  One of the hallmarks of time-reversal-symmetric topological insulators in
three dimensions is the topological magnetoelectric effect (TME). So far, a
time-reversal breaking variant of this effect has attracted much attention, in
the sense that the induced electric charge changes sign when the direction of
an externally applied magnetic field is reversed. Theoretically, this effect is
described by the so-called axion term. Here, we discuss a
time-reversal-symmetric TME, where the electric charge depends only on the
magnitude of the magnetic field but is independent of its sign. We obtain this
nonperturbative result by a combination of analytic and numerical arguments,
and suggest a mesoscopic setup to demonstrate it experimentally.
