Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session L41: Electronic Properties of Surfaces, Interfaces and Thin FilmsLive
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Sponsoring Units: DCMP Chair: Daniel Dougherty, North Carolina State University |
Wednesday, March 17, 2021 8:00AM - 8:12AM Live |
L41.00001: Fizeau Drag in Graphene Plasmonics Yinan Dong, Lin Xiong, Isabelle Y Phinney, Zhiyuan Sun, Ran Jing, Alexander McLeod, Shuai Zhang, Song Liu, Haoyang Gao, Zhiyu Dong, Richard Pan, James Edgar, Pablo Jarillo-Herrero, Leonid Levitov, Andrew Millis, Michael Fogler, Denis Bandurin, Dmitri Basov Dragging of light by moving dielectrics was predicted by Fresnel and verified by Fizeau’s celebrated experiments with flowing water. This momentous discovery is among the experimental cornerstones of Einstein’s special relativity and is well understood in the context of relativistic kinematics. In contrast, experiments on dragging photons by an electron flow in solids are eluded in agreement with the theory. Here we report on the electron flow dragging surface plasmon polaritons (SPPs): hybrid quasiparticles of infrared photons and electrons in graphene. The drag is visualized directly through infrared nano-imaging of propagating plasmonic waves in the presence of a high-density current. The polaritons in graphene shorten their wavelength when launched against the drifting carriers. Unlike the Fizeau effect for light, the SPP drag by electrical currents defies the simple kinematics interpretation and is linked to the nonlinear electrodynamics of the Dirac electrons in graphene. The observed plasmonic Fizeau drag enables breaking of time-reversal symmetry and reciprocity at infrared frequencies without resorting to magnetic fields, or chiral optical pumping. |
Wednesday, March 17, 2021 8:12AM - 8:24AM Live |
L41.00002: Superlattice-induced Minigap in Graphene Band structure Due to Underlying Periodicity Maya Narayanan Nair, Arlensiu Celis, Muriel Sicot, Francois Nicolas, Stefan Kubsky, Amina Taleb Ibrahimi, Daniel Malterre, Antonio Tejeda Different ways of functionalization in graphene have been already demonstrated [1-3]. In our recent work, we have investigated the influence of one dimensional periodic nanostructured substrate on graphene electronic band structure. We have shown that graphene is extremely sensitive to periodic arrays, as demonstrated on two different nanostructured substrates, namely Ir(332) and Pt (111)[4]. The observed minigaps in graphene band structure by angle-resolved photoemission spectroscopy (ARPES) is related to the spatial periodicity. In this talk, I will present, the successful preparation of graphene on periodically nanostructed substrates Ir(332) and Pt(111) and associated band gap openings in its electronic structure[5,6]. |
Wednesday, March 17, 2021 8:24AM - 8:36AM Live |
L41.00003: Electronic and magnetic properties of Gr/Fe/Ir(111) heterostructure Claudia Cardoso, Giulia Avvisati, Pierluigi Gargiani, Marco Sbroscia, Madan S. Jagadeesh, Carlo Mariani, Dario Leon Valido, Daniele Varsano, Andrea Ferretti, Maria Grazia Betti Coupling Graphene with ferromagnetic systems opens perspectives of efficient injection of spin-polarized electrons in devices. We investigate a well-defined heterostructure constituted by magnetic Fe layers intercalated between graphene (Gr) and Ir(111). Fe-C solubility and Fe-Ir intermixing were avoided by atomic controlled Fe-intercalation at moderate temperature. DFT calculations and ARPES measurements show the redistribution of the electronic states due to the graphene/metal hybridization with a downshift in energy of the Dirac cone and Fe states in the energy region just below the Fermi level. X-Ray Magnetic Circular Dichroism reveals the strong ferromagnetic response of the confined Fe with enhanced spin- and orbital- moments with respect to bcc-Fe bulk. Graphene acts not only as a protective membrane, but also promotes the ferromagnetic order on the Fe layer. |
Wednesday, March 17, 2021 8:36AM - 8:48AM Live |
L41.00004: Quantum Sensing of Insulator-to-Metal Transitions in a Mott Insulator Nathan McLaughlin, Yoav Kalcheim, Albert Suceava, Hailong Wang, Chunhui Du, Ivan Schuller We studied the resistive switching properties of pristine and ion-irradiated VO2 thin film devices by performing optically detected diamond Nitrogen Vacancy (NV) electron spin resonance measurements. This switching behavior is of interest in the field of neuromorphic computing, in its potential application as an artificial neuron. Our measurements probe the local temperature and magnetic field in electrically biased VO2 devices, which agree global transport measurement results. In pristine devices, the electrically-driven IMT proceeds through Joule heating up to the transition temperature while in ion-irradiated devices, the transition occurs non-thermally, well below the transition temperature. This provides the first direct evidence for non-thermal electrically induced IMT in a Mott insulator, highlighting the significant opportunities offered by NV quantum sensors in exploring nanoscale thermal and electrical behaviors in Mott materials. |
Wednesday, March 17, 2021 8:48AM - 9:00AM Live |
L41.00005: Electron pocket and (topological) surface states of the Yb(0001) surface Gustav Bihlmayer, Polina Sheverdyaeva, Paolo Moras, Stefan Bluegel, Francesco Offi, Carlo Carbone Among the lanthanides, Yb seems simple since it is non-magnetic with a filled 4f shell, but the electronic structure still holds some surprises: In the limit of vanishing spin-orbit coupling, fcc Yb was recently identified as nodal line semimetal. We present a combined experimental and theoretical study of Yb on Mo(110) that shows that Yb grows in hcp stacking and its (0001) surface hosts two surface state where one of them is of topological origin, located in a region between two nodal lines. Angular resolved photoemission spectroscopy clearly shows an electron pocket at the zone center that can be reproduced by density functional theory calculations including Hubbard U corrections on the (unoccupied) d-orbitals. We discuss the impact of spin-orbit coupling effects and similarities to topological properties of the lighter earth-alkaline elements like Be(0001) and Ca(111). |
Wednesday, March 17, 2021 9:00AM - 9:12AM Live |
L41.00006: Atomic and Electronic Properties of Molecular Beam Epitaxy Grown Monoclinic Ag2Se Thin Film Samira Daneshmandi, Yanfeng Lyu, Hanming Yuan, Moein Adnani Takantapeh, Paul C. W. Chu Silver chalcogenides have attracted a lot of interest as promising candidates for novel topological properties. Using scanning tunneling microscopy/spectroscopy (STM/S), we characterized the atomic structure and electronic properties of monoclinic Ag2Se thin film grown on SrTiO3 (STO)(001) substrate by molecular beam epitaxy (MBE) for the first time. Three kinds of atomic terminations of Ag2Se are observed on the surface: (i) homogeneous hexagonal-like, (ii) rough mixed and (iii) flat zigzag striped structures. The structural analysis indicates that the different atomic terminations are from different growth directions which can be attributed to the lattice mismatch between substrate and Ag2Se film. The STS of these atomic terminations exhibit different features near the Fermi level, indicating constituent- and direction-dependent electronic properties. Our findings provide a convenient method to produce the Ag2Se thin film and a deeper understanding of the physical properties of this compound. |
Wednesday, March 17, 2021 9:12AM - 9:24AM Live |
L41.00007: Coherently coupled quantum-well states in bimetallic Pb/Ag thin films Chi-Ruei Pan, Woojoo Lee, Chih-Kang Shih, Mei-Yin Chou It has been well established that the presence of quantum-well states in metal thin films plays an essential role in determining the thickness dependence of many physical properties with oscillatory features. Modern film growth capability has made it possible to create composite metal thin films with precise control of individual thickness. How the original quantum-well states evolve in the composite film becomes a critical issue in understanding the electronic structure of these new complex thin-film systems. We will present first-principles calculations and measurements by angle-resolved photoemission spectroscopy for electronic states in a bimetallic film composed of ten layers of Pb and nine layers of Ag in the [111] direction on a Si substrate. We found that the original quantum-well states in individual Pb and Ag films evolve into a new set of states in the bimetallic film by extending into the additional space, instead of directly coupling with each other as one would have expected. The new set of quantum-well states therefore has modified effective masses and energy values compared with the parent ones. The excellent agreement between theory and experiment confirms the physical picture proposed in this work. |
Wednesday, March 17, 2021 9:24AM - 9:36AM Live |
L41.00008: First-Principles Theory for Schottky Barrier Physics Dmitry Skachkov, Xiaoguang Zhang, Hai-Ping Cheng We develop a first-principles theory for Schottky barrier physics. The Poisson equation is solved self-consistently with the electrostatic charge density over the entire barrier using the density functional theory (DFT) electronic structure converged locally, allowing computation of a Schottky barrier entirely from DFT involving thousands of atomic layers in the semiconductor. The induced charge in the bulk consists of conduction and valence band charges from doping and band bending, as well as charge from the evanescent states in the gap of the semiconductor. The Schottky barrier height is determined when the induced charge density and the induced electrostatic potential reach self-consistency. A tests on the GaAs – graphene and Si/Al heterostructures are presented. |
Wednesday, March 17, 2021 9:36AM - 9:48AM Live |
L41.00009: General, Strong Impurity-Strength Dependence of Quasiparticle Interference Seung-Ju Hong, Jae-Mo Lihm, Cheol-Hwan Park Quasiparticle interference patterns in momentum space give rich and important information on the underlying electronic structure of surfaces and two-dimensional materials. The quasiparticle interference patterns are often compared with impurity-independent quantities, such as the joint density of states or spin-dependent scattering probability. In this presentation, we show that the quasiparticle interference pattern is strongly dependent on the strength of the impurity even in the simplest case of a single-site impurity on the square lattice with an s orbital per site. We analyze this pattern by decomposing the pattern into an impurity-dependent T-matrix and a momentum-dependent part, the product of two Green functions. Then, we show the results of our T-matrix analysis on TaAs, an archetype Weyl semimetal, obtained with first-principles calculations. The results show very rich, impurity-dependent quasiparticle interference patterns. Thus, our study demonstrates that quasiparticle-interference patterns should be analyzed using the information on the type of impurities. |
Wednesday, March 17, 2021 9:48AM - 10:00AM Live |
L41.00010: Site-specific valence-band of Pt monolayer on SrTiO3 (001) via X-ray standing wave excited photoelectron emission Yanna Chen, Leighton Jones, Anusheela Das, Tien Lin Lee, Denis Keane, George C Schatz, Michael J Bedzyk Platinum is widely used as a heterogeneous catalyst in chemical production. The interfacial atomic behavior of the Pt/support structure in redox processes remains ambiguous. In this work, X-ray standing wave (XSW) excited photoemission was used to measure the site-specific valence band for a Pt monolayer (ML) grown on a SrTiO3 (001) substrate (Pt/STO). The Pt ML was grown by pulsed laser deposition. XSW measurements were performed at the Diamond Light Source I09 beamline on the as-deposited, oxidized and reduced surfaces, where we found that ½ of the Pt was correlated with the substrate lattice. The XSW induced modulations in the core and valence photoemission signals from the surface and substrate atoms were monitored while scanning through three different hkl substrate Bragg peaks. This information was then compared to the DFT projected density of states from the surface and substrate atoms. We find that the Pt region of the valence-band shows the biggest redox-induced changes. Furthermore, this higher activity is primarily attributed to the portion of Pt that is uncorrelated with the substrate lattice. |
Wednesday, March 17, 2021 10:00AM - 10:12AM Live |
L41.00011: Coulomb blockade effects in tunneling measurements of a topological insulator grown on a high-Tc cuprate superconductor Bryan Rachmilowitz, He Zhao, Zheng Ren, Hong Li, Konrad H Thomas, John Marangola, Shang Gao, John Schneeloch, Ruidan Zhong, Genda Gu, Christian Flindt, Ilija Zeljkovic We use molecular-beam epitaxy to grow thin films of topological insulator Bi2Te3 on a high-Tc superconductor Bi2Sr2CaCu2O8+x, and study the surface of Bi2Te3 using low-temperature scanning tunneling microscopy and spectroscopy. In few unit-cell thick Bi2Te3 films, we find a V-shaped gap-like feature at the Fermi energy in dI/dV spectra. Reducing the coverage of Bi2Te3 films to create nanoscale islands, we discover that this spectral feature dramatically evolves into a much larger hard gap, which can be understood as a Coulomb blockade gap. This conclusion is supported by the evolution of dI/dV spectra with the lateral size of Bi2Te3 islands, as well as by topographic measurements that show an additional barrier separating Bi2Te3 and Bi2Sr2CaCu2O8+x. We conclude that the prominent gap-like feature in dI/dV spectra in the Bi2Te3 films can be explained by Coulomb blockade effects, which take into account additional resistive and capacitive coupling at the interface. Our experiments provide a fresh insight into the tunneling measurements of complex heterostructures with buried interfaces. |
Wednesday, March 17, 2021 10:12AM - 10:24AM Live |
L41.00012: The interfacial effect on the anomalous Hall effect of magnetic topological insulators Hee Taek Yi, Xiong Yao, Deepti Jain, Seongshik Oh A quantum anomalous Hall effect (QAHE) has been actively researched with great attention by virtue of its fascinating emergent phenomena of quantized Hall resistance. After theoretical works proposed that the QAHE can be realized when the time-reversal symmetry is broken in topological insulators by introducing ferromagnetic orders, the QAHE of magnetic topological insulators has been experimentally confirmed by various research groups. In this presentation, we investigate the interfacial effect, interplay between magnetic topological insulators (MTIs) and capping/buffer layers. First, we applied various materials as capping layers to investigate the capping layer dependence on Hall resistance of MTIs and significant enhancement of the Hall properties has been observed in Cr capped MTIs. Second, to understand the enhanced anomalous Hall effect on Cr capped MTIs, we performed several control tests. All results point out the proximity effect between Cr capping layer and MTIs as a dominant origin of the observed enhancement. This finding of interplay exchange coupling between Cr capping layers and the MTI will serve as the new platform to explore the high-temperature quantum anomalous Hall effect on MTI. |
Wednesday, March 17, 2021 10:24AM - 10:36AM Live |
L41.00013: Revisiting the electronic structure of ErAs/GaAs(001) interface Quoc-Dai Ho, Ruiqi Hu, Garnett Bryant, Anderson Janotti Rare-earth mono-pnictides, such as ErAs, have been integrated with III-V semiconductors to form heterostructures or composite materials, aiming at applications in terahertz and thermoelectric devices, both in the form of thin films or embedded nanoparticles. These pnictides are compensated semimetals, stable in the rock salt crystal structure sharing a sub-lattice with zinc blende semiconductors such as GaAs or InGaAs. Recent developments have also aimed at transforming these rare-earth pnictides from trivial to topological semimetals under hydrostatic and epitaxial strain. Integration of these pnictides with III-V semiconductors into devices will rely on a deeper understanding of interface electronic states. Taking ErAs and GaAs as examples, we carry out first principles calculations based on hybrid density functional theory of the ErAs/GaAs(001) interface, analyzing the interface states regarding their dispersion and charge distribution both across and parallel to the interfacial plane. The results are compared with previous calculations and available experimental data. |
Wednesday, March 17, 2021 10:36AM - 10:48AM Live |
L41.00014: Tight-binding model of rare-earth mono-pnictides Ruiqi Hu, Quoc-Dai Ho, Anderson Janotti, Garnett Bryant Rare-earth mono-pnictides, represented by ErAs, are compensated semimetals stable in the NaCl-type crystal structure at normal conditions. These pnictides have been integrated with conventional III-V semiconductors, forming thin epitaxial films or embedded nanoparticles. Possible applications of these pnictides include lattice matched epitaxial metal contacts to III-V semiconductors, thermoelectrics, and sources of terahertz radiation. Many of these rare earth pnictides are magnetic are low temperatures, and some are topological semimetals. Initially thought as semiconductors, the description of the electronic structure of rare-earth pnictides varies widely in the literature, depending on of the method employed, which include DFT-LDA/GGA, DFT+U, LDA+DMFT, and hybrid functionals. In this presentation we will describe a tight-binding parameterization of ErAs and GaAs aiming at describing the electronic structure of ErAs-GaAs containing a large number of atoms that is otherwise prohibitively large for first-principles calculations. |
Wednesday, March 17, 2021 10:48AM - 11:00AM Live |
L41.00015: Effect of electric field on the electron field emission current densities of Cu and Cu-O systems: A First-Principle Approach Leopoldo Diaz, Mahdi Sanati, Ravindra P Joshi In this study we investigated the electron field emission current densities for the 100, 110, and 111 surfaces of Cu and Cu with an oxygen adlayer. Using density functional theory (DFT), we calculated the potential energies and work functions to show the effect of the electric field for the various surface orientations. Predicted trends of current densities for the Cu surfaces were found to be J111 < J100 < J110. This relation was not shown for the Cu-O surfaces and resulted in little change with increasing field for each surface. To explain these trends, we calculated the density of states (DOS), without and with an external field, and charge densities for both materials. The Cu surfaces included a broadening over the entire spectrum of the DOS indicating a delocalization of electrons, especially near the Fermi level. This broadening is absent from the Cu-O surfaces because the Cu-O bonding is able to overcome the external electric field resulting in the lack of current density change. |
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