The graph below shows the temperature dependence of the Nernst signal measured in the normal metallic state of a family of electron doped cuprates Pr_{2-x}Ce_xCuO_4. It is taken from a 2007 PRB by Li and Greene.
-the signal is proportional to B and so not due to superconducting fluctuations
-the signal is proportional to temperature at low temperatures but has a non-monotonic temperature dependence
-the magnitude of the linear temperature dependence is an order of magnitude smaller than predicted by the simple quasi-particle theory of Behnia.
The authors consider how the data can be explained by a two-band with both electrons and holes, but point out such a model is inconsistent with the single hole Fermi surface seen in ARPES.
It would be interesting to re-consider this data in light of the recent experiments on these materials which showed a linear temperature dependence of resistivity (and thus a quasi-particle scattering rate) with a magnitude proportional to Tc [as in overdoped hole doped cuprates].
Ross wrote, "The authors consider how the data can be explained by a two-band with both electrons and holes, but point out such a model is inconsistent with the single hole Fermi surface seen in ARPES."
ReplyDeleteI wouldn't say this is the situation. The electron doped cuprates have a very complicated evolution of the Fermi surface with doping. It is clear that for underdoped samples there are both electron and hole pockets that appear to be qualititatively by some mean-field-like SDW like model. For optimal doping it is less clear. There are certainly all kinds of signatures of AF correlations in the ARPES spectra, but whether there is a true quasi-particle all the way around a single hole-like FS is unknown.
The authors of the paper you reference know this in that they state, "The sign change of the Hall coefficient and the enhanced normal-state Nernst effect were argued to result from a two-carrier electron and hole quasi-particle contribution around optimal doping of Ce = 0.15. This intriguing two-band behavior observed in transport experiments was later confirmed by angle-resolved photoemission spectroscopy ARPES."
Hi Peter,
ReplyDeleteThanks for your expert comment. I should have been more specific. The authors point out that for x=0.17 ARPES does show a single hole Fermi surface.
http://prb.aps.org/abstract/PRB/v75/i22/e224514
Hence, for these larger dopings it is not clear the two-band model is appropriate.