ELFT HÍRADÓ

[Janos Asboth <asboth.janos AT ttk.bme.hu>]

Meghívó

BME Elméleti Fizika Szeminárium,

feb. 28. péntek 10h15,
1111 Bp., Budafoki út 8., BME FIII. magasföldszint 1, szemináriumi szoba

Asbóth János (BME Elm. Fiz. tanszék és HUN-REN Wigner FK SZFI):
Topological fine structure of an energy band

A band with a nonzero Chern number cannot be fully localized by weak
disorder: There must remain at least one extended state, which “carries the
Chern number.” Here [1] we show that a trivial band can behave in a similar
way. Instead of fully localizing, arbitrarily weak disorder leads to the
emergence of two sets of extended states, positioned at two different
energy intervals, which carry opposite Chern numbers. Thus, a single
trivial band can show the same behavior as two separate Chern bands. We
show that this property is predicted by a topological invariant, the
“localizer index.” Even though the band as a whole is trivial as far as the
Chern number is concerned, the localizer index allows access to a
topological fine structure. This index changes as a function of energy
within the bandwidth of the trivial band, causing nontrivial extended
states to appear as soon as disorder is introduced. Our work points to a
previously overlooked manifestation of topology, which impacts the response
of systems to impurities beyond the information included in conventional
topological invariants.

[1]: Hui Liu, Cosma Fulga, Emil J. Bergholtz, Janos Asboth: Topological
fine structure of an energy band. arXiv:2312.08436

Minden érdeklődőt szeretettel várunk.
Asbóth János,
 szemináriumi koordinátor