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Neutron-scattering experiments have been performed on lightly-doped La2−xSrxCuO4 single crystals in both the insulating (x = 0.03, 0.04, 0.05) and superconducting (x = 0.06) regions. Elastic magnetic peaks are observed at low temperatures in all samples with the maximum peak linewidth occuring at the critical concentration xc = 0.05. New incommensurate peaks are observed only at x = 0.05, the positions of which are rotated by 45• in reciprocal space about (π, π) from those observed for x ≥ 0.06 in the superconducting phase.PACS numbers: 74.72. Dn, 75.10.Jm, 75.50.Ee, 71.45.Ln, 75.70.Kw The interplay between magnetism and superconductivity has been a central issue in research on high-T c superconductivity for over a decade. Recently Yamada et al.

We present an experimental study of the fluctuations of Coulomb blockade peak positions of a quantum dot. The dot is defined by patterning the two-dimensional electron gas of a silicon MOSFET structure using stacked gates. This permits variation of the number of electrons on the quantum dot without significant shape distortion. The ratio of charging energy to single particle energy is considerably larger than in comparable GaAs/AlGaAs quantum dots. The statistical distribution of the conductance peak spacings in the Coulomb blockade regime was found to be unimodal and does not follow the Wigner surmise. The fluctuations of the spacings are much larger than the typical single particle level spacing and thus clearly contradict the expectation of random matrix theory.PACS numbers: 73.23. Hk,05.45.+b,73.20.Dx The spectral properties of many quantum mechanical systems whose classical behavior is known to be chaotic are remarkably well described by the theory of random matrices (RMT) [1]. This has been experimentally confirmed, for example, in measurements of slow neutron resonances of nuclei [2] and in microwave reflection spectra of billiard shaped cavities [3]. Electron transport experiments performed on semiconductor quantum dots in the Coulomb blockade (CB) regime [4] provide a further possibility to check RMT predictions. The classical motion of electrons in these structures can be assumed to be chaotic due to an irregular potential landscape produced by impurities, an asymmetric confinement potential [5], and/or electron-electron interactions [6]. The transport properties of quantum dots are inherently related to their energy spectra and electronic wavefunctions and thus the connection with RMT is readily made [5,7].Indeed, experiments on the distribution of conductance peak heights of quantum dots in the Coulomb blockade regime have shown good agreement with the predictions of RMT [8,9]. On the other hand, the distribution of the CB peak spacings have been found to deviate from the expectations of RMT [10][11][12]. The results suggest that the peak spacings are not distributed according to the famous Wigner surmise. Furthermore, there is no indication of spin degeneracy which would result in a bimodal peak spacing distribution [12]. In Refs. [10,11] the fluctuations of the peak spacings are considerably larger than expected from RMT, whereas the experiments presented in Ref.[12] yield smaller peak spacing fluctuations, which, however, are still larger than those predicted by RMT.The deviations from the RMT predictions have been frequently interpreted as fluctuations in the charging energy. As the charging energy reflects the Coulomb interactions both between the electrons on the dot as well as between the dot and its environment, the dependence of the fluctuations on the interaction strength is of fundamental interest. Numerical studies suggest that the fluctuations are proportional to the charging energy rather than to the single particle level spacing [10,13,14]. This is also found theoretically for the c...