排序方式: 共有38条查询结果,搜索用时 15 毫秒
31.
S. Chaudhuri P. F. Bagwell D. McInturff J. C. P. Chang S. Paak M. R. Melloch J. M. Woodall T. M. Pekarek B. C. Crooker 《Superlattices and Microstructures》1999,25(5-6)
We correlate transmission electron microscope (TEM) pictures of superconducting In contacts to an AlGaAs/GaAs heterojunction with differential conductance spectroscopy performed on the same heterojunction. Metals deposited onto a (100) AlGaAs/GaAs heterostructure do not form planar contacts, but, during thermal annealing, grow down into the heterostructure along crystallographic planes in pyramid-like ‘point contacts’. Random surface nucleation and growth gives rise to a different interface transmission for each superconducting point contact. Samples annealed for different times, and therefore having different contact geometry, show variations in dI / dV characteristics of ballistic transport of Cooper pairs, wave interference between different point emitters, and different types of weak localization corrections to Giaever tunneling. We give a possible mechanism whereby the ‘finite bias anomaly’ of Poirier et al. [Phys. Rev. Lett. 79, 2105 (1997)], also observed in these samples, can arise by adding the conductance of independent superconducting point emitters in parallel. 相似文献
32.
We report on the dynamics of resonant energy transfer in monodisperse, mixed-size, and energy-gradient (layered) assemblies of CdSe nanocrystal quantum dots. Time-resolved and spectrally resolved photoluminescence directly reveals the energy-dependent transfer rate of excitons from smaller to larger dots via electrostatic coupling. The data show a rapid (0.7-1.9 ns) energy transfer directly across a large tens-of-meV energy gap (i.e., between dots of disparate size), and suggest that interdot energy transfer can approach picosecond time scales in structurally optimized systems. 相似文献
33.
Bowen SP Richard JC Mancini JD Fessatidis V Crooker B 《The Journal of the Acoustical Society of America》2003,113(5):2562-2573
A two-dimensional cylindrical shear-flow wave theory for the generation of microseisms and infrasound by hurricanes and cyclones is developed as a linearized theory paralleling the seminal work by Longuet-Higgins which was limited to one-dimensional plane waves. Both theories are based on Bernoulli's principle. A little appreciated consequence of the Bernoulli principle is that surface gravity waves induce a time dependent pressure on the sea floor through a vertical column of water. A significant difference exists between microseisms detected at the bottom of each column and seismic signals radiated into the crust through coherence over a region of the sea floor. The dominant measured frequency of radiated microseisms is matched by this new theory for seismic data gathered at the Fordham Seismic Station both for a hurricane and a mid-latitude cyclone in 1998. Implications for Bernoulli's principle and this cylindrical stress flow theory on observations in the literature are also discussed. 相似文献
34.
Abstract We have microscopically observed the textures of very large droplets of cholesteric liquid crystal in a polymer matrix under the influence of an electric field E. When E = 0, the droplets exhibit rings and often a disclination line extends from the centre to the periphery of the droplet. As E increases, the droplet undergoes a progressive transition to a uniform-appearing texture. This uniform region first occurs near the centre of the droplet, then increases in radius as the field is increased. We propose that the field-off texture corresponds to the Frank-Pryce spherulite model while the uniform field-on texture is the planar texture. 相似文献
35.
Zaric S Ostojic GN Shaver J Kono J Portugall O Frings PH Rikken GL Furis M Crooker SA Wei X Moore VC Hauge RH Smalley RE 《Physical review letters》2006,96(1):016406
Near-infrared magneto-optical spectroscopy of single-walled carbon nanotubes reveals two absorption peaks with an equal strength at high magnetic fields (>55 T). We show that the peak separation is determined by the Aharonov-Bohm phase due to the tube-threading magnetic flux, which breaks the time-reversal symmetry and lifts the valley degeneracy. This field-induced symmetry breaking thus overcomes the Coulomb-induced intervalley mixing which is predicted to make the lowest exciton state optically inactive (or dark). 相似文献
36.
Cumings J Moore LS Chou HT Ku KC Xiang G Crooker SA Samarth N Goldhaber-Gordon D 《Physical review letters》2006,96(19):196404
We measure the low-field Hall resistivity of a magnetically doped two-dimensional electron gas as a function of temperature and electrically gated carrier density. Comparing these results with the carrier density extracted from Shubnikov-de Haas oscillations reveals an excess Hall resistivity that increases with decreasing temperature. This excess Hall resistivity qualitatively tracks the paramagnetic polarization of the sample, in analogy to the ferromagnetic anomalous Hall effect. The data are consistent with skew scattering of carriers by disorder near the crossover to localization. 相似文献
37.
Li Y Sinitsyn N Smith DL Reuter D Wieck AD Yakovlev DR Bayer M Crooker SA 《Physical review letters》2012,108(18):186603
The problem of how single central spins interact with a nuclear spin bath is essential for understanding decoherence and relaxation in many quantum systems, yet is highly nontrivial owing to the many-body couplings involved. Different models yield widely varying time scales and dynamical responses (exponential, power-law, gaussian, etc.). Here we detect the small random fluctuations of central spins in thermal equilibrium [holes in singly charged (In,Ga)As quantum dots] to reveal the time scales and functional form of bath-induced spin relaxation. This spin noise indicates long (400 ns) spin correlation times at a zero magnetic field that increase to ~5 μs as dominant hole-nuclear relaxation channels are suppressed with small (100 G) applied fields. Concomitantly, the noise line shape evolves from Lorentzian to power law, indicating a crossover from exponential to slow [~1/log(t)] dynamics. 相似文献
38.
MM Altarawneh GW Chern N Harrison CD Batista A Uchida M Jaime DG Rickel SA Crooker CH Mielke JB Betts JF Mitchell MJ Hoch 《Physical review letters》2012,109(3):037201
We present magnetization and magnetostriction studies of LaCoO_{3} in magnetic fields approaching 100?T. In contrast with expectations from single-ion models, the data reveal two distinct first-order transitions and well-defined magnetization plateaus. The magnetization at the higher plateau is only about half the saturation value expected for spin-1 Co^{3+} ions. These findings strongly suggest collective behavior induced by interactions between different electronic configurations of Co^{3+} ions. We propose a model that predicts crystalline spin textures and a cascade of four magnetic phase transitions at high fields, of which the first two account for the experimental data. 相似文献