Field-Induced Commensurate Phase in Thiourea

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Abstract
An experimental observation of anomalies in the dielectric susceptibility of thiourea under field is reported. Four anomaly lines T± are determined; they follow the laws (T±−198.1)2=αE and (T±−198.8)2=αE, with α=0.11±0.01 K2 V−1 mm (for E<100 V/mm). A theoretical discussion, based on a Landau-Ginzburg formulation of the free energy, suggests that a pinned commensurate phase, of commensurability order p=8, exists under field at temperatures T−<T<T+. This clarifies the nature of the phase diagram of SC(ND2)2.