Measurement and modeling of the low-temperature penetration-depth anomaly in high-quality MgB2 thin films

作者：Agassi Y D; Oates D E^*; Moeckly B H

来源：Physica C-Superconductivity and Its Applications, 2012, 480: 79-93.

DOI：10.1016/j.physc.2012.04.034

• Magnesium diboride
• Energy-gap symmetry
• Penetration depth
• Surface impedance
• MgB2 thin films

Based on our measurements of intermodulation distortion in MgB2, we have previously proposed that the pi energy-gap in MgB2 entails six nodal lines [Y.D. Agassi, D. E. Oates, and B. H. Moeckly, Phys. Rev. B 80 (2009) 174522]. Here we report high-precision measurements in MgB2 stripline resonators that show an increase of the penetration depth as the temperature is decreased below 5 K. This increase is consistent with the l = 6 symmetry of the pi energy gap that we have proposed. We interpret the increase as a manifestation of Andreev surface-attached states that are associated with the nodal lines of the pi energy gap. Penetration-depth calculations are in good agreement with our data. To reconcile the present interpretation with existing literature, we review other penetration-depth data, magnetic-impurity and tunneling experiments, and data on the paramagnetic Meissner effect. We conclude that these data do not rule out the interpretation of our experimental data based on a nodal pi energy gap.

• 出版日期2012-10