A research group led by Prof. LI Xingxing of University of Science and Technology of China (USTC) of Chinese Academy of Chinese (CAS) made a reversible topological control in 2D organometallic lattices achieved through tautomerization. Their work was published on Advanced Functional Materials.

Topological materials have been gaining interest in condensed matter physics due to their topologically protected surface states that allow dissipationless electron transport. However, most of the current topological materials exhibit a single type of band topology, with simultaneous realization of multiple topological properties within the same material urgently needed to boost functionality. Up till now, a couple of physical methods have been developed in certain systems, while the chemical methods are significantly restricted and irreversible.

In the previous work of the group, reversible spin order transition has been achieved in organometallic lattices through lactam-lactim tautomerization. Based on this result, the group extended the method to organometallic frameworks and introduced tautomerization modules in organic linkers of organic topological insulator (OTI). The tautomerization then triggered a magnetic phase transition that changes the electronic band structure of the 2D organometallic lattices, consequently produced a controllable reversible topological phase transition by changing the Chern number.

Lactam-lactim tautomerization induces topological phase transition (Image by LI et al.)

Researchers employed 2,2′-bithiazole derivatives as the organic linkers planar. Combined with tricoordinated Co atoms, a 2D topological material is designed, with its feasibility theoretically illustrated in simulations. After the tautomerization, this organometallic lattice experienced a change from a ferrimagnetic half metal with a local gap having a Chern number of +1 to a ferromagnetic Chern insulator possessing a Chern number of −1, with the spin polarization direction of the charge carriers in the lattice was also reversed.

This study contributes to enable dissipationless electron transport and offer promising applications in spintronics and quantum computations.

paper link: https://doi.org/10.1002/adfm.202400610

(Written by SHI Yutian, edited by HUANG Rui, USTC News Center)