine interaction for conduction electrons, the dipole-dipole hyperfine interaction is anisotropic for a hole, for both pure or mixed hole states. We evaluate the coupling constants of the hole-nuclear interaction and demonstrate that they are only one order of magnitude smaller than the coupling constants of the electron-nuclear interaction. We also study, theoretically, the hole spin dephasing of an ensemble of quantum dots via the hyperfine interaction in the framework of frozen fluctuations of the nuclear field, in absence or in presence of an applied magnetic field. We also discuss experiments which could evidence the dipole-dipole hyperfine interaction and give information on hole mixing.Comment: 35 pages, 7 figures and 2 table

Bistability of the Nuclear Polarisation created through optical pumping in InGaAs Quantum Dots

We show that optical pumping of electron spins in individual InGaAs quantum dots leads to strong nuclear polarisation that we measure via the Overhauser shift (OHS) in magneto-photoluminescence experiments between 0 and 4T. We find a strongly non-monotonous dependence of the OHS on the applied magnetic field, with a maximum nuclear polarisation of 40% for intermediate magnetic fields. We observe that the OHS is larger for nuclear fields anti-parallel to the external field than in the parallel configuration. A bistability in the dependence of the OHS on the spin polarization of the optically injected electrons is found. All our findings are qualitatively understood with a model based on a simple perturbative approach.Comment: Phys Rev B (in press

Correcting the Shrinkage Effects of Formalin Fixation and Tissue Processing for Renal Tumors: toward Standardization of Pathological Reporting of Tumor Size

Given the importance of correctly staging renal cell carcinomas, specific guidelines should be in place for tumor size measurement. While a standard means of renal tumor measurement has not been established, intuitively, tumor size should be based on fresh measurements. We sought to assess the accuracy of postfixation and microscopic measurements of renal tumor size, as compared to fresh measurements and radiographic size. Thirty-four nephrectomy cases performed by a single surgeon were prospectively measured at different time points. The study cases included 23 clear cell renal cell carcinomas, 6 papillary renal cell carcinomas, and 5 other renal tumors. Radiologic tumors were 12.1% larger in diameter than fresh tumors (P<0.01). Furthermore, fresh specimens were 4.6% larger than formalin-fixed specimens (P<0.01), and postfixation measurements were 7.1% greater than microscopic measurements (P<0.01). The overall mean percentage of shrinkage between fresh and histological specimens was 11.4% (P<0.01). Histological processing would cause a tumor stage shift from pT1b to pT1a for two tumors in this study. The shrinkage effects of formalin fixation and histological processing may result in understaging of renal cell carcinomas. The shrinkage factor should be considered when reporting tumor size

Spatially-resolved potential measurement with ion crystals

We present a method to measure potentials over an extended region using one-dimensional ion crystals in a radio frequency (RF) ion trap. The equilibrium spacings of the ions within the crystal allow the determination of the external forces acting at each point. From this the overall potential, and also potentials due to specific trap features, are calculated. The method can be used to probe potentials near proximal objects in real time, and can be generalized to higher dimensions.Comment: 7 pages (double spaced), 3 figure