A backreacted holographic model of an anisotropic Dirac semimetal gives η/s below the KSS bound in the quantum critical region, with low-temperature scaling η/s ~ T^0.56 tied to a Lifshitz dynamical exponent z ≈ 1.9.
Tight-binding modeling and low-energy behavior of the semi-Dirac point
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abstract
We develop a tight-binding model description of semi-Dirac electronic spectra, with highly anisotropic dispersion around point Fermi surfaces, recently discovered in electronic structure calculations of VO$_2$/TiO$_2$ nano-heterostructures. We contrast their spectral properties with the well known Dirac points on the honeycomb lattice relevant to graphene layers and the spectra of bands touching each other in zero-gap semiconductors. We also consider the lowest order dispersion around one of the semi-Dirac points and calculate the resulting electronic energy levels in an external magnetic field. We find that these systems support apparently similar electronic structures but diverse low-energy physics.
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Out-of-bounds hydrodynamics in holographic anisotropic Dirac semimetals
A backreacted holographic model of an anisotropic Dirac semimetal gives η/s below the KSS bound in the quantum critical region, with low-temperature scaling η/s ~ T^0.56 tied to a Lifshitz dynamical exponent z ≈ 1.9.