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91.
Th. Gerrits H. A. M. van den Berg J. Hohlfeld O. Gielkens L. Br Th. Rasing 《Journal of magnetism and magnetic materials》2002,240(1-3):283-286
We have measured the response of a 20×10 μm, 8 nm thin NiFe (80:20) permalloy film due to excitation by short in-plane magnetic field pulses. We will show that using a two-pulse-technique a complete control of the precessional motion of the magnetisation can be achieved on picosecond timescales. Furthermore, we will present numerical calculations which show that a complete suppression of magnetisation ringing after switching can only be realised by a cascade of short field pulses. 相似文献
92.
Morenzoni E. Birke M. Hofer A. Kottmann F. Litterst J. Matthias B. Meyberg M. Niedermayer Ch. Prokscha Th. Schatz G. Wutzke Th. 《Hyperfine Interactions》1996,97(1):395-406
During the last few decades, a variety of methods has been developed which makes use of polarized positive muons as a microscopic probe of the magnetic properties of condensed matter (muon spin rotation, relaxation, resonance,SR). Until now, available beams for SR studies have delivered 100% polarized muons with energies in the MeV range, resulting in a deep penetration of the muons into the sample material under investigation. This presently limits the applications of theSR technique to the study of the bulk characteristics of matter. To be able to control the implantation depth, a very low energy beam of polarized muons is being developed at the Paul Scherrer Institute. Very slow polarized muons (kinetic energy 10 eV, polarization 90%) are obtained from the moderation of a high energy muon beam in a thin film of an appropriate condensed gas. These muons can be used as a source for a beam of tunable energy between a few tens of eV and some tens of keV. Implantation depths in the range of few to a few hundreds of nanometers can thus be achieved by varying the energy. 相似文献
93.
Summary A microwave coherent backscattering experiment has been carried out on Mirabelle, a weakly ionised plasma device, with the
objective of measuring the electron density fluctuation level. The experiment is a preliminary step in order to prepare the
detection system for a microwave stimulated backscattering experiment. The incident electromagnetic wave is focused in front
of a plane grid which excites ion acoustic or electron Bernstein waves inducing fluctuations in the plasma. The backscattering
signal is collected by the launching circuit and detected by homodyne mixing. The typical ratio of the scattered power to
the incident power is about 10−12 and the relative density fluctuations are of the order of δn
e/n
e=10−3 against a background electron density ofn
e=1–5·109 cm−3. The backscattering measurement is compared with Langmuir probe measurements. The spectral width of the backscattered signal
has also been studied, by taking into account effects due to the incident wave focusing and plasma wave damping.
The authors of this paper have agreed to not receive the proofs for correction 相似文献
94.
H. van de Stadt J. Mees Z. Barber M. Blamire P. Dieleman Th. de Graauw 《International Journal of Infrared and Millimeter Waves》1996,17(1):91-104
We describe heterodyne mixing experiments with NbCN/Nb quasi-particle tunnel junctions at submillimeter wavelengths. In this wavelength range junctions with niobium nitride as superconducting material are promising because of the high gap voltage, about 5.7 mV, as compared to 3 mV for the more commonly used niobium. As a first step towards all-NbN junctions we investigate the development of junctions with a NbN base electrode and a Nb upper electrode. We present results from samples with two different insulating barriers: aluminum oxide and magnesium oxide. Measured noise temperatures range from 500 K at 345 GHz and 1600 K at 482 GHz to 8500 K at 644 GHz. These results are about one order of magnitude worse than the best results obtained with all-Nb junctions. The difference can be attributed partly to the relatively high radio-frequency (rf) losses in NbN films as compared to Nb. Also sensitivity is reduced because of the relatively high leakage current in the sub-gap region of the I-V curve of the junction. 相似文献
95.
We prove that the maximum number N c of non-relativistic electrons that a nucleus of charge Z can bind is less than 1.22Z + 3Z 1/3. This improves Lieb’s upper bound N c < 2Z + 1 Lieb (Phys Rev A 29:3018–3028, 1984) when Z ≥ 6. Our method also applies to non-relativistic atoms in magnetic field and to pseudo-relativistic atoms. We show that in these cases, under appropriate conditions, \({\limsup_{Z \to \infty}N_c/Z \le 1.22}\). 相似文献
96.
A. Schwarz A. Kaluza Th. Schpers H. Hardtdegen H. Lüth D. Meertens Ch. Dieker A. C. Maciel J. Kim E. D. O'Sullivan J. F. Ryan 《Physica E: Low-dimensional Systems and Nanostructures》2000,7(3-4)
We report the growth of modulation-doped GaAs/AlxGa1−xAs v-groove quantum wires and structural, electrical and optical investigations of their electronic states and transport properties. By using alternative group III precursors on partially SiO2 masked pre-patterned GaAs substrates, samples have been fabricated which permit electrical measurements of single isolated wire structures without the need for additional electron-beam lithography. Magneto-transport was measured as a function of tilt angle of the incident magnetic field to identify the formation of low-dimensional electron gases in different parts of the structure. Photoluminescence investigations reveal 1D and 2D confined states which show different carrier heating when electric fields are applied along the wire structure. 相似文献
97.
We propose a simple friction model for isolated polymer chains on a solid substrate. The chains are pulled at constant velocity
by one end, the other end can be trapped on the solid substrate on localised sites. We focus on the energy dissipation due
to the traps. This simple model leads to nontrivial friction laws, depending on the velocity and the distance between traps.
Some refinements of the model such as the effect of thermal fluctuations are also reported.
Received 20 March 2000 相似文献
98.
M.B. Zölfl Th. Maier Th. Pruschke J. Keller 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):47-53
We study one-particle spectra and the electronic band-structure of a CuO
2
-plane within the three-band Hubbard model. The Dynamical Mean-Field Theory (DMFT) is used to solve the many particle problem.
The calculations show that the optical gap is given by excitations from the lower Hubbard band into the so called Zhang-Rice singlet band. The optical gap turns out to be considerably smaller than the bare charge transfer energy () for a typical set of parameters, which is in agreement with experiment. We also investigate the dependence of the shape
of the Fermi surface on the different hopping parameters t
CuO and t
OO. A value t
OO
/
t
CuO
>0 leads to a Fermi surface surrounding the M point.
Received 21 September 1998 and Received in final form 8 June 1999 相似文献
99.
Th. Mühge Yu. V. Goryunov K. Theis-Bröhl K. Westerholt H. Zabel I. A. Garifullin 《Applied magnetic resonance》1998,14(4):567-582
Magnetic and superconducting properties of Fe/Nb epitaxial bilayers have been studied. Single crystal Fe/Nb (110) bilayers with a Nb thicknessd Nb in the range from 250 to 650 Å and with a Fe thicknessd Fe in the range from 7 to 27 Å were prepared using molecular beam epitaxy techniques. Magnetization measurements showed the existence of a magnetically “dead” Fe-interface layer with a thicknessd NM varying strongly with minor modifications of the growth conditions. For bilayers with a small magnetic layer thicknessd M and a smalld NM the FMR measurements revealed an anomalous decrease of the effective magnetization 4πM eff of the ferromagnetic Fe layer below the superconducting transition temperatureT c. The absolute change of 4πM eff belowT c depends strongly on the actual values ofd M andd NM: upon decreasing bothd M andd NM the effect increases considerably. As a possible mechanism for the anomalous temperature dependence of 4πM eff belowT c we discuss a spatial modulation of ferromagnetic order due to a modification of the RKKY inter-action in the superconducting state. 相似文献
100.
O. Golinelli Th. Jolicœur E.S. Sørensen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):199-206
We study the magnetic excitation spectrum of the spin-1 chain with Hamiltonian .We focus on the range where the spin chain is in the gapped Haldane phase. The excitation spectrum and static structure factor is studied using
direct Lanczos diagonalization of small systems and density-matrix renormalization group techniques combined with the single-mode
approximation. The magnon dispersion has a minimum at until a critical value is reached at which the curvature (velocity) vanishes. Beyond this point, which is distinct from the VBS point and the Lifshitz
point, the minimum lies at an incommensurate value that goes smoothly to when approaches , the Lai-Sutherland point. The mode remains isolated from the other states: there is no evidence of spinon deconfinement
before the point .These findings explain recent observation of the behavior of the magnetization curve for .
Received 16 December 1998 相似文献