an:06776593
Zbl 1370.35093
Monaco, Domenico; Tauber, Cl??ment
Gauge-theoretic invariants for topological insulators: a bridge between Berry, Wess-Zumino, and Fu-Kane-Mele
EN
Lett. Math. Phys. 107, No. 7, 1315-1343 (2017).
00368070
2017
j
35J10 81Q30 81Q70
time-reversal symmetric topological insulators; Fu-Kane-Mele \(\mathbb {Z}_2\) invariant; Wess-Zumino amplitude; Berry connection; Polyakov-Wiegmann formula
Summary: We establish a connection between two recently proposed approaches to the understanding of the geometric origin of the Fu-Kane-Mele invariant \(\mathrm {FKM}\in \mathbb {Z}_2\), arising in the context of two-dimensional time-reversal symmetric topological insulators. On the one hand, the \(\mathbb {Z}_2\) invariant can be formulated in terms of the Berry connection and the Berry curvature of the Bloch bundle of occupied states over the Brillouin torus. On the other, using techniques from the theory of bundle gerbes, it is possible to provide an expression for \(\mathrm {FKM}\) containing the square root of the Wess-Zumino amplitude for a certain \(U(N)\)-valued field over the Brillouin torus. We link the two formulas by showing directly the equality between the above-mentioned Wess-Zumino amplitude and the Berry phase, as well as between their square roots. An essential tool of independent interest is an equivariant version of the adjoint Polyakov-Wiegmann formula for fields \(\mathbb {T}^2 \rightarrow U(N)\), of which we provide a proof employing only basic homotopy theory and circumventing the language of bundle gerbes.