Professeur agrégé


Filed in: Site.QuantumCriticalPoints · Modified on : Mon, 23 Dec 13

Recovery of Fermi liquid behaviour away from the QCP

It was Hertz, who realized in 1976 that classical statistics is no longer sufficient for describing the thermodynamic properties if the transition temperature of a second order phase transition, typically antiferromagnetic order in a metal, is suppressed to zero temperature by an external parameter x such as, pressure, chemical composition, or magnetic field. Instead, quantum mechanical statistics needs to be used and thermodynamical properties can all be described with the help of a single scaling function (T/x) whereas in the case of a finite transition temperature with classical statistics where they scale as a function (T) of the temperature alone.

When we studied the magnetic field dependence of the specific heat and electrical conductivity above the upper critical field Hc2 of the unconventional superconductor CeCoIn5 we were able to collapse, or scale, the data on a single curve. This led me to the conclusion that a quantum critical point (QCP) might be located in the vicinity of Hc2 (1). With flux growth it is possible to synthesize the entire series Ce(Co,Rh,Ir)In5 of of compounds. The sister compound CeRhIn5 orders antiferromagnetically at 3.8 K at ambient pressure and becomes only superconducting after applying a pressure of 1.77 GPa. This fact then naturally led to the conclusion that if it were not for the superconductivity, CeCoIn5 would have an antiferromagnetic ground state, and that the antiferromagnetism is destroyed by an applied magnetic field of the size of the upper critical field Hc2. Even more interesting is the scenario where CeCoIn5 would be the first example of a compound and where the QCP is associated with superconductivity, a proposition which lead to a great number of follow up experiments.

  1. A. Bianchi, R. Movshovich, I. Vekhter, P. G. Pagliuso, and J. L. Sarrao, “Avoided antiferromagnetic order and quantum critical point in CeCoIn5”, Phys. Rev. Lett. 91, 257001 (2003).

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