In Kato Lab., various phenomena in condensed-matter physics are studied theoretically by analytic and numerical methods.
What is condensed-matter physics?
Condensed-matter physics is one of the most popular research areas in physics. It includes research subjects important for application such as material technology, optics, and semiconductors.
Condensed-matter physics attracts researchers because a variety of novel materials are synthesized day after day, and new measurements by various experimental tools are obtained every day. These experimental results are compared with theoretical predictions, and sometimes show disagreement with them. In Kato Lab., we are trying to understand nature of materials in theoretical point of views, and to solve disagreement between theory and experiment.
Research subject of Kato Lab.
Research activities in Kato Lab. are summarized in the following keywords.
1. Physics of mesoscopic systems
Physics of mesoscopic physics treats artificially fabricated systems whose size is between macroscopic and microscopic ones (typically order of (or less than) one micrometer). In such systems, wave nature of electrons have to be considered to describe material properties. The most important feature of mesoscopic systems is that fundamental concepts in quantum mechanics such as indistinguishability of quantum particles and nonlocal quantum correlation (quantum entanglement) can be verified in a direct way.
2. Nonequilibrium statistical mechanics
In a course of undergraduate school of physics, one learns statistical mechanics, which is a very beautiful theory applicable to thermal equilibrium states. Nonequilibrium states, however, is beyond coverage of statistical physics, and should be described in a novel theoretical framework called nonequilibrium statistical mechanics.
In Kato Lab. we are trying to constitute a theory for nonequilibrium states in mesoscopic systems. Although this problem is not easy at all, we are approaching it by field theoretical methods and numerical simulations.
3. Strong electron correlation
In some kinds of materials, we have to consider strong Coulomb interaction between electrons. Effect of strong electron correlation, which appear in such materials, is an interesting research subject, but is difficult to be treated theoretically. Theoretical study of strong electron correlation has a long history, and continues actively even now.
Also in Kato Lab., strong electron correlation is an important keyword. For example, a quantum dot system shows the Kondo effect, one of strong electron correlation effect, under appropriate experimental conditions. Transport properties through a quantum dot in the Kondo state are an interesting research subject, and are connected to more difficult problems such as Mott insulators, high-temperature superconductivity, etc. We expect that study of strong electron correlation gives a hint for the future study of strong electron correlation.
4. “Soft” electronic states
In Kato Lab., a few research subjects far from mesoscopic physics are also studied. One of them is a glassy-like state of electrons and lattice ions in condensed matter physics. Relaxors in transition oxides and inhomogeneous electronic states in organic conductors are examples in such a direction.