Navinder Singh | Searcharxiv

arXiv2014

Theory of the electron phonon relaxation time in cuprates: Reproducing the observed temperature behaviour

We have studied the temperature dependence of the rate of energy transfer from electronic sub-system to phononic sub-system in the case of cuprates, when the system is photo-excited by a femtosecond laser pulse. In the pseudogap state, taking the electronic dispersion {\it as linear} near the nodal points of the Brillouin zone, we show that the rate of energy transfer from electronic sub-system to phononic sub-system is proportional to $T^{5}$ at lower temperatures ($T< >T_0$), here $T_0$ is the Debye temperature for cuprates. The linear electronic dispersion in the pseudogap state introduces new terms in the expression of energy transfer as given by M. I. KAGANOV et.al. \cite{kaganov}. {\it But the leading terms are the same which are found in the case of metals in the above reference.} The electron-phonon relaxation time follows $T^{-3}$ law for cuprates which agrees well with the experimental results \cite{demsar,Jdemsar}.

cond-mat.supr-con↗

arXiv2014

Emergence of statistical behavior in many particle mechanical systems: Boltzmann's ideas on macroscopic irreversibility

An attempt is made to de-mystify the apparent "paradox" between microscopic time revsersibility and macroscopic time irreversibility. It is our common experience that a hot cup of coffee cools down to room temperature and it never automatically becomes hot (unless we put that in a microwave for heating or on stove etc) and there are numerous examples. This "one sidedness" of physical processes (like cooling of hot cup) is in apparent contradiction with the time reversibility of the dynamical equations of motion (classical or quantum). The process of automatic heating of a cold cup etc is perfectly possible from the dynamical equations perspective. Ludwig Boltzmann explained this "one sidedness" of physical processes starting from dynamical equations (his H-theorem). A criticism was raised by Boltzmann's contemporaries. The origin of this criticism lies in the very philosophy of "mechanism" that was very prevalent in the 19th century. Everyone wanted to understand physical phenomena through Newtonian mechanics (even J. C. Maxwell devised a mechanical mechanism using gears to explain the electromagnetic field!). The central issue was how can one obtain this "one sidedness" (time irreversiblility) if the underlying dynamical laws are time reversible. Number of articles exist in literature on the issue. But those are mathematically oriented and a simple presentation from practical point of view is seriously lacking. This article is an attempt to de-mystify this "paradox" from simple and practical point of view.

cond-mat.stat-mech↗