The objective of this research is to explore the physical properties of low-dimensionality materials, i.e. material systems whose sizes, of the order of a few nanometers, are intermediate between that of atoms/molecules and that of bulk solids. Because of quantum size effects, the properties of such systems, in particular many-body interactions, are size- and shape-dependent and neither like those of atoms or of macroscopic solids. Semiconductors play a very special role of model systems. The combination of quantum size effects and ultrafast dynamics opens new avenues for experiments, testing the limits of our understanding of the physics of correlation in condensed matter.

2) Time resolved nonlinear spectroscopy of strongly correlated electron systems:

Many-body interactions of correlated charge carriers are of crucial importance for collective effects, such as colossal magnetoresistance or high-temperature (high-Tc) superconductivity. Although transition-metal oxides have been extensively studied, a full understanding of these strong correlation effects remains a fundamental challenge to contemporary condensed-matter physics. Time-resolved, ultrafast optical spectroscopy has evolved into a powerful arsenal of techniques enabling us to probe condensed matter with a resolution much smaller than the time scales of most scattering processes and correlations between elementary excitations. Thus time sequence, polarization, and frequency flexibility of ultrashort laser sources provide new tools to separate the various components of complex many-body systems.

L. V. Butov, A. C. Gossard, and D. S. Chemla, "Macroscopically Ordered State in Exciton Systems," Nature 418, 751 (2002).

L. V. Butov, C. W. Lai, A. L. Ivanov, A. C. Gossard, and D. S. Chemla, "Toward Bose-Einstein condensation of excitons in potential traps," Nature 417, 47 (2002).

R. A. Kaindl, M. A. Carnahan, J. Orenstein, D. S. Chemla, H. M. Christen, H-Y. Zhai, M. Paranthaman, and D. H. Lowndes, "Far-infrared optical conductivity gap in superconducting MgB2 films," Phys Rev. Lett. 88, 027003 (2002).

N. A. Fromer, C. E. Lai, D. S. Chemla, I. E. Perakis, D. Driscoll, and A. C. Gossard, "Dynamics of inter-Landau-level excitations of a two-dimensional electron gas in the quantum Hall regime," Phys. Rev. Lett. 89, 067401 (2002).

R. A. Kaindl, M. A. Carnahan, D. Häagele, R. Lövenich, and D. S. Chemla, "Ultrafast Terahertz probes of transient conducting and insulating phases within an electron-hole gas," Nature 423, 734 (2003).

L. V. Butov, L. S. Levitov, A. V. Mintsev, B. D. Simons, A. C. Gossard, and D. S. Chemla, “Formation Mechanism and Low-Temperature Instability of Exciton Rings”, Phys. Rev. Lett. 92, 117404 (2004).

C. W. Lai, J. Zoch, A. C. Gossard and D. S. Chemla , “Phase Diagram of Degenerate Exciton Systems” Science 303, 503 (2004).

R. A. Kaindl, M. A. Carnahan, D. S. Chemla, S. Oh, and J. N. Eckstein, “Dynamics of Cooper Pair Formation in Bi2Sr2CaCu2O8+d”, Phys. Rev. B72, 060510 (2005).

R. Huber, B. A. Schmid, Y.-R. Shen, D. S. Chemla, and R. A. Kaindl “Stimulated Terahertz Emission from Intra-Excitonic Transitions in Cu2O”, Phys. Rev. Lett. 96, 017402 (2006).

K. M. Dani, J. Tignon, M. Breit, D. S. Chemla, E. G. Kavousanaki, and I. E. Perakis, “Ultrafast dynamics of coherences in a quantum Hall system” Phys. Rev. Lett.97, 057401 (2006).

J. Wang, I. Cotoros, K. M. Dani, X. Liu, J. K. Furdyna, and D. S. Chemla, “Ultrafast Enhancement of Ferromagnetism via Photoexcited Holes in GaMnAs”, Phys. Rev. Lett.98, 217401 (2007).