Topological invariant responsible for the integer QHE and non-commutative geometry
This research explores a topological invariant, N3, used to explain why Hall conductivity is quantized in the Integer Quantum Hall Effect (IQHE) using noncommutative geometry. The authors found that under certain conditions, this invariant may not be an integer, suggesting that conductivity might not always be perfectly quantized when system inhomogeneities are strong.