Quantum Critical Phenomena and the Crystal Structure in Yb-based heavy fermion system

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We study the Yb based heavy fermion compounds, YbAlB4, which is example of quantum criticality in a mixed-valence system at ambient pressure and superconducting transition at 80mK. Our investigation for the pressure vs temperature phase diagram for the superconducting state near quantum critical point (QCP), a pressure-induced magnetic order, and crystal structure under pressure lead to an important result for the Yb based heavy fermion superconducting system near QCP.Specially, the superconducting state is isolated and exists without connecting magnetic order where Normally, quantum criticality of an Yb-based heavy fermion system is found next to a magnetic order stabilized by application of pressure.Moreover, this non-Fermi liquid hidden by the superconducting state is robust against the pressure. which is ever known at all. But, it is thought that this Yb material exhibits a new type superconductivity and a unconventional quantum criticality.