Friday, February 3, 2012

Befuddled by planckian dissipation

I am rather confused by a Nature News and Views Why the temperature is so high? by Jan Zaanen. A key claim in the article is that in quantum systems there is a fundamental limit to the "dissipation time"
 h/(2 pi k_B T).
(An earlier post on this article gives more background).

Here are some of Zaanen's claims:
In fact, according to the laws of quantum physics, it is impossible for any form of matter to dissipate more than these metals do....
the laws of quantum physics forbid the dissipation time to be any shorter at a given temperature than it is in the high-temperature superconductors. If the timescale were shorter, the motions in the superfluid would become purely quantum mechanical, like motion at zero temperature, and energy could not be turned into heat. In analogy with gravity, this timescale could be called the 'Planck scale' of dissipation (or 'planckian dissipation'). 
It is not clear if these statements concern dissipation of the energy of quasi-particles and whether or not they are fermionic.
Furthermore, I can find no reference which supports this claim that "the laws of quantum mechanics" require such a fundamental limit.
It seems to me, if it were true one could not have a electron-phonon system with a dimensionless coupling constant lambda larger than one. [Above the Debye temperature the electron scattering rate (times hbar) is roughly  lamba T].

I welcome clarifying comments.


  1. You have to take anything these guys say nowadays with a grain of salt. Still, it's nice to see that after 25 years of YBaCuO some of these people are being forced to revise their perspectives on the phenomenon of high Tc.

    It's ok to be wrong in science. Wrong is good. One less thing to worry about. Now, what about these charge transfer excitons, eh? It seems to me to be kinda quiet out there on the front lines of superconductivity.

  2. how does this generalize to the case of quantum (zero Temperature) dissipation, such as in the Caldeira-Leggett model?

  3. It is not clear to me how this relates to Calderia-Leggett models. Although it is intriguing that for the spin boson model one can have dissipation for an ohmic bath that goes like alpha T, where alpha is a dimensionless coupling constant, and for alpha > 1 one does not have quantum coherence.
    However, the two discrete states in a spin boson model seem a long way from the infinite number of delocalised states in a metal.