Theory of Composite Fermions

This grant supports work on quantum Hall effect. Nearly a decade ago, this PI proposed the notion of composite fermions, objects which are complexes consisting of an electron and an even number of flux quanta, formed when electrons in a layer are subjected to intense magnetic fields. A gas of independent composite fermions is the conceptual foundation underneath a physical understanding of fractional quantum Hall effect as well as the Fermi sea in the vicinity of a half-filled landau level. To incorporate effects of interaction between the composite fermions this PI has developed a wavefunction based approach, which has been successful in providing insight into several experiments. In the current grant period, he plans to build further. In particular, he plans to explore the conditions where the independent composite fermion picture breaks down and instabilities set in. He wants to study the composite fermion counterpart of instability towards ferromagnetism in low-density electrons (without any magnetic field), which was first discussed by Bloch seventy years ago.

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When a layer of electrons is subjected to high magnetic fields, their motion becomes strongly correlated and leads to integer and fractional quantum Hall effects. Some ten years ago, this PI proposed a simple, insightful framework, called composite fermions, to describe the properties associated with fractional quantum Hall effect. Over the past ten years, this conceptual device has been immensely successful in understanding experimental results and has helped develop insight and intuition. The current grant proceeds with a new twist: while the past studies have been limited to free composite fermions, when does this view break down, what happens when the breakdown occurs and what happens afterwards?

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