Two-Quantum 2D FT Electronic Spectroscopy of Biexcitons in GaAs Quantum Wells
Katherine W. Stone,1
Kenan Gundogdu,1
Daniel B. Turner,1
Xiaoqin Li,2
Steven T. Cundiff,3
Keith A. Nelson1,*
The motions of electrons in solids may be highly correlated
by strong, long-range Coulomb interactions. Correlated electron-hole
pairs (excitons) are accessed spectroscopically through their
allowed single-quantum transitions, but higher-order correlations
that may strongly influence electronic and optical properties
have been far more elusive to study. Here we report direct observation
of bound exciton pairs (biexcitons) that provide incisive signatures
of four-body correlations among electrons and holes in gallium
arsenide (GaAs) quantum wells. Four distinct, mutually coherent,
ultrashort optical pulses were used to create coherent exciton
states, transform these successively into coherent biexciton
states and then new radiative exciton states, and finally to
read out the radiated signals, yielding biexciton binding energies
through a technique closely analogous to multiple-quantum two-dimensional
Fourier transform (2D FT) nuclear magnetic resonance spectroscopy.
A measured variation of the biexciton dephasing rate indicated
still higher-order correlations.
2 Department of Physics, University of Texas at Austin, Austin, TX 78712-0264, USA.
3 JILA, University of Colorado, Boulder, and National Institute of Standards and Technology, Boulder, CO 80309-0440, USA.
* To whom correspondence should be addressed. E-mail: kanelson{at}mit.edu
