Monday, November 7, 2016

A concrete example of a quantum critical metal

I welcome comments on this preprint.

Quantum critical local spin dynamics near the Mott metal-insulator transition in infinite dimensions Nagamalleswararao Dasari, N. S. Vidhyadhiraja, Mark Jarrell, and Ross H. McKenzie
Finding microscopic models for metallic states that exhibit quantum critical properties such as $\omega/T$ scaling is a major theoretical challenge. We calculate the local dynamical spin susceptibility $\chi(T,\omega)$ for a Hubbard model at half filling using Dynamical Mean-Field Theory, which is exact in infinite dimensions. Qualitatively distinct behavior is found in the different regions of the phase diagram: Mott insulator, Fermi liquid metal, bad metal, and a quantum critical region above the finite temperature critical point. The signature of the latter is $\omega/T$ scaling where $T$ is the temperature. Our results are consistent with previous results showing scaling of the dc electrical conductivity and are relevant to experiments on organic charge transfer salts.
Here is the omega/T scaling, which I think is quite impressive.
We welcome comments.

2 comments:

  1. Hi Ross, I hope this is not a trivial question but I am not very familiar with non-finite Hubbard calculations. Is it possible to make a connection between your phase diagram and the pairing gap found in finite Hubbard systems? For instance Tsai/Kievelson finds a pairing gap in a broad region around U/t=8 (http://dx.doi.org/10.1103%2FPhysRevB.77.214502). From what I understand pairing mechanisms like this are hoped to be the basis of the high TC superconductivity in cuprates. Yet this region is Mott insulating in your phase diagram. Is there a way to relate the results of these two approaches? Thanks - and I really appreciate your blog. Just found it recently and it is very good.

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    1. Thanks for the question.

      There are important differences between our Hubbard model and theirs. Ours is homogenous (all the t hoppings are the same), at half filling, and we solve in the infinite-dimensional limit. Theirs has in homogenous t, is not at half filling, and is two-dimensional. this is why the phase diagrams are different.

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