Disorder and defects in topological systems
Topological phases are most revealing where translation symmetry breaks: at defects, boundaries, and through disorder. We study the real-space states and dynamical responses that survive imperfect crystals, and how local modes reorganize transport and screening.
Quantum Critical Dynamics Induced by Topological Zero Modes
Physical Review Letters 136, 136602 (2026).
In a chiral-disordered Su–Schrieffer–Heeger chain near the topological delocalization transition, hybridized domain-wall zero modes produce logarithmic ac-conductivity scaling at criticality. The scaling follows from the stretched-exponential spatial decay of the zero-mode wavefunctions.
Ring States in Topological Materials
Newton (in press).
Strong local impurities can generate in-gap states pinned near zeros of the impurity-projected Green function. These ring states have mixed band character and a node at the impurity site; their protection follows from the obstruction to symmetric exponentially localized Wannier functions, and linking them recovers boundary modes.
Topologically protected flatness in chiral moiré heterostructures
Physical Review X 15, 021056 (2025).
With Valentin Crépel and Nicolas Regnault, we show that exact band geometry at the first magic angle suppresses disorder broadening in chiral moiré heterostructures. This index-theorem protection survives lattice relaxation, while higher magic angles remain much more fragile.
Disorder as a controlled probe
Disorder couples local modes that were isolated in a clean sample. Their broadly distributed couplings can produce delocalization, critical transport, or long-lived dynamics. This turns disorder into a way to test topology rather than a nuisance to be averaged away.
Anderson critical metal phase in trivial states protected by average magnetic crystalline symmetry
Nature Communications 15, 3069 (2024).
A symmetry that survives only statistically can stabilize a scale-invariant metallic phase between localized states. The result connects crystalline topology to disorder-driven criticality without requiring a clean topological band structure.
Topology when translation symmetry fails
Momentum-space invariants assume a repeating crystal, while experiments see surfaces, corners, dislocations, impurities, and local charge. Real-space wavefunctions reveal which states remain fixed when translation symmetry is absent and which local probes can distinguish them.
Boundary-obstructed topological phases
Physical Review Research 3, 013239 (2021).
Bulk bands can agree while their boundary spectra remain distinct. The obstruction records how Wannier centers meet a particular termination, producing edge or corner states that periodic bulk data alone cannot predict.
Delocalization Transition of a Disordered Axion Insulator
Physical Review Letters 127, 016602 (2021).
Disorder drives an axion insulator through a delocalization transition controlled by its surface and bulk topology. The transition exposes how a quantized magnetoelectric response is lost in real space.
