Phase Diagram and Quantum Critical Point in Newly Discovered Superconductors: SmO_{1-x}F_xFeAs
msra(2008)
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 $LaO_{1-x}F_xFeAs$ with $T_c$=26 K\cite{yoichi},
and it competes with spin-density-wave (SDW) order\cite{dong}. Neutron
diffraction shows a long-rang SDW-type antiferromagnetic (AF) order at $\sim
134$ K in LaOFeAs\cite{cruz,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
$SmO_{1-x}F_xFeAs$ discovered by us\cite{chenxh}. It is found that
superconductivity emerges at $x\sim$0.07, and optimal doping takes place in the
$x\sim$0.20 sample with highest $T_c \sim $54 K. While $T_c$ increases
monotonically with doping, the SDW order is rapidly suppressed, suggesting a
QCP around $x \sim$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 $T_c$ 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-$T_c$ cuprates. The simultaneous occurrence of order, carrier
density change and criticality makes a compelling case for a quantum critical
point in this system.
MoreTranslated text
Key words
phase diagram,neutron diffraction,materials science,spin density wave,heavy fermion,iron,quantum critical point,superconductors
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