The electronic structure of La1−x_{1-x}Srx_{x}MnO3_{3} thin films and its TcT_c dependence as studied by angle-resolved photoemission

We present angle-resolved photoemission spectroscopy results for thin films of the three-dimensional manganese perovskite La$_{1-x}$Sr$_{x}$MnO$_{3}$. We show that the transition temperature ($T_c$) from the paramagnetic insulating to ferromagnetic metallic state is closely related to details of the electronic structure, particularly to the spectral weight at the ${\bf k}$-point, where the sharpest step at the Fermi level was observed. We found that this ${\bf k}$-point is the same for all the samples, despite their different $T_c$. The change of $T_c$ is discussed in terms of kinetic energy optimization. Our ARPES results suggest that the change of the electronic structure for the samples having different transition temperatures is different from the rigid band shift.Comment: Accepted by Journal of Physics: Condensed Matte

Fermi Surface and Quasiparticle Excitations of overdoped Tl2Ba2CuO6+d by ARPES

The electronic structure of the high-T_c superconductor Tl2Ba2CuO6+d is studied by ARPES. For a very overdoped Tc=30K sample, the Fermi surface consists of a single large hole pocket centered at (pi,pi) and is approaching a topological transition. Although a superconducting gap with d_x^2-y^2 symmetry is tentatively identified, the quasiparticle evolution with momentum and binding energy exhibits a marked departure from the behavior observed in under and optimally doped cuprates. The relevance of these findings to scattering, many-body, and quantum-critical phenomena is discussed.Comment: Revised manuscript, in press on PRL. A high-resolution version can be found at http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/Tl2201_LE.pdf and related material at http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/articles.htm

Total Angular Momentum Conservation During Tunnelling through Semiconductor Barriers

We have investigated the electrical transport through strained p-Si/Si_{1-x}Ge_x double-barrier resonant tunnelling diodes. The confinement shift for diodes with different well width, the shift due to a central potential spike in a well, and magnetotunnelling spectroscopy demonstrate that the first two resonances are due to tunnelling through heavy hole levels, whereas there is no sign of tunnelling through the first light hole state. This demonstrates for the first time the conservation of the total angular momentum in valence band resonant tunnelling. It is also shown that conduction through light hole states is possible in many structures due to tunnelling of carriers from bulk emitter states.Comment: 4 pages, 4 figure

Atomic scale strain relaxation in axial semiconductor III-V nanowire heterostructures

Combination of mismatched materials in semiconductor nanowire heterostructures offers a freedom of bandstructure engineering that is impossible in standard planar epitaxy. Nevertheless, the presence of strain and structural defects directly control the optoelectronic properties of these nanomaterials. Understanding with atomic accuracy how mismatched heterostructures release or accommodate strain, therefore, is highly desirable. By using atomic resolution high angle annular dark field scanning transmission electron microscopy combined with geometrical phase analyses and computer simulations, we are able to establish the relaxation mechanisms (including both elastic and plastic deformations) to release the mismatch strain in axial nanowire heterostructures. Formation of misfit dislocations, diffusion of atomic species, polarity transfer, and induced structural transformations are studied with atomic resolution at the intermediate ternary interfaces. Two nanowire heterostructure systems with promising applications (InAs/InSb and GaAs/GaSb) have been selected as key examples

Pulsed laser deposition of atomically flat La1-xSrxMnO3 thin films using a novel target geometry

A new ablation target geometry is presented that was used to produce thin films of La1-xSrxMnO3 grown heteroepitaxially on SrTiO3 by pulsed reactive crossed-beam laser ablation. The films were grown in order to perform angle-resolved photoelectron spectroscopy, which demands that the surface be atomically flat. In situ and ex situ analysis shows that this condition was met, even after depositing to a thickness of over 100n

Effect of rare-gas adsorption on the spin-orbit split bands of a surface alloy: Xe on Ag(111)-(root 3 x root 3) R30 degrees-Bi

We have investigated by angle-resolved photoemission spectroscopy changes induced by Xe adsorption on the spin-orbit-split bands of the epitaxial Ag(111) (root 3x root 3)R30 degrees-Bi surface alloy. We observe an extensive backfolding of the alloy band structure due to the formation of a 9 x 9 commensurate or quasicommensurate Xe overlayer and the opening of a small hybridization gap at the intersection of two sets of bands of (primarily) Bi sp(z) and p(xy) characters. The large spin-orbit splitting of the substrate bands is essentially unaffected by the Xe overlayer, in sharp contrast to the enhancement reported for the clean Au(111) surface. This points to different mechanisms at the origin of the splitting in the clean surfaces and in the surface alloy

Electronic structure of an ordered Pb/Ag(111) surface alloy: Theory and experiment

We have studied by angle-resolved photoelectron spectroscopy (ARPES) the band structure of the ordered surface alloy obtained by the deposition of 0.33 monolayers of Pb on the Ag(111) surface. We observe several dispersing features which are well described as Pb-Ag hybrid bands by a band structure calculation performed within the generalized gradient approximation of density functional theory. We also find that a band of mixed Pb p(z) and Ag s character is split in momentum space. We interpret this splitting as the combined result of spin-orbit interaction and broken inversion symmetry at the surface