Diyar Talbayev

Professor Mihaly is using infrared spectroscopy to probe the response of electrons in various interesting solids, like.fullerenes, high temperature superconductors and exotic magnets. He and his students have recently installed a new device at the National Synchrotron Light Source at Brookhaven Lab. The new spectrometer can be used to study the IR properties in the presence of very high magnetic fields. A particularly interesting application of this method, electron spin resonance at high fields.

The measurement was done on LaMnO3, a well-known anti-ferromagnet, and the parent compound of the so-called colossal magneto-resistance materials. The result is a unique, two-dimensional map of the spin resonance signal over the whole range of frequencies and magnetic fields. In the anti-ferromagnetic state the internal magnetic fields, due to the interaction between the electrons, causes a resonance feature at zero magnetic field. The application of external field splits this resonance into two branches.Using a new facility like this one provides ample opportunity for graduate studies in an exciting and inspiring environment. Working in Brookhaven Lab means constant exposure to the latest ideas and technology. Although we are using a large synchrotron facility, ours are in many ways simple "table top" experiments, where the experimenter has a direct control over every detail, and the few participants (typically a grad student and a postdoc) are in close personal contact all the time.

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Tom Bergeman’s Research

Theoretical work with Prof. Bergeman has contributed to the theory of laser cooling and atom trapping in the past, and continues to pursue these new possibilities. The development of techniques for cooling atoms to sub-milliKelvin temperatures by laser light, has led to a number of opportunities to address new questions in physics and in optics. Perhaps most prominent has been the achievement, in 1995, of Bose-Einstein condensation (BEC) of dilute atomic gases.
Some of our work is numerically intensive, and takes advantage of the remarkable expansion of computing power by personal computers. On certain questions, we have advanced the basic theory, such as recent computations on the damping of Bose condensate excitations. Our theoretical work on BEC has been directed toward:

• understanding the case of attractive atom-atom interactions, for which the Bose condensate is unstable with more than a critical number of atoms;
• the statistical mechanics of Bose ensembles;
• thermal sums below the critical temperature, including the condensate and quasi-particle states;
• resonant excitations and damping of these excitations by many-body interactions; and
• special effects when the trapping potential is constricted in one or two dimensions (''cigar'' or ''pancake'' geometries).

Another area for which cold atoms have opened new possibilities is that of cold atom collisions and the spectroscopy of weakly bound diatomic molecules. Temperatures in the sub-milliKelvin domain immensely simplify spectroscopy because only a few rotational states are occupied, thereby permitting the study of atoms interacting only by dispersion, rather than valence binding forces. Both areas, Bose condensates and cold collision spectroscopy, have implications for optics.

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