The Peierls Transition in a Magnetic Field for the Two-Chain Organic Conductor (Perylene) 2 [Pt(S 2 C 2 (CN) 2 ) 2 ]

We present and analyse microwave dielectric response data under magnetic field in the Peierls ordered state of the quasi-one-dimensional two-chain organic conductor (Per)2[Pt(S2C2(CN)2)2]. The data are shown to provide a unique opportunity to extract the full-temperature profile of the Peierls gap under field. Quantitative agreement with the fluctuation-free mean-field theory is found.