Wei-Cheng Lee (SIMES Seminar)

Date(s) - Oct 17 2017
10:30 AM - 11:30 AM

Room 335, McCullough Building


Effects of Umklapp Processes on Correlated Materials

Wei-Cheng Lee

Department of Physics, Applied Physics, and Astronomy,

Binghamton University – SUNY




Correlated materials exhibiting a number of exotic electronic states of matters have been one of the most studied subjects in condensed matter physics. A well-accepted scheme is that due to the strong short-range repulsive interactions, the quasi-particle picture, the central dogma of Fermi liquid theory, breaks down. Instead of being sharp in momentum-frequency space, the spectral weight of electrons spreads out in a wide range of frequency, which is believed to be the cause of novel temperature and frequency dependences of physical properties like DC resistivity and optical conductivity. However, since all these physical properties require a momentum-relaxing mechanism to have finite values, the interaction that breaks the momentum conservation has to be identified in order to understand the experimental results. In this talk, I will argue that since all the correlated materials are crystalline, Umklapp process is the most natural candidate for the momentum-relaxing mechanism. I will show that with the inclusion of Umklapp processes and long-range Coulomb interaction, new collective excitations leading to novel frequency dependence of optical conductivity can emerge in mid-infrared region, and these collective excitations are sensitive to superconducting phase transition. Implications for new energy scale to affect superconducting transition temperature Tc will be discussed.