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101.
M. N. Khannanov I. V. Kukushkin S. I. Gubarev J. Smet K. von Klitzing W. Wegscheider C. Gerl 《JETP Letters》2007,85(5):242-245
The dependence of the heavy-hole cyclotron mass in GaAs(001) quantum wells on the 2D-hole density has been measured by the optical detection method for resonance microwave by-absorption. A significant increase (almost doubling) has been observed in the cyclotron mass of heavy holes with an increase in the charge carrier density from 1.2 × 1010 cm?2 to 1.3 × 1011 cm?2. 相似文献
102.
103.
M. Sigrist S. Gustavsson T. Ihn K. Ensslin D. Driscoll A. Gossard M. Reinwald W. Wegscheider 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):5
Few-electron quantum dots with integrated charge read-out have been fabricated by layered local anodic oxidation of a Ga[Al]As heterostructure and a thin Titanium top gate. The additional set of gates provided by the metallic film is used to tune the quantum dots into the few-electron regime. Current through the quantum dots and the quantum dot charge have been simultaneously measured for electron numbers varying between zero and two. The singlet–triplet splitting varies in two different samples between 0.5 and 1.5 meV. The Zeeman splitting of the first conductance resonance is observed in parallel magnetic field. The high tunability and straightforward implementation of these structures are promising for future nanostructure design. 相似文献
104.
Keyser UF Fühner C Borck S Haug RJ Bichler M Abstreiter G Wegscheider W 《Physical review letters》2003,90(19):196601
A small quantum ring with less than ten electrons was studied by transport spectroscopy. For strong coupling to the leads a Kondo effect is observed and used to characterize the spin structure of the system in a wide range of magnetic fields. At small magnetic fields Aharonov-Bohm oscillations influenced by Coulomb interaction appear. They exhibit phase jumps by pi at the Coulomb-blockade resonances. Inside Coulomb-blockade valleys the Aharonov-Bohm oscillations can also be studied due to the finite conductance caused by the Kondo effect. Astonishingly, the maxima of the oscillations show linear shifts with increasing magnetic field and gate voltage. 相似文献
105.
Reinhard Sehwesinger Rudolf Waditschatka James Rigby Ren Nordmann Wolfhard B. Schweizer Engelbert Zass Albert Eschenmoser 《Helvetica chimica acta》1982,65(2):600-610
The Pyrrocorphin Ligand System: Synthesis of 2,2,7,7,12,12,17-Heptamethyl-2,3,7,8,12,13-hexahydroporphyrin Reaction Schemes 4 and 6 summarize the synthesis of the title compound, a representative of a recently described novel type of hexahydroporphinoid ligand system (‘pyrrocorphin’). Pyrrocorphins incorporate structural elements of both corrins and porphyrins and are chemically closely related to the tautomeric non-pyrrolic corphins (Scheme 1). The synthesis exemplifies a methodology for constructing pyrrolic hydro-porphinoids with the methods of corrin instead of porphyrin synthesis. An X-ray analysis of 2-(cyanomethyl)-2-methyl-3-oxobutanamide has been carried out. 相似文献
106.
Reliable standardization is a serious problem for most analytical methods. In spite of extensive work on interferences, the results are not suited for prediction of gross errors in any particular case. This paper is intended to show the power of sequential testing in practical atomic-absorption spectrometric analyses for the efficient detection of interferences causing changes in sensitivity; this test is carried out by comparing the sensitivity of the standard with the sensitivity for the sample, as determined by the difference between the signals for the spiked and unspiked samples. The simple computations can be carried out instantly and experimentation is terminated as soon as a conclusion can be drawn. The major advantage over the traditional tests lies in the smaller number of independent measurements, requiring less time and sample. Three separate cases are discussed: with the mean sensitivity of the standard known and the deviation expected to occur in one direction only (single-sided alternative hypothesis); with the standard deviation of the determination known and the deviation possibly occurring in both directions (double-sided alternative hypothesis); and with the mean and the standard deviation unknown but estimated during the test (sequential t-test). It is shown that assumptions about the normal distribution of the data do not impose serious restrictions in practical AAS work. 相似文献
107.
Ganichev SD Ivchenko EL Danilov SN Eroms J Wegscheider W Weiss D Prettl W 《Physical review letters》2001,86(19):4358-4361
A nonequilibrium population of spin-up and spin-down states in quantum well structures has been achieved applying circularly polarized radiation. The spin polarization results in a directed motion of free carriers in the plane of a quantum well perpendicular to the direction of light propagation. Because of the spin selection rules the direction of the current is determined by the helicity of the light and can be reversed by switching the helicity from right to left handed. A microscopic model is presented which describes the origin of the photon helicity driven current. The model suggests that the system behaves as a battery which generates a spin polarized current. 相似文献
108.
Stefan Schnabel Wolfhard Janke Michael Bachmann 《Journal of computational physics》2011,230(12):4454-4465
The investigation of freezing transitions of single polymers is computationally demanding, since surface effects dominate the nucleation process. In recent studies we have systematically shown that the freezing properties of flexible, elastic polymers depend on the precise chain length. Performing multicanonical Monte Carlo simulations, we faced several computational challenges in connection with liquid–solid and solid–solid transitions. For this reason, we developed novel methods and update strategies to overcome the arising problems. We introduce novel Monte Carlo moves and two extensions to the multicanonical method. 相似文献
109.
Hirmer M Hirmer M Schuh D Wegscheider W Korn T Winkler R Schüller C 《Physical review letters》2011,107(21):216805
In resonant inelastic light scattering experiments on two-dimensional hole systems in GaAs-Al(x)Ga(1-x)As single quantum wells we find evidence for the strongly anisotropic spin-split hole dispersion at finite in-plane momenta. In all our samples we detect a low-energy spin-density excitation of a few meV, stemming from excitation of holes of the spin-split ground state. The detailed spectral shape of the excitation depends sensitively on the orientations of the linear light polarizations with respect to the in-plane crystal axes. In particular, we observe a doublet structure, which is most pronounced if the polarization of the incident light is parallel to the [110] in-plane direction. Theoretical calculations of the Raman spectra based on a multiband k · p approach confirm that the observed doublet structure is due to the anisotropic spin-split hole dispersion. 相似文献
110.
Wolfhard H. G. Koch 《International journal of quantum chemistry》2013,113(10):1568-1572
After having reviewed some pioneer integral approximations closely related to Rüdenberg's expansions of one‐ and two‐electron orbital products, we apply the previously described “Implicit Multi‐Center Integration” techniques on Roothaan's “restricted” Fock‐matrix components over standard atomic orbital bases. The resulting compact forms are very similar to the well‐known “Wolfsberg–Helmholz Conjecture” of “Extended‐Hückel Theory,” which relates the various off‐diagonal matrix elements of “restricted” Fock‐type to their corresponding diagonal counterparts. In this way, a “nonempirical Extended‐Hückel Theory” can be created. © 2012 Wiley Periodicals, Inc. 相似文献