The electronic structure of Bi(001) ultrathin films (thickness > or =7 bilayers) on Si(111)-7x7 was studied by angle-resolved photoemission spectroscopy and first-principles calculations. In contrast with the semimetallic nature of bulk Bi, both the experiment and theory demonstrate the metallic character of the films with the Fermi surface formed by spin-orbit-split surface states (SSs) showing little thickness dependence. Below the Fermi level, we clearly detected quantum well states (QWSs) at the M point, which were surprisingly found to be non-spin-orbit split; the films are "electronically symmetric" despite the obvious structural nonequivalence of the top and bottom interfaces. We found that the SSs hybridize with the QWSs near M and lose their spin-orbit-split character.

Employing first-principles calculations, we perform a systematic study of the electronic properties of thin ͑one to six bilayers͒ films of the semimetal bismuth in ͑111͒ and ͑110͒ orientation. Due to the different coordination of the surface atoms in these two cases, we find a large variation of the conducting properties of the films, ranging from small-band-gap semiconducting to semimetallic and metallic. The evolution of the Bi͑111͒ and Bi͑110͒ surface states can be monitored as a function of the film thickness. Another interesting feature is provided by the strong spin-orbit effects in Bi and the resulting Rashba-type spin splitting of the surface states. The relaxations, band structures, Fermi surfaces, and densities of states are presented and discussed with respect to possible applications in the field of spintronics.

An interplay of spin-orbit coupling and intrinsic magnetism is known to give rise to the quantum anomalous Hall and topological magnetoelectric effects under certain conditions. Their realization could open access to low power consumption electronics as well as many fundamental phenomena like image magnetic monopoles, Majorana fermions and others. Unfortunately, being realized very recently, these effects are only accessible at extremely low temperatures and the lack of appropriate materials that would enable the temperature increase is a most severe challenge. Here, we propose a novel material platform with unique combination of properties making it perfectly suitable for the realization of both effects at elevated temperatures. The key element of the computational material design is an extension of a topological insulator (TI) surface by a thin film of ferromagnetic insulator, which is both structurally and compositionally compatible with the TI. Following this proposal we suggest a variety of specific systems and discuss their numerous advantages, in particular wide band gaps with the Fermi level located in the gap.