Tuesday, March 6, 2012

The beauty of the Drude model

I have been teaching the Drude model for the umpteenth time, but have a new slant I am emphasizing to the students. It only involves a single new parameter, the scattering time. Yet it is able to capture the details of a wide range of experiments on elemental metals. I think it is important for students to appreciate the importance of considering the simplest possible models, with as few free parameters as possible, and see what they can and cannot explain. Only then one should move to more advanced models which are closer to the "truth".


  1. Hello Prof. McKenzie, this is a student appreciating the single-parameter wonder of the Drude model! What also struck me as being interesting is that Drude took the kinetic model and applied it almost directly to the electron gas case and then merely surmised that the 'scattering time' was electron scattering; according to Ashcroft and Mermin, he had not devised his model with the particular intent of modelling electron-ion collisions. I wonder what would have emerged had he done this...?

  2. There is also the plasma frequency. I'd say it is a two parameter model.

  3. Josh,

    The beauty of the model is that one does not need to know the physical origin of the scattering.


    In Drude's version the plasma frequency is given by the density. For elemental metals I do not take to be a free parameter, being determined by the atomic density.
    I agree that in the "Drude" model that pops out of the Bloch-Boltzmann model that the plasma frequency is an additional parameter. It is determined by the band structure rather than the electron density.