Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session K35: Electronic Structure of Surfaces |
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Sponsoring Units: DCMP Chair: Dan Dougherty, North Carolina State University Room: 298 |
Wednesday, March 15, 2017 8:00AM - 8:12AM |
K35.00001: Observation of oscillatory relaxation in the Sn-terminated surface of epitaxial rock-salt SnSe $\{111\}$ topological crystalline insulator Wencan Jin, Suresh Vishwanath, Jianpeng Liu, Lingyuan Kong, Rui Lou, Zhongwei Dai, Jerzy Sadowski, Xinyu Liu, Huai-Hsun Lien, Alexander Chaney, Junzhang Ma, Tian Qian, Jerry Dadap, Karsten Pohl, Shancai Wang, Jacek Furdyna, Hong Ding, Huili Xing, Richard Osgood Topological crystalline insulators have been recently observed in rock-salt SnSe $\{111\}$ thin films. Previous studies have suggested that the Se-terminated surface of this thin film with hydrogen passivation is a preferred configuration. In this work, synchrotron-based angle-resolved photoemission spectroscopy, along with density functional theory calculations, are used to demonstrate conclusively that a rock-salt SnSe $\{111\}$ thin film has a stable Sn-terminated surface. These observations are supported by low energy electron diffraction (LEED) intensity-voltage measurements and dynamical LEED calculations, which further show that the Sn-terminated SnSe $\{111\}$ thin film has undergone an oscillatory surface structural relaxation. In sharp contrast to the Se-terminated counterpart, the Dirac surface state in the Sn-terminated SnSe $\{111\}$ thin film yields a high Fermi velocity, $0.50\times10^6$m/s, which may lead to high-speed electronic device applications. [Preview Abstract] |
Wednesday, March 15, 2017 8:12AM - 8:24AM |
K35.00002: First-principles study of the electronic structure of single-layer MnX/TM(001) (X=B, N, TM=Ag, Cu) surfaces Shogo Nakamura, Yoshihiro Gohda We propose new candidates of ferromagnetic monolayer, manganese boride (MnB), on the TM(001) substrate by first--principles calculations. Ferromagnetic thin films have attracted great attention not only as key materials for developing spintronic devices but also scientific interest in the magnetic mechanism. Our calculated results show that MnB/TM(001) and MnN/TM(001) become ferromagnetic and antiferromagnetic, respectively. We have also revealed the differences of the electronic structures of MnX/TM(001), suggesting the key role of the Mn $3d_{x^{2}-y^{2}}$ contribution to the hybridization around the Fermi energy for obtaining ferromagnetism. The exchange interaction constants are also evaluated from first--principles calculations. Moreover, we show the spin band splitting of MnN/Cu(001) in only a peculiar direction, whose electron--spin degeneracy is lifted as a consequence of the strain effects induced by a lattice mismatch. [Preview Abstract] |
Wednesday, March 15, 2017 8:24AM - 8:36AM |
K35.00003: Influence of the Material Band Structure on Attosecond Many-Body Electron-Electron Interactions in Transition Metals. Cong Chen, Zhensheng Tao, Adra Carr, Piotr Matyba, Tibor Szilvási, Sebastian Emmerich, Martin Piecuch, Mark Keller, Dmitriy Zusin, Steffen Eich, Markus Rollinger, Wenjing You, Stefan Mathias, Uwe Thumm, Manos Mavrikakis, Martin Aeschlimann, Peter Oppeneer, Henry Kapteyn, Margaret Murnane Many-body electron-electron interactions play prominent roles in correlated electron systems. Here we show that by using attosecond pulse trains, we can observe many-body electron-electron interactions that occur on attosecond timescales during photoemission. We extract the time delays associated with photoemission from occupied bands in Ni and Cu into free-electron final states. This allows us to show that photoemission from the $d$ band of Cu is delayed by \textasciitilde 100 attoseconds relative to photoemission from the same band of Ni. We attribute this difference to the fact that the $d$ band in Ni is not fully occupied, resulting in enhanced electron-electron scattering. Finally, we present a unified picture of electron-electron interactions in transition metals across a broad energy range, from \textasciitilde 0.5eV to 40eV. [Preview Abstract] |
Wednesday, March 15, 2017 8:36AM - 8:48AM |
K35.00004: Direct time-domain observation of attosecond final-state lifetimes in photoemission from solids Wenjing You, Zhensheng Tao, Cong Chen, Tibor Szilvasi, Mark Keller, Manos Mavrikakis, Henry Kapteyn, Margaret Murnane Recently, attosecond spectroscopic techniques have made it possible to measure differences in transport times for photoelectrons from localized core levels and delocalized valence bands in solids. Here, we report the application of attosecond pulse trains to directly and unambiguously measure the difference in lifetimes between photoelectrons born into free-electron-like states and those excited into unoccupied excited states in the band structure of nickel (111). A significant increase in lifetime of 212 $\pm$ 30 as occurs when the final state coincides with a short-lived excited state. Moreover, a strong dependence of this lifetime on emission angle is directly related to the final-state band dispersion as a function of electron transverse momentum. This finding emphasizes the importance of the material band structure on photoemission lifetimes and corresponding electron escape depths. [Preview Abstract] |
Wednesday, March 15, 2017 8:48AM - 9:00AM |
K35.00005: Photon energy dependent circular dichroism in angle-resolved photoemission from Au(111) surface states Hanyoung Yoo, Inkyung Song, Beomyoung Kim, Soohyun Cho, Shoresh Soltani, Timur Kim, Moritz Hoesch, Choong H. Kim, Changyoung Kim Circular dichoism in angle-resolved spectroscopy (CD-ARPES) has been widely used because of their potential possibility as a tool to investigate various physical aspects on electronic system. In spite of this intense interest to CD-ARPES, there is still controversy about the major factor of CD signal. To elucidate the major factor of CD, we performed ARPES experiments on Au(111) surface with circularly polarized light. Data were taken with photon energies in the range between 20 and 100 eV in order to investigate the photon energy dependent behavior in the CD. The sign of CD does not change for the photon energy within the range, inconsistent with the previous the density-functional theory (DFT) calculation. With the help of the DFT calculation with free electron final state, our results indicate that the dominant factor of CD is the orbital angular momentum (OAM) in initial state and the final state effect does minor role in CD. [Preview Abstract] |
Wednesday, March 15, 2017 9:00AM - 9:12AM |
K35.00006: Designing the Rashba spin texture by adsorption of inorganic molecules Rico Friedrich, Vasile Caciuc, Gustav Bihlmayer, Nicolae Atodiresei, Stefan Bl\"ugel We present an approach in which we show that the spin texture of a surface Rashba system can be adjusted by the adsorption of molecules. By selecting physisorbed and chemisorbed inorganic molecules on the BiAg$_2$/Ag(111) surface alloy [1] we demonstrate from \emph{ab initio} that both the spin-orbit splitting and the spin direction of Rashba-split surface states can be controlled selectively. The physisorption of NH$_3$ gives rise to a slightly enhanced outward buckling of the surface Bi which enlarges the magnitude of the Rashba splitting. On the contrary, the weak chemisorption of BH$_3$ defines a strong inward relaxation of the surface Bi. This causes the occupied Rashba split state to shift into Ag bulk states. In addition a new Rashba splitting is created in an unoccupied state upon BH$_3$ adsorption. Most importantly, in contrast to the clean surface [1] in case of the BH$_3$-BiAg$_2$/Ag(111) system the out-of-plane spin polarization is significantly larger than the in-plane one. \newline [1] C. R. Ast, \emph{et al.}, PRL \textbf{98}, 186807 (2007). [Preview Abstract] |
Wednesday, March 15, 2017 9:12AM - 9:24AM |
K35.00007: Hidden phase in a two-dimensional Sn layer stabilized by modulation hole doping. Fangfei Ming, Daniel Mulugeta, Weisong Tu, Tyler Smith, Paolo Vilmercati, Geunseop Lee, Ying-Tzu Huang, Renee Diehl, Paul Snijders, Hanno Weitering Semiconductor surfaces and ultrathin interfaces exhibit an interesting variety of two-dimensional (2D) quantum matter phases, such as charge density waves, spin density waves, and superconducting condensates. Yet, the electronic properties of these broken symmetry phases are extremely difficult to control due to the inherent difficulty of doping a strictly 2D material without introducing chemical disorder. The solution to this problem would allow access to novel phases of matter, and could open up completely new directions in surface physics and quantum matter research. Here we successfully exploit a modulation doping scheme to uncover, in conjunction with a scanning tunneling microscope tip-assist, a hidden equilibrium phase in a hole-doped bilayer of Sn on Si(111). This new phase is intrinsically phase separated into insulating domains with polar and non-polar symmetries. Its formation involves a spontaneous symmetry breaking process that appears to be electronically driven, notwithstanding the lack of metallicity in this system. This modulation doping approach promises new avenues for exploring competing quantum matter phases on a silicon platform. [Preview Abstract] |
Wednesday, March 15, 2017 9:24AM - 9:36AM |
K35.00008: Ferromagnetism in 3$\times$3 Pb/Ge(111) and Sn/Ge(111) Surface Reconstructions Geovani Montoya, Jose Rodriguez We look for magnetic instabilities in 3$\times$3 surface reconstructions of Pb/Ge(111) and of Sn/Ge(111) by studying the one-orbital Hubbard model over a honeycomb-distorted triangular lattice at half filling. Two graphene-like bands exist above and below the Fermi level. A flat band that crosses the Fermi level lies in between them. It results in a large density of states at the Fermi level. We thereby predict a Stoner ferromagnetic instability at weak on-site Coulomb repulsion. It is consistent with the surface ferromagnetism predicted previously at large on-site Coulomb repulsion on the basis of the spin-1/2 Heisenberg model over the honeycomb-distorted triangular lattice[1]. Comparison of the magnetic energy gain with the elastic energy cost at the surface yields a threshold coupling strength for the electron-phonon interaction related to the 3$\times$3 reconstruction. [1] J.P. Rodriguez and E. Artacho, Phys. Rev. B 59, R705 (1999). [Preview Abstract] |
Wednesday, March 15, 2017 9:36AM - 9:48AM |
K35.00009: Magnetic Dirac Fermions and Chern Insulator Supported on Pristine Silicon Surface Huixia Fu, Zheng Liu, Jia-Tao Sun, Sheng Meng Emergence of ferromagnetism in non-magnetic semiconductors is strongly desirable, especially in topological materials thanks to the possibility to achieve quantum anomalous Hall effect. Based on first principles calculations, we propose that for Si thin film grown on metal substrate, the pristine Si(111)-r3xr3 surface with a spontaneous weak reconstruction has a strong tendency of ferromagnetism and nontrivial topological properties, characterized by spin polarized Dirac-fermion surface states. In contrast to conventional routes relying on introduction of alien charge carriers or specially patterned substrates, the spontaneous magnetic order and spin-orbit coupling on the pristine silicon surface together gives rise to quantized anomalous Hall effect with a finite Chern number $C =$ -1. This work suggests exciting opportunities in silicon-based spintronics and quantum computing free from alien dopants or proximity effects. [Preview Abstract] |
Wednesday, March 15, 2017 9:48AM - 10:00AM |
K35.00010: Direct measurement of quantum capacitance transition with variable tunneling barriers Bernat Olivera, Benjamin Hammann, Joaquin Fernandez-Rossier, Carlos Untiedt Electrical current measurements on atomic-size systems accessed with Scanning Tunneling Microscope (STM) or Mechanically Controllable Break Junction (MCBJ) techniques\footnote{N. Agra\"{i}t, A. Levy-Yeyati and J.M. van Ruitenbeek. Phys. Rep. 377 (2003), 81.} are commonly studied considering only electrical conductance. Fully impedance (or admittance) measurements on such systems would provide greater understanding and new physical phenomena to be studied. In the present work we show simultaneous conductance-capacitance measurements at variable tunneling junctions. We use STM technique under cryogenic conditions, where vacuum acts as the barrier, and tip and sample consist of faced-sharpened tips made out of the very same pure metal. With a four-probe AC Lock-In technique we provide direct measurements of the quantum transition\footnote{T. Christen and M. B\"uttiker. Phys. Rev. Letters 77 (1996), 1.} from the purely geometrical capacitance (very long distances) to the leak of capacitance when tunneling regime is accessed\footnote{X. Zhao \textit{et al.} Phys. Rev. B 60 (1999), 24.}. [Preview Abstract] |
Wednesday, March 15, 2017 10:00AM - 10:12AM |
K35.00011: Surface roughness scattering in multisubband accumulation layers Han Fu, Konstantin Reich, Boris Shklovskii Accumulation layers with very large concentrations of electrons where many subbands are filled became recently available due to ionic liquid and other new methods of gating. The low temperature mobility in such layers is limited by the surface roughness scattering. However theories of roughness scattering so far dealt only with the small-density single subband two-dimensional electron gas (2DEG). Here we develop a theory of roughness-scattering limited mobility for the multisubband large concentration case. We show that with growing 2D electron concentration $n$ the surface dimensionless conductivity $\sigma/(2e^2/h)$ first decreases as $\propto n^{-6/5}$ and then saturates as $\sim(da_B/\Delta^2)\gg 1$, where $d$ and $\Delta$ are the characteristic length and height of the surface roughness, $a_B$ is the effective Bohr radius. This means that in spite of the shrinkage of the 2DEG width and the related increase of the scattering rate, the 2DEG remains a good metal. Thus, there is no re-entrant metal-insulator transition at high concentrations. [Preview Abstract] |
Wednesday, March 15, 2017 10:12AM - 10:24AM |
K35.00012: Signatures of Silicide Formation in Measurements of Nanoscale Interface Electrostatics with BEEM Westly Nolting, Chris Durcan, Vincent LaBella Nanoscale fluctuations in the electrostatics of a metal semiconductor interface impact performance and are important to understand and measure, which can be accomplished with ballistic electron emission microscopy (BEEM), an STM based technique. In this work, we perform BEEM on Cr/Si and W/Si Schottky contacts to visualize the interface electrostatics to nanoscale dimensions. This is accomplished by acquiring tens of thousands of spectra on a regularly spaced grid and fitting the results to determine the local Schottky barrier height. A Monte-Carlo model is then utilized to simulate the distributions of barrier heights that includes effects from the interface and transport of the hot electrons as well as indication of a multi-barrier height interface. The agreement between the measurements and modeling provides strong evidence that localized silicide formation is occurring that is difficult to observe in the average spectra or conventional current voltage measurements. [Preview Abstract] |
Wednesday, March 15, 2017 10:24AM - 10:36AM |
K35.00013: BEEMfit: Ballistic Electron Emission Microscopy Spectra Fitting for Schottky Barrier Visualization Vincent LaBella, Westly Nolting The Schottky barrier is the electrostatic barrier between rectifying metal-semiconductor interfaces that has high technological impact. Visualizing the nanoscale fluctuations in barrier height can be accomplished by mapping the barrier height with ballistic electron emission microscopy (BEEM) an STM based technique. Crucial to this technique is a high speed and robust algorithm for fitting the tens of thousands of BEEM spectra that are collected to generate the map. This presentation will describe our algorithm that fits to the simplified power law form of the Bell and Kaiser BEEM model by linearizing the data and utilizing linear regression. It searches over all possible fits and returns the Schottky barrier height $\phi_b$ and amplitude of the best fit according to the $R^2$ value. It is freely available on-line at www.labellagroup.org and does not require initial guessing of the fitting parameters that are often needed in non-linear curve fitting methods. Its performance will be demonstrated as well as the insight it provides into the physics of the interface and transport of the hot electrons by utilizing it across numerous metal-semiconductor systems. [Preview Abstract] |
Wednesday, March 15, 2017 10:36AM - 10:48AM |
K35.00014: Iridium silicide nanowires on Si(110) surface Nuri Oncel, Rasika Mohottike, Soumya Banerjee, Karren More, Deniz Cakir As continuous miniaturization challenges lithography techniques in electronics, self-assembly based processes become more attractive. One particularly important self-assembled component is metal-silicide nanowires. These type of nanowires can function as low-resistance interconnects, as fins in FinFET devices and as plasmonic interconnects in optoelectronics applications. We studied physical and electronic properties of Iridium (Ir) silicide nanowires grown on the Si (silicon) (110) surface with the help of various experimental and theoretical techniques such as Scanning Tunneling Microscopy and Spectroscopy, High Resolution Transmission Electron Microscopy (HR-TEM), X-ray Photoelectron Spectroscopy and ab-initio Density Functional Theory. The nanowires grow along the [001] direction with an average length of about 100 nm. They have a band gap of \textasciitilde 0.5 eV.~ Analysis of the HR-TEM images showed that Ir-silicide nanowires are made out of IrSi$_{2}$~lattice and they exhibit endotaxial growth. ~ Reference: ~ 1-~~~~~~Iridium-silicide nanowires on Si(110) surface, R. N. Mohattige, N. Oncel, Surf. Sci. 641, 237, 2015 [Preview Abstract] |
Wednesday, March 15, 2017 10:48AM - 11:00AM |
K35.00015: Structural Stabilities and Electronic Properties of High-Angle Grain Boundaries in Perovskite Cesium Lead Halides. Yaguang Guo Organometal trihalide perovskites are emerging as very promising photovoltaic materials, which is rivaling that of single crystal silicon solar cells despite their polycrystalline nature with relatively high density of grain boundaries (GBs). There is a lack of understanding of the effects of GBs on halide perovskites as their presence in silicon and other photovoltaic materials is generally determinated to their photovoltaic properties. Using first-principles calculations, we systematically investigate the geometric structures of high-angle tilt GBs in halide perovskites CsPbX3 (X $=$ Cl, Br, and I) by the coincidence site lattice (CSL) model and mapping their $\gamma $ surfaces. We show that, after crystal shift, $\Sigma $5(210)(0.4,0) is proved to be most stable among all the GB models. Electronic properties calculations further reveal that, different from the class GB model, GBs in halides perovskites have no harmful effects on optoelectronic properties of the bulk phase because of the large distance between the unsaturated atoms and the atomic reconstruction in the GB region. We also extend the results to MAPbI3 GBs and also show their benign effect on optoelectronic properties. [Preview Abstract] |
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