Point-contact spectroscopic studies on normal and superconducting AFe 2As2-type iron pnictide single crystals

Xin Lu, W. K. Park, H. Q. Yuan, G. F. Chen, G. L. Luo, N. L. Wang, A. S. Sefat, M. A. McGuire, R. Jin, B. C. Sales, D. Mandrus, J. Gillett, Suchitra E. Sebastian, L. H. Greene

Research output: Contribution to journalArticlepeer-review

Abstract

Point-contact Andreev reflection spectroscopy is applied to investigate the gap structure in iron pnictide single-crystal superconductors of the AFe 2As2 (A = Ba, Sr) family ('Fe-122'). The observed point-contact junction conductance curves, G(V), can be divided into two categories: one where Andreev reflection is present for both (Ba 0.6K0.4)Fe2As2 and Ba(Fe 0.9Co0.1)2As2, and the other with a V2/3 background conductance universally observed, extending even up to 100meV for Sr0.6Na0.4Fe2As2 and Sr(Fe0.9Co0.1)2As2. The latter is also observed in point-contact junctions on the nonsuperconducting parent compound BaFe2As2 and superconducting (Ba 0.6K0.4)Fe2As2 crystals. Mesoscopic phase-separated coexistence of magnetic and superconducting orders is considered to explain distinct behaviors in the superconducting samples. For Ba 0.6K0.4Fe2As2, double peaks due to Andreev reflection with a strongly sloping background are frequently observed for point contacts on freshly cleaved c-axis surfaces. If normalized using a background baseline and analyzed using the Blonder-Tinkham-Klapwijk model, the data show a gap size of ∼ 3.0-4.0meV with 2Δ0/k BTc ∼ 2.0-2.6, consistent with the smaller gap size reported for the LnFeAsO family ('Fe-1111'). For the Ba(Fe0.9Co 0.1)2As2, the G(V) curves typically display a zero-bias conductance peak.

Original languageEnglish (US)
Article number054009
JournalSuperconductor Science and Technology
Volume23
Issue number5
DOIs
StatePublished - 2010

ASJC Scopus subject areas

  • Ceramics and Composites
  • Condensed Matter Physics
  • Metals and Alloys
  • Electrical and Electronic Engineering
  • Materials Chemistry

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