Experimentally the issue has been raised with renewed intensity by the recent discovery of high temperature superconductivity. It is commonly believed, that the systems exhibiting these extraordinary phenomena are characterized by strong interactions. The quest for understanding high temperature superconductivity brings a renaissance experience for many of its practitioners, as this research spans from the most esoteric to the most useful, demonstrating those unifying principles at work, which make condensed matter physics so attractive. On one end of the spectrum of the research there is a strong and inspiring connection with advanced field theories known from high energy physics. The magnetic properties of the system are approached by SU(N) Heisenberg models, gauge theories, Berry phase arguments, instanton methods, and non-linear sigma models. Often, involved topological considerations are invoked as well. As another link, many theories assume that, due to the strong interactions between them, the electrons can be thought of as composite particles, made up of spin-carrying and charge-carrying components. A second front of studies is to develop powerful and unconventional phenomenologies for the experimental data, which will provide further insights in order to develop the eventual microscopic theory. These include the marginal fermi liquid theory, its extensions via renormalization group calculations, and the nearly antiferromagnetic fermi-liquid theories. The main emphasis is on the features of the low energy excitations, the nature of the superconducting gap, and the symmetry of the order parameter. Finally there is tremendous experimental effort to develop technical applications of these extraordinary phenomena. My students and I are actively involved in the first two areas of research.
The other main field of our research is the field of quantum phase transitions in ordered and disordered systems. Some of the outstanding experimental problems are: the different phases of superfluid helium in disordered substrates; the suppression of superconductivity by impurities in granular and homogeneously disordered thin films; and the many different experimental realizations of quantum spin-glasses.
A related rapidly emerging area is that of the mesoscopic physics, where a genuinely new, intermediate level of understanding has to be developed between the better understood micro- and macro-levels of description. These phenomena promise to revolutionize electronics, as the single electron transistor is already a reality, as are the many phenomena associated with the Coulomb blockade. We apply numerical techniques, such as quantum Monte Carlo programs, and renormalization group methods, often based on extended sine-Gordon formalisms, to explore the features of the phases themselves and the nature of the transitions between them. Our close contact with experimentalists serves as a continued guidance in the research.
E-mail zimanyi@physics.ucdavis.edu
View a list of awards and honors or go back to people page.