Kavli Affiliate: Ke Wang
| First 5 Authors: , , , ,
| Summary:
While there are many different mechanisms which have been proposed to
understand the physics behind light induced “superconductivity", what seems to
be common to the class of materials in which this is observed are strong
pairing correlations, which are present in the normal state. Here we argue,
that the original ideas of Eliashberg are applicable to such a pseudogap phase
and that with exposure to radiation the fermions are redistributed to higher
energies where they are less deleterious to pairing. What results then is a
photo-induced state with dramatically enhanced number of nearly condensed
fermion pairs. In this phase, because the a.c. conductivity, $sigma(omega) =
sigma_1(omega) + i sigma_2(omega)$, is dominated by the bosonic
contribution, it can be computed using conventional (Aslamazov Larkin)
fluctuation theory. We, thereby, observe the expected fingerprint of this
photoinduced “superconducting" state which is a $1/omega$ dependence in
$sigma_2$ with fits to the data of the same quality as found for the so-called
photo-enhanced (Drude) conductivity scenario. Here, however, we have a
microscopic understanding of the characteristic low energy scale which appears
in transport and which is necessarily temperature dependent. This approach also
provides insight into recent observations of concomitant diamagnetic
fluctuations. Our calculations suggest that the observed light-induced phase in
these strongly paired superconductors has only short range phase coherence
without long range superconducting order.
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