Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session N42: 2D Materials: Advanced Characterization IIIFocus
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Sponsoring Units: DMP Chair: Sujitra Pookpanratana, National Institute of Standards and Tech Room: Room 318 |
Wednesday, March 8, 2023 11:30AM - 12:06PM |
N42.00001: Interaction of Light with Density Waves and Other Superlattices Invited Speaker: Anshul Kogar In recent years, light has been used to manipulate the electronic properties of various charge density wave compounds. A metastable insulator-metal transition as well as mirror domain creation has been observed upon the application of a single light pulse in 1T-TaS2, while competing density waves can be observed away from thermal equilibrium in LaTe3. In this talk, I will present data demonstrating that chemical changes can also be instigated photo-thermally in the form of chemical intercalation in 1T-TaS2. Within a couple seconds of exposure to high intensity pulsed light, a polytypic structural transition can be induced along with chemical self-intercalation into the van der Waals gap. These intercalated atoms can order structurally and in other ways. Our work illustrates a new route towards photo-thermal manipulation of density wave compounds and paves the way for studies on similar quasi-two dimensional materials. |
Wednesday, March 8, 2023 12:06PM - 12:18PM |
N42.00002: An Operando Spectroscopic Imaging Ellipsometry Study of HfS2 Oxidation Irina Chirca, AbdulAziz AlMutairi, Stephan Hofmann The advancement of 2D technologies and the application potential of 2D heterostructures relies on controlled, clean interfacing. The interest in HfS2 as a 2D semiconductor is tied to its native oxide, and the potential of a well-defined interface with a stable high k dielectric. However, the understanding of the underpinning oxidation kinetics remains in its infancy, as reactions at buried interfaces are challenging to resolve across scales and at relevant conditions. |
Wednesday, March 8, 2023 12:18PM - 12:30PM |
N42.00003: Frequency-dependent Faraday and Kerr rotation in anisotropic nonsymmorphic Dirac semimetals in a magnetic field Amarnath Chakraborty, Giovanni Vignale, Guang Bian We calculate the frequency-dependent longitudinal and Hall conductivities and the Faraday and Kerr rotation angles for a single sheet of anisotropic Dirac semimetal protected by nonsymmorphic symmetry in the presence of a magnetic field induces a gap in the band structure. While the magnetic field causes a rotation of the plane of polarization of the light, the anisotropy causes the appearance of an elliptically polarized component in an initially linearly polarized beam. The two effects can be combined in a single complex Faraday rotation angle. At the zero-frequency limit, we find a finite value of the Faraday rotation angle, which is given by 2αF, where αF is the effective fine structure constant associated with the velocity of the linearly dispersing Dirac fermions. We also find a logarithmic enhancement of the Faraday (and Kerr) rotation angles as the frequency of the light approaches the absorption edge associated with the magnetic field-induced gap. While the enhancement is reduced by impurity scattering, it remains significant for attainable levels of material purity. We provide general formulas expressing the polarizations of the transmitted and reflected light as a function of frequency for arbitrary initial polarizations and arbitrary directions of incidence. These results indicate that two-dimensional Dirac materials protected by non-symmorphic symmetry are responsive to weak magnetic fields and can be used as platforms for magneto-optic applications, such as the realization of polarization-rotating devices. |
Wednesday, March 8, 2023 12:30PM - 12:42PM |
N42.00004: Angle-dependent identification of twisted bilayer graphene using multi-spectral ellipsometric contrast microscopy Teja Potocnik, Oliver Burton, Stephan Hofmann, Jack Alexander-Webber The electronic properties of bilayer graphene can be tuned by changing the relative twist angle between the two layers. Optical resonances can occur in twisted bilayer graphene due to van Hove singularities which have a twist angle dependent energy separation continuously tuneable from infrared to UV. This enhanced absorption has been demonstrated to be beneficial to the performance of photodetectors and other optoelectronic devices, motivating the development of fast, precise techniques to identify these regions. |
Wednesday, March 8, 2023 12:42PM - 12:54PM |
N42.00005: In situ nano-optical and tunneling characterization of quantum phases in TMDs Thomas P Darlington, Xuehao Wu, Madisen A Holbrook, Emanuil S Yanev, Dmitri N Basov, James C Hone, James Schuck, Abhay N Pasupathy In the monolayer, the transition metal dichalcogenides (TMD) host strongly bound exciton states. The strong light-matter interaction of these excitons, combined with large tunability via interaction with electronic and vibronic degrees of freedom have made this a hot topic in semiconductor research including observations of single-photon emitting quantum dot states and multi-exciton correlations. While these powerful connections between different material properties provide a rich physical landscape, it also poses challenges for study. Nanoscale optical probes have shown large variations in exciton emission energy and intensity that correlates with changes in the lattice and dielectric environment. Further, scanning tunneling microscopy has shown the emergence of deep localized electronic associated with structural deformations. For a full characterization, however, optical signatures must be correlated with the lattice down to the nanometer or even atomic scale. In this presentation we will demonstrate the use of a newly built low-temperature scanning tunneling microscope integrated with a nano-optical probe allowing for co-localized near-field light delivery with high intensity, with scanning tunneling current measurements. We will show the application of this tool to the monolayer TMDs, studying how the STS spectra evolve as a function of optical pump intensity. |
Wednesday, March 8, 2023 12:54PM - 1:06PM |
N42.00006: Atomic-Scale Inelastic Electron Tunneling Spectroscopic Mapping of Bilayer Borophene Hui Li, Qiucheng Li, Qiyuan Ruan, Boris I Yakobson, Mark C Hersam The synthesis of bilayer borophene was recently reported [1], but many questions remain about the atomic-scale physical and electronic properties of this new 2D phase of boron. Predicted to be a phonon-mediated superconductor [2], the low-energy electronic and vibrational properties of 2D boron are of particular interest. Here, we use atomically resolved inelastic electron tunneling spectroscopy (IETS) mapping to study bilayer borophene with a CO-functionalized scanning tunneling microscope tip. The resulting IETS spectra possess low-energy features that are distinct from single-layer borophene, providing experimental evidence for theoretically predicted interlayer vibrational modes. Moreover, IETS mapping reveals spatially resolved differences between the hollow hexagon sites and interlayer bonding sites for bilayer borophene, thus providing unprecedented atomic-scale insight into 2D boron beyond the single-atomic-layer limit. |
Wednesday, March 8, 2023 1:06PM - 1:18PM |
N42.00007: Exploring band structure in MoS2 with high harmonic generation spectroscopy Bailey R Nebgen, Lun Yue, Richard Hollinger, Can B Uzundal, Ziyang Gan, Emad Najafidehaghani, Antony George, Christian Spielmann, Daniil Kartashov, Andrey Turchanin, Diana Y Qiu, Mette B Gaarde, Michael W Zuerch Solid-state High-harmonic generation (sHHG) from intense laser pulses is being developed as a probe of ultrafast electronic processes and crystalline symmetries in condensed matter [1]. Atomically thin semiconductors such as monolayer MoS2 provide a model system in which to study band structure without the interference of light propagation effects through a bulk material [2]. In addition, few-layer transition metal dichalcogenides (TMDCs) offer a tunable material platform with unique properties to interrogate with solid-state HHG and diverse applications in optoelectronics and spintronics [3]. Here, we investigate the polarization properties of sHHG from monolayer MoS2 as a function of crystal orientation relative to the mid-IR laser field polarization [4]. We experimentally observe that crystal symmetries impose constraints on harmonic emissions, leading to pronounced nodes in the HHG spectra at certain angles. Building on previous studies,[5] we find an angular shift such that for several mid-IR wavelengths, the parallel-polarized odd-order harmonics below (above) 3.5 eV are enhanced for driver polarization along the armchair (zigzag) direction. By solving the time-dependent density matrix equations involving a valence band and two conduction bands, we trace these angular shifts to electron-hole recombinations from different conduction bands, mapping lower energy harmonics to recombinations involving the first conduction band and higher energy harmonics to recombinations involving the second conduction band. This measurement effectively probes the vectorial nature of recombination dipoles from different bands in MoS2, building up from the single conduction band picture of solid-state HHG that has been considered previously. This material specific analysis paves the way for solid-state HHG as a detailed probe of ultrafast dynamics in condensed matter systems. |
Wednesday, March 8, 2023 1:18PM - 1:30PM |
N42.00008: Probing depth-resolved electronic structure of two-dimensional layered materials and their heterostructures using standing-wave photoemission microscopy Jay R Paudel, Ryan Muzzio, Matthew E Matzelle, Florian Kronast, Slavomir Nemsak, Jouko Nieminen, Arun Bansil, Jyoti Katoch, Alexander Gray Atomically thin and ultra-flexible two-dimensional materials and their heterostructures have been extensively studied as alternative materials platforms for logic and memory devices. Here, we demonstrate the capability to extract depth-resolved electronic structural information from single monolayers of transition-metal dichalcogenides and their heterostructures using standing-wave photoemission microscopy [1-2]. Depth resolution in the measurements is achieved by generating an x-ray standing wave within the sample by using a W/C multilayer mirror substrate in the first-order Bragg reflection geometry. The standing wave is translated vertically through the samples consisting of single-layer WS2 flakes and WSe2/MoS2 heterostructures deposited or transferred on top of such substrates. Both core-level and valence-band experimental results are analyzed using x-ray optical optimization code and compared to first-principles theoretical electronic-structure calculations. |
Wednesday, March 8, 2023 1:30PM - 1:42PM |
N42.00009: Near-field Imaging of Excitons in Transition Metal Dichalcogenides Anna Roche, Rachel L Nieken, Fateme Mahdikhanysarvejahany, Takashi Taniguchi, Kenji Watanabe, Michael Koehler, David G Mandrus, John Schaibley, Brian J LeRoy Atomically thin monolayer transition metal dichalcogenides (TMDs) exhibit remarkable physical properties resulting from their reduced dimensionality. These materials give rise to an especially promising platform for fundamental studies of two-dimensional (2D) systems with wide reaching applications in optoelectronics. A direct consequence of this reduced dimensionality is the formation of strongly bound electron-hole pairs, or excitons, which govern the material's optical properties. Previous measurements of excitons in these systems have primarily relied on far-field optical spectroscopy techniques which are diffraction limited to several hundred nanometers. Here, we present a study of the exciton spectra of TMD heterostructures using a cryogenic scattering-type scanning near-field optical microscope (s-SNOM). Using a tunable visible source, we map the exciton resonances in the TMD materials with sub 100 nm spatial resolution at both room temperature and 10 K. As the temperature is lowered to 10 K, the exciton resonance spectrally blueshifts and narrows by at least an order of magnitude. These preliminary results demonstrate cryogenic visible s-SNOM to be an effective nanoscale excitonic probe. |
Wednesday, March 8, 2023 1:42PM - 1:54PM |
N42.00010: Harvesting Planck radiation for free-space optical communications in the LWIR band Haley A Weinstein, Jonathan Habif, Stephen B Cronin, Zhi Cai We demonstrate a free-space optical communication link with an optical transmitter that harvests naturally occurring Planck radiation from a warm body and modulates the emitted intensity. The transmitter exploits an electro-thermo-optic effect in a multilayer graphene device that electrically controls the surface emissivity of the device resulting in control of the intensity of the emitted Planck radiation. We design and demonstrate multiple amplitude-modulated optical communication schemes and provide a link budget for communications data rate and range based on our experimental electro-optic characterization of the transmitter. We present an experimental demonstration achieving error-free communications at one hundred bits per second over laboratory scales and discuss how to scale this to >25km links. Finally, we discuss how to apply this system to achieve steganographic communications. https://arxiv.org/abs/2210.06942 |
Wednesday, March 8, 2023 1:54PM - 2:06PM |
N42.00011: Characterizing hBN-protected atomically thin Bi2Sr2CaCu2O8+x using ultrafast optical pump-probe spectroscopy Yunhuan Xiao, Jingda Wu, Jerry I Dadap, Ziliang Ye Atomically thin high-Tc superconductor Bi2Sr2CaCu2O8+x (Bi2212) has recently been isolated successfully, which opens exciting possibilities of engineering for emergent phenomena. However, Bi2212 at its thinnest limit easily deteriorates during usual nanofabrication processes, thus calling for unconventional preparation and characterization methods. Here we present an all-optical pump-probe technique for identifying superconductivity in atomically thin Bi2212 flakes with hBN protection. As the superconducting gap opens below Tc, a slowing of the recovery dynamics is observed in the transient reflection signal. The effectiveness of hBN protection is evidenced by a sharp contrast between the hBN capped and uncapped regions. We find that the Tc in a pristine Bi2212 atomically thin flake can approach the bulk limit. Our hBN protection and optical pump-probe characterization methods can be helpful for future studies of thin Bi2212-based devices. |
Wednesday, March 8, 2023 2:06PM - 2:18PM |
N42.00012: Thermal Conductivity of Highly Anisotropic 2D Polymerized Fullerenes Milena Milich 2D polymerized fullerene sheets with weak van der Waals interfaces offer many advantages as future optoelectronic materials. To create the carbon allotrope studied in the work, magnesium is used as a dopant to create covalent bonds between fullerenes within a single plane. By locking rotation between fullerenes in the same sheet and losing a degree of motion, heat transfer is enhanced within the polymerized sheets, but remains low between the van der Waals bonded layers. |
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