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29 March 2024 |
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Temperature and junction-type dependency of Andreev reflection in MgB2 | R.S. Gonnelli
; A. Calzolari
; D. Daghero
; G.A. Ummarino
; V.A. Stepanov
; P. Fino
; G. Giunchi
; S. Ceresara
; G. Ripamonti
; | Date: |
11 Jul 2001 | Journal: | J. Phys. Chem. Solids 63, 2319 (2002) | Subject: | Superconductivity | cond-mat.supr-con | Abstract: | We studied the voltage and temperature dependency of the dynamic conductance of normal metal-MgB2 junctions obtained either with the point-contact technique (with Au and Pt tips) or by making Ag-paint spots on the surface of high-quality single-crystal-like MgB2 samples. The fit of the conductance curves with the generalized BTK model gives evidence of pure s-wave gap symmetry. The temperature dependency of the gap, measured in Ag-paint junctions (dirty limit), follows the standard BCS curve with 2Delta/kTc = 3.3. In out-of-plane, high-pressure point contacts we obtained almost ideal Andreev reflection characteristics showing a single small s-wave gap Delta = 2.6 +/- 0.2 (clean limit). These results support the two-gap model of superconductivity, the presence of a modified layer at the surface of the crystals and an important and non-conventional role of the impurities in MgB2. | Source: | arXiv, cond-mat/0107239 | Services: | Forum | Review | PDF | Favorites |
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