Magnetic field as a probe of gap energy scales in YBa2Cu3O7-x

Among high-T-c materials, the YBa2Cu3O7-x compounds are special since they have superconducting chains as well as planes. We show that a discontinuity in the density of states as a function of magnetic field may appear at a new energy scale, characteristic of the chain and distinct from that set by the d-wave gap. This is observable in experimental studies of the thermodynamic properties of these systems, such as the specific heat.