ELFT HÍRADÓ

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

Meghívó

BME Elméleti Fizika Szeminárium

márc. 4. péntek 10h15,

1111 Budapest, Budafoki út 8., BME F III. magasföldszint 01.,
Elméleti Fizika Tanszék szemináriumi szoba
és
online
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Pintér Gergő (BME Elméleti Fizika Tanszék):

Birth Quota of Non-Generic Degeneracy Points

Weyl points are generic and stable features in the energy spectrum of
Hamiltonians
that depend on a three-dimensional parameter space. Non-generic isolated
two-fold
degeneracy points, such as multi-Weyl points, split into Weyl points upon a
generic
perturbation that removes the fine-tuning or protecting symmetry. The
number of the
resulting Weyl points is at least |Q|, where Q is the topological charge
associated to
the non-generic degeneracy point. Here[1], we show that such a non-generic
degeneracy
point also has a birth quota, i.e., a maximum number of Weyl points that
can be born
from it upon any perturbation. The birth quota is a local multiplicity
associated to
the non-generic degeneracy point, an invariant of map germs known from
singularity
theory. This holds not only for the case of a three-dimensional parameter
space with
a Hermitian Hamiltonian, but also for the case of a two-dimensional
parameter space
with a chiral symmetric Hamiltonian. We illustrate the power of this result
for electronic
band structures of two- and three-dimensional crystals.
Our work establishes a strong connection between singularity theory and
topological band structures, and more broadly, parameter-dependent quantum
systems.

[1]: Birth Quota of Non-Generic Degeneracy Points,
Gergő Pintér, György Frank, Dániel Varjas, András Pályi, arXiv:2202.05825

Minden érdeklődőt szeretettel várunk,
 Asbóth János
  szemináriumi koordinátor