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Browsing by Subject "Nematicity"

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    Interplay between electronic nematicity and elasticity in finite-size samples and surfaces
    (2021-05) Lahiri, Aritra
    In the phase diagram of iron-based superconductors, the proximity of superconductivityto electronic nematicity, the spontaneous breaking of the discrete rotational symmetry, has prompted numerous studies of a detailed understanding of nematicity and its interplay with superconductivity. Several studies have suggested the onset of nematic order above the bulk nematic critical temperature, along with indications of it being associated with the surface of the sample. In this work, motivated by the strong nemato-elastic interaction, we consider aspects of the interplay of elasticity and nematicity in realistic finite-size samples, considering both bulk and surface effects. First, we demonstrate non-trivial boundary effects in a finite-size sample, which significantly alter the order parameter profiles and the critical temperature. Elaborate finite-element simulations are carried out to solve the full nemato-elastic problem, demonstrating a strong inhomogeneity, dependent on the sample aspect ratio and geometric constraints. We find that the nematic critical temperature is bounded by the corresponding bulk value and, in fact, decreases rapidly with decreasing sample thickness, thereby necessitating the presence of other mechanisms to generate supercritical nematicity. We propose surface elastic disorder, such as domains of anisotropic defects, as possible avenues to realize supercritical nematicity. We show that these, in fact, lead to an incommensurate supercritical smectic state, localized at the sample surface, eventually transitioning into the standard uniform bulk nematic state. The smectic modulation wavevector is dependent only on the elastic parameters, and the coefficients entering the nematic free energy.