Scanning tunneling spectroscopy and break junction spectroscopy on iron-oxypnictide superconductor NdFeAs(O sub(0.9)F sub(0.1))

• Published in: Physica. C, Superconductivity Vol. 470; no. 20; pp. 1070 - 1072
• Main Authors: Sugimoto, A, Ekino, T, Ukita, R, Shohara, K, Okabe, H, Akimitsu, J, Gabovich, A M
• Format: Journal Article
• Language: English
• Published: 01.11.2010
• Subjects: Breaking; Coherence; Energy gap; Scanning tunneling microscopy; Spectroscopy; Superconductor junctions; Superconductors
• ISSN: 0921-4534
• DOI: 10.1016/j.physc.2010.05.038

Iron-oxypnictide superconductor NdFeAs(O sub(0.9)F sub(0.1)) was studied using both low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) and tunnel break junction (BJ) methods. STM topography showed granular and spot structures with a typical size of several nanometers, most probably governed by fluorine atom distribution. The majority of STS conductance, G, versus voltage, V, curves revealed V-shaped structures, whereas some of G(V) dependences possessed coherent gap peaks or kinks at gap energies. At the same time, G(V) dependences obtained by the BJ technique showed clear-cut coherence peaks with peak-to-peak distances V sub(p)p= 4 Delta /e [inline image] 25 mV at 4.2 K, where Delta is the superconducting energy gap, e > 0 is the elementary charge. This yields Delta (0) = 6-7 meV, so that the ratio 2 Delta (0)/k sub(B) sub(c)is about 3-4, k sub(B)being the Boltzmann constant. This value is consistent with the conventional weak-coupling s-wave Bardeen-Cooper-Schrieffer theory.