Abstract
Materials that possess nontrivial topology and magnetism is known to exhibit exotic quantum phenomena such as the quantum anomalous Hall effect. Here, we fabricate a novel magnetic ...topological heterostructure Mn
4
Bi
2
Te
7
/Bi
2
Te
3
where multiple magnetic layers are inserted into the topmost quintuple layer of the original topological insulator Bi
2
Te
3
. A massive Dirac cone (DC) with a gap of 40–75 meV at 16 K is observed. By tracing the temperature evolution, this gap is shown to gradually decrease with increasing temperature and a blunt transition from a massive to a massless DC occurs around 200–250 K. Structural analysis shows that the samples also contain MnBi
2
Te
4
/Bi
2
Te
3
. Magnetic measurements show that there are two distinct Mn components in the system that corresponds to the two heterostructures; MnBi
2
Te
4
/Bi
2
Te
3
is paramagnetic at 6 K while Mn
4
Bi
2
Te
7
/Bi
2
Te
3
is ferromagnetic with a negative hysteresis (critical temperature ~20 K). This novel heterostructure is potentially important for future device applications.
A comprehensive study of the evolution of electronic structure and chemical bonding in disordered Ti1−xAlxN and Ti1−x−yAlxTayN systems was performed by means of ab initio density functional theory ...calculations using crystal orbital Hamilton population technique. Progressive changes in the character of interatomic chemical bonding were revealed when sequentially alloyed TiN with Al and Ta. Alloying TiN with Al leads to the change in the TiN bonding character from ionic to covalent, whereas AlN bonds being strongly ionic. The following alloying of Ti1−xAlxN solid solutions with Ta results in a significant reduction of the ionicity of the AlN bonds, while retaining the covalency of the TiN bonds. In addition, alloying with Ta introduces metallic character of chemical bonding in Ti1−x−yAlxTayN, with the degree of metallicity increasing with growing Ta concentration. The gain in metallicity was found to be provided not only by TaTa bonds, which make the main contribution, but also by TaN bonds, which have covalent-metallic character. A strong dependence of bonding energies in Ti1−x AlxN and Ti1−x−y AlxTayN on local atomic surrounding was found.
•COHP analysis allows unveiling of chemical bonding in Ti1-x-yAlxTayN solid solutions.•Alloying with Al decreases ionisity of TiN bonds.•Ta alloying provides metallic character of interatomic bonding in the quaternary solutions.•Dependence of chemical bonding on content and arrangement of alloying elements correlates with elastic behaviour.
Based on the relativistic spin-polarized density functional theory calculations we investigate the crystal structure, electronic and magnetic properties of a family MnPn2Ch4 compounds, where ...pnictogen metal atoms (Pn) are Sb and Bi; chalcogens (Ch) are Se, Te. We show that in the series the compounds of this family with heavier elements prefer to adopt rhombohedral crystal structure composed of weakly bonded septuple monoatomic layers while those with lighter elements tend to be in the monoclinic structure. Irrespective of the crystal structure all compounds of the MnPn2Ch4 series demonstrate a weak energy gain (of a few meV per formula unit or even smaller than meV) for antiferromagnetic (AFM) coupling for magnetic moments on Mn atoms with respect to their ferromagnetic (FM) state. For rhombohedral structures the interlayer AFM coupling is preferable while in monoclinic phases intralayer AFM configuration with ferromagnetic ordering along the Mn chain and antiferromagnetic ordering between the chains has a minimum energy. Over the series the monoclinic compounds are characterized by substantially wider bandgap than compounds with rhombohedral structure.
•DFT calculations show the structure of MnPn2Ch4 compounds depends on composition.•Irrespective of the structure all compounds demonstrate antiferromagnetic ordering.•The type of crystal structure significantly influences the bandgap width.
The interplay of the atomic structure and phonon spectra in a variety of two dimensional phases forming during submonolayer Pb adsorption on a Cu(001) surface has been investigated using embedded ...atom method interatomic interaction potentials. Complementary calculations of the equilibrium atomic structure of these phases were performed using density functional theory. It has been shown that the dynamic stability of the Pb/Cu(001) structures increases with increasing the coverage from 0.375 ML to ultimately 0.6 ML, when a dense Pb layer is formed. The increase of the coverage also results in progressive shift of the Rayleigh mode of the copper surface to higher energy and the appearance of new mixed adsorbate-substrate vibration modes.
The interplay of the atomic structure and phonon spectra of various two-dimensional ordered phases forming during submonolayer (from 0.375 ML to ultimate 0.6 ML) Pb adsorption on a Cu(001) surface is investigated using embedded atom method interatomic interaction potentials.
The structure and magnetic properties of small Cr clusters, Cr
3
and Cr
4
, adsorbed on the Cu(111) surface have been investigated using density functional theory (DFT) calculations and their ...vibrational properties have been studied within calculations based on tight-binding second moment approximation interatomic interaction potentials (TBSMA). It has been shown that the magnetic ordering in the Cr clusters significantly affects their crystal structure and symmetry, which influences the vibrational modes of the clusters and nearest neighbor copper atoms. In turn, these modes select potentially possible structures of Cr
3
and Cr
4
, prohibiting the lowest total energy cluster structure as dynamically unstable.
The structure and magnetic properties of small Cr clusters adsorbed on the Cu(111) surface have been investigated using DFT theory and their vibrational properties have been calculated using tight-binding second moment approximation interatomic interaction potentials.
Discovered in 1962, the divalent ferromagnetic semiconductor EuS (T C = 16.5 K, E g = 1.65 eV) has remained constantly relevant to the engineering of novel magnetically active interfaces, ...heterostructures, and multilayer sequences and to combination with topological materials. Because detailed information on the electronic structure of EuS and, in particular, its evolution across T C is not well-represented in the literature but is essential for the development of new functional systems, the present work aims at filling this gap. Our angle-resolved photoemission measurements complemented with first-principles calculations demonstrate how the electronic structure of EuS evolves across a paramagnetic–ferromagnetic transition. Our results emphasize the importance of the strong Eu 4f–S 3p mixing for exchange-magnetic splittings of the sulfur-derived bands as well as coupling between f and d orbitals of neighboring Eu atoms to derive the value of T C accurately. The 4f–3p mixing facilitates the coupling between 4f and 5d orbitals of neighboring Eu atoms, which mainly governs the exchange interaction in EuS.
Spintronics is aimed at actively controlling and manipulating the spin degrees of freedom in semiconductor devices. A promising way to achieve this goal is to make use of the tunable Rashba effect ...that relies on the spin-orbit interaction in a two-dimensional electron system immersed in an inversion-asymmetric environment. The spin-orbit-induced spin splitting of the two-dimensional electron state provides a basis for many theoretically proposed spintronic devices. However, the lack of semiconductors with large Rashba effect hinders realization of these devices in actual practice. Here we report on a giant Rashba-type spin splitting in two-dimensional electron systems that reside at tellurium-terminated surfaces of bismuth tellurohalides. Among these semiconductors, BiTeCl stands out for its isotropic metallic surface-state band with the Γ-point energy lying deep inside the bulk band gap. The giant spin splitting of this band ensures a substantial spin asymmetry of the inelastic mean free path of quasiparticles with different spin orientations.
Rashba split surface states in BiTeBr Eremeev, S V; Rusinov, I P; Nechaev, I A ...
New journal of physics,
07/2013, Letnik:
15, Številka:
7
Journal Article
Recenzirano
Odprti dostop
Within density functional theory, we study the bulk band structure and surface states of BiTeBr. We consider both ordered and disordered phases, which differ in atomic order in the Te-Br sublattice. ...On the basis of relativistic ab initio calculations, we show that the ordered BiTeBr is energetically preferable as compared with the disordered one. We demonstrate that both Te- and Br-terminated surfaces of the ordered BiTeBr hold surface states with a giant spin-orbit splitting. The Te-terminated surface-state spin splitting has Rashba-type behavior with the coupling parameter αR ∼ 2 eVÅ.
First-principles and model calculations show that the Dirac surface state of the topological insulator Bi(2)Te(3) survives upon moderate Mn doping of the surface layers but can lose its topological ...character as a function of magnetization direction. The dispersion depends considerably on the direction of the Mn magnetization: for perpendicular magnetization, a gap of 16 meV opens up at the Dirac point; for in-plane magnetization, a tiny gap can be opened or closed in dependence on the magnetization azimuth. The ground state is ferromagnetic, with a critical temperature of 12 K. The results provide a path towards a magnetic control of the topological character of the Dirac surface state and its consequences to spin-dependent transport properties.
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