Ferroelectrically Switchable Chirality in Topological Superconductivity

TL;DR

The paper proposes a polar-stacking MnBi2Te4 bilayer in proximity to Fe(Se,Te) as a controllable platform for switchable chiral topological superconductivity, enabled by interlayer sliding-induced ferroelectricity that breaks $\,\mathcal{M}_{z}\mathcal{T}$ and $\mathcal{PT}$. It develops an effective theory for ferroelectricity, demonstrates a switchable anomalous Hall effect, and maps out CTSC phase diagrams with Chern numbers $N=\pm1$ for AB/BA stacking, while anti-AA yields $N=0$. A key insight is that the superconducting Chern number is tied to the residual chirality of Fermi loops, with a general relation $N=\sum_i |n_i|\mathrm{sgn}(\sigma_H^i)$, and its manifestation can persist under continuous deformation from massless HQHE to gapped AHE. The authors propose thermal Hall conductivity as a temperature-dependent experimental signature, offering a practical route to detect CTSC and explore Majorana physics in a tunable, experimentally feasible heterostructure.

Abstract

The interplay between ferroelectricity, magnetism, and superconductivity provides a rich platform for discovering novel quantum phenomena. Here, we develop an effective theory and propose a heterostructure composed of an antiferromagnetic bilayer MnBi$_{2}$Te$_{4}$ coupled with the s-wave superconductor Fe(Se,Te), enabling the realization of chiral topological superconductivity (CTSC) with switchable chirality. The chirality of the CTSC is controlled by the direction of spontaneous polarization, which arises from interlayer sliding-induced ferroelectricity or charge transfer in the bilayer MnBi$_{2}$Te$_{4}$. This sliding mechanism breaks the $\mathcal{M}_{z}\mathcal{T}$ and $\mathcal{PT}$ symmetries, leading to the anomalous Hall effect in the spin polarized metallic Dirac band and drives the emergence of CTSC when the s-wave superconductivity appears. Our work not only provides a new pathway to achieve and control topological superconductivity but also opens avenues for experimental exploration of Majorana physics and topological quantum computation.

Figures (7)

• Figure 1: Schematic of the bilayer MnBi$_{2}$Te$_{4}$/Fe(Se,Te) heterostructure. In the polar stacking configuration, the crystal orientation of the bilayer MnBi$_{2}$Te$_{4}$ exhibits z-mirror symmetry, with two stable configurations (anti-AB and anti-BA) showing ferroelectricity due to interlayer sliding. Both configurations maintain interlayer antiferromagnetism and exhibit spin-splitting in the band structure. When coupled with Fe(Se,Te), chiral topological superconductivity (CTSC) emerges as the chemical potential lies within a single spin band. The chirality of the CTSC can be switched by the direction of ferroelectric polarization.
• Figure 2: Comparison of atomic structures between the normal and the stable polar stacking of bilayer MnBi$_{2}$Te$_{4}$ (side views). We utilize green stripe to denote the crystal orientation in each SL. From left to right, the normal stacking, anti-AA, AB and BA stacking are depicted.
• Figure 3: Band structure, spontaneous polarization and anomalous Hall effect in polar stacking bilayer MnBi$_{2}$Te$_{4}$. (a) (b) Band structures of the BA and AB stacking phases, with the color representing the spin polarization. The electric polarizations in the two phases are positive and negative, respectively. (c) Spontaneous polarization $P_{z}$ as a function of the ferroelectricity potential $V_{b}$. (d) Anomalous Hall conductance as a function of the chemical potential of the AB and BA stacking phases, with anti-AA stacking phase serving as a reference.
• Figure 4: Topological phase diagram (a), a schematic diagram illustrating the how the position of chemical potential influence the Fermi surface loop structure (b) and superconducting Chern number $N$ and anomalous Hall conductance $\sigma_{H}$ for (c) AB and (d) BA stacking cases in bilayer MnBi$_{2}$Te$_{4}$/Fe(Se,Te) heterostructure. In the phase diagram of (a), the three $V_{b}$-constant lines indicate the three stacking manners. We also define $V_{b}^{c}=|\Delta m_{0}|/\sqrt{g^{2}-\Delta^{2}}$ as the critical FEP intensity for the realization of the topological superconductor.
• Figure 5: CTSC evolving from that in HQHE to that in gapped AHE. From the left to right, we show (a) normal state for a regulated massless Dirac cone, (b) particle-hole doubled states for regulated massless Dirac cone, (c) (d) superconducting state for regulated massless Dirac cone (middle two), (e) superconducting state for regulated massive Dirac cone, and (f) normal state for a regulated massive Dirac cone.