Emergent reduction of electronic state dimensionality in dense ordered Li-Be alloys

High pressure is known to influence electronic structure and crystal packing, and can in some cases even induce compound formation between elements that do not bond under ambient conditions(1-3). Here we present a computational study showing that high pressure fundamentally alters the reactivity of the light elements lithium ( Li) and beryllium ( Be), which are the first of the metals in the condensed state and immiscible under normal conditions(4,5). We identify four stoichiometric LixBe1-x compounds that are stable over a range of pressures, and find that the electronic density of states of one of them displays a remarkable step-like feature near the bottom of the valence band and then remains almost constant with increasing energy. These characteristics are typical of a quasi- two- dimensional electronic structure, the emergence of which in a three- dimensional environment is rather unexpected. We attribute this observation to large size differences between the ionic cores of Li and Be: as the density increases, the Li cores start to overlap and thereby expel valence electrons into quasi- two- dimensional layers characterized by delocalized free- particle- like states in the vicinity of Be ions.