Enhancement of the Superconducting Transition Temperature under Pressure in Rare-Earth Doped Ca$_{1-x}$La$_x$Fe$_2$As$_2$ (x=0.27)

Goh, Swee K.; Klintberg, Lina E.; Silver, J. M.; Grosche, F. M.; Saha, S. R.; Drye, T.; Paglione, J.; Sutherland, M.

doi:10.48550/arxiv.1107.0689

Cited by 2 publications

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“…23) in CaFe 2 As 2 mainly due to close matching between ionic-radii of RE and Ca, and that their incorporation suppresses the low temperature AFM ordering in favor of the superconducting phase. Application of hydrostatic pressure on the doped materials is shown to increase further the critical temperature 25 .…”

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First-principles study of rare-earth-doped superconducting CaFe2As2

et al. 2012

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We report a systematic and ab-initio electronic structure calculation of Ca0.75M0.25Fe2As2 with M = Ca, Sr, Eu, La, Ce, Pr, Nd, Pm, Sm, Na, K, Rb. The recently reported experimentally observed structural trends in rare earths-doped CaFe2As2 compounds are successfully predicted and a complete theoretical description of the pressure induced orthorhombic to collapsed tetragonal transition is given. We demonstrate that the transition pressure is reduced by electron doping and rises linearly with the ionic size of the dopants. We discuss the implications of our description for the realization of a superconducting phase. PACS numbers:The family of iron based superconductors (SC) continues to grow with the discovery of new systems that add to the hundreds already known 1-3 . However, in spite of this enormous amount of experimental data, an ab-initio theory describing these superconductors is still missing, and the search for new materials is guided only by some observed features that appear to be in common.Even if it is not a general rule, the so-called parent compounds do not superconduct without doping 3 or without applying high pressure 4 . The rationale for this behavior could be naively ascribed to the necessity to destabilize the orthorhombic (O) antiferromagnetic order of the parent compounds to promote a magnetic mediated pairing field 5 . Indeed, superconductivity is realized in tetragonal (T) phases only after the magnetic order is suppressed, although some coexisting phases were discovered in 122 compounds 6 . In the so-called 122 family (MFe 2 As 2 , M=Ca, Ba, Sr) superconductivity can be induced under high pressure 4 . The critical pressures at which superconductivity is detected varies with M 7,8 and with the pressure conditions 9-14 (hydrostatic and non-hydrostatic). At the same time, the members of the 122 family show a pressure induced structural phase transition to a collapsed tetragonal (CT) phase 15,16 . The main experimental evidence of the CT phase transition is the sudden decrease of the c lattice parameter and a subsequent increase of the in-plane a lattice constant. First-principles calculations were able to describe this phase transition as induced by the formation of a direct As-As bond along the c-axis of the tetragonal phase 11,17 . The CT phase is predicted to be a non-magnetic phase (the magnetic moment being zero on the Fe sites) in agreement with experimental results 15 which report the disappearance of the magnetic response.In Ba and Sr 122 compounds, where the O-T and T-CT are well separated in pressure 8,9 , it seems that the superconducting phase is realized across the O-T transition (even if the role of non-hydrostaticity of the pressure medium is not clear), while it was debated in CaFe 2 As 2 where the transitions are very near in pressure 18 and hysteresis effects are relevant. In fact, for CaFe 2 As 2 the precise nature of the crystallographic structure of the superconducting phase is under debate, but the CT phase obtained under hydrostatic pressure conditions 18-20 seems to ...

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“…This subject was revived with the discovery of high temperature superconductivity (up to 45-49 K) in CaFe 2 As 2 doped with trivalent rare-earth (RE) metal atoms (La, Pr, Ce, Nd) substituting the divalent Ca atoms [21][22][23][24][25] . It was demonstrated that rare earths have high solubility (up to 27% in Ref.…”

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First-principles study of rare-earth-doped superconducting CaFe2As2

et al. 2012

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“…Theoretical calculations show clear differences between hole-and electron-doped systems [7] and predict that superconductivity can sustain higher hole than electron doping [8]. Despite of this fact it was found recently that the superconducting transition temperature T c reaches 45 K (under pressure) in the case of La 3+ for Ca 2+ substitution [9][10][11], and as high as 49 K for Pr 3+ indirect doping, as shown by resistive, magnetic and thermoelectric measurements [12]. It is unclear, however, whether the superconducting transition observed is bulk [9] or non-bulk [12] due to interfacial or filamentary superconductivity.…”

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Raman scattering study of electron-doped Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$ superconductors

Litvinchuk,

Lv,

Chu

2011

Preprint

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Temperature-dependent polarized Raman spectra of electron-doped superconducting PrxCa1−xFe2As2 (x ≈ 0.12) single crystals are reported. All four allowed by symmetry even-parity phonons are identified. Phonon mode of B1g symmetry at 222 cm −1 , which is associated with the c-axis motion of Fe ions, is found to exhibit an anomalous frequency hardening at low temperatures, that signals non-vanishing electron-phonon coupling in the superconducting state and implies that the superconducting gap magnitude 2∆c < 27meV.

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Enhancement of the Superconducting Transition Temperature under Pressure in Rare-Earth Doped Ca$_{1-x}$La$_x$Fe$_2$As$_2$ (x=0.27)

Cited by 2 publications

References 29 publications

First-principles study of rare-earth-doped superconducting CaFe2As2

First-principles study of rare-earth-doped superconducting CaFe2As2

Raman scattering study of electron-doped Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$ superconductors

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