Monday, August 8, 2011

Deconstructing electron-doped cuprates

Last week there was an interesting paper in Nature Link between spin fluctuations and electron pairing in copper oxide superconductors 
Most high-Tc cuprate superconductors are hole doped. However, the past decade has seen studies of electron doped cuprates which have some similarities but also some significant qualitative differences. Thus there is electron-hole asymmetry.
In particular there appears to be no pseudogap in the electron-doped materials and they are not as strongly correlated.

The authors measured the temperature and doping dependence of the intralayer resistivity and deduced the phase diagram below.
Specifically, they found that for dopings x less than approx. 0.17 they could fit the resistivity to a linear in T form over 3 decades of temperature. As x decreased the co-efficient of proportionality increased roughly proportional to Tc.
For x larger than 0.17 there is no superconductivity and the resistivity could be fit to a quadratic T dependence, characteristic of Fermi liquid theory. The coefficient of proportionality becomes larger as x=0.17 is approached.

The authors note similar behaviour is seen in the Bechgaard salt (TMTSF)2PF6.

Later I will compare the above behaviour to what happens in the hole-doped cuprates, reported in a 2009 Science paper.

If one sticks with a one band Hubbard or t-J model and a band structure with next-nearest neighbour hopping t' [which produces electron-hole asymmetry] can one reproduce the key aspects of the electron-hole asymmetry in the phase diagram?
Maybe. But if one looks at the underlying electronic structure the electron and hole doped materials are different, according to this recent Nature Physics paper.

I thank Nigel Hussey for bringing the paper to my attention.


  1. Ross wrote:

    "In particular there appears to be no pseudogap in the electron-doped materials..."

    I wouldn't say this is really true, but to be precise it depends on what you mean by pseudogap. It is clear that there is a tremendous of low energy spectral weight suppression that seems to derive from p,p AFism (or other p,p order). If one associates similar PG features with density wave order (broadly construed) on the hole doped side, then there is a remarkable symmetry between the physics of two sides of the phase diagram.

    But it is true that there does not seem to be any signs of the "spin-gap"-type pseudogap of the sort found via the suppression of the spin susceptibility at high temperatures via NMR. It also looks that signs of scing fluctuations are weaker on the e-doped side of the phase diagram.

    There is a recent RMP that discusses alot of these issues in reasonable detail. :)

  2. Concerning "In particular there appears to be no pseudogap in the electron-doped materials and they are not as strongly correlated."

    I would add to Peter Armitage's comment that even at weak coupling a pseudogap can appear at finite T in two dimensions. In e-doped cuprates the optical pseudogap appears when the antiferromagnetic correlation length equals the thermal de Broglie wave length. A clear signature of the origin of the phenomenon.

    For the experiment see

    AM Tremblay