Observation of Large-Number Corner Modes in ℤ-class Higher-Order Topolectrical Circuits
arxiv(2023)
摘要
Topological corner states are exotic topological boundary states that are
bounded to zero-dimensional geometry even the dimension of systems is large
than one. As an elegant physical correspondence, their numbers are dictated by
the bulk topological invariants. So far, all previous realizations of HOTIs are
hallmarked by ℤ_2 topological invariants and therefore have only one
corner state at each corner. Here we report an experimental demonstration of
ℤ-class HOTI phases in electric circuits, hosting N corner modes
at each single corner structure. By measuring the impedance spectra and
distributions, we clearly demonstrate the ℤ-class HOTI phases,
including the zero-energy corner modes and their density distributions.
Moreover, we reveal that the local density of states (LDOS) at each corner for
N=4 are equally distributed at four corner unit cells, prominently differing
from ℤ_2-class case where the LDOS only dominates over one corner
unit cell. Our results extend the observation of HOTIs from ℤ_2
class to ℤ class and the coexistence of spatially overlapped large
number of corner modes which may enable exotic topological devices that require
high degeneracy boundary states.
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