Event

We studied the pair breaking effect of an external magnetic field up to 7 T on the type-II superconductor niobium (Nb) using terahertz time-domain spectroscopy at 1.5 K. Our measurement technique can directly obtain transmission spectra of Nb thin films and extract the optical conductivity. The superconductivity is systematically suppressed by the external magnetic field as the quasiparticle excitation gap closes. We confirmed this by fitting the pair-breaking parameter and the superconducting order parameter data to the theory of Skalski et al. [Phys. Rev. 136, A1500-A1518 (1964)]. We believe that gapless superconductivity is a welcome addition to the vast family of topological gapped and gapless materials.