|Speaker:||Takashi Oka (U. Tokyo Hongo)|
|Title:||Strong field QFT in condensed matter – photo-induced topological phase transition and many-body Schwinger mechanism|
|Date (JST):||Wed, Mar 28, 2012, 13:30 - 15:00|
|Place:||Seminar Room A|
Control of phase transitions by strong laser is now becoming possible in condensed matter systems. Old ideas in "strong field quantum field theory" developed in the 19-th century such as the Volkov states, Euler-Heisenberg's effective action and the Schwinger mechanism, now have renewed interest. One new aspect in the present research is the marriage with newer notions such as topological phase transition and Mott transition.
Topological phase transition is a condensed matter jargon for a transition between quantum states with different topological number and can be viewed as a lattice analogue of (a change of) quantum anomaly in QFT. An example of a topological number is the Chern number. We found that one can control the parity anomaly, characterized by the 1st Chern number, in 2+1 dimensional Dirac systems such as grapheme, by applying circularly polarized light which leads to a photo-induced quantum Hall state [Oka et.al. Phys. Rev. B 79, 081406 (R) (2009)].
The Mott transition stands for a metal-insulator transition driven by strong electron repulsion and is characterized by confinement of charged carriers. Application of strong laser leads to a pair creation of carriers, an analogue of the Schwinger mechanism in QED. We analytically calculated the creation rate by combining the imaginary time method with the exact solution of one dimensional Hubbard model, and found that a Keldysh crossover between multi-photon absorption and quantum tunneling takes place [Oka et.al. Phys. Rev. B 81, 033103 (2010), arXiv:1105.3145].
|Remarks:||may be for 1.5 hours|