Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSelf consistent GW determination of the interaction strength: application to the iron arsenide superconductors
455
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We introduce a first principles approach to determine the strength of the electronic correlations based on the fully self consistent GW approximation. The approach provides a seamless interface with dynamical mean field theory, and gives good results for well studied correlated materials such as NiO. Applied to the recently discovered iron arsenide materials, it accounts for the noticeable correlation features observed in optics and photoemission while explaining the absence of visible satellites in X-ray absorption experiments and other high energy spectroscopies.
rate research
Read More
Elucidating the nature of the magnetic ground state of iron-based superconductors is of paramount importance in unveiling the mechanism behind their high temperature superconductivity. Until recently, it was thought that superconductivity emerges only from an orthorhombic antiferromagnetic stripe phase, which can in principle be described in terms of either localized or itinerant spins. However, we recently reported that tetragonal symmetry is restored inside the magnetically ordered state of a hole-doped BaFe2As2. This observation was interpreted as indirect evidence of a new double-Q magnetic structure, but alternative models of orbital order could not be ruled out. Here, we present Mossbauer data that show unambiguously that half of the iron sites in this tetragonal phase are non-magnetic, establishing conclusively the existence of a novel magnetic ground state with a non-uniform magnetization that is inconsistent with localized spins. We show that this state is naturally explained as the interference between two spin-density waves, demonstrating the itinerant character of the magnetism of these materials and the primary role played by magnetic over orbital degrees of freedom.
A novel feature of the iron arsenides is the magnetoelastic coupling between the long wavelength in-plane strains of the lattice and the collective spin fluctuations of the electrons near the magnetic ordering wavevectors. Here, we study its microscopic origin from an electronic model with nested Fermi pockets and a nominal interaction. We find the couplings diverge with a power-law as the system is tuned to perfect nesting. Furthermore, the theory reveals how nematicity is boosted by nesting. These results are relevant for other systems with nesting driven density wave transitions.
NdFeAsO0.88F0.12 belongs to the recently discovered family of high-TC iron-based superconductors. The influence of high pressure on transport properties of this material has been studied. Contrary to La-based compounds, we did not observe a maximum in TC under pressure. Under compression, TC drops rapidly as a linear function of pressure with the slope k = -2.8 pm 0.1 K / GPa. The extrapolated value of TC at zero pressure is about TC (0) = 51.7 pm 0.4 K. At pressures higher than ~18.4 GPa, the superconducting state disappears at all measured temperatures. The resistance changes slope and shows a turn-up behavior, which may be related to the Kondo effect or a weak localization of two-dimensional carriers below ~45 K that is above TC and thus competing with the superconducting phase. The behavior of the sample is completely reversible at the decompression. On the bases of our experimental data, we propose a tentative P-T phase diagram of NdFeAsO0.88F0.12.
In the temperature-concentration phase diagram of most iron-based superconductors, antiferromagnetic order is gradually suppressed to zero at a critical point, and a dome of superconductivity forms around that point. The nature of the magnetic phase and its fluctuations is of fundamental importance for elucidating the pairing mechanism. In Ba{1-x}KxFe2As2 and Ba{1-x}NaxFe2As2, it has recently become clear that the usual stripe-like magnetic phase, of orthorhombic symmetry, gives way to a second magnetic phase, of tetragonal symmetry, near the critical point, between x = 0.24 and x = 0.28. Here we report measurements of the electrical resistivity of Ba{1-x}KxFe2As2 under applied hydrostatic pressures up to 2.75 GPa, for x = 0.22, 0.24 and 0.28. We track the onset of the tetragonal magnetic phase using the sharp anomaly it produces in the resistivity. In the temperature-concentration phase diagram of Ba{1-x}KxFe2As2, we find that pressure greatly expands the tetragonal magnetic phase, while the stripe-like phase shrinks. This raises the interesting possibility that the fluctuations of the former phase might be involved in the pairing mechanism responsible for the superconductivity.
We apply the quasiparticle self-consistent GW method (QSGW) to slab models of ionic materials, LiF, KF, NaCl, MgO, and CaO, under electric field. Then we obtain the optical dielectric constants E(Slab) from the differences of the slopes of the electrostatic potential in the bulk and vacuum regions. Calculated E(Slab) show very good agreements with experiments. For example, we have E(Slab)=2.91 for MgO, in agreement with the experimental value E(Experiment)=2.96. This is in contrast to E(RPA)=2.37, which is calculated in the random-phase approximation for the bulk MgO in QSGW. After we explain the difference between the quasiparticle-based perturbation theory and the Greens function based perturbation theory, we interpret the large difference E(Slab)-E(RPA)=2.91-2.37 as the contribution from the vertex correction of the proper polarization which determines the screened Coulomb interaction W. Our result encourages the theoretical development of self-consistent G0W approximation along the line of QSGW self-consistency, as was performed by Shishkin, Marsman and Kresse [Phys. Rev. Lett. 99, 246403(2007)].
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
