### Condensed Matter Theory Group

#### 1. What's the condensed-matter theory ?

When many electrons, atoms, and molecules, which are microscopic components of materials in quantum mechanics, interact with each other, such many-body systems often lead to new quantum phenomena, --- superconductivity, superfluidity, Bose-Einstein condensation, magnetism and metal-insulator transition --- which we cannot imagine from only nature of individual elements. Our theoretical group investigates such various type of physical phenomena on the basis of quantum many-body theory. These many-body problems cannot be explained from Reductionism, that is, only fundamental laws which govern individual elements. In this point, we say that the condensed-matter physics has the potential to find new fascinating phenomena even today. We are aiming to find a new universal law and to construct a theoretical framework describing it. Theoretical methods are wide-ranging approaches from analytic methods like quantum field theory to computer simulations.

#### 2. Current topics

- Quantum fluids,
^{4}He,^{3}He and quantum Solid^{3}He. - Mechanism of superconductivity in the high-Tc cuprates.
- Phase diagram under magnetic field in the type-II superconductivity with strong superconducting fluctuations.
- Normal and superconducting states in heavy fermion systems.
- Metal-Insulator transition and Magnetism in strongly correlated electron systems.
- Critical phenomena in one-dimensional systems with strong quantum fluctuations on the basis of the Bethe Ansatz and conformal field theory.
- Superconducting transition in two-dimensional dirty systems with strong quantum fluctuations.
- Effects of randomness in unconventional superconductivity and superfluidity.
- Quantum condensate in optical lattice fermion systems.

#### 3. Theoretical Background

We investigate the above topics on the basis of quantum physics, statistical physics, electromagnetism, mathematical physics, and hydrodynamics. You need also to understand advanced mathematical methods like quantum field theory. However, what is the most important is to grasp "the physics".