The thermodynamic and transport properties of the unitary Fermi gas at finite temperature $T$ are governed by a quantum critical point at $T=0$ and zero density. We compute the universal shear viscosity to entropy ratio $\ensuremath{\eta}/s$ in the high-temperature quantum critical regime $T\ensuremath{\gg}|\ensuremath{\mu}|$ and find that this strongly coupled quantum fluid comes close to perfect fluidity $\ensuremath{\eta}/s=\ensuremath{\hbar}/(4\ensuremath{\pi}{k}_{B})$. Using a controlled large- $N$ expansion, we show that already at the first nontrivial order the equation of state and the Tan contact density $C$ agree well with the most recent experimental measurements and theoretical Luttinger-Ward and bold diagrammatic Monte Carlo calculations.The thermodynamic and transport properties of the unitary Fermi gas at finite temperature $T$ are governed by a quantum critical point at $T=0$ and zero density. We compute the universal shear viscosity to entropy ratio $\ensuremath{\eta}/s$ in the high-temperature quantum critical regime $T\ensuremath{\gg}|\ensuremath{\mu}|$ and find that this strongly coupled quantum fluid comes close to perfect fluidity $\ensuremath{\eta}/s=\ensuremath{\hbar}/(4\ensuremath{\pi}{k}_{B})$. Using a controlled large-$N$ expansion, we show that already at the first nontrivial order the equation of state and the Tan contact density $C$ agree well with the most recent experimental measurements and theoretical Luttinger-Ward and bold diagrammatic Monte Carlo calculations.

arXiv:1204.1980Physical Review AJul 12, 201246 citations

Shear viscosity in a non-Fermi-liquid phase of a quadratic semimetal

Philipp T. Dumitrescu

We study finite temperature transport in the Luttinger-Abrikosov-Beneslavskii phase---an interacting, scale invariant, non-Fermi-liquid phase found in quadratic semimetals. We develop a kinetic equation formalism to describe the dc transport properties, which are dominated by collisions, and compute the shear viscosity $\ensuremath{\eta}$. The ratio of shear viscosity to entropy density $\ensuremath{\eta}/s$ is a measure of the strength of interaction between the excitations of a quantum fluid. As a consequence of the quantum critical nature of the system, $\ensuremath{\eta}/s$ is a universal number and we find it to be consistent with a bound proposed from gauge-gravity duality.We study finite temperature transport in the Luttinger-Abrikosov-Beneslavskii phase---an interacting, scale invariant, non-Fermi-liquid phase found in quadratic semimetals. We develop a kinetic equation formalism to describe the dc transport properties, which are dominated by collisions, and compute the shear viscosity $\ensuremath{\eta}$. The ratio of shear viscosity to entropy density $\ensuremath{\eta}/s$ is a measure of the strength of interaction between the excitations of a quantum fluid. As a consequence of the quantum critical nature of the system, $\ensuremath{\eta}/s$ is a universal number and we find it to be consistent with a bound proposed from gauge-gravity duality.

arXiv:1406.6337Physical Review BSep 2, 201512 citations

Transport Phenomena in Strongly Correlated Fermi Liquids

Hiroshi Kontani

Springer tracts in modern physicsJan 1, 201316 citations

The thermodynamic and transport properties of the unitary Fermi gas at finite temperature

T

are governed by a quantum critical point at

T=0

and zero density. We compute the universal shear viscosity to entropy ratio $\ensuremath{\eta}/s$ in the high-temperature quantum critical regime $T\ensuremath{\gg}|\ensuremath{\mu}|$ and find that this strongly coupled quantum fluid comes close to perfect fluidity $\ensuremath{\eta}/s=\ensuremath{\hbar}/(4\ensuremath{\pi}{k}_{B})$. Using a controlled large-

N

expansion, we show that already at the first nontrivial order the equation of state and the Tan contact density

C

agree well with the most recent experimental measurements and theoretical Luttinger-Ward and bold diagrammatic Monte Carlo calculations.