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

► We present measurement and modeling showing that MgB2 has unconventional symmetry. ► We conclude that the small gap has six nodal lines. ► We have measured an increase in penetration depth of MgB2 at low temperatures. ► We model the increase as the result of Andreev bound states and get good agreement. ► These conclusions are consistent with our previous finding of a nodal gap.