Maxim Dzero: Symplectic spins and Pu 115

Time reversal and the symplectic spin of the electron: application to Pu 115 superconductors

Collaborators: R. Flint, P. Coleman

(1) The discovery of the talk

- Superconductivity in the fluctuating valence compounds Pu 115 may arise from two-body interference between two-Kondo screening channels.

Results and contact with experiment:

- The superconducting critical temperature reaches its maximum when the energy levels of excited valence configurations are almost degenerate. This is the case of PuGaIn5.
- One can probably explain the fact that Curie Weiss behavior in these compounds ends at the critical superconducting transition temperature.
- It is predicted that the symmetry of the order parameter is determined by the product of the Wannier factors in the interfering conduction channels. For example, kz2(kx2-ky2).

Assumptions

- That it is the virtual valence fluctuations of the magnetic Pu configuration that create two conduction channels of different symmetry.
- That the two-channel Kondo lattice model is an appropriate description.
- That the mean-field theory corresponding to the large N limit of the symplectic Sp(N) representation of the SU(2) spins is an accurate description.


(2) Questions it raises

Subir: Superconductivity does not occur in this formalism in the single-impurity limit. What symmetry garantees that the V2 and D2 coefficients in the Hubbard-Stratonovich transformation are identical?
Answer: Particle-hole symmetry.

Does the Sp(N) large N solution correspond to the SU(N) large N solution?
Answer: Yes at mean-field but not for the fluctuations.

Why should we consider that the Sp(N) representation is better?
Answer: Because it gets rid of the "dipole" degrees of freedom of the SU(N) representation that do not transform like spin under time-reversal and charge conjugation symmetry. Sp(N) preserves that fundamental property of the physical spins.

Can the antiferromagnetic phase be described in this formalism?
Answer: One probably needs to use bosons.

(3) Questions left open

How big are the fluctuations, at least at the gaussian level?

Should we expect that all two-channel Kondo systems should have superconducting ground states?


Reference