#
2006 APS March Meeting

##
Monday–Friday, March 13–17, 2006;
Baltimore, MD

### Session R2: Fractional Quantum Hall Systems

2:30 PM–5:30 PM,
Wednesday, March 15, 2006

Baltimore Convention Center
Room: Ballroom III

Sponsoring
Unit:
DCMP

Chair: Horst Stormer, Columbia University

Abstract ID: BAPS.2006.MAR.R2.5

### Abstract: R2.00005 : Phonon Absorption Experiments on Composite Fermions

4:54 PM–5:30 PM

Preview Abstract
Abstract

####
Author:

Fritz Schulze-Wischeler

(Institut f\"ur Festk\"orperphysik, Universit\"at Hannover, Appelstra\ss{}e 2, 30167 Hannover, Germany)

We present a time-resolved phonon absorption technique as an
efficient tool to investigate the properties of the fractional
quantum Hall effect (FQHE). We interpret our data within the
Composite Fermion (CF) picture of the FQHE, were the CF
quasiparticles are constructed by attaching two magnetic flux
quanta $\phi_0$ to each electron. As a result, the CFs at filling
factor $\nu$ and electron density $n$ experience only an reduced
magnetic field $B^* = B - 2 \phi_0 n$, so that they behave in
$B^*$ in analogy to electrons in the magnetic field $B$ and form
Landau levels of CFs with effective filling factor $p =
\frac{\nu}{1-2\nu}$ in particular. In a first set of experiments,
we measure phonon excitation gaps in the FQH regime for various
filling factors and find that the measured gaps can be well
described in the framework of Landau-level transitions of CFs
involving no spin flip [1]. We are able to deduce the CF mass
$m^*(10~\rm{T}) = 0,5m_0$ from these transitions. We apply the
same model to energy gaps which we deduce from transport
experiments. These gaps are transitions from one level to another
reduced by disorder. Here, spin flip are allowed. From results
near the crossing of two levels, we were able to deduce the
g-factor of CFs [2]. A second set of phonon absorption experiments
focuses on the specific heat $C$ of the 2DES at various filling
factors $\nu$ [3]. Here, we find an exponential dependence $C
\propto (1/T)^2 exp(-\Delta/T)$ on temperature $T$ if the 2DES is
in a state with an energy gap $\Delta$. At $\nu = 1/2$, where the
external magnetic field is fully cancelled by the gauge field, we
find a linear temperature dependence as expected for a Fermi sea
of CFs.
\begin{enumerate}
\item F. Schulze-Wischeler, F. Hohls, U. Zeitler, D. Reuter, A. D.
Wieck, and R. J. Haug, Phys. Rev. Lett. \textbf{93}, 026801
(2004).
\item F. Schulze-Wischeler, E. Mariani, F. Hohls, and R.
J. Haug, Phys. Rev. Lett. \textbf{92}, 156401 (2004).
\item F. Schulze-Wischeler \emph{et al.}, to be published in 2006.
\end{enumerate}

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2006.MAR.R2.5