## SCL Seminar by Ross McKenzie

Scientific Computing Laboratory seminar will be held on Wednesday, August 31, at 14:00 in the library reading room “Dr. Dragan Popović" of the Institute of Physics Belgrade. The talk entitled

will be given by Prof. Ross McKenzie (University of Queensland, Brisbane, Australia, condensedconcepts.blogspot.com)

Are there fundamental limits to how small the shear viscosity of a macroscopic fluid can be? Could Planck’s constant and the Heisenberg uncertainty

principle determine that lower bound? In 2005 mathematical techniques from string theory and black hole physics (!) were used to conjecture a lower bound for the ratio of the shear viscosity to the entropy of all fluids. From both theory and experiment, this bound appears to be respected in ultracold atoms and the quark-gluon plasma.

However, we have shown that this bound is strongly violated in the “bad metal” regime that occurs near a Mott insulator, and described by a Hubbard model [1]. I will give a basic introduction to shear viscosity, the conjectured bounds, bad metals, and our results.

[1] N. Pakhira and R.H. McKenzie, Phys. Rev. B 92, 125103 (2015).

**"Absence of a quantum limit to the shear viscosity of strongly interacting fermion systems"**will be given by Prof. Ross McKenzie (University of Queensland, Brisbane, Australia, condensedconcepts.blogspot.com)

**Abstract of the talk:**Are there fundamental limits to how small the shear viscosity of a macroscopic fluid can be? Could Planck’s constant and the Heisenberg uncertainty

principle determine that lower bound? In 2005 mathematical techniques from string theory and black hole physics (!) were used to conjecture a lower bound for the ratio of the shear viscosity to the entropy of all fluids. From both theory and experiment, this bound appears to be respected in ultracold atoms and the quark-gluon plasma.

However, we have shown that this bound is strongly violated in the “bad metal” regime that occurs near a Mott insulator, and described by a Hubbard model [1]. I will give a basic introduction to shear viscosity, the conjectured bounds, bad metals, and our results.

[1] N. Pakhira and R.H. McKenzie, Phys. Rev. B 92, 125103 (2015).