nLab quaternionic K-theory





Special and general types

Special notions


Extra structure



Algebraic topology



What is called symplectic K-theory (denoted KSpK Sp) or, equivalently, quaternionic K-theory (denoted KQK Q) is the topological K-theory of quaternionic vector bundles.

This is in direct analogy with how complex K-theory (KU) is the topological K-theory of complex vector bundles and KO that of real vector bundles.

In fact, quaternionic K-theory is equivalently KO-theory in degrees which are multiples of 4.



To topological phases of matter

In solid state physics, under the K-theory classification of topological phases of matter, quaternionic K-theory is thought to classify crystalline topological insulator-phases of materials whose electron-dynamics respects time-reversal symmetry (this makes the classification be by KO KO^\bullet ) but no parity symmetry? (this restricts the classification further to KO 4nKQ nKO^{4 n} \simeq K Q^n). Then spin-less such phases are classified by KQ 0KO 0K Q^0 \simeq K O^0, while spin-ful such phases are classified by KQ 1K Q^1.

In this context, the Kane-Mele invariant is a projection KQ 1(𝕋 d)/2K Q^1(\mathbb{T}^d) \to \mathbb{Z}/2 from the quaternionic K-theory of the Brillouin torus of a material, which detects (in particular, for d=2d = 2) the non-triviality of the graphene-phase (which is a time-reversal-symmetric topological insulator when its spin-orbit coupling is taken into account).

Created on May 7, 2022 at 09:43:26. See the history of this page for a list of all contributions to it.