Shaved by Occam’s Razor: Minimal Fractional Topological Insulator
Cenke Xu
University of California, Santa Barbara
Wednesday, October 22, 2025
2:00 p.m.
In-person: QNC 1201
Abstract: We propose a "minimal" fractional topological insulator (mFTI), motivated by the recent experimental report on the signatures of FTI in a transition metal dichalcogenide (TMD) moiré system. The observed FTI is likely given by a topological state living in a pair of half-filled conjugate Chern bands with opposite Chern numbers. We propose the mFTI as a strong candidate topological state in the half-filled conjugate Chern bands. The mFTI is characterized by the following features: (1) It is a fully gapped topological order (TO) with 16 Abelian anyons if the electron is considered trivial; (2) the minimally-charged anyon carries electric charge e/2, together with the fractional quantum spin-Hall conductivity, implying the robustness of the mFTI's gapless edge state whenever time-reversal symmetry and charge conversation are present; (3) the mFTI is "minimal" in the sense that it has the smallest total quantum dimension (a metric for the TO's complexity) within all the TOs that can potentially be realized at the same electron filling and with the same Hall transports; the mFTI is also the unique one that respects time-reversal symmetry. (4) the mFTI is the common descendant of multiple valley-decoupled "product TOs" with larger quantum dimensions. Similar mFTIs can be constructed for a pair of partially-filled conjugate Chern bands.