Magnetic Field Dependence of the Density of States of YBa2Cu3O6.95 as Determined from the Specific Heat

Abstract

The magnetic field dependence of the electronic density of states at the Fermi level, $N(E_F,H)$, is determined in single-crystal Y${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6.95}$ by specific heat measurements. The total specific heat is best described by including two predictions for the electronic specific heat of $d$-wave superconductivity: a $T^2$ term in zero field and an increased linear term in a magnetic field applied perpendicular to the Cu${\mathrm{O}}_2$ planes. The additional linear term, which implies a finite $N(E_F,H)$, obeys $N(E_F,H)\propto {\left(\frac{H}{H_{c2\mathrm{}}}\right)}^{\frac{1}{2}}$ as predicted by Volovik for superconductivity with lines of nodes in the gap.