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711 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I06-Nanoscience (XPEEM)	3d and 5d electronic structures and orbital hybridization in Ba- and Ca-doped La2CoIrO6 double perovskites J. R. L. Mardegan , L. S. I. Veiga , T. Pohlmann , S. S. Dhesi , S. Francoual , J. R. Jesus , C. Macchiutti , E. M. Bittar , L. Bufaiçal Physical Review B 107 DOI: 10.1103/PhysRevB.107.214427 Diamond Proposal Number(s): [29620] Open Access Show Abstract ▼ Abstract: Here we present a detailed investigation of the Co and Ir local electronic structures in La 1.5 A 0.5 CoIrO 6 ( A = Ba , Ca) compounds in order to unravel the orbital hybridization mechanism in these CoIr-based double perovskites. Our results of x-ray powder diffraction, ac and dc magnetization, Co and Ir L 2 , 3 -edge and Co K -edge x-ray absorption spectroscopy and x-ray magnetic circular dichroism suggest a competition between magnetic interactions. A dominant antiferromagnetic coupling is found to be responsible for the ferrimagnetic behavior observed for A = Ca below ∼ 96 K , the competing magnetic phases, and the cationic disorder in this compound giving rise to a spin-glass state at low temperatures. For the A = Ba , on the other hand, there is no evidence of long-range order down to its spin-glass transition temperature. The remarkably different magnetic properties observed between these two compounds are discussed in terms of the structural distortion that alters the strength of the Co-Ir couplings, with a relevant role played by the Co 3 d e g – Ir 5 d j eff = 1 / 2 hybridization.	Jun 2023
I05-ARPES	A unifying phase diagram with correlation-driven superconductor-to-insulator transition for the 122 ☆ series of iron chalcogenides X. Niu , S. D. Chen , J. Jiang , Z. R. Ye , T. L. Yu , D. F. Xu , M. Xu , Y. Feng , Y. J. Yan , B. P. Xie , J. Zhao , D. C. Gu , L. L. Sun , Q. Mao , H. Wang , M. Fang , C. J. Zhang , J. P. Hu , Z. Sun , D. L. Feng Physical Review B 93 DOI: 10.1103/PhysRevB.93.054516 Diamond Proposal Number(s): [10213] Show Abstract ▼ Abstract: The 122☆ series of iron chalcogenide superconductors, for example KxFe2−ySe2, only possesses electron Fermi pockets. Their distinctive electronic structure challenges the picture built upon iron pnictide superconductors, where both electron and hole Fermi pockets coexist. However, partly due to the intrinsic phase separation in this family of compounds, many aspects of their behavior remain elusive. In particular, the evolution of the 122☆ series of iron chalcogenides with chemical substitution still lacks a microscopic and unified interpretation. Using angle-resolved photoemission spectroscopy, we studied a major fraction of 122☆ iron chalcogenides, including the isovalently “doped” KxFe2−ySe2−zSz,RbxFe2−ySe2−zTez, and (Tl,K)xFe2−ySe2−zSz. We found that the bandwidths of the low energy Fe 3d bands in these materials depend on doping; and more crucially, as the bandwidth decreases, the ground state evolves from a metal to a superconductor, and eventually to an insulator, yet the Fermi surface in the metallic phases is unaffected by the isovalent dopants. Moreover, the correlation-driven insulator found here with small band filling may be a novel insulating phase. Our study shows that almost all the known 122☆-series iron chalcogenides can be understood via one unifying phase diagram which implies that moderate correlation strength is beneficial for the superconductivity.	Feb 2016
I05-ARPES	Absence of Dirac fermions in layered BaZnBi2 S. Thirupathaiah , D. Efremov , Y. Kushnirenko , E. Haubold , T. K. Kim , B. R. Pienning , I. Morozov , S. Aswartham , B. Büchner , S. V. Borisenko Physical Review Materials 3 DOI: 10.1103/PhysRevMaterials.3.024202 Diamond Proposal Number(s): [18586] Show Abstract ▼ Abstract: Using angle-resolved photoemission spectroscopy and density functional theory (DFT) we study the electronic structure of layered BaZnBi2. Our experimental results show no evidence of Dirac states in BaZnBi2 originated either from the bulk or the surface. The calculated band structure without spin-orbit interaction shows linear band dispersions at X along the X−M high-symmetry line. In addition, the calculations suggest a gapless band crossing point along the Γ−M high-symmetry line. However, as soon as the spin-orbit interaction is turned on, the band crossing point is significantly gapped out. These observations suggest that the Dirac fermions in BaZnBi2 are trivial similar to the Dirac states observed in grapheme. The experimental observations are in good agreement with the DFT calculations.	Feb 2019
I05-ARPES	Absence of giant spin splitting in the two-dimensional electron liquid at the surface of SrTiO3 (001) Siobhan Mckeown Walker , S. Riccò , F. Bruno , Alberto De La Torre , Anna Tamai , E. Golias , A. Varykhalov , D. Marchenko , Moritz Hoesch , M. S. Bahramy , Philip King , J. Sánchez-Barriga , Felix Baumberger Physical Review B 93, 245143 DOI: 10.1103/PhysRevB.93.245143 Diamond Proposal Number(s): [11741] Show Abstract ▼ Abstract: We reinvestigate the putative giant spin splitting at the surface of SrTiO3 reported by Santander–Syro et al. [Nat. Mater. 13, 1085 (2014)]. Our spin- and angle-resolved photoemission experiments on fractured (001) oriented surfaces supporting a two-dimensional electron liquid with high carrier density show no detectable spin polarization in the photocurrent. We demonstrate that this result excludes a giant spin splitting while it is consistent with the unconventional Rashba-like splitting seen in band structure calculations that reproduce the experimentally observed ladder of quantum confined subbands.	Jun 2016
	Absence of magnetic proximity effect at the interface of Bi2Se3 and (Bi,Sb)2Te3 with EuS A. I. Figueroa , F. Bonell , M. g. Cuxart , M. Valvidares , P. Gargiani , G. Van Der Laan , A. Mugarza , S. o. Valenzuela Physical Review Letters 125, 226801 DOI: 10.1103/PhysRevLett.125.226801 Show Abstract ▼ Abstract: We performed x-ray magnetic circular dichroism (XMCD) measurements on heterostructures comprising topological insulators (TIs) of the (Bi,Sb)2(Se,Te)3 family and the magnetic insulator EuS. XMCD measurements allow us to investigate element-selective magnetic proximity effects at the very TI/EuS interface. A systematic analysis reveals that there is neither significant induced magnetism within the TI nor an enhancement of the Eu magnetic moment at such interface. The induced magnetic moments in Bi, Sb, Te, and Se sites are lower than the estimated detection limit of the XMCD measurements of ∼10−3 μB/at.	Nov 2020
I16-Materials and Magnetism	Absolute crystal and magnetic chiralities in the langasite compound Ba3NbFe3Si2O14 determined by polarized neutron and x-ray scattering N. Qureshi , A. Bombardi , S. Picozzi , P. Barone , E. Lelièvre-Berna , X. Xu , C. Stock , D. F. Mcmorrow , A. Hearmon , F. Fabrizi , P. G. Radaelli , S.-W. Cheong , L. C. Chapon Physical Review B 102 DOI: 10.1103/PhysRevB.102.054417 Diamond Proposal Number(s): [4073, 1803, 17569] Show Abstract ▼ Abstract: We present a combined polarized neutron and x-ray scattering study on two enantiopure langasite single crystals aimed at the determination of their absolute structural and magnetic chiralities and the coupling between them. Our respective data sets unambiguously reveal two samples of opposite structural chirality, where the magnetic handedness is pinned by the structural one. Simple energy considerations of the magnetic exchange and single-ion anisotropy parameters reveal that it is not the Dzyaloshinskii-Moriya interaction but the local single-ion anisotropy on a triangular plaquette which plays a key role in stabilizing one of the two magnetic helices.	Aug 2020
I05-ARPES	Accessing the spectral function in a current-carrying device Davide Curcio , Alfred J. H. Jones , Ryan Muzzio , Klara Volckaert , Deepnarayan Biswas , Charlotte E. Sanders , Pavel Dudin , Cephise Cacho , Simranjeet Singh , Kenji Watanabe , Takashi Taniguchi , Jill A. Miwa , Jyoti Katoch , Soeren Ulstrup , Philip Hofmann Physical Review Letters 125 DOI: 10.1103/PhysRevLett.125.236403 Diamond Proposal Number(s): [20218] Show Abstract ▼ Abstract: The presence of an electrical transport current in a material is one of the simplest and most important realizations of nonequilibrium physics. The current density breaks the crystalline symmetry and can give rise to dramatic phenomena, such as sliding charge density waves, insulator-to-metal transitions, or gap openings in topologically protected states. Almost nothing is known about how a current influences the electron spectral function, which characterizes most of the solid’s electronic, optical, and chemical properties. Here we show that angle-resolved photoemission spectroscopy with a nanoscale light spot provides not only a wealth of information on local equilibrium properties, but also opens the possibility to access the local nonequilibrium spectral function in the presence of a transport current. Unifying spectroscopic and transport measurements in this way allows simultaneous noninvasive local measurements of the composition, structure, many-body effects, and carrier mobility in the presence of high current densities. In the particular case of our graphene-based device, we are able to correlate the presence of structural defects with locally reduced carrier lifetimes in the spectral function and a locally reduced mobility with a spatial resolution of 500 nm.	Dec 2020
I09-Surface and Interface Structural Analysis	Adsorption height alignment at heteromolecular hybrid interfaces Benjamin Stadtmuller , Sonja Schroder , Francois Bocquet , Caroline Henneke , Christoph Kleimann , Serguei Soubatch , Martin Willenbockel , Blanka Detlefs , Jorg Zegenhagen , Tien--Lin Lee , Stefan Tautz , Christian Kumpf Physical Review B 89, 161407(R) DOI: 10.1103/PhysRevB.89.161407 Diamond Proposal Number(s): [8449, 9231] Show Abstract ▼ Abstract: The formation of metalorganic hybrid interfaces is determined by the fine balance between molecule-substrate and molecule-molecule interactions at the interface. Here, we report on a systematic investigation of interfaces between a metal surface and organic monolayer films that consist of two different molecular species, one donor and one acceptor of electronic charge. Our x-ray standing wave data show that in heteromolecular structures, the molecules tend to align themselves to an adsorption height between those observed in the respective homomolecular structures. We attribute this alignment effect to a substrate-mediated charge transfer between the molecules, which causes a mutual enhancement of their respective donor and acceptor characters. We argue that this effect is of general validity for π-conjugated molecules adsorbing on noble metal surfaces.	Apr 2014
I09-Surface and Interface Structural Analysis	Adsorption heights and bonding strength of organic molecules on a Pb-Ag surface alloy Benjamin Stadtmueller , Norman Haag , Johannes Seidel , Gerben Van Straaten , Markus Franke , Christian Kumpf , Mirko Cinchetti , Martin Aeschlimann Physical Review B 94, 235436 DOI: 10.1103/PhysRevB.94.235436 Diamond Proposal Number(s): [10370, 11915] Show Abstract ▼ Abstract: The understanding of the fundamental geometric and electronic properties of metal-organic hybrid interfaces is a key issue on the way to improving the performance of organic electronic and spintronic devices. Here, we studied the adsorption heights of copper-II-phthalocyanine (CuPc) and 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) on a Pb 1 Ag 2 surface alloy on Ag(111) using the normal-incidence x-ray standing waves technique. We find a significantly larger adsorption height of both molecules on the Pb-Ag surface alloy compared to the bare Ag(111) surface which is caused by the larger size of Pb. This increased adsorption height suppresses the partial chemical interaction of both molecules with Ag surface atoms. Instead, CuPc and PTCDA molecules bond only to the Pb atoms with different interaction strength ranging from a van der Waals–like interaction for CuPc to a weak chemical interaction with additional local bonds for PTCDA. The different adsorption heights for CuPc and PTCDA on Pb 1 Ag 2 are the result of local site-specific molecule-surface bonds mediated by functional molecular groups and the different charge donating and accepting character of CuPc and PTCDA.	Dec 2016
I09-Surface and Interface Structural Analysis	Adsorption-induced pyramidal distortion of the trimetallic nitride core inside the endohedral fullerene Sc 3 N @ C 80 on the Ag(111) surface Johannes Seidel , Leah L. Kelly , Markus Franke , G. Van Straaten , Christian Kumpf , Mirko Cinchetti , Martin Aeschlimann , Benjamin Stadtmueller Physical Review B 98, 085434 DOI: 10.1103/PhysRevB.98.085434 Diamond Proposal Number(s): [13773] Show Abstract ▼ Abstract: Our ability to understand and tailor metal-organic interfaces is mandatory to functionalize organic complexes for next generation electronic and spintronic devices. For magnetic data storage applications, metal-carrying organic molecules, the so-called single molecular magnets (SMM) are of particular interest as they yield the possibility to store information on the molecular scale. In this work, we focus on the adsorption properties of the prototypical SMM Sc3N@C80 grown in a monolayer film on the Ag(111) substrate. We provide clear evidence of a pyramidal distortion of the otherwise planar Sc3N core inside the carbon cage upon the adsorption on the Ag(111) surface. This adsorption-induced structural change of the Sc3N@C80 molecule can be correlated to a charge transfer from the substrate into the lowest unoccupied molecular orbital of Sc3N@C80, which significantly alters the charge density of the fullerene core. Our comprehensive characterization of the Sc3N@C80-Ag(111) interface hence reveals an indirect coupling mechanism between the Sc3N core of the fullerene molecule and the noble metal surface mediated via an interfacial charge transfer. Our work shows that such an indirect coupling between the encapsulated metal centers of SMM and metal surfaces can strongly affect the geometric structure of the metallic centers and thereby potentially also alters the magnetic properties of SMMs on surfaces.	Aug 2018

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