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Patterns of co-existing order parameters and universal escapeway to the magnetic quantum critical point

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We show that particle-hole asymmetry induced by doping or pressure leads to patterns of order parameters that necessarily coexist whenever two of the order parameters are present. We have found a systematic way to predict all such patterns of unconventional superconducting and particle-hole condensates. We report novel magnetic field induced transitions to the multiphase pattern states that exhibit some of the thermodynamic characteristics of Fulde-Ferrel phases. For example, above a given field, we report a transition from d-wave singlet SC to a state in which d-wave singlet SC coexists with staggered triplet SC and SDW the other two partners of the given pattern. We will argue based on experiments on CeCoIn_5 that this may correspond to the high field so called “Q-phase” state observed in this material. A very similar behavior is obtained in a CDW system where we report field induced transitions with Fulde-Ferrel signatures to a state in which CDW , SDW and FM all coexist. Double step metamagnetic transitions in bilayered ruthenites and other materials as well as hidden orders like in URu_2Si_2 can all be understood in this context. By reporting similar results on these two examples of completely different physical situations we will argue that these “Fulde-Ferrel”-like transitions to the multiphase state may represent a universal escapeway to the magnetic quantum critical point. We may verify this conjencture on additional patterns.

For some related Refs. see e.g. arxiv:0804.2450; arxiv:0804.2460; arxiv:0802.4093; arxiv:0709.1025; arxiv:0802.4080

This talk is part of the Irregular seminars in TCM series.

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