DQMP Informal Seminar - Prof. Tristan CREN - Topological defects in a moiré pattern

23.07.2024 10:30 – 11:30

Van der Waals materials are emerging as extremely versatile building blocks for many fields of research, both at the fundamental and applied level. They offer tremendous possibilities for fine tuning spintronics, superconducting, nanoelectronics, optical devices. They appear extremely attractive for exploring new exotic physics due to their ability to be staked with an infinite number of combinations that leads to unexpected physical properties. The toolbox of van der Waals heterostructures is continuously growing with for instance the recent discovery of ferromagnetic order down to the monolayer limit in the family of chromium trihalide, CrCl3, CrBr3 and CrI3 (CrX3, X= I, Br, Cl) [1]. Several works have related some observations of moiré structure due to the mismatch between the CrX3 monolayers and their substrate which leads to a wealth of new exotic effects [2, 3]. Combining a chromium trihalide layer with a superconductor might lead for instance to topological superconductivity as recently reported in CrBr3/NbSe2 heterostructures [4]. In this hybrid structure, it was proposed that the mechanism leading to a topological order in this hybrid structures was intimately related to the presence of a moiré pattern [2]. Another fascinating observation concerns the influence of a moiré on the magnetic properties. In the CrX3 family, till now, the magnetization was shown to be essentially colinear, however, in CrI3 double bilayer some hint of non-colinear magnetism was found and was related to the moiré pattern which leads to a non- negligible spatial modulation of the magnetic interaction [3]. In this seminar, we will present our scanning tunneling microscopy investigation of a CrCl3 monolayer deposited on Au(111) which exhibit a second order moiré pattern [5]. We report the presence of edge dislocations in this moiré pattern. Based on a comprehensive analytical model, we will show that these well know edge dislocations can be reexamined in the framework of topological concepts where they are described as topological defects analogous to vortices carrying a Berry phase characterized by a Chern winding number. They might therefore be used as a pinning center to host topological spin texture or Majorana bound states in CrX3/superconductor heterostructures.

References :
[1] D. Soriano et. al, Nano Lett. 20, 6225 (2020)
[2] S. Kezilebieke et. al., Nano Lett. 22, 328 (2022)
[3] H. Xie, et. al., Nat. Phys. 19, 1150 (2023)
[4] S. Kezilebieke et. al, Nature 588, 424 (2020)
[5] E. Gambari et al., to be published, Adv. Func Mater. (2024)


Organized by Prof. C. Renner

Lieu

Bâtiment: Ecole de Physique

Auditoire Stückelberg

entrée libre