Click here to flash read.
We have derived an expression for the magnetic susceptibility of
topologically trivial insulators, however an important consideration for any
response tensor is whether it is gauge-invariant. By this we refer to the
gauge-freedom in choosing the Bloch functions one uses in a computation since
multiplication by an arbitrary $\textbf{k}$-dependent complex phase produces
equally valid Bloch functions. Additionally Wannier functions, which can be
constructed by a unitary mixing of the Bloch functions, are a useful basis for
computation due to their localized properties, but are strongly non-unique.
Therefore, we show that the theoretical expression we derived is independent of
the choice of Bloch functions or Wannier functions used, and thus is
gauge-invariant in this sense.
No creative common's license