Tunneling spectroscopy of the superconducting gap inMgB2

Scanning tunnelling microscopy and spectroscopy of MgB2

“…As shown in the figure, the conductance is better fitted by the correlated 2-gap model than by the single-gap broadened BCS model, especially for the depression in the zero-bias region [3,4]. This is consistent with the existence of the second gap commonly observed in this compound [5,6], although there is no apparent double-gap structure in the fitted curve. In terms of the correlated 2-gap model, the gap broadening in Fig.…”

“…It is obvious from Fig. 5 that the gap value of the STS is very consistent with that of the BJTS [5,6]. The conductance of the STS is almost two orders of magnitude lower than that of the BJTS, and it is broadened in comparison with that for the BJTS.…”

“…The observed tunnelling spectra were well reproduced in details by this model, thereby indicating that the multiple gaps are intimately correlating with each other. From the agreements between the experimental data and the calculations, we have obtained the representative gap values 2D = 4 -5 meV, 8 -14 meV, and 18 -24 meV [5,6]. The smallest gap is commonly observed except for the NMR technique, and the existence of the middle-size gap is consistent with the photoemission data suggesting the surface gap [5,6,7,8].…”

“…In terms of the correlated 2-gap model, the gap broadening in Fig. 4 can be due to the strong mutual scatterings of quasiparticles between two phases, which perhaps results in the broadening feature similar to that for the probability distribution of the gap [5]. The gap value of 2D = 20 -24 meV obtained from these fittings almost corresponds to the conductance peak separation, and this is the largest gap value among the STS measurements [2].…”

“…From the agreements between the experimental data and the calculations, we have obtained the representative gap values 2D = 4 -5 meV, 8 -14 meV, and 18 -24 meV [5,6]. The smallest gap is commonly observed except for the NMR technique, and the existence of the middle-size gap is consistent with the photoemission data suggesting the surface gap [5,6,7,8]. For the largest gap, the tunnelling conductance can be described by the Gaussian gap distribution model, which suggests the existence of the spatial inhomogeneity and/or the gap anisotropy arising from the layered crystal structure [5,9].…”