Elementary structural building blocks encountered in silicon surface reconstructions

Driven by the reduction of dangling bonds and the minimization of surface stress, reconstruction of silicon surfaces leads to a striking diversity of outcomes. Despite this variety even very elaborate structures are generally comprised of a small number of structural building blocks. We here identify important elementary building blocks and discuss their integration into the structural models as well as their impact on the electronic structure of the surface

Applications for ultimate spatial resolution in LASER based μ\mu-ARPES: A FeSe case study

Combining Angle resolved photoelectron spectroscopy (ARPES) and a $\mu$-focused Laser, we have performed scanning ARPES microscopy measurements of the domain population within the nematic phase of FeSe single crystals. We are able to demonstrate a variation of the domain population density on a scale of a few 10 $\mu$m while constraining the upper limit of the single domain size to less than 5 $\mu m$. This experiment serves as a demonstration of how combining the advantages of high resolution Laser ARPES and an ultimate control over the spatial dimension can improve investigations of materials by reducing the cross contamination of spectral features of different domains

Mealtime support for adults with intellectual disabilities: Understanding an everyday activity

Background: Mealtime support has a direct bearing on the diet-related health of men and women with intellectual disabilities as well as opportunities for expressing dietary preferences. Method: Semi-structured interviews with a sample of direct support staff providing mealtime support to adults with intellectual disabilities. Results: When managing tensions between a person's dietary preferences and ensuring safe and adequate nutrition and hydration, direct support staff are sensitive to a wide range of factors. These include the following: clinical advice; service users’ rights to choose; their (in)capacity to weigh up risks; how service users communicate; the constituents of a healthy diet; and a duty to protect service users' health. Conclusions: Those responsible for setting standards and regulating the care practices need to look beyond too simple ideas of choice and safety to recognize ways in which providing support at mealtimes is a complex activity with serious consequences for people's health and well-being

Nature of the Dirac gap modulation and surface magnetic interaction in axion antiferromagnetic topological insulator MnBi2Te4A

Modification of the gap at the Dirac point (DP) in axion antiferromagnetic topological insulator MnBi2Te4 and its electronic and spin structure have been studied by angle- and spin-resolved photoemission spectroscopy (ARPES) under laser excitation at various temperatures (9-35 K), light polarizations and photon energies. We have distinguished both large (60-70 meV) and reduced (< 20 meV) gaps at the DP in the ARPES dispersions, which remain open above the Neel temperature (T-N = 24.5 K). We propose that the gap above T-N remains open due to a short-range magnetic field generated by chiral spin fluctuations. Spin-resolved ARPES, XMCD and circular dichroism ARPES measurements show a surface ferromagnetic ordering for the "large gap" sample and apparently significantly reduced effective magnetic moment for the "reduced gap" sample. These observations can be explained by a shift of the Dirac cone (DC) state localization towards the second Mn layer due to structural disturbance and surface relaxation effects, where DC state is influenced by compensated opposite magnetic moments. As we have shown by means of ab-initio calculations surface structural modification can result in a significant modulation of the DP gap.The authors acknowledge support by the Saint Petersburg State University (Grant No. 51126254), Russian Science Foundation (Grant No. 18-12-00062 in part of the photoemission measurements and Grant No. 18-12-00169 in part of the electronic band structure calculations) and by Russian Foundation of Basic Researches (Grants Nos. 18-52-06009 and 20-32-70179) and Science Development Foundation under the President of the Republic of Azerbaijan (Grant No. EI F-BGM-4-RFTF1/2017-21/04/1-M-02). A. Kimura was financially supported by KAKENHI (Grants No. 17H06138, No. 17H06152, and No. 18H03683). S.V.E. and E.V.C. acknowledge support by the Fundamental Research Program of the State Academies of Sciences (line of research III.23.2.9). The authors kindly acknowledge the HiSOR staff and A. Harasawa at ISSP for technical support and help with the experiment. The ARPES measurements at HiSOR were performed with the approval of the Proposal Assessing Committee (Proposal Numbers: 18BG027 and 19AG048). XAS and XMCD measurements were performed at BL23SU of SPring-8 (Proposal Nos. 2018A3842 and 2018B3842) under the Shared Use Program of JAEA Facilities (Proposal Nos. 2018A-E25 and 2018B-E24) with the approval of Nanotechnology Platform project supported by MEXT, Japan (Proposal Nos. A-18-AE-0020 and A-18-AE-0042). M. M. Otrokov acknowledges the support by Spanish Ministerio de Ciencia e Innovacion (Grant no. PID2019-103910GB-I00). K. Yaji was financially supported by KAKENHI (Grants No. 18K03484)

Nature of the Dirac gap modulation and surface magnetic interaction in axion antiferromagnetic topological insulator MnBi2_2Te4_4

Modification of the gap at the Dirac point (DP) in antiferromagnetic (AFM) axion topological insulator MnBi$_2$Te$_4$ and its electronic and spin structure has been studied by angle- and spin-resolved photoemission spectroscopy (ARPES) under laser excitation with variation of temperature (9-35~K), light polarization and photon energy. We have distinguished both a large (62-67~meV) and a reduced (15-18~meV) gap at the DP in the ARPES dispersions, which remains open above the N\'eel temperature ($T_\mathrm{N}=24.5$~K). We propose that the gap above $T_\mathrm{N}$ remains open due to short-range magnetic field generated by chiral spin fluctuations. Spin-resolved ARPES, XMCD and circular dichroism ARPES measurements show a surface ferromagnetic ordering for large-gap sample and significantly reduced effective magnetic moment for the reduced-gap sample. These effects can be associated with a shift of the topological DC state towards the second Mn layer due to structural defects and mechanical disturbance, where it is influenced by a compensated effect of opposite magnetic moments

Fermi surfaces and orbital polarization in superconducting CeO0.5 F0.5BiS2 revealed by angle-resolved photoemission spectroscopy

We have investigated the electronic structure of BiS2-based CeO0.5F0.5BiS2 superconductor using polarization-dependent angle-resolved photoemission spectroscopy (ARPES), and succeeded in elucidating the orbital characters on the Fermi surfaces. In the rectangular Fermi pockets around the X point, the straight portion parallel to the ky direction is dominated by Bi 6px character. The orbital polarization indicates the underlying quasi-one-dimensional electronic structure of the BiS2 system. Moreover, distortions on tetragonally aligned Bi could give rise to the band Jahn-Teller effect