  The quantum Hall system can be used to study many-body physics owing to its
multiple internal electronic degrees of freedom and tunability. While quantum
phase transitions have been studied intensively, research on the
temperature-induced phase transitions of this system is limited. We measured
the pure bulk conductivity of a quantum Hall antiferromagnetic state in bilayer
graphene over a wide range of temperatures and revealed the two-step phase
transition associated with the breaking of the long-range order and short-range
antiferromagnetic order. Our findings are fundamental to understanding electron
correlation in quantum Hall systems.
