Superconductivity in the heavy fermion system PrOs₄Sb₁₂

Abu Alrub, Tayseer Rafe (2008) Superconductivity in the heavy fermion system PrOs₄Sb₁₂. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Superconductivity was observed in the Pr-filled skutterudite heavy fermion system PrOs₄Sb₁₂in 2002. Symmetry considerations, based on the Landau theory of second order phase transitions, were used to derive all possible superconducting states in this material. It was found that a three-component order parameter that belongs to the Tu irreducible representation of the tetrahedral point group Th best describes superconductivity in PrOs₄Sb₁₂. Two different superconducting phases have been observed in PrOs₄Sb₁₂; the lower temperature B phase occupies the bulk of the phase diagram, while the higher temperature A phase is found in a narrow region below Hc2 , and possibly does not exist at all. The proposed gap function in the A phase is unitary and has two point nodes in the [00 ± 1] directions. In the B phase, the proposed gap function is nonunitary and the lower branch has four point nodes in the [±α,0,±β] directions. Hence, thermodynamic and transport properties of a nonunitary superconducting state are analyzed. It is shown that the conductivity tensor has inequivalent diagonal components due to the off-axis nodal positions of the B phase. Moreover, nonuniversal conductivities (impurity scattering dependent) have been obtained. A semi-classical approach based on the Doppler shift of the quasiparticle energy is used to calculate the oscillatory past of the magnetic field-angle dependent density of states and thermal conductivity. All possible point node configurations for superconducting phases of a tetrahedral superconductor are considered.

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