Transition to Fulde-Ferrel-Larkin-Ovchinnikov phases near the tricritical point: an analytical study |
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Authors: | R Combescot C Mora |
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Institution: | (1) Laboratoire de Physique Statistique, école Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 05, France, FR |
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Abstract: | We explore analytically the nature of the transition to the Fulde-Ferrel-Larkin-Ovchinnikov superfluid phases in the vicinity
of the tricritical point, where these phases begin to appear. We make use of an expansion of the free energy up to an overall
sixth order, both in order parameter amplitude and in wavevector. We first explore the minimization of this free energy within
a subspace, made of arbitrary superpositions of plane waves with wavevectors of different orientations but same modulus. We
show that the standard second order FFLO phase transition is unstable and that a first order transition occurs at higher temperature.
Within this subspace we prove that it is favorable to have a real order parameter and that, among these states, those with
the smallest number of plane waves are preferred. This leads to an order parameter with a cos(
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) dependence, in agreement with preceding work. Finally we show that the order parameter at the transition is only very slightly
modified by higher harmonics contributions when the constraint of working within the above subspace is released.
Received 20 February 2002 / Received in final form 4 June 2002 Published online 13 August 2002 |
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Keywords: | PACS 74 20 Fg BCS theory and its development – 74 60 Ec Mixed state critical fields and surface sheath |
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