Abstract
The interplay of high- and low-energy mass renormalizations with band shifts reflected by the positions of van Hove singularities (VHS) in the normal-state spectrum of the most strongly hole-overdoped correlated AFe2As2 (A122) with A=K, Cs is discussed phenomenologically from ARPES data and band-structure (GGA) calculations with full spin-orbit coupling. The big increase of the Sommerfeld coefficient γ from K122 to Cs122 is ascribed to an enhanced coupling to low-energy bosons in the vicinity of a quantum critical point to an unknown, yet incommensurate phase different from the commensurate Mott one. We find no sizeable increase in correlations for Cs122 in contrast to Eilers et al. (Phys. Rev. Lett. 116, 237003 2016). The empirical (ARPES) VHS positions as compared with GGA predictions point even to slightly weaker correlations in Cs122 in accord with low-T magnetic susceptibility χ(T) data and a decreasing Wilson ratio ∝ χ(0)/γ.
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Notes
(Scanning tunneling measurements). It includes in our opinion, however, an artificial upshift of about 10 meV of the entire ARPES spectrum, see also Section 5.
We mention that among a large number of known (until 2000) heavy-fermion superconductors, only three of them (CeCu2Si2, UPt3, and UBe13) exhibiting surprisingly formally “free electron” Wilson ratios R W ≈ 1 [23].
Note that our results differ quantitatively by a systematic shift of nearly 10 meV for the entire spectrum as compared to Ref. [4], and even qualitatively in that previous Cs122-STM [5] showed no VHS at all. We speculatively ascribe this to surface reconstructions and charging in those samples most detrimental for STM. The position in STM of the VHS was given as -5 to -6 meV for K122.
Beyond the error bars of about 2 meV for sharp peaks.
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Acknowledgements
Discussions with M. Daghofer, D. Efremov, J. Fink, E. Goremychkin, and L. dé Medici are gratefully acknowledged.
Funding
S-LD, SW, SA, LM, and AB thank the Volkswagenstiftung for financial support. IM acknowledges support by the RSF grant No. 16-42-01100. VG and SB are grateful to the DFG for financial support through grant Nos. GR4667 and BO1912/6-1 and BO1912/7-1, respectively.
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Drechsler, SL., Rosner, H., Grinenko, V. et al. Mass Enhancements and Band Shifts in Strongly Hole-Overdoped Fe-Based Pnictide Superconductors: KFe2As2 and CsFe2As2. J Supercond Nov Magn 31, 777–783 (2018). https://doi.org/10.1007/s10948-017-4434-5
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DOI: https://doi.org/10.1007/s10948-017-4434-5