International Research Fellowship Program: Infrared and Optical Studies of Quantum Phase Transitions

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0402699ArmitageThe International Research Fellowship Program enables U.S. scientists and engineers to conduct three to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a sixteen-month research fellowship by Dr. Norman P. Armitage to work with Dr. Dirk van der Marle at the University of Geneva in Switzerland. This project concerns the study of optical and infrared properties of condensed matter systems near so-called quantum phase transition (QPTs). This a topic at the forefront of some of the most challenging and interesting problems in condensed matter physics. Once thought to be a theoretical curiosity, it is becoming increasingly clear that the existence of nearby QPTs may hold the key to understanding the unusual behavior of many systems at the forefront of condensed matter physics. The optical and infrared response of correlated electron systems, such as superconductors and novel magnetic states, are being investigated as they are tuned via an external parameter (e.g. pressure, carrier density, or magnetic field) through such a transition between various magnetic and superconducting ground states near absolute zero temperature. The work is being done in the group of Prof. Dirk van der Marel at the University of Geneva using both the state-of-the-art facilities of Dr. van der Marel's lab and new infrared systems being currently installed at the Swiss Light Source (SLS) synchrotron. Prof. van der Marel's present work concentrates on the low energy excitation spectra of strongly correlated electron systems, using various infrared and optical spectroscopic probes. The lab in Geneva is uniquely equipped for this project as one of the top laboratories in the world for such investigations. However, the optical study of pressure-tuned QPTs (such as those found in heavy fermion systems), necessitates the use of small beam spots for coupling into a diamond anvil pressure cells. This is a requirement incompatible with traditional lab based infrared or optical sources, but made possible by the advent of infrared synchrotron radiation (IRSR) sources. One of the unique aspects of this project is the use of newly commissioned infrared beamlines at the SLS.