Phase Diagram and Quantum Critical Point in Newly Discovered Superconductors: SmO1-xFxFeAs
Abstract
The magnetic fluctuations associated with a quantum critical point (QCP) are widely believed to cause the non-Fermi liquid behaviors and unconventional superconductivities, for example, in heavy fermion systems and high temperature cuprate superconductors. Recently, superconductivity has been discovered in iron-based layered compound LaO1-xFxFeAs with Tc=26 Kyoichi, and it competes with spin-density-wave (SDW) orderdong. Neutron diffraction shows a long-rang SDW-type antiferromagnetic (AF) order at 134 K in LaOFeAscruz,mcguire. Therefore, a possible QCP and its role in this system are of great interests. Here we report the detailed phase diagram and anomalous transport properties of the new high-Tc superconductors SmO1-xFxFeAs discovered by uschenxh. It is found that superconductivity emerges at x0.07, and optimal doping takes place in the x0.20 sample with highest Tc 54 K. While Tc increases monotonically with doping, the SDW order is rapidly suppressed, suggesting a QCP around x 0.14. As manifestations, a linear temperature dependence of the resistivity shows up at high temperatures in the x<0.14 regime, but at low temperatures just above Tc in the x>0.14 regime; a drop in carrier density evidenced by a pronounced rise in Hall coefficient are observed, which mimic the high-Tc cuprates. The simultaneous occurrence of order, carrier density change and criticality makes a compelling case for a quantum critical point in this system.