Isotropic superconducting gaps with enhanced pairing on electron Fermi surfaces in FeTe0.55Se0.45

Abstract

The momentum distribution of the energy gap opening at the Fermi level of superconductors is a direct fingerprint of the pairing mechanism. While the phase diagram of the iron-based superconductors promotes antiferromagnetic fluctuations as a natural candidate for electron pairing, the precise origin of the interaction is highly debated. We used angle-resolved photoemission spectroscopy to reveal directly the momentum distribution of the superconducting gap in FeTe 1-x Se x , which has the simplest structure of all iron-based superconductors. We found isotropic superconducting gaps on all Fermi surfaces whose sizes can be fitted by a single gap function derived from a strong coupling approach, strongly suggesting local antiferromagnetic exchange interactions as the pairing origin.

Direct evidence of two superconducting gaps in FeSe0.5Te0.5: SnS-Andreev spectroscopy and the lower critical field

“…Turning to literature [10][11][12][13][14][15][16][17][18][19], in Fig. 5 we summarize the values of the large and the small superconducting gaps in dependence of critical temperature.…”

“…The available experimental data with Tesubstituted iron selenide are rather contradictory. Single superconducting gap with BCS-ratio 2.9 − 7 was observed in [10][11][12][13], whereas point-contact Andreev reflection (PCAR) [14], muon-spin-rotation (µSR) [15], tunneling [16], angle-resolved photoemission spectroscopy (ARPES) [17], specific heat [18], and scanning tunneling microscopy (STM) [19] measurements resolved two distinct gaps with 2∆ L /k B T C = 3.6 − 7.2 and 1) e-mail: kute@sci.lebedev.ru 2∆ S /k B T C = 0.8 − 4. Using PCAR technique, Daghero et al [14] studied superconducting order parameter for FeSe 1−x Te x with various Te concentration and T C = 10 − 18 K. They observed approximate scaling between both gaps and T C with the BCS-ratio for the large gap 4.9 − 7.2.…”

“…Using PCAR technique, Daghero et al [14] studied superconducting order parameter for FeSe 1−x Te x with various Te concentration and T C = 10 − 18 K. They observed approximate scaling between both gaps and T C with the BCS-ratio for the large gap 4.9 − 7.2. Taking into account well-established synthesis of qualitative single crystals [5], the significant data dispersion arose from literature [10][11][12][13][15][16][17][18][19] may originate from, in particular, whether each technique is applicable to Fe(Se,Te), or its superconducting properties sensitivity to crystal surface. In this sense, exemplary could be a combination of a bulk and a local probe with one and the same crystal.…”

Two-band conductivity of a FeSe$_{0.5}$Te$_{0.5}$ film by reflectance measurements in the terahertz and infrared range

“…Finally, of particular interest is the finding that T c can increase up to 65 K in a single layered FeSe film on SrTiO 3 [4]. As to the possible superconducting energy gaps in FeSe 1−x Te x systems, several experimental reports on their number, symmetry and value have not provided unambiguous results [5,6,7,8], presumably owing to differences in sample quality, disorder effects, and to the different sensitivity of the various experimental techniques to different gaps. On the above basis, further studies on different FeSe 1−x Te x systems are mandatory.…”

Iron-based superconductors: Magnetism, superconductivity, and electronic structure (Review Article)

“…The crystals grow with excess ( y ) Fe atoms that present beyond those needed to fill the Fe square lattice layers and go into interstitial positions within the Te layers [7]. For ARPES on 11 family, see [77][78][79][80].…”