Physics – Condensed Matter – Mesoscale and Nanoscale Physics
Scientific paper
2011-09-02
Physical Review B, vol. 85, 085304 (2012)
Physics
Condensed Matter
Mesoscale and Nanoscale Physics
7 PRB pages, one table, one figure; thoroughly revised and extended version, more discussion of physical examples in graphene
Scientific paper
10.1103/PhysRevB.85.085304
We study the Dirac quasiparticles in $d$-dimensional lattice systems of electrons in the presence of domain walls ($d=1$), vortices ($d=2$), or hedgehogs ($d=3$) of superconducting and/or insulating, order parameters, which appear as mass terms in the Dirac equation. Such topological defects have been known to carry non-trivial quantum numbers such as charge and spin. Here we discuss their additional internal degree of freedom: irrespectively of the dimensionality of space and the nature of orders that support the defect, an extra mass-order-parameter is found to emerge in their core. Six linearly independent local orders, which close two mutually commuting three-dimensional Clifford algebras are proven to be in general possible. We show how the particle-hole symmetry restricts the defects to always carry the quantum numbers of a single effective isospin-1/2, quite independently of the values of their electric charge or true spin. Examples of this new degree of freedom in graphene and on surfaces of topological insulators are discussed.
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