Hydrodynamic Equations in Quantum Hall Systems at Large Currents

Hydrodynamic equations (HDEQs) are derived which describe spatio-temporal evolutions of the electron temperature and the chemical potential of two-dimensional systems in strong magnetic fields in states with large diagonal resistivity appearing at the breakdown of the quantum Hall effect. The derivation is based on microscopic electronic processes consisting of drift motions in a slowly-fluctuating potential and scattering processes due to electron-electron and electron-phonon interactions. In contrast with the usual HDEQs, one of the derived HDEQs has a term with an energy flux perpendicular to the electric field due to the drift motions in the magnetic field. As an illustration, the current distribution is calculated using the derived HDEQs.Comment: 10 pages, 2 Postscript figures, to be published in J. Phys. Soc. Jpn. 71 (2002) No.

Hydrodynamic Equation for the Breakdown of the Quantum Hall Effect in a Uniform Current

The hydrodynamic equation for the spatial and temporal evolution of the electron temperature T_e in the breakdown of the quantum Hall effect at even-integer filling factors in a uniform current density j is derived from the Boltzmann-type equation, which takes into account electron-electron and electron-phonon scatterings. The derived equation has a drift term, which is proportional to j and to the first spatial derivative of T_e. Applied to the spatial evolution of T_e in a sample with an abrupt change of the width along the current direction, the equation gives a distinct dependence on the current direction as well as a critical relaxation, in agreement with the recent experiments.Comment: 4 pages, 1 Postscript figure, corrected equations, to be published in J. Phys. Soc. Jpn. 70 (2001) No.

Electronic Processes at the Breakdown of the Quantum Hall Effect

Microscopic processes giving the energy gain and loss of a two-dimensional electron system in long-range potential fluctuations are studied theoretically at the breakdown of the quantum Hall effect in the case of even-integer filling factors. The Coulomb scattering within a broadened Landau level is proposed to give the gain, while the phonon scattering to give the loss. The energy balance equation shows that the electron temperature T_e and the diagonal conductivity sigma_{xx} exhibit a bistability above the lower critical electric field E_{c1}. Calculated values of E_{c1} as well as T_e and sigma_{xx} at E_{c1} are in agreement with the observed values in their orders of magnitude.Comment: 4 pages, 2 Postscript figures, submitted to the Journal of the Physical Society of Japa

Sonorous memory in Jonathan Perel’s El predio (2010) and Los murales (2011)

Throughout his filmic production, Argentine director Jonathan Perel has demonstrated strict adherence to a unique aesthetic programme in which human agents appear to have only a minimal role. Each film contains only diegetic sounds and consists of fixed shots of architectural spaces and objects closely associated with the most recent Argentine military dictatorship (1976–1983) and recent attempts to memorialise the atrocities they committed. Through the close analysis of Perel’s first two films – El predio (2010) and Los murales (2011) – this article focusses on Perel’s highly distinctive use of environmental sound and argues that they are, in fact, uniquely musical works. Drawing on the work of John Cage, Michel Chion, Deleuze and Guattari, and Doreen Massey, the article proposes that Perel manipulates sound in order to situate debates over the memorialisation of recent atrocities in a perpetual present and thus critique contemporary abuses of power in Argentina

Strong, Ultra-narrow Peaks of Longitudinal and Hall Resistances in the Regime of Breakdown of the Quantum Hall Effect

With unusually slow and high-resolution sweeps of magnetic field, strong, ultra-narrow (width down to $100 {\rm \mu T}$) resistance peaks are observed in the regime of breakdown of the quantum Hall effect. The peaks are dependent on the directions and even the history of magnetic field sweeps, indicating the involvement of a very slow physical process. Such a process and the sharp peaks are, however, not predicted by existing theories. We also find a clear connection between the resistance peaks and nuclear spin polarization.Comment: 5 pages with 3 figures. To appear in PR

Field-induced breakdown of the quantum Hall effect

A numerical analysis is made of the breakdown of the quantum Hall effect caused by the Hall electric field in competition with disorder. It turns out that in the regime of dense impurities, in particular, the number of localized states decreases exponentially with the Hall field, with its dependence on the magnetic and electric field summarized in a simple scaling law. The physical picture underlying the scaling law is clarified. This intra-subband process, the competition of the Hall field with disorder, leads to critical breakdown fields of magnitude of a few hundred V/cm, consistent with observations, and accounts for their magnetic-field dependence \propto B^{3/2} observed experimentally. Some testable consequences of the scaling law are discussed.Comment: 7 pages, Revtex, 3 figures, to appear in Phys. Rev.

Improved Theory of the Muonium Hyperfine Structure

Terms contributing to the hyperfine structure of the muonium ground state at the level of few tenths of kHz have been evaluated. The $\alpha^2 (Z\alpha)$ radiative correction has been calculated numerically to the precision of 0.02 kHz. Leading $\ln (Z\alpha )$ terms of order $\alpha^{4-n} (Z\alpha)^n , n=1,2,3,$ and some relativistic corrections have been evaluated analytically. The theoretical uncertainty is now reduced to 0.17 kHz. At present, however, it is not possible to test QED to this precision because of the 1.34 kHz uncertainty due to the muon mass.Comment: 11 pages + 2 figures (included), RevTeX 3.0, CLNS 94/127

In re: ‘Experimental Music’

John Cage is universally associated with the phrase experimental music. But what did that phrase mean, for Cage and for Cage’s predecessors? I begin with Cage and Lejaren Hiller, both writing important texts on ‘experimental music’ in 1959. From there, I trace the phrase backwards, eventually reaching Emile Zola, Gertrude Stein, and William James. A final section traces the phrase forward to Cage and Hiller’s collaboration on HPSCHD (1969)