Condensed-Matter Physics & Materials Science Seminar

I discuss two recent works on optimally-doped cuprates.
I begin with recent work with Mike Norman (Argonne) on
the optical conductivity in the normal state, and argue that the
observed high frequency behavior,
which has been
suggested as evidence for quantum critical scaling, is generally
characteristic of electrons interacting with a broad spectrum of bosons.
From explicit calculations, we
find a frequency exponent for the modulus of the conductivity, and a phase angle, in good agreement with experiment. The data indicate an upper cut-off of the boson spectrum of order 300 meV. This implies that the bosons are of
electronic origin rather than phonons.

I then move on to discuss the pairing mediated by the bosonic continuum, and the similarities and differences between hole-doped and electron-doped materials.
I argue that the pairing is in the d_{x^2-y^2} channel in both cases,
but for the same
interaction strength, T_{c} is strongly reduced in electron-doped materials
due to critical role of the Fermi surface
curvature. The same effect leads to a non-monotonic
d_{x^{2}-y^{2}}-pairing
gap in electron-doped cuprates.