摘要:

AbstractIn this paper we report on the observation of response of a Bloch oscillator at room temperature to a THz‐field of a frequency larger than the Bloch frequency. The oscillator consisted of a semiconductor superlattice structure, with an applied dc voltage giving rise to a dc electron drift current. Submitting the oscillator to a field at a frequency of 3.3 THz caused a sizeable reduction of the current; the THz‐field was generated by use of intense THz‐radiation pulses focused on an antenna coupled to the superlattice. We attribute the THz‐field induced reduction of the current to a frequency modulation of the Bloch oscillations of electrons at the frequency of the THz‐field, leading to reduction of the electron drift velocity and, consequently, of th

ISSN:0003-3804    

DOI:10.1002/andp.19945060302

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe crossover from Bardeen‐Cooper‐Schrieffer pairing to Bose‐Einstein condensation is considered with special emphasis to a consistent description of bound pair formation. A nonequilibrium approach is considered, and wave equations for the two‐particle states and the pair amplitude are derived in the stationary state. The critical temperature is calculated for a simple model

ISSN:0003-3804    

DOI:10.1002/andp.19945060303

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe 1D system of correlated electrons characterized in addition to the usual on‐site (U) and nearest‐neighbour (V) repulsion by a correlated‐hopping term (t*) is considered. The ground state phase diagram is studied within the framework of the weak‐coupling continuum‐limit approach. At fillingvthe effective interaction originating from the correlated‐hopping term which appears in the continuum‐limit theory is given byt* cos (πv). Being repulsive for v1/2, this interaction leads to a characteristic band‐filling dependence of the phase diagram of the system. For v ≠ 1/2, depending on the relation between the bare values of the coupling constants (U, V, t* cos (π v)) and, hence, on the band‐filling, the system shows three different phases in the infrared limit: a Luttinger metal, a nonmagnetic metal and a singlet superconducting phase. For v = 1/2, the correlated‐hopping interaction is dynamically trivial, leading only to a renormalization of the oneelectron hopping amplitude and the phase diagram of the model coincides with that of the

ISSN:0003-3804    

DOI:10.1002/andp.19945060304

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe phase diagram of a layered superconductor in a large parallel magnetic field is calculated. This includes a calculation of the lower critical field beyond which the superconductor is in the FFLO‐state and possesses a spatially modulated order parameter and spin polarization. The order parameter, spin polarization, free‐energy density, and phase boundaries of this unconventional superconducting phase are evaluated numerically in the completeB–Tplane. The analysis suggests that the transition at the lower critical field is of second order, and not of first order, as previously assumed. The order parameter of the FFLO‐state merges continuously into the uniform superconductin

ISSN:0003-3804    

DOI:10.1002/andp.19945060305

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractMeasurements of the viscosity of a fluid by means of a parallel plate torsional oscillator are conventionally limited to a plate separation that is much larger than the viscous penetration depth of the fluid contained between the plates. Here we demonstrate that, in principle, useful measurements can be carried out in the opposite regime where the thickness is smaller than the penetration depth. An alternative method, described in the last part of this paper, for alleviating the restriction imposed by the density stratification that results from the earth's gravity, is to use electrostriction, rather than the inertial force, to drive the fluid between the plates.

ISSN:0003-3804    

DOI:10.1002/andp.19945060306

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractA nonlinear generalization of autoregressive scheme of first order is suggested as approximate model for 1/fknoises. The iterative generation makes use of reducing function instead of a constant. Computer simulations – carried out over three decades of frequency – have demonstrated that there is such a family of these functions that to any function of the family there exists a unique value of standard deviation of white noise source such that the noise generated by the iterative scheme has the spectral factork≈ 1.Implications of the results for understanding the origin, structural stability and ubiquity of 1/f noise are disc

ISSN:0003-3804    

DOI:10.1002/andp.19945060307

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

ISSN:0003-3804    

DOI:10.1002/andp.19945060301

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY