Mott-Anderson Transition in Molecular Conductors: Influence of Randomness on Strongly Correlated Electrons in the κ-(BEDT-TTF)2X System
by Takahiko Sasaki
It reviews some very nice experiments done by Sasaki and collaborators where they used X-ray irradiation to systematically vary the amount of disorder.
There are several things I find puzzling about the experimental results for X=Cu[N(CN)2]Br. I also think they are inconsistent with the offered interpretation in terms of Anderson localisation.
It is observed that irradiation does longer than 200 hours drive the material from a metallic phase to a Mott insulating phase.
First, I don't think invoking Anderson localization is relevant because the amount of disorder is relatively small, compared to the electronic bandwidth. Specifically, even for doses of 200 hours the sample is still a superconductor [probably d-wave] with a Tc of about 6 K, reduced from about 12 K in non-irradiated samples. This means [cf. Figure 9 in the paper] that the scattering rate due to impurities is about 6 K ~ 0.5 meV which is two orders of magnitude less than the hopping integral t.
Second, theory [at least at the level of DMFT] predicts that disorder [much less than the band width] stabilises the metallic phase not the Mott insulating phase. This can be seen in the phase diagram below taken from this PRL by Krzysztof Byczuk, Walter Hofstetter, and Dieter Vollhardt.
I also note that the experiments found that the for X=Cu[N(CN)2]Cl and X=Cu2(CN)3 irradiation (disorder) drove the Mott insulating phase towards the metallic phase, consistent with the above phase diagram.
So I think the paper shows how a metallic system very close to the Mott transition can be driven into the insulating phase by a relatively small amount of disorder. Current theory seems unable to explain this.