  We report thermodynamic measurements in a magnetic-field-driven quantum
critical point of a heavy fermion metal, YbRh$_2$Si$_2$. The data provide
evidence for an energy scale in the equilibrium excitation spectrum, that is in
addition to the one expected from the slow fluctuations of the order parameter.
Both energy scales approach zero as the quantum critical point is reached,
thereby providing evidence for a new class of quantum criticality.
