Structural determination of the Bi(110) semimetal surface by LEED analysis and ab initio calculations

The surface structure of Bi(110) has been investigated by low-energy electron diffraction intensity analysis and by first-principles calculations. Diffraction patterns at a sample temperature of 110 K and normal incidence reveal a bulk truncated (1x1) surface without indication of any structural reconstruction despite the presence of dangling bonds on the surface layer. Good agreement is obtained between the calculated and measured diffraction intensities for this surface containing only one mirror-plane symmetry element and a buckled bilayer structure. No significant interlayer spacing relaxations are found. The Debye temperature for the surface layer is found to be lower than in the bulk, which is indicative of larger atomic vibrational amplitudes at the surface. Meanwhile, the second layer shows a Debye temperature close to the bulk value. The experimental results for the relaxations agree well with those of our first-principles calculation

Structural determination of a low-symmetry surface by low-energy electron diffraction and ab initio calculations: Bi(110)

he surface structure of Bi(110) has been investigated by low-energy electron diffraction (LEED) intensity analysis and by first-principles calculations. Diffraction patterns at a sample temperature of 110 K and normal incidence reveal a bulk truncated (1×1) surface without indication of any structural reconstruction despite the presence of dangling bonds on the surface layer. Good agreement is obtained between the calculated and measured diffraction intensities for this complex, low-symmetry surface containing only one mirror-plane symmetry element. No significant interlayer spacing relaxations are found. The Debye temperature for the surface layer is found to be lower than in the bulk, which is indicative of larger vibrational atomic amplitudes at the surface. Meanwhile, the second layer shows a Debye temperature close to the bulk value. The experimental results for the relaxations agree well with those of our first-principles calculation

Spin-resolved two-photon photoemission study of the surface resonance state on Co/Cu(001)

Bulk and surface states of a clean and Cs-doped surface of a Co film grown on Cu(001) have been studied by spin-resolved photoemission (SR-PE) and compared with band structure calculation results. One-photon (1PPE) and two-photon (2PPE) photoemission spectra from clean Co films are found to be dominated by a peak located at a binding energy of about 0.4 eV with respect to E-F, which is assigned to the spin up 3d bulk state. Slight Cs-doping of a Co(001) surface shifts an image potential state in resonance with the sp-states of the conduction band. SR-2PPE study of the optically-induced electron population in such an image resonance reveals a strong dependence on the set polarization of the laser light. We are able to directly detect the spin polarization of electrons photoemitted from the image resonance state, which can be varied from highly-polarized (about bulk values) to almost unpolarized when tuning light polarization of the pump laser pulse from s to p

Strong Rashba Effect and Different f d Hybridization Phenomena at the Surface of the Heavy Fermion Superconductor CeIrIn5

New temperature scales and remarkable differences from bulk properties have increasingly placed the surfaces of strongly correlated f materials into the focus of research activities. Applying first principles calculations and angle resolved photoelectron spectroscopy measurements, a strong Rashba effect and spin split surface states at the CeIn surface of the heavy fermion superconductor CeIrIn5 are revealed. The unveiled 4f derived electron landscape is remarkably distinct for surface and bulk Ce implying the existence of novel temperature scales near the surface region in this material. These results show that ab initio calculations can reliably predict the unusual electronic and spin structure of surfaces of strongly correlated 4f systems where Rashba spin orbit coupling phenomena emerge. It is suggested that the structural blocks of such materials can be combined with magnetically active layers for engineering of novel nanostructural objects with appropriate substrates where the diversity of f driven properties can be applied for the development of novel functionalitie

Prediction and observation of an antiferromagnetic topological insulator

Magnetic topological insulators are narrow-gap semiconductor materials that combine non-trivial band topology and magnetic order1. Unlike their nonmagnetic counterparts, magnetic topological insulators may have some of the surfaces gapped, which enables a number of exotic phenomena that have potential applications in spintronics1, such as the quantum anomalous Hall effect2 and chiral Majorana fermions3. So far, magnetic topological insulators have only been created by means of doping nonmagnetic topological insulators with 3d transition-metal elements; however, such an approach leads to strongly inhomogeneous magnetic4 and electronic5 properties of these materials, restricting the observation of important effects to very low temperatures2,3. An intrinsic magnetic topological insulator -a stoichiometric well ordered magnetic compound- could be an ideal solution to these problems, but no such material has been observed so far. Here we predict by ab initio calculations and further confirm using various experimental techniques the realization of an antiferromagnetic topological insulator in the layered van der Waals compound MnBi2Te4. The antiferromagnetic ordering that MnBi2Te4 shows makes it invariant with respect to the combination of the time-reversal and primitive-lattice translation symmetries, giving rise to a ℤ2 topological classification; ℤ2 = 1 for MnBi2Te4, confirming its topologically nontrivial nature. Our experiments indicate that the symmetry-breaking (0001) surface of MnBi2Te4 exhibits a large bandgap in the topological surface state. We expect this property to eventually enable the observation of a number of fundamental phenomena, among them quantized magnetoelectric coupling6,7,8 and axion electrodynamics9,10. Other exotic phenomena could become accessible at much higher temperatures than those reached so far, such as the quantum anomalous Hall effect2 and chiral Majorana fermions3