Ph.D. 1977, University of Stuttgart, Germany
Fall 2005: E4901
Spring 2006: N/A
I joined Columbia University in the beginning of 1998 after having worked for 20 years in the Research Area of Bell Labs. My area of expertise is in condensed matter physics with an emphasis on semiconductors. In particular, I am interested in the physics of lower-dimensional systems, such as two-dimensional, one-dimensional and zero-dimensional systems. In these structures, electrons are quantum-mechanically bound to a plane, a line or to a small dot. At very low temperatures of about 1K and below, these quantum structures exhibit bizarre new properties.
Quantum sheets in high magnetic fields show a resistance that is quantized to a few parts in 108. This is known as the integral quantum Hall effect. Yet more unusual things happen in the highest-quality samples. Novel electron quantum-fluids form, which exhibit fractional quantum numbers (such as 3/7, 5/11…) and they harbor objects that carry an exact fraction of an electron charge, e.g. 1/3 e. Furthermore, the magnetic field seems to transform fermions into bosons and vice-versa. These class of phenomena is known as the fractional quantum Hall effect which was discovered some 20 years ago but keeps surprising us with new revelations. Transport in quantum-wires is also full of surprises. Again, the resistance is quantized and electron motion is more appropriately described in terms of a many-particle waves than in terms of individual electron. In quantum-dots one can achieve the controlled addition and subtraction of individual electrons.
The interaction of many electrons rather than the property of any individual particle is at the origin of all such observation. The associate theory is challenging and at the forefront of today's efforts to understand complex many-particle systems.
Our samples are based on the semiconductor Gallium-Arsenide which plays an important role in photonics and high-frequency electronics. Extraordinarily high-quality specimens can be synthesized by Molecular Beam Epitaxy (a high-vacuum evaporation technique) and clean-room processing. Experiments focus on electron transport in superconducting magnets at temperatures close to absolute zero generated by dilution refrigerators. Most experiments will be performed in-house and in close collaboration with Bell Labs, Lucent Technologies. For the ultimate in magnet field we use the National High-Magnetic Field Laboratory in Florida.
For a complete listing of publications, see Spires or the like.
"The Fractional Quantum Hall Effect," H.L. Stormer, D.C. Tsui, and A. C. Gossard, APS-Centennial Issue, Rev. Mod. Physics 71, 298 (1999)
"Four-terminal resistance of a ballistic quantum wire," R. de Picciotto, H. L. Stormer, L. N. Pfeiffer, K. W. Baldwin, and K. W. West, Nature 411, 51 (2001)
"Quantization of the diagonal resistance: Density gradients and the empirical resistance rule in a 2D system," W. Pan, J.S. Xia, H.L. Stormer, D.C. Tsui, C.L. Vicente, E.D. Adams, N.S. Sullivan, L.N. Pfeiffer, K.W. Baldwin, and K.W. West, Phys. Rev. Lett. 95, 066808 (2005)
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"Disorder mediated splitting of the cyclotron resonance in two-dimensional electron Systems," E. A. Henriksen, S. Syed, Y.-J. Wang, H. L. Stormer, L. N. Pfeiffer, and K. W. West, Phys. Rev. B 73, 241309 (2006)
"Spin Susceptibility of a 2D Electron System in GaAs towards the Weak Interaction Region," Y.W. Tan, J. Zhu, H. L. Stormer, L. N. Pfeiffer, K. W. Baldwin, and K. W. West, Phys. Rev. B 73, 045334 (2006)