Massive and massless charge carriers in an epitaxially strained alkali metal quantum well on graphene
Martin Hell, Niels Ehlen, Giovanni Marini, Yannic Falke, Boris V. Senkovskiy, Charlotte Herbig, Christian Teichert, Wouter Jolie, Thomas Michely, J. Ávila, Giovanni Di Santo, Diego M. de la Torre, L. Petaccia, G. Profeta, A. Grüneis
Abstract
We show that Cs intercalated bilayer graphene acts as a substrate for the growth of a strained Cs film hosting quantum well states with high electronic quality. The Cs film grows in an fcc phase with a substantially reduced lattice constant of 4.9 Å corresponding to a compressive strain of 11% compared to bulk Cs. We investigate its electronic structure using angle-resolved photoemission spectroscopy and show the coexistence of massless Dirac and massive Schrödinger charge carriers in two dimensions. Analysis of the electronic self-energy of the massive charge carriers reveals the crystallographic direction in which a two-dimensional Fermi gas is realized. Our work introduces the growth of strained metal quantum wells on intercalated Dirac matter.