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January - December 2011

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University of Minnesota Twin Cities
College of Science and Engineering
School of Physics and Astronomy

PI: Charles E. Campbell

Microscopic Study of Quantum Spin-Lattice Systems and Their Phase Transitions

The discovery of high-temperature superconductors has been accompanied by an enormous interest in the study of quantum spin systems. In fact the general field of quantum magnetism has become an important and fascinating subject in its own right in recent years, and one that is at the forefront of modern condensed matter physics research. In particular, frustrated quantum Heisenberg magnets are paradigms of systems that may be used to study (zero-temperature) quantum phase transitions between quasiclassical magnetically ordered phases and magnetically disordered quantum phases.  This research centers on applying the coupled cluster method (CCM) to a large and diverse array of two-dimensional quantum spin systems of theoretical and experimental interest, particularly those involving strong frustration, that are difficult to treat by other methods. The interesting magnetic phenomena displayed by such systems also make them suitable candidates for many technological applications. The nature of the paramagnetic or nonmagnetic phases without long-range magnetic order in some quantum antiferromagnets has particularly attracted much interest too, in the hope of tracing their possible association with the mechanism of high-temperature superconductivity. Indeed, more generally, the whole subject of quantum-phase transitions in frustrated quantum magnets has become an extremely active and fast-moving topic in recent years. The CCM is now widely accepted as being one of the most successful and most widely applicable of all modern methods of microscopic quantum many-body theory. The CCM techniques pioneered by collaborator Raymond Bishop are arguably now the best available for these strongly frustrated two-dimensional quantum spin-lattice systems, and this group’s results are now setting the benchmarks in the field. They are also very interested to extend previous results at zero temperatures to finite temperatures, in order to investigate the effects of thermal fluctuations on quantum phase transitions. If successful this will open up a whole new research area of enormous interest to both the statistical physics and condensed matter communities.

Group Members

Raymond F. Bishop, School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
Peggy H. Y. Li, School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom