Title : 
Are there quantum limits to diffusion in quantum manybody systems?Are there quantum limits to diffusion in quantum manybody systems? 

Speaker  :  Dr. Nandan Pakhira, School of Mathematics & Physics, The University of Queensland 
Date  :  October 10, 2014 
Time  :  12:00 PM 
Venue  :  Room no 450 
Abstract  : 
Good metals like copper and gold show a high optical reflectivity (shiny), electrical and thermal conductivity. Good metals are characterised by diffusive transport of coherent quasiparticle states and the resistivity in these materials is well within the MottIoffeRegel (MIR) limit, $\\frac{ha}{e^{2}}$ (where $a$ is the lattice constant). But in a wide range of strongly correlated materials and most notably in the strange metal regime of doped cuprates (high $T_{c}$ superconductor) the resistivity exceeds the MIR limit and the picture of coherent quasiparticle based transport breaks down. Recent cold atom experiments [1] and theory [2] of fermions near the unitary limit suggest a lower bound for the spin diffusion constant. Sean Hartnoll, loosely motivated by holographic duality (AdS/CFT correspondence) in string theory, proposed a lower bound to the charge diffusion constant $D \\gtrsim \\hbar v_{F}^{2}/(k_{B}T)$ in the incoherent regime of transport [3]. Using dynamical mean field theory (DMFT) we calculate the diffusion constant in the Hubbard model and find significant violation of Hartnoll\'s bound in the incoherent regime of transport [4]. 