London penetration depth measurements of the heavy-fermion superconductor CeCoIn5 near a magnetic quantum critical point

We have measured the London penetration depth lambda( T) of CeCoIn5, a quantum-critical metal where superconductivity arises from a non-Fermi-liquid normal state. Using a tunnel diode oscillator with a novel coil geometry designed to avoid spurious contributions to lambda(T), we have established the existence of intrinsic and anomalous power law behaviour at low temperature. A systematic analysis raises the possibility that the unusual observations might be due to an extension of quantum criticality into the superconducting state.