Noncommutative Geometry and the Quantum Hall Effect

Matilde Marcolli

MAT1314HS Winter 2019, University of Toronto T 12-2 and W 12 BA6180

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Based on

M. Marcolli, V. Mathai, Towards the fractional quantum Hall effect: a noncommutative geometry perspective, in “Noncommutative geometry and number theory”, 235–261, Aspects Math., E37, Vieweg, 2006 M. Marcolli, V. Mathai, Twisted index theory on good orbifolds, II: fractional quantum numbers, Communications in Mathematical Physics, 217 (2001) no.1, 55–87 M. Marcolli, V. Mathai, Twisted index theory on good orbifolds, I: noncommutative Bloch theory, Communications in Contemporary Mathematics, 1 (1999) 553–587

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Integer Quantum Hall Effect and NCG • earliest application of Noncommutative Geometry to Physics J. Bellissard, A. van Elst, H. Schulz-Baldes, The noncommutative geometry of the quantum Hall effect. Topology and physics. J. Math. Phys. 35 (1994), no. 10, 5373–5451

quantization of Hall conductance in the presence of magnetic field sees as values of an index theorem magnetic field renders the Brillouin zone (torus for an electron moving in a periodic structure) into a noncommutative torus index theorem on a noncommutive torus

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Breakdown of classical Bloch theory: magnetic field (quantum Hall) aperiodicity (quasicrystals)

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Integer Quantum Hall Effect (von Klitzing 1980) 2 σH as function of ν has plateaux at integer multiples of e /h at values of ν corresponding to plateaux, conductivity along current density axis vanishes

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Magnetic Translations

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Harper Operator symmetric set of generators {γi } of Γ r X R = Rσ σ γi i=1

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect NC Torus as Twisted Group C ∗-algebra

multiplier

0 0 0 0 σ((m , n ), (m, n)) = exp(−i(α1m n + α2n m))

0 0 2 for fixed α1, α2 ∈ R and for all (n, m), (n , m ) ∈ Z θ = α2 − α1 0 (Uf )(m0, n0) = f (m0, n0 + 1)e−iα2m and 0 (Vf )(m0, n0) = f (m0 + 1, n0)e−iα1n

UV = eiθVU

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Hofstadter butterfly

spectrum (energy) as function of magnetic flux

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect is there a NCG model for FQHE? plateaux at certain rational multiples of e2/h strongly interacting electrons (many particles not single particle model)

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Toy model using a single particle model but with interaction simulated by curvature • need to: account for strong electron interactions recover observed fractions (+predictions) account for varying width of plateaux

• simulation of interaction by curvature: single electron in curved geometry behaves “as if” subject to an average strong multi-electron interaction potential

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Qg νj Presentation: Γ = {ai , bi , cj | i=1[ai , bi ]c1 ··· cn = 1, cj = 1}

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect • zero temperature limit: charge carriers occupy all levels below Fermi level, so P = PF

σH = tr(PF [δ1PF , δ2PF ])

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect K C σH = tr (PF , PF , PF ) = tr (PF , PF , PF ) ∈ Zχorb(Σ)

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect Problems does not discriminate against even denominators (and too many fractions) Relation to Chern–Simons approach? Anyons? Effective field theories that interpolate between this one-particle toy model and QFT models? What happens to Bloch variety and periods in NCG Quantum Hall case?

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect More recent work addressing some of these problems M. Marcolli, K. Seipp, Twisted index theory on orbifold symmetric products and the fractional quantum Hall effect, Adv. Theor. Math. Phys. 21 (2017), no. 2, 451–501. D. Li, The algebraic geometry of Harper operators, J. Phys. A 44 (2011), no. 40, 405204, 27 pp.

Matilde Marcolli Noncommutative Geometry and the Quantum Hall Effect