2 research outputs found
The effect of internal pressure on the tetragonal to monoclinic structural phase transition in ReOFeAs: the case of NdOFeAs
We report the temperature dependent x-ray powder diffraction of the
quaternary compound NdOFeAs (also called NdFeAsO) in the range between 300 K
and 95 K. We have detected the structural phase transition from the tetragonal
phase, with P4/nmm space group, to the orthorhombic or monoclinic phase, with
Cmma or P112/a1 (or P2/c) space group, over a broad temperature range from 150
K to 120 K, centered at T0 ~137 K. Therefore the temperature of this structural
phase transition is strongly reduced, by about ~30K, by increasing the internal
chemical pressure going from LaOFeAs to NdOFeAs. In contrast the
superconducting critical temperature increases from 27 K to 51 K going from
LaOFeAs to NdOFeAs doped samples. This result shows that the normal striped
orthorhombic Cmma phase competes with the superconducting tetragonal phase.
Therefore by controlling the internal chemical pressure in new materials it
should be possible to push toward zero the critical temperature T0 of the
structural phase transition, giving the striped phase, in order to get
superconductors with higher Tc.Comment: 9 pages, 3 figure
Electron-hole Asymmetry and Quantum Critical Point in Hole-doped BaFeAs
We show, from first-principles calculations, that the hole-doped side of
FeAs-based compounds is different from its electron-doped counterparts. The
electron side is characterized as Fermi surface nesting, and SDW-to-NM quantum
critical point (QCP) is realized by doping. For the hole-doped side, on the
other hand, orbital-selective partial orbital ordering develops together with
checkboard antiferromagnetic (AF) ordering without lattice distortion. A unique
SDW-to-AF QCP is achieved, and = criteria (in the approximate
J_1&J_2 model) is satisfied. The observed superconductivity is located in the
vicinity of QCP for both sides.Comment: 4 page