Topology and superconductivity: complexity without complex numbers

Two-dimensional superconductors with broken time-reversal symmetry have
been predicted to support topologically protected chiral edge states,
providing a thermal analogue of the electrical quantum Hall effect in
semiconductors. Several decades of search for these edge states
(notably in strontium ruthenate) have not yet produced convincing evidence for
their existence. The key difficulty is that the edge states are charge
neutral, and therefore would seem to be out reach of conventional
electrical probes. Here we discuss some recent developments in our
understanding of the Majorana nature of the superconducting edge
states, which suggests that shot noise measurements would provide for a purely
electrical method of detection.