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Structural Order Parameter in the Pyrochlore Superconductor Cd2Re2O7

I. A. Sergienko·S. H. Curnoe
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Abstract

It is shown that both structural phase transitions in Cd2Re2O7, which occur at T_{s1}=200 K and T_{s2}=120 K, are due to an instability of the Re tetrahedral network with respect to the same doubly degenerate long-wavelength phonon mode. The primary structural order parameter transforms according to the irreducible representation E_u of the point group O_h. We argue that the transition at T_{s1} may be of second order, in accordance with experimental data. We obtain the phase diagram in the space of phenomenological parameters and propose a thermodynamic path that Cd2Re2O7 follows upon cooling. Couplings of the itinerant electronic system and localized spin states in pyrochlores and spinels to atomic displacements are discussed.

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I. A. Sergienko, S. H. Curnoe. 2003-01-04. Structural Order Parameter in the Pyrochlore Superconductor Cd2Re2O7. https://doi.org/10.1143/jpsj.72.1607

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