# Horst Stormer

#### Professor Emeritus of Applied Physics and I.I. Rabi Professor Emeritus of Physics

#### Research Interests

Semiconductors, electronic transport, lower-dimensional physicsI 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 15 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.

## Nobel Prize

Prof. Horst Stormer shared the 1998 Nobel Prize in Physics: Discovery in Electron Behavior

## Select Publications

"High Frequency Magneto Oscillations in GaAs/AlGaAs Quantum Wells", Tan, Y.-W. et al. (H. L. Stormer), Phys. Rev. Lett. 98, 036804 (2007)

"Experimental observation of the quantum Hall effect and Berry's phase in graphene", Zhang, Y., et al. (H. L. Stormer), Nature 438, 201 (2005)

"Quantization of the diagonal resistance: Density gradients and the empirical resistance rule in a 2D system", Pan, W., et al. (H. L. Stormer), Phys. Rev. Lett. 95, 066808 (2005)

"Evidence for Skyrmion Crystallization from NMR Relaxation Experiments" Gervais, G., et al. (H. L. Stormer), Phys. Rev. Lett. 94, 196803 (2005)

"Measurements of the density-dependent many-body electron mass in two-dimensional GaAs/AlGaAs heterostructures", Tan, Y. -W., et al. (H. L. Stormer). Phys. Rev. Lett. 94: 016405 (2005).

"Fractional quantum Hall effect of composite fermions", Pan, W., et al. (H. L. Stormer). Phys. Rev. Lett. 90:16801 (2003).

"Spin susceptibility of an ultra-low density, two-dimensional electron gas system", Zhu, J., et al. (H. L. Stormer). Phys. Rev. Lett. 90:056805 (2003).

"Large splitting of the cyclotron-resonance line in AlGaN/GaN heterostructures", Syed, S., et al. (H. L. Stormer). Phys. Rev. B 67:241304 (2003).

"Four-terminal resistance of a ballistic quantum wire", De Picciotto, R., et al (H. L. Stormer) Nature 411:51 (2001).

"Tunneling between the edges of two lateral quantum Hall systems", Kang, W., et al. (H. L. Stormer). Nature 403:59 (2000).

"The fractional quantum Hall effect", Stormer, H. L. Rev. Mod. Phys. 71:875 (1999).

"Composite Fermions in the Fractional Quantum Hall Effect, in Perspectives in Quantum Hall Effects", Das Sarma and Pinczuk edts, John Wiley (1996).

"How Real are Composite Fermions?", Phys . Rev. Lett. 71, 3850 (1993).

"The Fractional Quantum Hall Effect", Science, 248, 1510 (1990).

"Nonuniversal Conductance Quantization in Quantum Wires", Phys. Rev. Lett. 77, 4612 (1996).

"N-Electron Ground State Energies of a Quantum Dot in a Magnetic Field", Phys. Rev. Lett. 71, 613 (1993).