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We describe an infrared transmission study of a thin layer of bulk graphite in magnetic fields up to B = 34 T. Two series of absorption lines whose energy scales as √ B and B are present in the spectra and identified as contributions of massless holes at the H point and massive electrons in the vicinity of the K point, respectively. We find that the optical response of the K point electrons corresponds, over a wide range of energy and magnetic field, to a graphene bilayer with an effective inter-layer coupling 2γ1, twice the value for a real graphene bilayer, which reflects the crystal ordering of bulk graphite along the c axis. The K point electrons thus behave as massive Dirac fermions with a mass enhanced twice in comparison to a true graphene bilayer.PACS numbers: 71.70. Di, 76.40.+b, 81.05.Uw Recent interest in graphene [1, 2], a truly twodimensional system with its simple, but nevertheless, for solids, unconventional electronic states, has focused attention on the properties of Dirac-like fermions in condensed matter physics in general. Whereas, twodimensional massless Dirac fermions [3,4,5], characteristic of graphene have been widely investigated, far fewer experiments have been devoted to massive Dirac fermions which are specific to a graphene bilayer [6,7], which represents a further example of a two-dimensional system with a highly unusual band structure [8]. Perhaps surprisingly, Dirac dispersion relations can also be found in graphite, a three dimensional, bulk material which consists of Bernal-stacked weakly coupled graphene layers.The standard Slonczewski-Weiss-McClure (SWM) model of electronic states in graphite [9, 10] predicts a complex form for the in-plane dispersion relation which changes considerably depending upon the value of the momentum k z in the direction perpendicular to the layers. Intriguingly, the SWM model predicts that in the vicinity of the H point (k z = 0.5) the in-plane dispersion is linear and thus resembles a Dirac cone. Such a dispersion has indeed been found in angle resolved photoemission spectroscopy [11,12], tunneling spectroscopy [13,14], as well as in Landau level (LL)-spectroscopy [15]. The latter experiments, mainly focused on transitions between LLs whose energy scales as √ B, are generally believed to exhibit far richer spectra in comparison to true graphene [16,17,18], reflecting the inherent complexity of the SWM model which includes no fewer than seven parameters [19,20].We show in this Letter that infrared magnetoabsorption spectra of graphite, measured over a wide range of the energy and magnetic field, can be interpreted in a very simple, transparent and elegant manner. Our results confirm, in agreement with theoretical considerations [21], that graphite can be viewed as an effective graphene monolayer and bilayer. This theoretical picture is derived using a drastically simplified SWM model, which includes only two parameters γ 0 and γ 1 , describing the intra-and inter-layer tunneling respectively. In this simplified picture, the dominant contribution ...

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We use polarized magneto-Raman scattering to study purely electronic excitations and the electron-phonon coupling in bulk graphite. At a temperature of 4.2 K and in magnetic fields up to 28 T we observe K-point electronic excitations involving Landau bands with ∆|n| = 0 and with ∆|n| = ±2 that can be selected by controlling the angular momentum of the excitation laser and of the scattered light. The magneto-phonon effect involving the E2g optical phonon and K-point inter Landau bands electronic excitations with ∆|n| = ±1 is revealed and analyzed within a model taking into account the full kz dispersion. These polarization resolved results are explained in the frame of the Slonczewski-Weiss-McClure (SWM) model which directly allows to quantify the electron-hole asymmetry.

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The Lagrange Equations of Motion are written in generalized coordinates which describe small departures from the spherical equilibrium configuration of a conducting liquid droplet. It is initially assumed that the actual shape differs only very slightly from the equilibrium sphere. The equation representing the surface is, then, written as a series of surface zonal harmonics in which the coefficients are shown to be the normal coordinates of the droplet. The frequency of oscillation of the normal coordinates is shown to depend on the total charge on the droplet in such a manner that for all values of charge below a certain limit, the frequency is real. For all values of charge above a certain limit, the frequency is imaginary; and, thus, the droplet is unstable. This paper presents a detailed derivation of a result communicated by Rayleigh in 1882. The results of this communication have been widely quoted but, until now, this particular derivation has not appeared in the literature.

Results of experiments with thermocapillary flow in shallow liquid layers heated from the side are presented. The fluid has Prandtl number 17 and the main configuration investigated is an annular gap to avoid side-wall effects. The liquid depth d was d≤3.00 mm to have negligible buoyancy effects. Various instabilities have been observed. At a Marangoni number M≂6⋅102, a transition to steady multicellular flow occurred. The convection cells are longitudinal rolls embedded in the main flow all rotating in the same direction. At M≂3⋅103, a transition of the steady multicellular flow to time-dependent flow states (t) was observed. Two different t-flow states have been identified by thermocouple measurements and by visualization of the dynamic-free surface deformations of oscillatory flow. Both t states can be described by disturbances in the form of traveling waves. A short-wavelength t state with small surface deformations and with waves traveling in azimuthal direction is the preferred mode for d≤1.4 mm. A long-wavelength t state with larger surface deformations and with waves traveling in radial and in azimuthal directions is preferred for d≥1.4 mm. The stability diagram, wavelength, frequency, and phase speed of both t states are presented and the findings in comparison to an already existing theory by Smith and Davis [J. Fluid Mech. 132, 119, 145 (1983)] are discussed.