Comment on anomalous dispersion and scattering rates for multiphonon spontaneous decay in He II

We report on new measurements of the spontaneous decay threshold energy Ec for high-frequency phonon propagation in He II at saturated vapor pressure at T=0.1 K. Superconducting tin tunnel generators and aluminum tunnel detectors were used in this study. The measurements show that the mean free path becomes much larger than the propagation length of 1.1 mm for a value of Ec =9.8±0.15 K. This agrees with the value originally reported (Ec =9.5±0.4 K) by Dynes and Narayanamurti using aluminum tunnel generators, but is shown to correspond to the point where the phase velocity equals the sound velocity, when the phonons become stable, as first proposed by Pitayevski and Levinson. Evidence for n-phonon decay at energies lower than Ec is presented for n≥2 with a short mean free path (<0.3 mm) at the two-phonon decay energy. The measured values of the dispersion parameters are shown to agree closely with the spline fit to neutron data due to donnelly, donnelly, and Hills

Integer Quantum Hall Effect in Double-Layer Systems

We consider the localization of independent electron orbitals in double-layer two-dimensional electron systems in the strong magnetic field limit. Our study is based on numerical Thouless number calculations for realistic microscopic models and on transfer matrix calculations for phenomenological network models. The microscopic calculations indicate a crossover regime for weak interlayer tunneling in which the correlation length exponent appears to increase. Comparison of network model calculations with microscopic calculations casts doubt on their generic applicability.Comment: 14 pages, 12 figures included, RevTeX 3.0 and epsf. Additional reference

Propagation of near-zone-boundary, acoustic phonons in solid <SUP>4</SUP>He with the use of superconducting tunnel junctions

We demonstrate the long lifetime, against spontaneous decay (h&#969;&gt;&gt;kT), of transverse phonons in the highly anharmonic solid 4He. This is proved through the quantum generation and detection of the propagating phonons using superconducting tunnel junctions of Sn and Al. Phonons of wavelength 10-20 &#197; are shown to propagate macroscopic distances ~1 mm at T&#8804;0.2 K

SURFACE INDUCED FERROMAGNETISM IN 3He

La susceptibilité et les temps de relaxation transverses et longitudinaux des noyaux d'3He dans une poudre de charbon (ϕ 9 nm) ont été mesurés jusqu'à 0.4 mK par RMN pulsée. Les résultats indiquent que l'3He près de l'interface solide-liquide a une tendance ferromagnétique aux plus basses températures.Pulsed NMR measurements of the susceptibility and of the transverse and longitudinal relaxation times of 3He intermixed with 9 nm carbon particles down to 0.4 mK show that the solid-liquid system near the surfaces favours ferromagnetic order below 10 mK and approaches a ferromagnetic transition at the lowest temperatures

Observation of a high-frequency cutoff for phonon propagation in liquid <SUP>4</SUP>He

A new high-frequency cutoff for phonon propagation which lies beyond the well-known low-frequency cutoff due to anomalous dispersion is observed in phonon propagation experiments in liquid 4He using superconducting Sn and A1 tunnel-junction generators and detectors. The cutoff depends strongly on pressure and is interpreted as arising from a strong increase in phase space for phonon-roton scattering as normal dispersion in the phonon branch sets in

A magnetically diluted CMN thermometer

A powdered Ce0.03La0.97 magnesium nitrate thermometer has been developed to facilitate specific heat measurements in liquid 3He. Comparison with a platinum NMR thermometer suggests that the magnetic temperature T* is related to the absolute temperature T by T = T* + Δ, where Δ = - 0.16 ± 0.01 mK.Un thermomètre à poudre de CMN dilué (Ce0,03La0,97) et un thermomètre à poudre de platine destinés à mesurer la chaleur spécifique de l'hélium-3 superfluide ont été réalisés. Leur comparaison suggère que la température magnétique T* du CMN dilué est reliée à la température absolue T par la relation T = T* + Δ où Δ = - 0,16 ± 0,01 mK