Determination of the shape of the energy gap in unconventional
superconductors via the bulk measurements is still an outstanding
problem. A candidate technique for finding the positions of zeroes
(nodes) of the gap is via measurements of the anisotropy of
thermal and transport properties under a rotated magnetic field.
This anisotropy was predicted from a semiclassical analysis and
subsequently found experimentally in the specific heat and thermal
conductivity in several compounds. However, comparison of the two
sets of measurements in some compounds, such as heavy fermion CeCoIn5,
led to sometimes contradictory conclusions about the gap symmetry.
After a review of the field, I will present the results of a
microscopic calculation of the anisotropy of the specific heat and thermal
conductivity in anisotropic superconductors across the T-H phase
diagram. I will propose that an inversion of the specific heat anisotropy at
moderate field and temperatures reconciles the existing experimental data, and
will explain the physical origin for this inversion.
I will discuss the implications of these results for other unconventional
superconductors, and for future efforts to determine the gap symmetry from the
thermodynamic and transport measurements.