Doping Induced Gap Anisotropy in Iron-Based Superconductors： a Point-Contact Andreev Reflection Study of BaFe2-xNixAs2 Single Crystals

• Published in: 中国物理快报：英文版 no. 7; pp. 179 - 182
• Main Author: 朱军 王钊胜 王震宇 侯兴元 罗会仟 鲁兴业 李春红 单磊 闻海虎 任聪
• Format: Journal Article
• Language: English
• Published: 01.07.2015
• Subjects: 单晶体; 反射系统; 各向异性; 欠掺杂; 点接触; 超导体; 铁基; 间隙
• ISSN: 0256-307X; 1741-3540
• DOI: 10.1088/0256-307X/32/7/077401

We report a systematic investigation on c-axis point-contact Andreev reflection （PCAR） in BaFe2-xNixAs2 superconducting single crystals from underdoped to overdoped regions （0.075≤ x ≤0.15）. At low temperatures, an in-gap sharp peak at low-bias voltage is observed in PCAR for overdoped samples, in contrast to the case of underdoped junctions, in which an in-gap plateau is observed. The variety of the conductance spectra with doping can be well described by using a generalized Blonder-Tinkham-Klapwijk formalism with an angle-dependent gap. This gap shows a clear crossover from a nodeless in the underdoped side to a nodal feature in the overdoped region. This result provides evidence of the doping-induced evolution of the superconducting order parameter when the inter-pocket and intra-pocket scattering are tuned through doping, as expected in the s± scenario.