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تسجيل مستخدم جديدComplete Fermi surface in BaFe$_2$As$_2$ observed via Shubnikov-de Haas oscillation measurements on detwinned single crystals
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We show that the Fermi surface (FS) in the antiferromagnetic phase of BaFe$_2$As$_2$ is composed of one hole and two electron pockets, all of which are three dimensional and closed, in sharp contrast to the FS observed by angle-resolved photoemission spectroscopy. Considerations on the carrier compensation and Sommerfeld coefficient rule out existence of unobserved FS pockets of significant sizes. A standard band structure calculation reasonably accounts for the observed FS, despite the overestimated ordered moment. The mass enhancement, the ratio of the effective mass to the band mass, is 2--3.
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We have observed Shubnikov-de Haas oscillations in FeSe. The Fermi surface deviates significantly from predictions of band-structure calculations and most likely consists of one electron and one hole thin cylinder. The carrier density is in the order
of 0.01 carriers/ Fe, an order-of-magnitude smaller than predicted. Effective Fermi energies as small as 3.6 meV are estimated. These findings call for elaborate theoretical investigations incorporating both electronic correlations and orbital ordering.
We have completely determined the Fermi surface in KFe$_2$As$_2$ via de Haas-van Alphen (dHvA) measurements. Fundamental frequencies $epsilon$, $alpha$, $zeta$, and $beta$ are observed in KFe$_2$As$_2$. The first one is attributed to a hole cylinder
near the X point of the Brillouin zone, while the others to hole cylinders at the $Gamma$ point. We also observe magnetic breakdown frequencies between $alpha$ and $zeta$ and suggest a plausible explanation for them. The experimental frequencies show deviations from frequencies predicted by band structure calculations. Large effective masses up to 19 $m_e$ for $B parallel c$ have been found, $m_e$ being the free electron mass. The carrier number and Sommerfeld coefficient of the specific heat are estimated to be 1.01 -- 1.03 holes per formula unit and 82 -- 94 mJmol$^{-1}$K$^{-2}$, respectively, which are consistent with the chemical stoichiometry and a direct measure of 93 mJmol$^{-1}$K$^{-2}$ [H. Fukazawa textit{et al}., J. Phys. Soc. Jpn. textbf{80SA}, SA118 (2011)]. The Sommerfeld coefficient is about 9 times enhanced over a band value, suggesting the importance of low-energy spin and/or orbital fluctuations, and places KFe$_2$As$_2$ among strongly correlated metals. We have also performed dHvA measurements on Ba$_{0.07}$K$_{0.93}$Fe$_2$As$_2$ and have observed the $alpha$ and $beta$ frequencies.
We report on a band structure calculation and de Haas-van Alphen measurements of KFe$_2$As$_2$. Three cylindrical Fermi surfaces are found. Effective masses of electrons range from 6 to 18$m_e$, $m_e$ being the free electron mass. Remarkable discrepa
ncies between the calculated and observed Fermi surface areas and the large mass enhancement ($gtrsim 3$) highlight the importance of electronic correlations in determining the electronic structures of iron pnicitide superconductors.
The three-dimensional Fermi surface morphology of superconducting BaFe_2(As_0.37}P_0.63)_2 with T_c=9K, is determined using the de Haas-van Alphen effect (dHvA). The inner electron pocket has a similar area and k_z interplane warping to the observed
hole pocket, revealing that the Fermi surfaces are geometrically well nested in the (pi,pi) direction. These results are in stark contrast to the Fermiology of the non-superconducting phosphides (x=1), and therefore suggests an important role for nesting in pnictide superconductivity.
Understanding magnetic interactions in the parent compounds of high-temperature superconductors forms the basis for determining their role for the mechanism of superconductivity. For parent compounds of iron pnictide superconductors such as $A$Fe$_2$
As$_2$ ($A=$ Ba, Ca, Sr), although spin excitations have been mapped out throughout the entire Brillouin zone (BZ), measurements were carried out on twinned samples and did not allow for a conclusive determination of the spin dynamics. Here we use inelastic neutron scattering to completely map out spin excitations of $sim$100% detwinned BaFe$_2$As$_2$. By comparing observed spectra with theoretical calculations, we conclude that the spin excitations can be well described by an itinerant model with important contributions from electronic correlations.
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