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26 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I09-Surface and Interface Structural Analysis	Bi-intercalated epitaxial graphene on SiC(0001) Susanne Wolff , Mark Hutter , Philip Schädlich , Hao Yin , Monja Stettner , Sabine Wenzel , Frank Stefan Tautz , Francois Bocquet , Thomas Seyller , Christian Kumpf New Journal Of Physics DOI: 10.1088/1367-2630/ad7f7d Diamond Proposal Number(s): [26188, 33755] Open Access Show Abstract ▼ Abstract: The intercalation of graphene with suitable atomic species is one of the most frequently applied methods to decouple the graphene layer from the substrate in order to establish the classical electronic properties of graphene. In this context, we studied the bismuth (Bi) intercalation of the (6√3×6√3)R30° reconstructed so-called "zeroth layer graphene'' on SiC(0001). As reported earlier by Sohn et al. [J. Korean Phys. Soc. 78, 157 (2021)], two phases are formed depending on the amount of intercalated Bi, which in turn is controlled by the annealing temperature: The α phase, showing a 1×1 periodicity with respect to the substrate, and, at higher temperatures, the √3×√3 reconstructed β phase. We characterise both phases and the transformation from the α to the β phase by photoelectron spectroscopy, normal incidence x-ray standing waves, electron diffraction and electron microscopy. We clearly see an almost complete intercalation of the graphene layers in both phases, with strong (covalent) interaction between the topmost Si atoms of the substrate and the Bi intercalant, but only weak (van der Waals) interaction between Bi and the graphene layer. The n-doping of the graphene found for the α phase decreases continuously during the phase transformation, in agreement with a reduced density of the Bi intercalating layer. Missing core level shifts of the surface species as well as the normal incidence x-ray standing waves results indicate that all surface Si atoms remain saturated during the transition and no dangling bonds are formed. Low energy electron microscopy and diffraction reveal the coexistance of both phases after annealing to intermediate temperatures and allow a quantitative analysis of island sizes and numbers.	Sep 2024
I05-ARPES	Strong surface termination dependence of the electronic structure of polar superconductor LaFeAsO revealed by nano-ARPES Sungwon Jung , Luke C. Rhodes , Matthew D. Watson , Daniil V. Evtushynsky , Cephise Cacho , Saicharan Aswartham , Rhea Kappenberger , Sabine Wurmehl , Bernd Büchner , Timur Kim New Journal Of Physics DOI: 10.1088/1367-2630/ac9d5e Diamond Proposal Number(s): [15074, 23890] Open Access Show Abstract ▼ Abstract: The electronic structures of the iron-based superconductors have been intensively studied by using angle-resolved photoemission spectroscopy (ARPES). A considerable amount of research has been focused on the LaFeAsO family, showing the highest transition temperatures, where previous ARPES studies have found much larger Fermi surfaces than bulk theoretical calculations would predict. The discrepancy has been attributed to the presence of termination-dependent surface states. Here, using photoemission spectroscopy with a sub-micron focused beam spot (nano-ARPES) we have successfully measured the electronic structures of both the LaO and FeAs terminations in LaFeAsO. Our data reveal very different band dispersions and core-level spectra for different surface terminations, showing that previous macro-focus ARPES measurements were incomplete. Our results give direct evidence for the surface-driven electronic structure reconstruction in LaFeAsO, including formation of the termination-dependent surface states at the Fermi level. This experimental technique, which we have shown to be very powerful when applied to this prototypical compound, can now be used to study various materials with different surface terminations.	Oct 2022
	Canted standing spin-wave modes of Permalloy thin films observed by Ferromagnetic Resonance Maciej Dabrowski , Robert J. Hicken , Andreas Frisk , David G. Newman , Alpha T N'Diaye , Christoph Klewe , Padraic Shafer , Gerrit Van Der Laan , Thorsten Hesjedal , Graham Bowden New Journal Of Physics DOI: 10.1088/1367-2630/abdd6b Open Access Show Abstract ▼ Abstract: Ferromagnetic resonance (FMR) and x-ray detected FMR (XFMR) results for Permalloy (Py) and [Co/Pt]10/Py films, with and without thin Pt spacers between the [Co/Pt]10 and Py layers, are presented and discussed. The first layer [Co/Pt]10 was chosen due its characteristic perpendicular anisotropy, with the potential to pin neighboring Py spins. However, in practice, the FMR results were found to be dominated by the 50-nm-thick Py films, especially when the thickness of the Pt spacer exceeds 1.5 nm. Nonetheless, out-of-plane FMR measurements reveal interesting behavior. In particular, the uniform k=0 mode is extremely sensitive to the alignment of the magnetic field normal to the film. Misalignment by just 3° shifts the cusp, at Bappz ~ μ0M in the plot of resonance frequency against applied field, upwards to ~ 6 GHz. In addition, out-of-plane VNA-FMR maps reveal the presence of additional modes. For example, a perpendicular standing spin-wave (PSSW)-state, above the cusp at Bappz ≥ μ0M, is clearly identified. However, as the magnetic field is reduced below the cusp, the PSSW state morphs, continuously, through a series of canted spin-wave states (CSSW) into a horizontal standing spin-wave (HSSW) state, increasing in frequency to ~ 9.5 GHz. Finally, the PSSW, CSSW and HSSW states, are accurately interpreted, using a multi-layer model of the Py film.	Jan 2021
	X-ray standing wave studies of molecular adsorption: why coherent fractions matter D. P. Woodruff , D. A. Duncan New Journal Of Physics 22 DOI: 10.1088/1367-2630/abc63a Open Access Show Abstract ▼ Abstract: The normal incidence x-ray standing wave (NIXSW) technique is the primary source of quantitative experimental information on the adsorption height of many near-planar molecules on metal surfaces, of relevance to organic electronics. The technique yields two structural parameters, the coherent position and the coherent fraction. For high values of the coherent fraction the coherent position can be related directly to the adsorption height, but because the coherent fraction is effectively an order parameter, low values of this parameter are often attributed to partial disorder. It is certainly true that in depositing these large molecules on a surface it is very challenging to produce a perfectly ordered surface. However, is the type of disorder that is likely to occur able to account for no other effect on measured NIXSW data than a lowering of the coherent fraction? Here we show, by considering a wide range of possible types of 'disorder', that in almost all such situations it is improbable that the coherent positions associated with very low coherent fractions actually provide a reliable measure of the adsorption height of the ordered component, as is often assumed to be the case. As such, presentations of NIXSW data that only consider coherent position values are likely to be extremely misleading, and provide an unreliable benchmark for detailed understanding of these interfaces.	Nov 2020
E02-JEM ARM 300CF	Effects of Rashba-spin–orbit coupling on superconducting boron-doped nanocrystalline diamond films: evidence of interfacial triplet superconductivity Somnath Bhattacharyya , Davie Mtsuko , Christopher Allen , Christopher Coleman New Journal Of Physics 22 DOI: 10.1088/1367-2630/abafe9 Diamond Proposal Number(s): [18627] Open Access Show Abstract ▼ Abstract: Among the many remarkable properties of diamond, the ability to superconduct when heavily doped with boron has attracted much interest in the carbon community. When considering the nanocrystalline boron doped system, the reduced dimensionality and confinement effects have led to several intriguing observations most notably, signatures of a mixed superconducting phase. Here we present ultra-high-resolution transmission electron microscopy imaging of the grain boundary and demonstrate how the complex microstructure leads to enhanced carrier correlations. We observe hallmark features of spin–orbit coupling (SOC) manifested as the weak anti-localization effect. The enhanced SOC is believed to result from a combination of inversion symmetry breaking at the grain boundary interfaces along with antisymmetric confinement potential between grains, inducing a Rashba-type SOC. From a pronounced zero bias peak in the differential conductance, we demonstrate signatures of a triplet component believed to result from spin mixing caused by tunneling of singlet Cooper pairs through such Rashba-SOC grain boundary junctions.	Sep 2020
I05-ARPES	Electronic structure and superconductivity of the non-centrosymmetric Sn4As3 Carolina De Almeida Marques , Matthew James Neat , Chi Ming Yim , Matthew D. Watson , Luke Charles Rhodes , Christoph Heil , Kirill Pervakov , Vladimir Vlasenko , Vladimir Pudalov , Andrei Muratov , Timur Kim , Peter Wahl New Journal Of Physics DOI: 10.1088/1367-2630/ab890a Diamond Proposal Number(s): [15663] Open Access Show Abstract ▼ Abstract: In a superconductor that lacks inversion symmetry, the spatial part of the Cooper pair wave function has a reduced symmetry, allowing for the mixing of spin-singlet and spin-triplet Cooper pairing channels and thus providing a pathway to a non-trivial superconducting state. Materials with a non-centrosymmetric crystal structure and with strong spin-orbit coupling are a platform to realize these possibilities. Here, we report the synthesis and characterisation of high quality crystals of Sn4As3, with non-centrosymmetric unit cell (R3m). We have characterised the normal and superconducting state using a range of methods. Angle-resolved photoemission spectroscopy shows a multiband Fermi surface and the presence of two surface states, confirmed by Density-functional theory calculations. Specific heat measurements reveal a superconducting critical temperature of T c~ 1.14 K and an upper critical magnetic field of H cgsim 7 mT, which are both confirmed by ultra-low temperature scanning tunneling microscopy and spectroscopy. Scanning tunneling spectroscopy shows a fully formed superconducting gap, consistent with conventional s-wave superconductivity.	Apr 2020
Theoretical Physics	Expanding the Lorentz concept in magnetism Graham J. Bowden , Gerrit Van Der Laan , Thorsten Hesjedal , Robert J. Hicken New Journal Of Physics DOI: 10.1088/1367-2630/ab2f63 Open Access Show Abstract ▼ Abstract: In 1878, the Dutch physicist Hendrik Antoon Lorentz first addressed the calculation of the local electric field at an atomic site in a ferroelectric material, generated by all the other electric dipoles within the sample. This calculation, which applies equally well to ferromagnets, is taught in Universities around the World. Here we demonstrate that the Lorentz concept can be used to speed up calculations of the local dipolar field in square, circular, and elliptical shaped monolayers and thin films, not only at the center of the film, but across the sample. Calculations show that long elliptical and rectangular films should exhibit the narrowest ferromagnetic resonance linewidth. In addition, discrete dipole calculations show that the Lorentz cavity field does not hold in tetragonal films. Depending on the ratio (b/a), the local field can be either less/greater than : an observation that has implications for ferromagnetic resonance. 3D simple cubic (SC) systems are also examined. For example, while most texts discuss the Lorentz cavity field in terms of a Lorentz sphere, the Lorentz cavity field still holds when a Lorentz sphere is replaced by a the Lorentz cube, but only in cubic SC, FCC and BCC systems. Finally, while the primary emphasis is on the discrete dipole-dipole interaction, contact is made with the continuum model. For example, in the continuous SC dipole model, just one monolayer is required to generate the Lorentz cavity field. This is in marked contrast to the discrete dipole model, where a minimum of five adjacent monolayers is required.	Jul 2019
I07-Surface & interface diffraction	Bragg coherent diffraction imaging of iron diffusion into gold nanocrystals Ana Katrina Estandarte , Christopher Lynch , Marianne Monteforte , Jonathan Rawle , Chris Nicklin , Ian K. Robinson New Journal Of Physics DOI: 10.1088/1367-2630/aaebc1 Open Access Show Abstract ▼ Abstract: Understanding how diffusion takes place within nanocrystals is of great importance for their stability and for controlling their synthesis. In this study, we used the strain sensitivity of Bragg coherent diffraction imaging (BCDI) to study the diffusion of iron into individual gold nanocrystals in situ at elevated temperatures. The BCDI experiments were performed at the I-07 beamline at Diamond Light Source, UK. The diffraction pattern of individual gold nanocrystals was measured around the (11-1) Bragg peak of gold before and after iron deposition as a function of temperature and time. Phase retrieval algorithms were used to obtain real space reconstructions of the nanocrystals from their measured diffraction patterns. Alloying of iron with gold at sample temperatures of 300°C-500°C and dealloying of iron from gold at 600°C were observed. The volume of the alloyed region in the nanocrystals was found to increase with the dose of iron. However, no significant time dependence was observed for the structure following each iron deposition, suggesting that the samples reached equilibrium relatively quickly. The resulting phase distribution within the gold nanocrystals after the iron depositions suggests a contraction due to diffusion of iron. Our results show that BCDI is a useful technique for studying diffusion in three dimensions (3D) and alloying behaviour in individual crystalline grains.	Oct 2018
I05-ARPES	Electronic anisotropies revealed by detwinned ARPES measurements of FeSe Matthew Watson , Amir Abbas Haghighirad , Luke Rhodes , Moritz Hoesch , Timur Kim New Journal Of Physics DOI: 10.1088/1367-2630/aa8a04 Diamond Proposal Number(s): [12153, 15663] Open Access Show Abstract ▼ Abstract: We report high resolution ARPES measurements of detwinned FeSe single crystals. The application of a mechanical strain is used to promote the volume fraction of one of the orthorhombic domains in the sample, which we estimate to be 80% detwinned. While the full structure of the electron pockets consisting of two crossed ellipses may be observed in the tetragonal phase at temperatures above 90 K, we find that remarkably, only one peanut-shaped electron pocket oriented along the longer <i>a</i> axis contributes to the ARPES measurement at low temperatures in the nematic phase, with the expected pocket along <i>b</i> being not observed. Thus the low temperature Fermi surface of FeSe as experimentally determined by ARPES consists of one elliptical hole pocket and one orthogonally-oriented peanut-shaped electron pocket. Our measurements clarify the long-standing controversies over the interpretation of ARPES measurements of FeSe.	Sep 2017
I05-ARPES	Observation of nodal line in non-symmorphic topological semimetal InBi Sandy Adhitia Ekahana , Shu-Chun Wu , Juan Jiang , Kenjiro Okawa , Dharmalingam Prabhakaran , Chan-Cuk Hwang , Sung-Kwan Mo , Takao Sasagawa , Claudia Felser , Binghai Yan , Zhongkai Liu , Yulin Chen New Journal Of Physics DOI: 10.1088/1367-2630/aa75a1 Open Access Show Abstract ▼ Abstract: Topological Nodal Semimetal (TNS), characterised by its touching conduction and valence bands, is a newly discovered state of quantum matter which exhibits various exotic physical phenomena. Recently, a new type of TNS called Topological Nodal Line Semimetal (TNLS) is predicted where its conduction and valence band form a degenerate 1D line which is further protected by its crystal symmetry. In this work, we systematically investigated the bulk and surface electronic structure of the non-symmorphic, TNLS in InBi with strong spin-orbit coupling by using Angle Resolved Photoemission Spectroscopy (ARPES). By tracking the crossing points of the bulk bands at the Brillouin zone boundary, we discovered the nodal-line feature along the XRX line, in agreement with the ab-initio calculations and confirmed it to be a new compound in the TNLS family. Our discovery provides new material platform for the study of these exotic topological quantum phases and paves the way for possible future applications.	Jun 2017

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