Showing papers by "Venkatesh Narayanamurti published in 1986"
10 citations
AT&T1
TL;DR: In this article, a phonon spectroscopy technique for the study of the 2-D electron gas was proposed and data on the integrally quantized 2DEG was presented.
Abstract: The intense interest over the last few years in the quantum Hall effect[1], occuring in the 2-D electron gas (2DEG), has been sustained largely by electronic transport measurements. For example, the prediction of a gap in the spectrum of elementary excitations of the fractionally quantized 2DEG has been tested only via observation of activated conductivity. No spectroscopic measurement of the gap has been made. We outline here a new phonon spectroscopy technique for the study of the 2-D electron gas and present data on the integrally quantized 2DEG.
4 citations
01 Jan 1986
TL;DR: In this paper, the authors present a Monte Carlo algorithm for handling transport of high frequency TA phonons in GaAs, where mode conversion: TA → LA (by isotope scattering) and down conversion: LA → TA + TA (by anharmonic coupling) are included analytic solutions appear hopeless.
Abstract: To understand recent experiments [1l on propagation of high frequency TA phonons in GaAs we need numerical/analytic procedures for handling transport across layers not much larger than the mean free path. When mode conversion: TA → LA (by isotope scattering) and down conversion: LA → TA + TA and LA → TA + LA (by anharmonic coupling) are included analytic solutions appear hopeless, and Monte Carlo calculations have been performed.
3 citations
AT&T1
TL;DR: In this article, it has been shown that within a narrow window of Au concentration that these films have excellent temperature responses, these concentrations were determined by Rutherford backscattering after fabrication and variations on either side of this window resulted in films that are metallic or insulating.
Abstract: GeAu films operating near the metal insulator transition are ideally suited for high magnetic field thermometry. Until now, difficulties in fabrication, unpredictable temperature responsivity and their inherently high impedances(R up to 100M ohms) have prevented their uses as fast heat pulse detectors. It has been found [1] that within a narrow window of Au concentration that these films have excellent temperature responses. However, these concentrations were determined by Rutherford backscattering after fabrication. Variations on either side of this window resulted in films that are metallic(small R(T)) or insulating (exceedingly large resistances). In addition the responsivity was strongly dependent on whether or not these films were amorphous or polycrystalline.
1 citations
AT&T1
TL;DR: In this article, it was shown that at low pressures and temperatures, the 3-phonon process dominates the mean free path in the low temperature, phonon dominated regime.
Abstract: In the low temperature, phonon dominated, regime the velocity of second sound in superfluid helium approaches \( {c_0}/\sqrt {3} \), where c 0 is the ordinary acoustic sound velocity. Observation of this limiting behavior is difficult owing to the rapid decrease of the wide-angle scattering rate τ ⊥ −1 as the temperature is reduced. At a given frequency ω, the product ωτ ⊥ soon exceeds unity and the mode collapses. Although wide-angle phonon scattering is required for the propagation of second sound, at low pressures and temperatures it is the nearly collinear (~5°) 3-phonon process that dominates the mean free path[l]. This is due to the phonon dispersion being anomalous or “upward” at small wavevector. Maris[2] showed that for times intermediate between τ ‖, the small-angle time and τ ⊥ a pseudo-temperature can be assigned to groups of phonons propagating in a given direction and equilibrating amongst themselves via the 3-phonon process. He further predicted that a new type of second sound would propagate in this one-dimensional regime with velocity close to c0. It is the study of this new mode that we report on here.