  Recent in-plane thermal (Nernst) and interlayer (tunnelling) transport
experiments in Bi$_2$Sr$_2$CaCu$_2$O$_{8+y}$ high temperature superconductors
report hugely different limiting magnetic fields. Based on pairing (and the
uncertainty principle) combined with the definitions of the Zeeman energy and
the magnetic length, we show that in the underdoped regime both fields convert
to the same (normal state) pseudogap energy scale $T^*$ upon transformation as
orbital and spin (Zeeman) critical fields, respectively. We reconcile these
seemingly disparate findings invoking separated spin and charge degrees of
freedom residing in different regions of a truncated Fermi surface.
