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 E41: Surface Studies of Two Dimensional MaterialsLive
|
Hide Abstracts |
Sponsoring Units: DCMP Chair: Hee Taek Yi, Rutgers, The State University of New Jersey |
Tuesday, March 16, 2021 8:00AM - 8:12AM Live |
E41.00001: Charge Instability in Single-Layer TiTe2 Mediated by van-der-Waals Bonding to Substrates Meng-Kai Lin, Joseph Hlevyack, Peng Chen, Ro-Ya Liu, Sung-Kwan Mo, Tai-Chang Chiang Single layers of transition metal dichalcogenides (TMDCs) are of interest for their emergent properties at the two-dimensional limit. However, the role of substrate effects is rarely discussed. For van-der-Waals bonding to an incommensurate substrate, the interaction can be expected to be weak, but is it negligible? Here, we report an experimental study of a model system to address this issue. The charge instability in a single-layer TiTe2 grown on PtTe2 films is examined as a function of the thickness of PtTe2 films, which are themselves grown on a bilayer-graphene-terminated SiC substrate. The results show that the (2x2) charge density wave in single-layer TiTe2 is strongly suppressed by increasing the film thickness of PtTe2. Given the interfacial bonding remains of the weak incommensurate van-der-Waals type, the observed changes are correlated with a thickness-dependent metallicity transformation in the PtTe2 substrate (from a wide-gap semiconductor to a semimetal). The results illustrate the crucial role of the substrate in single-layer physics. |
Tuesday, March 16, 2021 8:12AM - 8:24AM Live |
E41.00002: Electronic structure of VTe2 thin films studied by high-resolution ARPES Tappei Kawakami, Takemi Kato, Katsuaki Sugawara, Taiki Taguchi, Yasuaki Saruta, Takafumi Sato Atomically-thin transition metal dichalcogenides are a target of intensive studies since they show variety of exotic physical properties such as robust charge-density-waves (CDW) and two-dimensional superconductivity. We have fabricated monolayer and multilayer VTe2 thin films on bilayer graphene by molecular-beam-epitaxy method and studied their electronic states by angle-resolved photoemission spectroscopy. We clearly found a drastic difference in the Fermi-surface topology between monolayer and multilayer VTe2 films, suggesting an occurrence of structural phase transition from regular octahedral (1T) to distorted octahedral (1T') phase. We discuss the origin of structural phase transition in terms of the CDW and Jahn-Teller effect. |
Tuesday, March 16, 2021 8:24AM - 8:36AM Live |
E41.00003: High-Tc Two-dimensional Ferromagnetism in Epitaxial CrTe2 Nanofilms Xiaoqian Zhang, Qiangsheng Lu, Jacob Cook Layered compounds and thin films with intrinsic 2D ferromagnetism provide extraordinary functionalities for device applications. However, 2D magnetic materials usually exhibit weak magnetic ordering temperature compared to conventional bulk magnets due to the reduced dimensionality. We report the growth and properties of a new 2D ferromagnet, CrTe2, with an intrinsic Curie temperature (Tc) of ~250 K for thin films ranging from 3 monolayer (ML) to 15 ML. The high Tc is preserved with film thickness down to 3 ML, which is consistent with weak interlayer magnetic coupling. Using the synchrotron-based X-ray technique, the atomic magnetic moment was identified as ~3 μB per atom. The intrinsic Tc and atomic magnetic moments are the highest among the known 2D magnetic materials. Using angle-resolved photoemission spectroscopy (ARPES), we observed the splitting of majority and minority electronic states of the nanofilms, which indicates the spin polarized electronic structure of the 2D magnet. Our work identifies the remarkable robustness of magnetic order in epitaxial CrTe2 nanofilms which provides an ideal material infrastructure for studying spin physics and exploring new applications of nano-spintronics. |
Tuesday, March 16, 2021 8:36AM - 8:48AM Live |
E41.00004: Softening phonon modes drive the structural phase transition in silicene John Villanova, Salvador Barraza-Lopez
|
Tuesday, March 16, 2021 8:48AM - 9:00AM Live |
E41.00005: Scanning Tunneling Microscopy and Spectroscopy (STM/S) Reveals Small Energy Gap of CrBr3 Dinesh Baral, Zhuangen Fu, Andrei S. Zadorozhnyi, Rabindra Dulal, Aaron Wang, Narendra Shrestha, Uppalaiah Erugu, Jinke Tang, Yuri Dahnovsky, Jifa Tian, Te-Yu Chien CrBr3 is a 2D van der Waals magnetic material. Despite the great attention on the magnetic properties, the electronic properties of the CrBr3 are relatively unexplored. The energy gap of CrBr3 is believed to be in the range of 1.68-2.1 eV, based on the optical measurements. Density fluctuation theory (DFT) calculations show even higher deviation in the energy gap. These controversies have indicated that the energy gap of CrBr3 is not well studied. Here, we present results from scanning tunneling microscopy and spectroscopy (STM/S) on a defect free surface that is confirmed by atomic resolution topography, having much smaller energy gap (0.57 ± 0.04eV) in thick flake. The multi-peak dI/dV spectrum measured at 77K represents the energies of high density of states (DOS). The energy difference between the conduction band-valance band peak pairs in multi-peak spectrum agrees well with the reported optical transitions further confirming that the measured peaks are intrinsic to CrBr3. DFT calculations with U = 5 eV and J = 3 eV reproduce this energy gap. Finally, the mono- and bi-layer flake shows edge degradation due to ~15 minutes of air exposure during sample transfer. These observations of energy states provide important information towards the fundamental understanding of CrBr3. |
Tuesday, March 16, 2021 9:00AM - 9:12AM Live |
E41.00006: Electronic Structure of Two-Dimensional CoO2 Ann Julie Holt, Sahar Pakdel, Jonathan Rodríguez-Fernández, Yu Zhang, Davide Curcio, Zhaozong Sun, Paolo Lacovig, Jeppe V. Lauritsen, Silvano Lizzit, Nicola Lanata, Philip Hofmann, Marco Bianchi, Charlotte Sanders The transition metal oxide CoO2 forms layered bulk “pseudo-two-dimensional” structures that exhibit correlated electronic states and a complex interplay between superconductivity and charge/spin ordering. Recently, it has been shown [1] that CoO2 can be stabilized in the single-layer limit. However, little has been known about the single layer’s electronic structure. We have now studied the crystalline and electronic structure of single-layer epitaxial CoO2/Au(111). Angle-resolved photoemission spectroscopy (ARPES) reveals a band structure with parallels to that of the superconducting layered bulk material Na0.35CoO2 ● 1.3H2O. Using x-ray photoelectron diffraction, we have obtained detailed information about the crystal structure, and have used this information as a basis for density functional theory calculations to support the interpretation of our ARPES data. The results emphasize the interest of oxides as a new subject within two-dimensional materials research. They also contribute to our understanding of the electronic properties of layered bulk crystals based on CoO2. [1] ACS Nano 9 (2015) 2445 |
Tuesday, March 16, 2021 9:12AM - 9:24AM Live |
E41.00007: Broken Myth of Inter-layer Electronic Decoupling at ReS2: Theoretical understanding, experimental corroboration and application Debjani Karmakar, Tuhin Maji, Anasuya Karmakar, Ranjit Hawaldar, Kausik Majumdar, K V Adarsh, Samit Kumar Ray ReS2 had generated unresolved controversies about its inter-layer electronic coupling, layer-dependent optical response and electronic structure. While earlier studies predict electronically decoupled layers, experimental reports manifest layer dependent optical response and 3D electronic dispersion across the van der Waals gap. Using DFT and TDDFT, we resolved the structural and electronic disputes of ReS2. The ReS6 face-shared distorted octahedral chain along b-axis are bridged along a-axis via a couplet of face-shared warped ReS5 square pyramides. The coordination of S-atoms in ReS5 controls the inter and intra-layer electronic dispersion, leading to an indirect and direct bandgap in monolayers and bulk respectively. Next, we have grown large-area CVD films of ReS2. With increasing temperature, it shows a tendency of vertical growth. The TEM micrograph of the films suggests the same crystal structure as per the theoretical outcome. The static and transient optical studies clearly indicates the presence of both excitons. After an optimization of growth temperature, the film with best optical response is demonstrated to have an optoelectronic application having a good responsivity and detectivity. |
Tuesday, March 16, 2021 9:24AM - 9:36AM Live |
E41.00008: Amorphous WSi2 Thin Film Growth: Exploring Nanoscale Local Dynamics versus Average Kinetics Chenyu Wang, Christa Wagenbach, Jeffrey G Ulbrandt, Meliha Gozde Rainville, Suresh Narayanan, Hua Zhou, Randall L Headrick, Karl F Ludwig We have studied the average kinetics and real-time dynamics during amorphous WSi2 film growth as a function of pressure by means of X-ray photon correlation spectroscopy (XPCS). It's known that, as a consequence of kinetic behavior, there is a transition from smooth to rough growth surfaces with increasing pressure. It's observed that the speckle-averaged X-ray scattering intensity doesn't change after the film reaches a kinetic steady-state. Timescale parameters were determined for each pressure condition. Peaks found in intensity vs. time curves characterize the time when the local roughness is maximum at the length scale 2π/q//. Dynamic behavior is analyzed by means of two-time correlation functions and g2 functions. The timescales for reaching dynamic and kinetic steady states, and the correlation time of surface structure in the final dynamic steady state all decrease as growth pressure and final surface roughness increase. In high q// regions, an average local structure may be stabilized while deposition, relaxation and coarsening in nanoscale have not yet reached a dynamic equilibrium. |
Tuesday, March 16, 2021 9:36AM - 9:48AM Live |
E41.00009: Interface-enhanced superconductivity of single layer FeSe grown on non-TiO2 based oxides Yuan-He Song, Xia Lou, Xiaoyang Chen, Qinghua Zhang, Lin Gu, Zheng Chen, Yan-Wu Xie, Xiaofeng Xu, Xuetao Zhu, Jiandong Guo, Ran Tao, Tianlun Yu, Hao Ru, Yi-Hua Wang, Haichao Xu, Rui Peng, Donglai Feng The single layer FeSe film on SrTiO3 indicates that interfaces can play a significant role in high-temperature superconductivity. Here we report a new FeSe-based interface, single layer FeSe grown on non-TiO2 based oxides by molecular beam epitaxy (MBE) method, was successfully obtained. The structure of the interface was determined by high resolution transmission electron microscopy (HRTEM). The angle-resolved photoemission spectroscopy (ARPES) shows that it is superconducting with a large gap, while the ex-situ mutual inductance measurements indicate it has a high onset temperature for diamagnetism. This heterostructure can provide a new platform for understanding the interface-enhanced superconductivity. |
Tuesday, March 16, 2021 9:48AM - 10:00AM Live |
E41.00010: Defect Engineering within Transition Metal Dichalcogenides Using Magnetic and Rare-Earth Metals John Thomas, Katherine Cochrane, Alexander Weber-Bargioni Monolayer transition metal dichalcogenides (TMDs), such as WS2 and WSe2, have gained substantial interest for point-defect control, serving as host substrates for quantum emitters, exhibiting spin-valley splitting properties, and showing capability towards tunable band gap engineering. Sulfur vacancies can be controllably created to serve as target sites for photo- and spin- active functionalization [e.g., decorated cobalt or rare-earth atoms in TMDs]. Scanning probe microscopy (held in ultra-high vacuum and low temperature) can measure the electronic characteristics at the atomic level of induced defects, while also providing a path to excite single-defect optical transitions. Here, we delve into filling defect vacancies in synthetic host TMD materials to enable investigations in localized photon emission, determine spin-orbit interaction, and identify subsequent band structure with scanning probe microscopy and spectroscopy. The nature and study of adsorbed metals on heterostructure materials, with induced defectivity and new routes for subsequent defect functionalization, provide growth and impact in the fields of next-generation color centers and two-dimensional quantum materials. |
Tuesday, March 16, 2021 10:00AM - 10:12AM Live |
E41.00011: Spin-Orbit-Induced Topological Flat Bands in Line and Split Graphs of Bipartite Lattices. Da-Shuai Ma, Yuanfeng Xu, Christie S. Chiu, Nicolas Regnault, Andrew Houck, Zhida Song, Andrei B Bernevig Topological flat bands, such as the band in twisted bilayer graphene, are becoming a promising platform to study topics such as correlation physics, superconductivity, and transport. In this work, we introduce a generic approach to construct two-dimensional (2D) topological quasi-flat bands from line graphs and split graphs of bipartite lattices. The flat band in these lattices connects to the dispersive bands through a degenerate state at some momentum. We find that, with spin-orbit coupling (SOC), the flat band becomes quasi-flat and gapped from the dispersive bands. We find that (i) if the flat band (without SOC) has inversion or C2 symmetry and is non-degenerate, then the resulting quasi-flat band must be topologically nontrivial, and (ii) if the flat band (without SOC) is degenerate, then there exists an SOC potential such that the resulting quasi-flat band is topologically nontrivial. This generic mechanism serves as a paradigm for finding topological quasi-flat bands in 2D crystalline materials and meta-materials. |
Tuesday, March 16, 2021 10:12AM - 10:24AM Live |
E41.00012: Construction of graphene/silicene heterostructure by Si intercalation Geng Li, Shixuan Du, Hongjun Gao The easy oxidation of silicene in air limits its applications in device design and fabrication. Here we report the experimental fabrication of silicene protected by a graphene overlayer. The graphene layer is grown first on a Ru(0001) substrate and silicene is grown under it by Si intercalation. By controlling the amount of silicon, ordered arrays of pseudomorphic silicene nano flakes as well as single layers and multilayers of silicene can be successfully fabricated under graphene that is epitaxially grown on Ru(0001). Density-functional-theory calculations show weak interactions between graphene and silicene layers, indicating that the fabricated structures are silicene/graphene van der Waals heterostructures. The as-prepared silicene-based structures show no observable damage after air exposure for two weeks. |
Tuesday, March 16, 2021 10:24AM - 10:36AM Live |
E41.00013: First-principles study on the ferroelectricity properties of two-dimensional SnTe films Meng Liu, Jia-Tao Sun, Zhaoming Fu The ferroelectric properties of low-dimensional nanomaterials have become one of the hot spots in the field of materials science. Two-dimensional (2D) SnTe films are confirmed to possess very strong in-plane ferroelectricity compared to bulk SnTe. However, the existence of surface effect and size effect restricts the application of traditional bulk ferroelectric materials at the nanoscale. Consequently, the substrate effects and single atom adsorption effects should be of great concern to control the 2D ferroelctricity. Here, these two effects on the ferroelectric properties of layered SnTe were investigated by the Vienna Ab initio Simulation Package (VASP) code based on density functional theory (DFT). Our results indicate the suitable substrates can significantly enhance the ferroelectricity of two-dimensional SnTe and the coexistence of the ferromagnetism and ferroelectric (i.e. multiferroics) is observed in some single atom adsorbed SnTe. It is found that, in Pt- and MgO-supported SnTe films, the in-plane polar displacement is significantly enhanced, with adsorbing H and B have nonzero magnetic moments and good stability. According to our study, we find two way to control the properties of 2D SnTe maybe can obtaining the multiferroicity and magnetoelectric coupling. |
Tuesday, March 16, 2021 10:36AM - 10:48AM Live |
E41.00014: Epitaxial growth of superconducting FeTe1-xSex film on a topological insulator Xiong Yao, Matthew Brahlek, Hee Taek Yi, Deepti Jain, Seongshik Oh Integrating a superconductor (SC) and a topological insulator (TI) in a heterostructure via proximity effect is a promising approach for realizing topological superconductor. In particular, superconducting Fe(Te,Se) is one of the best candidates to create such a heterostructure with chalcogenide TIs. Nonetheless, stringent lattice-matching requirement of the Fe(Te,Se) films does not allow four-fold Fe(Te,Se) layer to grow properly on six-fold TI platform, although TI films can grow well on Fe(Te,Se) via van der Waals epitaxy. Here, surprisingly we discover that Fe(Te,Se) can grow epitaxially on a TI (Bi2Te3) layer with Tc as high as 13 K. Furthermore, this is the very first TI-SC heterostructure platform that can be formed in either of TI-on-SC or SC-on-TI sequence, opening a route to unprecedented topological heterostructures such as Weyl superconductors. |
Tuesday, March 16, 2021 10:48AM - 11:00AM Live |
E41.00015: In-gap States Induced by Distortion and Topology in Ultrathin Bi(110) Films Yanfeng Lyu, Samira Daneshmandi, Shuyuan Huyan, Paul C. W. Chu Ultrathin Bi(110) films have attracted significant attention recently as a potential candidate for two-dimensional topological insulators. The topological band structure induces one-dimensional (1D) helical edge states inside bulk band gap; however, the modification of density of states on Bi atomic distortion has also been suggested. Here, we report the distortion modified electronic states of two-monolayer Bi(110) films grown on graphene/6H-SiC(0001) by using low-temperature scanning tunneling microscopy/spectroscopy. We found that the edge states are locally topographic dependent and most probably originate from distortion, which thereby gives an illusion of the appearance of nontrivial edge states. Steps from substrate, stripes and domain boundaries also induce additional site-dependent in-gap states. Besides, we located an inversion domain boundary across which atoms are configured in opposite order. The defect has extended spatial distribution and 1D parabolic energy dispersion. Hence, we suggest this defect as a very potential candidate for nontrivial 1D states. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700