4 research outputs found
Pressure shift of the superconducting T_c of LiFeAs
The effect of hydrostatic pressure on the superconductivity in LiFeAs is
investigated up to 1.8 GPa. The superconducting transition temperature, T_c,
decreases linearly with pressure at a rate of 1.5 K/GPa. The negative pressure
coefficient of T_c and the high ambient pressure T_c indicate that LiFeAs is
the high-pressure analogue of the isoelectronic SrFe_2As_2 and BaFe_2As_2.Comment: 3 pages, 2 figure
Structural study on hole-doped superconductors Pr1-xSrxFeAsO
The structural details in Pr1-xSrxFeAsO (1111) superconducting system are
analyzed using data obtained from synchrotron X-ray diffraction and the
structural parameters are carefully studied as the system is moving from
non-superconducting to hole-doped superconducting with the Sr concentration.
Superconductivity emerges when the Sr doping amount reaches 0.221. The linear
increase of the lattice constants proves that Sr is successfully introduced
into the system and its concentration can accurately be determined by the
electron density analyses. The evolution of structural parameters with Sr
concentration in Pr1-xSrxFeAsO and their comparison to other similar structural
parameters of the related Fe-based superconductors suggest that the interlayer
space between the conducting As-Fe-As layer and the insulating Pr-O-Pr layer is
important for improving Tc in the hole-doped (1111) superconductors, which
seems to be different from electron-doped systems.Comment: 17 pages, 7 figures, 1 tabl
The electronic structure of LiFeAs and NaFeAs probed by resonant inelastic x-ray scattering spectra
Results of resonant inelastic X-ray scattering (RIXS) measurements at Fe
L-edges and electronic structure calculations of LiFeAs and NaFeAs are
presented. Both experiment and theory show that in the vicinity of the Fermi
energy, the density of states is dominated by contributions from Fe 3d-states.
The comparison of Fe L2,3 non-resonant and resonant (excited at L2-threshold)
X-ray emission spectra with spectra of LaOFeAs and CaFe2As2 show a great
similarity in energy and I(L2)/I(L3) intensity ratio. The I(L2)/I(L3) intensity
ratio of all FeAs-based superconductors is found to be more similar to metallic
Fe than to correlated FeO. Basing on these measurements we conclude that
iron-based superconductors are weakly or moderately correlated systems.Comment: 11 pages, 6 figure
Feshbach resonances and mesoscopic phase separation near a quantum critical point in multiband FeAs-based superconductors
High Tc superconductivity in FeAs-based multilayers (pnictides), evading
temperature decoherence effects in a quantum condensate, is assigned to a
Feshbach resonance (called also shape resonance) in the exchange-like interband
pairing. The resonance is switched on by tuning the chemical potential at an
electronic topological transition (ETT) near a band edge, where the Fermi
surface topology of one of the subbands changes from 1D to 2D topology. We show
that the tuning is realized by changing i) the misfit strain between the
superconducting planes and the spacers ii) the charge density and iii) the
disorder. The system is at the verge of a catastrophe i.e. near a structural
and magnetic phase transition associated with the stripes (analogous to the 1/8
stripe phase in cuprates) order to disorder phase transition. Fine tuning of
both the chemical potential and the disorder pushes the critical temperature Ts
of this phase transition to zero giving a quantum critical point. Here the
quantum lattice and magnetic fluctuations promote the Feshbach resonance of the
exchange-like anisotropic pairing. This superconducting phase that resists to
the attacks of temperature is shown to be controlled by the interplay of the
hopping energy between stripes and the quantum fluctuations. The
superconducting gaps in the multiple Fermi surface spots reported by the recent
ARPES experiment of D. V. Evtushinsky et al. arXiv:0809.4455 are shown to
support the Feshbach scenario.Comment: 31 pages, 7 figure