ELFT HÍRADÓ

[Andras Palyi <andraspalyi AT caesar.elte.hu>]

A BME-MTA Egzotikus Kvantumfázisok csoport következő szemináriuma:

Asbóth János (Wigner FK)
Spectral flow and winding of the gaps in the Hofstadter butterfly of Chern 
and Floquet insulators

2016. november 8., kedd, 14:15
BME Elméleti Fizika Tanszék szemináriumi szobája (F épület, 3. lépcsőház, 
magasföldszint)

Kivonat: 
“The Hofstadter butterfly[1] -- the spectrum of an electron hopping on a 
square lattice in strong magnetic fields (Harper model) -- has inspired 
researchers and played an instrumental role in the exploration of the quantum 
Hall effect. One of its interesting features is that if the Fermi energy is 
fixed in a topological gap, i.e., a gap with nonzero Chern index, the 
fraction of occupied states can be changed by altering the magnetic field[2]. 
We rephrase this property as an energy eigenvalue flow across topological 
gaps, and show that it applies to any lattice model. This includes the 
Floquet spectra of periodically driven systems, also in the nonperturbative 
regime of low frequency and high amplitude driving, where there is no simple 
notion of occupied and unoccupied states. We show how the response of the 
spectrum to a small change in the magnetic field gives us a simple way to 
calculate the Rudner invariant[3].

[1]: D. R. Hofstadter, Phys. Rev. B 14, 2239–2249 (1976)
[2]: G. Wannier, physica status solidi (b) 88, 757 (1978)
[3]: M. S. Rudner et al, Phys. Rev. X 3, 031005 (2013)”

Minden érdeklődőt szeretettel várunk.

A szemináriumsorozat további programja: 
http://exotic.phy.bme.hu/seminars.html

Üdvözlettel,
Pályi András