| 1. |
- Araya Day, Isidora, et al.
(författare)
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Topological defects in a double-mirror quadrupole insulator displace diverging charge
- 2022
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Ingår i: Scipost Physics Core. - 2666-9366. ; 5:4
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Tidskriftsartikel (refereegranskat)abstract
- We show that topological defects in quadrupole insulators do not host quantized fractional charges, contrary to what their Wannier representation indicates. In particular, we test the charge quantization hypothesis based on the Wannier representation of a disclination and a parametric defect. Since disclinations necessarily strain the lattice and parametric defects require closed curves in parameter space, both defects break four-fold rotation symmetry, even away from their origin. The Wannier representation of the defects is thus determined by local reflection symmetries. Contrary to the hypothesis, we find that the local charge density decays as ∼1/r2 with distance, leading to a diverging defect charge. Because topological defects are incompatible with four-fold rotation symmetry, we conclude that defect charge quantization is protected by sublattice symmetry, and not higher order topology.
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| 2. |
- Day, Isidora Araya, et al.
(författare)
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Pfaffian invariant identifies magnetic obstructed atomic insulators
- 2023
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Ingår i: SciPost Physics. - 2542-4653. ; 15:3
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Tidskriftsartikel (refereegranskat)abstract
- We derive a Z4 topological invariant that extends beyond symmetry eigenvalues and Wilson loops and classifies two-dimensional insulators with a C4T symmetry. To formulate this invariant, we consider an irreducible Brillouin zone and constrain the spectrum of the open Wilson lines that compose its boundary. We fix the gauge ambiguity of the Wilson lines by using the Pfaffian at high symmetry momenta. As a result, we distinguish the four C4T-protected atomic insulators, each of which is adiabatically connected to a different atomic limit. We establish the correspondence between the invariant and the obstructed phases by constructing both the atomic limit Hamiltonians and a C4T-symmetric model that interpolates between them. The phase diagram shows that C4T insulators allow ±1 and 2 changes of the invariant, where the latter is overlooked by symmetry indicators.
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| 3. |
- Hou, Chang-Yu, et al.
(författare)
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Probing Majorana edge states with a flux qubit
- 2011
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Ingår i: Phys. Rev. B.. ; 84
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Tidskriftsartikel (refereegranskat)abstract
- A pair of counterpropagating Majorana edge modes appears in chiral p-wave superconductors and in other superconducting systems belonging to the same universality class. These modes can be described by an Ising conformal field theory. We show how a superconducting flux qubit attached to such a system couples to the two chiral edge modes via the disorder field of the Ising model. Due to this coupling, measuring the backaction of the edge states on the qubit allows us to probe the properties of Majorana edge modes.
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| 4. |
- Pöyhönen, Kim, et al.
(författare)
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Minimal Zeeman field requirement for a topological transition in superconductors
- 2021
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Ingår i: SciPost Physics. - 2542-4653. ; 10:5
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Tidskriftsartikel (refereegranskat)abstract
- Platforms for creating Majorana quasiparticles rely on superconductivity and breaking of time-reversal symmetry. By studying continuous deformations to known trivial states, we find that the relationship between superconducting pairing and time reversal breaking imposes rigorous bounds on the topology of the system. Applying these bounds to s-wave systems with a Zeeman field, we conclude that a topological phase transition requires that the Zeeman energy at least locally exceed the superconducting pairing by the energy gap of the full Hamiltonian. Our results are independent of the geometry and dimensionality of the system.
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