Abstract: The heavy fermion metal YbRh
2Si
2 is superconducting below about 10 mK, and is a candidate odd parity, and hence topological, superconductor. Previous 4-terminal electrical transport study on a number of samples demonstrates the important role played by sample inhomogeneity in the measured response. However, the magnetic susceptibility reaches full diamagnetic screening at T = 0 and thus we use these measurements to determine the complex conductivity of the superconducting state. A slab-like sample 380 µm thick is placed in magnetically shielded environment to < 20 nT, and studied as a function of magnetic field applied perpendicular to the c-axis. The setup operates at frequencies < 1 kHz.As a first step, the results are analysed in terms of an effective London penetration depth λ, which shows an unusual temperature dependence with the effective λ(T=0) significantly larger than anticipated. On cooling, a distinct downward step in λ clearly shows a transition into a new superconducting regime at TA ~ 2 mK, coinciding with a sharp heat capacity signature and by a drop in sample inductance seen in electrical transport. Since the onset of more robust superconductivity below TA in zero field is associated with a new SDW antiferromagnetic order, it is a candidate odd-parity PDW.We will also report the strong field dependence of the complex conductivity in the context of non-linear Meissner effect, and discuss evidence for line nodes in the gap structure, and topological surface states.
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