F. Bertran

Two-dimensional electron gas with universal subbands at the surface of SrTiO3

As silicon is the basis of conventional electronics, so strontium titanate (SrTiO3) is the foundation of the emerging field of oxide electronics. SrTiO3 is the preferred template for the creation of exotic, two-dimensional (2D) phases of electron matter at oxide interfaces that have metal–insulator transitions, superconductivity or large negative magnetoresistance. However, the physical nature of the electronic structure underlying these 2D electron gases (2DEGs), which is crucial to understanding their remarkable properties, remains elusive. Here we show, using angle-resolved photoemission spectroscopy, that there is a highly metallic universal 2DEG at the vacuum-cleaved surface of SrTiO3 (including the non-doped insulating material) independently of bulk carrier densities over more than seven decades. This 2DEG is confined within a region of about five unit cells and has a sheet carrier density of ∼0.33 electrons per square lattice parameter. The electronic structure consists of multiple subbands of heavy and light electrons. The similarity of this 2DEG to those reported in SrTiO3-based heterostructures and field-effect transistors suggests that different forms of electron confinement at the surface of SrTiO3 lead to essentially the same 2DEG. Our discovery provides a model system for the study of the electronic structure of 2DEGs in SrTiO3-based devices and a novel means of generating 2DEGs at the surfaces of transition-metal oxides.

First Direct Observation of a Nearly Ideal Graphene Band Structure

Angle-resolved photoemission and x-ray diffraction experiments show that multilayer epitaxial graphene grown on the SiC(0001) surface is a new form of carbon that is composed of effectively isolated graphene sheets. The unique rotational stacking of these films causes adjacent graphene layers to electronically decouple leading to a set of nearly independent linearly dispersing bands (Dirac cones) at the graphene K point. Each cone corresponds to an individual macroscale graphene sheet in a multilayer stack where AB-stacked sheets can be considered as low density faults.

A wide-bandgap metal-semiconductor-metal nanostructure made entirely from graphene

The electronic properties of graphene are spatially controlled from metallic to semiconducting by patterning steps into the underlying silicon carbide substrate. This bottom-up approach could be the basis for integrated graphene electronics.

Direct observation of a highly spin-polarized organic spinterface at room temperature

Organic semiconductors constitute promising candidates toward large-scale electronic circuits that are entirely spintronics-driven. Toward this goal, tunneling magnetoresistance values above 300% at low temperature suggested the presence of highly spin-polarized device interfaces. However, such spinterfaces have not been observed directly, let alone at room temperature. Thanks to experiments and theory on the model spinterface between phthalocyanine molecules and a Co single crystal surface, we clearly evidence a highly efficient spinterface. Spin-polarised direct and inverse photoemission experiments reveal a high degree of spin polarisation at room temperature at this interface. We measured a magnetic moment on the molecules nitrogen π orbitals, which substantiates an ab-initio theoretical description of highly spin-polarised charge conduction across the interface due to differing spinterface formation mechanisms in each spin channel. We propose, through this example, a recipe to engineer simple organic-inorganic interfaces with remarkable spintronic properties that can endure well above room temperature.

Spin to Charge Conversion at Room Temperature by Spin Pumping into a New Type of Topological Insulator: α -Sn Films

We present results on spin to charge current conversion in experiments of resonant spin pumping into the Dirac cone with helical spin polarization of the elemental topological insulator (TI) α-Sn. By angle-resolved photoelectron spectroscopy (ARPES), we first check that the Dirac cone (DC) at the α-Sn (0 0 1) surface subsists after covering Sn with Ag. Then we show that resonant spin pumping at room temperature from Fe through Ag into α-Sn layers induces a lateral charge current that can be ascribed to the inverse Edelstein effect by the DC states. Our observation of an inverse Edelstein effect length much longer than those generally found for Rashba interfaces demonstrates the potential of TIs for the conversion between spin and charge in spintronic devices. By comparing our results with data on the relaxation time of TI free surface states from time-resolved ARPES, we can anticipate the ultimate potential of the TI for spin to charge conversion and the conditions to reach it.1 Unité Mixte de Physique CNRS/Thales, 91767 Palaiseau, France 2 Université Paris-Sud, Université Paris-Saclay, UMR137, 91767 Palaiseau, France 3 Université Grenoble Alpes, INAC-SP2M, F-38000 Grenoble, France 4 CEA, Institut Nanosciences et Cryogénie, F-38000 Grenoble, France 5 Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan 6 Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan 7 UR1 CNRS, Synchrotron SOLEIL, Saint-Aubin, 91192 Gif sur Yvette, France 8 Synchrotron SOLEIL, Saint-Aubin, 91192 Gif sur Yvette, France

Multilayer epitaxial graphene grown on the ({\rm SiC}\,\,000\bar{1}) surface; structure and electronic properties

We review the progress towards developing epitaxial graphene as a material for carbon electronics. In particular, we discuss improvements in epitaxial graphene growth, interface control and the understanding of multilayer epitaxial graphenes (MEGs) electronic properties. Although graphene grown on both polar faces of SiC will be discussed, our discussions will focus on graphene grown on the C-face of SiC. The unique properties of C-face MEG have become apparent. These films behave electronically like a stack of nearly independent graphene sheets rather than a thin Bernal stacked graphite sample. The origins of multilayer graphenes electronic behaviour are its unique highly ordered stacking of non-Bernal rotated graphene planes. While these rotations do not significantly affect the inter-layer interactions, they do break the stacking symmetry of graphite. It is this broken symmetry that leads to each sheet behaving like isolated graphene planes.

Symmetry breaking in commensurate graphene rotational stacking: Comparison of theory and experiment

Graphene stacked in a Bernal configuration (

Fermi arc electronic structure and Chern numbers in the type-II Weyl semimetal candidateMoxW1−xTe2

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Large area molybdenum disulphide-epitaxial graphene vertical Van der Waals heterostructures

relative rotations between sheets) differs electronically from isolated graphene due to the broken symmetry introduced by interlayer bonds forming between only one of the two graphene unit cell atoms. A variety of experiments have shown that non-Bernal rotations restore this broken symmetry; consequently, these stacking varieties have been the subject of intensive theoretical interest. Most theories predict substantial changes in the band structure ranging from the development of a Van Hove singularity and an angle-dependent electron localization that causes the Fermi velocity to go to zero as the relative rotation angle between sheets goes to zero. In this work we show by direct measurement that non-Bernal rotations preserve the graphene symmetry with only a small perturbation due to weak effective interlayer coupling. We detect neither a Van Hove singularity nor any significant change in the Fermi velocity. These results suggest significant problems in our current theoretical understanding of the origins of the band structure of this material.

Nesting between hole and electron pockets in Ba ( Fe 1 − x Co x ) 2 As 2 ( x = 0 – 0.3 ) observed with angle-resolved photoemission

Weyl semimetal MoxW1−xTe2 Ilya Belopolski∗,1, † Su-Yang Xu∗,1 Yukiaki Ishida∗,2 Xingchen Pan∗,3 Peng Yu∗,4 Daniel S. Sanchez, Madhab Neupane, Nasser Alidoust, Guoqing Chang, 7 Tay-Rong Chang, Yun Wu, Guang Bian, Hao Zheng, Shin-Ming Huang, 7, 10 Chi-Cheng Lee, 7 Daixiang Mou, Lunan Huang, You Song, Baigeng Wang, Guanghou Wang, Yao-Wen Yeh, Nan Yao, Julien E. Rault, Patrick Le Fèvre, François Bertran, Horng-Tay Jeng, 14 Takeshi Kondo, Adam Kaminski, Hsin Lin, 7 Zheng Liu, 15, 16, ‡ Fengqi Song, § Shik Shin, and M. Zahid Hasan 12, ¶ Laboratory for Topological Quantum Matter and Spectroscopy (B7), Department of Physics, Princeton University, Princeton, New Jersey 08544, USA The Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa-no-ha, Kashiwa, Chiba 277-8581, Japan National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, and Department of Physics, Nanjing University, Nanjing, 210093, P. R. China Centre for Programmable Materials, School of Materials Science and Engineering, Nanyang Technological University, 639798, Singapore Department of Physics, University of Central Florida, Orlando, FL 32816, USA Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, 117546, Singapore Department of Physics, National University of Singapore, 2 Science Drive 3, 117546, Singapore Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan Ames Laboratory, U.S. DOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA Department of Physics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, P. R. China Princeton Institute for Science and Technology of Materials, Princeton University, Princeton, New Jersey, 08544, USA Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin-BP 48, 91192 Gif-sur-Yvette, France Institute of Physics, Academia Sinica, Taipei 11529, Taiwan NOVITAS, Nanoelectronics Centre of Excellence, School of Electrical and Electronic Engineering, Nanyang Technological University, 639798, Singapore CINTRA CNRS/NTU/THALES, UMI 3288, Research Techno Plaza, 50 Nanyang Drive, Border X Block, Level 6, 637553, Singapore (Dated: April 26, 2016)