Photoemission electron microscopy imaging of moiré ferroelectricity in a twisted hBN heterostructure

Hexagonal boron nitride (hBN) is an essential building block for 2D heterostructures due to its insulator properties (~6eV bandgap), low levels of charge disorder, and its large flat terraces. It has been shown recently that a twisted hBN/hBN interface can be engineered with an out-of-plane ferroelectric polarization by breaking inversion symmetry (i.e., with AB stacking, twisted 60º from bulk AA’ order) [1–3] . Adding a small (<0.5deg) twist between the layers creates a moiré pattern where each moiré unit cell host one “up” and one “down” ferroelectric domain. In this talk, we will discuss our latest research exploring moiré ferroelectricity in a twisted hBN heterostructure using low energy microscopy techniques such as Photoemission electron microscopy (PEEM) and Low Energy Electron Microscopy (LEEM) to map real space electronic distribution at different energies, providing high resolution imaging and spectroscopic information of our sample.

References:

1. C. R. Woods, P. Ares, H. Nevison-Andrews, M. J. Holwill, R. Fabregas, F. Guinea, A. K. Geim, K. S. Novoselov, N. R. Walet, and L. Fumagalli, "Charge-polarized interfacial superlattices in marginally twisted hexagonal boron nitride," Nat Commun 12, 347 (2021).

2. K. Yasuda, X. Wang, K. Watanabe, T. Taniguchi, and P. Jarillo-Herrero, "Stacking-engineered ferroelectricity in bilayer boron nitride," Science 372, 1458–1462 (2021).

3. M. Vizner Stern, Y. Waschitz, W. Cao, I. Nevo, K. Watanabe, T. Taniguchi, E. Sela, M. Urbakh, O. Hod, and M. Ben Shalom, "Interfacial ferroelectricity by van der Waals sliding," Science 372, 1462–1466 (2021).