Fermi glass- experiments

2021 Observation of a marginal Fermi glass

The linear-in-frequency relaxation rate with a slope close to unity is a dependence reminiscent of strongly correlated metals
that exhibit the marginal Fermi liquid phenomenology

The low-frequency excitations above the localized state are resonant particle–hole excitations, in which a particle is moved between two
nearby localized orbitals. These excitations are local electric dipoles, and thus naturally interact via 1/R3
dipole–dipole interactions

A dipolar excitation can coherently hop on this network, at a rate one can calculate (Supplementary Section IV) to be ~ω.

supplements

The analysis of the previous section shows how a combination of Coulomb blockade and dipolar hopping can
give rise to the experimentally observed Γ(ω) ∼ ω for the relaxation of a TLS in an electron glass. The prefactor
(ignoring logarithms) is $ξ^3 (V/W)^2$, which is not necessarily small, if the typical microscopic hopping amplitude between
adjacent P sites is comparable to the Coulomb interaction between them. This framework also naturally reproduces
the sharpening of the TLS frequency as one increases the temperature up to T ' ω: when delocalization takes place
through coherent tunneling at zero temperature, the finite-temperature corrections usually suppress transport through
decoherence

Within our zero-temperature theory the processes responsible for T1 and T2 are the same, so we expect these
quantities to be related by some simple scale factor; this is indeed what we observe. However, the trends with
increasing temperature are different: T1 grows with temperature, while T2 remains roughly constant (so the ratio T1/T2
increases). A natural interpretation is that this approximate temperature-independence comes from a competition
between the increasing T1 time and the opening of thermal dephasing channels

Acknowledgements
We thank A. Burin, Y. Galperin, Y.-B. Kim, A. Legros, I. Martin, A. Millis, V. Oganesyan,
S. Paramesweran, B. Shklovskii and Y. Yuan for helpful discussions.

Recent advances in spectroscopy give access to the decay time of excitations in disordered insulating silicon close to the metal–insulator transition, revealing similarities to high-temperature cuprate superconductors

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