Abstract

The energy gap in many novel superconductors is highly anisotropic, with either nodes (zeroes) or deep minima at the Fermi surface. Locating these nodes, i.e. identifying the directions along which the gap vanishes is a crucial step in identifying the correct underlying pairing interactions. I will show that rotation of the applied magnetic field relative to the nodes produces oscillations in the specific heat and electronic thermal conductivity that can be used to determine the location of the gap nodes or minima from bulk measurements. I will review the relevant experimental results, and describe the current status of the theoretical underpinnings of these measurements, emphasizing the new physics that resolved apparent contradictions between different probes. I will pay special attention to the inversion of the anisotropy as a function of temperature and field, theoretically predicted and recently found experimentally. I will provide a comparison of experiment and theory in the 115 heavy fermion compounds, two-dimensional organic superconductors, and pnictides.