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The properties that distinguish topological crystalline insulator (TCI) and topological insulator (TI) rely on crystalline symmetry and time-reversal symmetry, respectively, which encodes different bulk and surface/edge properties. Here, we predict theoretically that electron-doped TlM (M = S and Se) (110) monolayers realize a family of two-dimensional (2D) TCIs characterized by mirror Chern number CM = -2. Remarkably, under uniaxial strain (≈ 1%), a topological phase transition between 2D TCI and 2D TI is revealed with the calculated spin Chern number CS = -1 for the 2D TI. Using spin-resolved edge states analysis, we show different edge-state behaviors, especially at the time reversal invariant points. Finally, a TlBiSe2/NaCl quantum well is proposed to realize an undoped 2D TCI with inverted gap as large as 0.37 eV, indicating the high possibility for room-temperature observation.

We present a density functional theory (DFT) investigation of magnetically frustrated Mn monolayers deposited on the triangular lattice of the Cu(1 1 1) surface. Noncollinear magnetic structures are treated on the basis of the vector spin-density formulation of the DFT. The spin-polarized scanning tunneling microscope operated in the constant-current mode is proposed as a powerful tool to investigate these complex magnetic structures.

At ferroelectric longitudinal domain walls there is an uncompensated charge, which could form a two-dimensional electron gas in the insulator. However, the uncompensated charges can be accommodated by, e.g., defects or localized states that split off from the conduction band. We carried out density functional theory calculations to study these scenarios in PbTiO3 with and without consideration of strong correlation effects simulated via inclusion of a Hubbard parameter U. The optimized structure and electronic structure depend on the choice of this parameter: For vanishing U, a broad, conducting domain wall is obtained, while increasing U leads to localized Ti 3d states and an insulating, sharp domain wall. We also investigated the effects of varying the ferroelectric polarization on the electronic structure of these domain walls.

Electrons mediate many of the interactions between atoms in a solid. Their propagation in a material determines its thermal, electrical, optical, magnetic and transport properties. Therefore, the constant energy contours characterizing the electrons, in particular the Fermi surface, have a prime impact on the behavior of materials. If anisotropic, the contours induce strong directional dependence at the nanoscale in the Friedel oscillations surrounding impurities. Here we report on giant anisotropic charge density oscillations focused along specific directions with strong spin-filtering after scattering at an oxygen impurity embedded in the surface of a ferromagnetic thin film of Fe grown on W(001). Utilizing density functional theory, we demonstrate that by changing the thickness of the Fe films, we control quantum well states confined to two dimensions that manifest as multiple flat energy contours, impinging and tuning the strength of the induced charge oscillations which allow to detect the oxygen impurity at large distances ($\approx$ 50nm)., Comment: This paper has an explanatory supplement

We report on the epitaxial fabrication and electronic properties of a topological phase in strained \alpha-Sn on InSb. The topological surface state forms in the presence of an unusual band order not based on direct spin-orbit coupling, as shown in density functional and GW slab-layer calculations. Angle-resolved photoemission including spin detection probes experimentally how the topological spin-polarized state emerges from the second bulk valence band. Moreover, we demonstrate the precise control of the Fermi level by dopants., Comment: version 2 with supplementary information

We examined by two-dimensional photoemission band mapping the electronic structure of Au films epitaxially grown on an Ag(111) substrate. The very similar structural and electronic properties of the two metals make this system extremely unfavorable for the occurrence and observation of electron confinement effects. At variance with previous spectroscopic studies, we show that the electron reflectivity at the interface sustains the formation of well-defined $sp$-derived quantum well states (QWS) and weak quantum well resonance states (QWRS) in the Au layers. The character and degree of confinement of these states are analyzed and quantitatively related to the Au/Ag interface reflectivity on the basis of density functional theory (DFT) band structure calculations.

Electronic tunneling through ferroelectric insulators is considered to be a key ingredient of future oxide electronics. We investigate the role of the electronic band structure of the decaying electronic states in the band gap by first discussing the expected behavior of tunneling in the effective mass model. We demonstrate that, even for the simple prototype ferroelectric oxides in the perovskite structures PbTiO${}_{3}$ and BaTiO${}_{3}$, the basic assumption of the effective mass model is not appropriate, and that the correct interpretation of tunneling in these materials requires a material-specific description of the evanescent states as provided by the complex band structure.

A half-metal has been defined as a material with propagating electron states at the Fermi energy only for one of the two possible spin projections, and as such has been promoted as an interesting research direction for spin electronics. This review details recent advances on manganite thin film research within the field of spintronics, before presenting the structural, electronic and spin-polarized solid-state tunnelling transport studies that we have performed on heterostructures involving La(2/3)Sr(1/3)MnO(3) thin films separated by SrTiO(3) barriers. These experiments demonstrate that, with a polarization of spin [Formula: see text] electrons at the Fermi level that can reach 99%, the La(2/3)Sr(1/3)MnO(3)/SrTiO(3) interface for all practical purposes exhibits half-metallic behaviour. We offer insight into the electronic structure of the interface, including the electronic symmetry of any remaining spin [Formula: see text] states at the Fermi level. Finally, we present experiments that use the experimental half-metallic property of manganites as tools to reveal novel features of spintronics.

The spin-polarized scanning tunneling microscope (SP-STM) operated in the constant current mode is proposed as a powerful tool to investigate complex atomic-scale magnetic structures of otherwise chemically equivalent atoms. The potential of this approach is demonstrated by successfully resolving the magnetic structure of Cr/Ag(111), which is predicted on the basis of ab initio vector spin-density calculations to be a coplanar noncollinear periodic 120\ifmmode^\circ\else\textdegree\fi{} N\'eel structure. Different operating modes of the SP-STM are discussed on the basis of the model of Tersoff and Hamann.