Evolution of the Fermi Surface ofBaFe2(As1−xPx)2on Entering the Superconducting D

Abstract

Using the de Haas-van Alphen effect we have measured the evolution of the Fermi surface of BaFe2(As1-xPx){2} as a function of isoelectric substitution (As/P) for 0.41<x<1 (T{c} up to 25 K). We find that the volumes of electron and hole Fermi surfaces shrink linearly with decreasing x. This shrinking is accompanied by a strong increase in the quasiparticle effective mass as x is tuned toward the maximum T{c}. These results are not explained by simple band structure calculations, and it is likely that these trends originate from the same many-body interactions which give rise to superconductivity.

Quantum oscillations probe the normal electronic states of novel superconductors

“…The values corresponding to the averaged electron sheets between different compounds vary from 2.38 in SC LaFePO (Coldea et al 2008) to 1.85 in SrFe 2 P 2 (Analytis et al 2009b) and 1.5 in both CaFe 2 P 2 (Coldea et al 2009) and BaFe 2 P 2 (Shishido et al 2010). It is worth emphasizing that in the three-dimensional CaFe 2 P 2 the enhancement is the same for both electron and hole sheets.…”

“…The shift of the bands necessary to finely tune the band structure calculations to the experimental data led to smaller electron and hole sheets, as seen before in LaFePO. Shrinking of the electronic sheets was also found approaching the maximum T c in BaFe 2 (As 1−x P x ) 2 from quantum oscillations measurements (Shishido et al 2010) and also in BaFe 1−x Co x As 2 from ARPES studies (Brouet et al 2009). This tendency towards shrinking of the Fermi surface sheets in relation to the band structure calculations is not caused by simple band renormalization effects and seems to be a more general feature of iron pnictides, reflecting the domination of the interband interactions over interband ones, and/or the important role of spin fluctuations which may also be responsible for the pairing mechanism (Ortenzi et al 2009).…”

“…The torque signal in the quantum oscillations experiments in iron phosphides and SC As-substituted iron phosphides (Shishido et al 2010) is dominated by the contribution from the electronic pockets (figure 2c). In LaFePO, SrFe 2 P 2 and CaFe 2 P 2 , the mean free paths of electrons are at least a factor of 2 larger than those of the holes, which may be caused by differences in the orbital character between the electron and hole sheets (Analytis et al 2009b;Coldea et al 2009).…”

Impact of Disorder on the Superconducting Phase Diagram in BaFe2(As1−xPx)2

“…6) Among the iron pnictides, Phosphorus(P)-substituted BaFe 2 As 2 is a particularly clean system, and moreover, is unique in the fact that there is growing evidence for the existence of a QCP inside the superconducting dome near the optimal composition. [8][9][10][11][12][13] Although a QCP located at the maximum T c naturally leads to the consideration that the quantum-critical fluctuations help to enhance superconductivity, there has been no direct evidence against a scenario that it is just a coincidence. A direct test to address this issue is to investigate how the superconducting dome traces when the AFM phase is shifted.…”

“…9) The quality of the single crystals was confirmed by their sharp superconducting transitions 9) and quantum oscillation measurements. 11) In order to introduce uniform point defects into the BaFe 2 (As 1−x P x ) 2 single crystals, we irradiated the sample with an electron beam with an incident energy of 2.5 MeV, which is far above the threshold energy required for the formation of vacancy-interstitial (Frenkel) pairs. 16) The sample was kept at 20 K to prevent defect migration and clustering effects during the irradiation.…”