Materials Science Research Lecture

Webinar Link:

https://caltech.zoom.us/j/83276652110

Webinar ID: 832 7665 2110

NOTE: At this time, in-person APhMS seminars are open to all Caltech students/staff/faculty/visitors with a valid Caltech ID. Outside community members are welcome to join our online event.

Abstract:

Two-dimensional bismuth <111> is theoretically predicted to be a room temperature topological insulator with a large bulk bandgap. However, traditional growth methods for bismuth thin films are limited to sub-hundred nanometer grains, providing an obstacle to electronic studies. We have developed a new approach to ultrathin crystal growth in which bismuth is molded between van der Waals materials. By applying heat and uniaxial pressure to bismuth encapsulated between crystals of hexagonal boron nitride, we consistently produce 5 nanometer thick bismuth crystals with atomically flat surfaces. TEM analysis reveals 10 micron size single crystal domains with the <111> orientation, corresponding to stacked hexagonal layers of bismuth.

Due to the ultraflat structure of the crystals, we are able to perform the first electronic measurements on bismuth of uniform layer thickness. Cryogenic magnetotransport reveal clear quantum oscillations originating from the bismuth topological surface states. These are the first observations of quantum oscillations in thin bismuth films and indicate an electronic quality at least an order magnitude better than bismuth grown by molecular beam epitaxy. These results pave a path towards achieving two-dimensional bismuthene, which has applications in both spintronics and quantum computing. Moreover, our initial tests show that the 2D squeeze-growth technique is generalizable to other soft materials such tin, indium and gold.

Bio:

Javier Sanchez-Yamagishi is an Assistant Professor in the Department of Physics & Astronomy at the University of California, Irvine. His lab studies quantum electronic transport in van der Waals and topological materials with a special emphasis on developing new nanofabrication and measurement techniques. Previously, he was a postdoctoral fellow at the Harvard Quantum Optics Center, where he explored the application of spin qubits as nanoscale magnetometers for 2D materials. He did his PhD at MIT studying the electronic properties of twisted graphene heterostructures.