Heavy Electrons Moving Through CeSiI (IMAGE) Columbia University Caption Electrons that interact with magnetic spins in heavy fermion materials have a heavier-than-usual effective mass. In addition to being a heavy fermion, CeSiI is a van der Waals crystal that can be peeled into atom-thin layers. Credit Nicoletta Barolini, Columbia University Usage Restrictions Re-use with Credit License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.