Evidence for nodal superconductivity in quasi-one-dimensional K2Cr3As3

The recent discovery of superconductivity in the quasi-one-dimensional compound K2Cr3As3, which consists of double-walled tubes of [(Cr3As3)(2)-]infinity that run along the c axis, has attracted immediate attention as a potential system for studying superconductors with reduced dimensionality. Here we report clear experimental evidence for the unconventional nature of the superconducting order parameter in K2Cr3As3, by precisely measuring the temperature dependence of the change in the penetration depth Delta lambda(T) using a tunnel-diode oscillator. Linear behavior of Delta lambda(T) is observed for T << T-c, instead of the exponential behavior of conventional superconductors, indicating that there are line nodes in the superconducting gap. This is strong evidence for unconventional behavior and may provide key information for identifying the pairing state of this superconductor.