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41.
Fernández-Rossier J Piermarocchi C Chen P MacDonald AH Sham LJ 《Physical review letters》2004,93(12):127201
Ferromagnetism is predicted in undoped diluted magnetic semiconductors illuminated by intense sub-band-gap laser radiation. The mechanism for photoinduced ferromagnetism is coherence between conduction and valence bands induced by the light which leads to an optical exchange interaction. The ferromagnetic critical temperature T(C) depends both on the properties of the material and on the frequency and intensity of the laser and could be above 1K. 相似文献
42.
Cooper CG MacDonald JC Soto E McGimpsey WG 《Journal of the American Chemical Society》2004,126(4):1032-1033
A noncovalently bound multilayered thin film in which individual layers are linked by metal ligand interactions undergoes a photochemically initiated permanent change in surface wettability. The film consists of three separate layers: a SAM on gold of 4-[(10-mercaptodecyl)oxy]pyridine-2,6-dicarboxylic acid, a layer of Cu(II) ions that are deposited onto the SAM and bind symmetrically in the site provided by the two carboxylate groups and the pyridyl nitrogen atom, and a layer of cis-2,2'-dipyridylethylene, which caps the Cu(II) layer by complexation through both pyridyl nitrogen atoms (Film I). Photoexcitation of the film in chloroform at 300 nm leads to substantial cis-trans isomerization as indicated by conductivity, impedance, grazing incidence IR, and contact angle measurements. The latter show a decrease in contact angle (increase in wettability) of 17 degrees , which is attributed to exposure of both the underlying Cu(II) layer and one of the pyridyl ring nitrogen atoms following isomerization to the trans isomer. 相似文献
43.
Bilayer quantum Hall systems develop strong interlayer phase coherence when the distance between layers is comparable to the typical distance between electrons within a layer. The phase-coherent state has until now been investigated primarily via transport measurements. We argue here that interlayer current and charge-imbalance noise studies in these systems will be able to address some of the key experimental questions. We show that the characteristic frequency of current noise is that of the zero wave vector collective mode, which is sensitive to the degree of order in the system. Local electric potential noise measured in a plane above the bilayer system, on the other hand, is sensitive to finite-wave-vector collective modes and, hence, to the soft-magnetoroton picture of the order-disorder phase transition. 相似文献
44.
Yao Y Kleinman L MacDonald AH Sinova J Jungwirth T Wang DS Wang E Niu Q 《Physical review letters》2004,92(3):037204
We perform a first principles calculation of the anomalous Hall effect in ferromagnetic bcc Fe. Our theory identifies an intrinsic contribution to the anomalous Hall conductivity and relates it to the k-space Berry phase of occupied Bloch states. This dc conductivity has the same origin as the well-known magneto-optical effect, and our result accounts for experimental measurement on Fe crystals with no adjustable parameters. 相似文献
45.
Pan W Jungwirth T Stormer HL Tsui DC MacDonald AH Girvin SM Smrcka L Pfeiffer LN Baldwin KW West KW 《Physical review letters》2000,85(15):3257-3260
We have measured magnetotransport at half-filled high Landau levels in a quantum well with two occupied electric subbands. We find resistivities that are isotropic in perpendicular magnetic field but become strongly anisotropic at nu = 9/2 and 11/2 on tilting the field. The anisotropy appears at an in-plane field, B(ip) approximately 2.5 T, with the easy-current direction parallel to B(ip) but rotates by 90 degrees at B(ip) approximately 10 T and points now in the same direction as in single-subband samples. This complex behavior is in quantitative agreement with theoretical calculations based on a unidirectional charge density wave state model. 相似文献
46.
The radiative decay of (1)P(o) doubly excited states in helium has been investigated using a novel apparatus in which metastable atoms and vacuum ultraviolet photons are detected. The intensity ratio of the energetically narrow (sp,2n-)(1)P(o) and (2p,nd)(1)P(o) series to the broader (sp,2n+)(1)P(o) series is strikingly enhanced in comparison with conventional photoabsorption, photoion, or photoelectron measurements using synchrotron radiation. The experimental approach is a new way forward for the study of energetically narrow doubly excited states. 相似文献
47.
Bhattacharya M Goodman CD Raghavan RS Palarczyk M Garcia A Rapaport J van Heerden IJ Zupranski P 《Physical review letters》2000,85(21):4446-4449
We report a 0 degrees 176Yb(p,n)176Lu measurement at IUCF where we used 120 and 160 MeV protons and the energy dependence method to determine Gamow-Teller (GT) matrix elements relative to the model independent Fermi matrix element. The data show that there is an isolated concentration of GT strength in the low-lying 1(+) states making the proposed Low Energy Neutrino Spectroscopy detector (based on neutrino captures on 176Yb) sensitive to pp and 7Be neutrinos and a promising detector to resolve the solar neutrino problem. 相似文献
48.
Tobias Niebel Daniel G. MacDonald Chhatra B. Khadka John F. Corrigan Prof. Dr. 《无机化学与普通化学杂志》2010,636(6):1095-1099
The trans‐bis(trimethylsilyl)chalcogenolate palladium complexes, trans‐[Pd(ESiMe3)2(PnBu3)2] [E = S ( 1 ) and Se ( 2 )] were synthesized in good yields and high purity by reacting trans‐[PdCl2(PBu3)2] with LiESiMe3 (E = S, Se), respectively. These complexes were characterized by 1H, 13C{1H}, 31P{1H} (and 77Se{1H}) NMR spectroscopy and single‐crystal X‐ray analysis. The reaction of 2 with propionyl chloride led to the formation of trans‐[Pd(SeC(O)CH2CH3)2(PnBu3)2] ( 3 ), a trans‐bis(selenocarboxylato) palladium complex and thus established a new method for the formation of this type of complex. Complex 3 was characterized by 1H, 13C{1H}, 31P{1H} and 77Se{1H} NMR spectroscopy and a single‐crystal X‐ray structure analysis. 相似文献
49.
MacDonald EN Purcell DW Munhall KG 《The Journal of the Acoustical Society of America》2011,129(2):955-965
Two auditory feedback perturbation experiments were conducted to examine the nature of control of the first two formants in vowels. In the first experiment, talkers heard their auditory feedback with either F1 or F2 shifted in frequency. Talkers altered production of the perturbed formant by changing its frequency in the opposite direction to the perturbation but did not produce a correlated alteration of the unperturbed formant. Thus, the motor control system is capable of fine-grained independent control of F1 and F2. In the second experiment, a large meta-analysis was conducted on data from talkers who received feedback where both F1 and F2 had been perturbed. A moderate correlation was found between individual compensations in F1 and F2 suggesting that the control of F1 and F2 is processed in a common manner at some level. While a wide range of individual compensation magnitudes were observed, no significant correlations were found between individuals' compensations and vowel space differences. Similarly, no significant correlations were found between individuals' compensations and variability in normal vowel production. Further, when receiving normal auditory feedback, most of the population exhibited no significant correlation between the natural variation in production of F1 and F2. 相似文献
50.
Chirally stacked N-layer graphene systems with N≥2 exhibit a variety of distinct broken symmetry states in which charge density contributions from different spins and valleys are spontaneously transferred between layers. We explain how these states are distinguished by their charge, spin, and valley Hall conductivities, by their orbital magnetizations, and by their edge state properties. We argue that valley Hall states have [N/2] edge channels per spin valley. 相似文献