Abstract
Bipartite quantum systems from the chiral universality classes admit topologically protected zero modes at point defects. However, in two-dimensional systems these states can be difficult to separate from compacton-like localized states that arise from flat bands, formed if the two sublattices support a different number of sites within a unit cell. Here we identify a natural reduction of chiral symmetry, obtained by coupling sites on the majority sublattice, which gives rise to spectrally isolated point-defect states, topologically characterized as zero modes supported by the complementary minority sublattice. We observe these states in a microwave realization of a dimerized Lieb lattice with next-nearest neighbour coupling, and also demonstrate topological mode selection via sublattice-staggered absorption.
Highlights
Symmetry-protected zero modes are an ubiquitous feature of quantum systems exhibiting nontrivial topological phases
We demonstrate that the finite sublattice polarization of the point-defect state can be exploited for mode selection, which we here achieve by inducing absorption onto the majority sublattice
We showed that a partial breaking of chiral symmetry can be employed to stabilize and isolate point-defect zero modes in two-dimensional bipartite systems with flat bands
Summary
Symmetry-protected zero modes are an ubiquitous feature of quantum systems exhibiting nontrivial topological phases. This can be achieved by a well-defined reduction of the chiral symmetry on the majority sublattice, which detunes the compacton-like states due to their finite sublattice polarization (imbalanced weight on the sublattices) This situation, which we express as a partial chiral symmetry, is realized most naturally in the context of two-dimensional systems, where point-defect states residing on the minority sublattice can be formed when Dirac cones are lifted [see Fig. 1(d)]. This leaves behind a spatially localized zero mode supported by the minority sublattice, on which the chiral symmetry remains operational
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