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 EE10: V: 2D- Ferroelectric, Magnetic and Optical PropertiesFocus
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Sponsoring Units: DMP Chair: Salvador Barraza-Lopez, University of Arkansas Room: Virtual Room 10 |
Monday, March 20, 2023 10:00AM - 10:36AM |
EE10.00001: Sliding Ferroelectricity in 2D Materials: Related Physics and Extensions Invited Speaker: Menghao Wu The prediction of so-called "sliding ferroelectricity" has been confirmed recently in a series of experiments that have stimulated remarkable interest. Such ferroelectricity exists widely and exists only in 2D van der Waals stacked layers, where the vertical electric polarization is switched by in-plane interlayer sliding. The unique combination of intralayer stiffness and interlayer slipperiness of 2D van der Waals layers greatly facilitate such switching while still maintaining environmental and mechanical robustness at ambient conditions. This discovery broadens 2D ferroelectrics from very few material candidates to most of known 2D materials. Their low switching barriers enable high-speed data writing with low energy cost. In addition to its unique switching mode, other related new physics like Moiré ferroelectricity, metallic ferroelectricity, ferroelectric nonlinear anomalous Hall effect, sliding multiferroic couplings, as well as related extensions like semi-sliding ferroelectricity, are emerging. |
Monday, March 20, 2023 10:36AM - 10:48AM |
EE10.00002: Surface oxidation and magnetic instability of two-dimensional chromium tellurides Amanda L Coughlin, Sammy Bourji, Jun-Jie Zhang, Bingqiang Wei, Gaihua Ye, Zhipeng Ye, Jeonghoon Hong, Boris I Yakobson, Rui He, Jian Wang, Yaroslav Losovyj, Liangzi Deng, Ching-Wu Chu, Shixiong Zhang Two-dimensional (2D) chromium tellurides (Cr1+δTe2) have recently attracted growing interest owing to their versatile magnetic and electronic properties, including high-temperature perpendicular ferromagnetism, topologically nontrivial spin textures, and a large anomalous Hall effect, which offer great opportunities for 2D spintronic applications. To realize practical applications, one must also consider the stability of the 2D materials. While most 2D ferromagnets discovered thus far do not show robust stability in ambient conditions, various Cr1+δTe2 compounds have been reported to be air-stable, despite the known sensitivity of tellurides in air. In this work, we have performed detailed and systematic studies on the stability of a representative Cr1+δTe2 phase (Cr2Te3), where we evidenced its rapid oxidation in an ambient environment via dramatic changes in Raman vibrational modes, growth of oxides in X-ray photoelectron spectroscopy and transmission electron microscopy studies, as well as significant reductions of magnetization over time. Density functional theory calculations suggest that the surface oxidation of chromium tellurides is thermodynamically favorable. |
Monday, March 20, 2023 10:48AM - 11:00AM |
EE10.00003: Enhanced strong confinement in low refractive index photonic crystal slab using bound states in the continuum and its interaction with TMDCs Brijesh Kumar, Anuj k singh, Kishor K Mandal, Parul Sharma, ANSHUMAN KUMAR Radiative losses in nanophotonic devices are a fundamental challenge in their miniaturization. Plasmonic metals overcome the radiation losses, but high ohmic losses hinder the optical performance. Bound states in the continuum (BIC), help circumvent this problem. In this work, we propose a low refractive index polymeric 2D-periodic slab that supports symmetry protected BIC and accidental BIC at off-gamma point. This BIC point is very fascinating to study the exciton-cavity interaction. To study the exciton-cavity, TMDCs have the great potential to generate the exciton. This exciton is coupled with BIC mode to generate the polariton state in a strong coupling region. |
Monday, March 20, 2023 11:00AM - 11:12AM |
EE10.00004: Recent advances in engineering strategies of Bi-based photocatalysts for environmental remediation Jahan Zeb Hassan A bismuth-based material is innovative class of visible-light-driven photocatalysts that have paid a lot of attraction towards exceptional photo-oxidation capacity. Decomposition of water oxidation and organic contaminants have been documented with the aid of photocatalytic strategies. Although Bi provides advanced outcomes for photocatalysts towards energy development and environmental remediation, their productivity still is not at supreme level. Prompting recombination of e--h+ pairs (photogenerated) along with characteristic structural instability has restricted its usage. To resolve these issues, some strategies have been tendency to bismuth-rich strategy, elemental doping, facet control, defect engineering, and heterojunction. In this article, complete outline of electronic structures, fundamental compositions, and synthesis schemes have been conferred such as degradation of water pollutants, H2-evolution, and CO2 photoreduction, N2- fixation, as well as treatment of atmospheric pollutants. Utilizing the structural-property-activity associations, comprehensive methodologies for improvement of photocatalytic progress have been discussed, including oxygen vacancies (Ov), heterojunction construction, bismuth-rich strategy, and morphology. Finally, a superior understanding for development of Bi-based photocatalysts and realistic design headed for environmental remediation via solar energy harvesting are outlined |
Monday, March 20, 2023 11:12AM - 11:24AM |
EE10.00005: Autonomous experimentation in 4D-STEM and EELS with deep kernel learning Kevin M Roccapriore, Maxim Ziatdinov, Ondrej Dyck, Ayana Ghosh, Sergei V Kalinin In the scanning transmission electron microscope (STEM), a variety of techniques exist to characterize matter at atomic and nanometer scales. Electron energy loss spectroscopy (EELS) and 4D-STEM allows to study electronic, vibrational, chemical, and structural properties of a specimen. The locations from which to acquire such data is chosen by the operator. There exists a vast and unexplored space within a given sample, where many features may be overlooked due to operator bias. The measurement location for EELS or diffraction data are chosen based on structure, typically in the form of high angle annular dark field (HAADF)-STEM images. |
Monday, March 20, 2023 11:24AM - 11:36AM |
EE10.00006: Strong Terahertz Field Induced Nonlinear Optical Effects in WSe2 and MoS2 Yun-Shik Lee, Viela A Guay, Spencer G Thorp, Yue Zhang, Arend van der Zande, Matthew Graham We study the effect of intense THz fields on the optical properties in WSe2 and MoS2, observing optical transmission through CVD grown large-grain samples. The transition metal dichalcogenides (TMDs) are 2D semiconductors exhibiting strong optical responses of excitonic nature. We employ time-resolved optical-pump/THz-probe and THz-control/optical-probe spectroscopy to investigate the ultrafast dynamics of photocarriers and nonlinear optical effects in TMD monolayer and multilayers induced by strong THz fields. We optically excite the sample with 400 or 800-nm, 100-fs pulses, where the photocarriers are injected at different side valleys. The optical excitation above the bandgap induce large absorption of THz radiation in the sample, while the unexcited sample, an insulator, is transparent in the THz range. The photocarrier relaxation shows distinctive dynamics depending on the sidevalleys where they are injected. The relaxation dynamics depends not only on the optical pump intensity and the photon energy, but also on the THz field strength. Furthermore, the strong THz fields produce large modulation of optical transmission, where the sign of change depends on the excitation photon energy. The differential transmission increases linearly with the THz field strength. The nonlinear optical effects exhibit sub-picosecond dynamics, comparable to the THz pulse duration. The optical responses are not completely transient, indicating that the THz induced modulation of the photocarrier relaxation occurs in several hundreds of femtosecond. The measurements on the high-field photocarrier dynamics provide insight into the light-matter interaction with many-bodies in the 2D semiconductors. |
Monday, March 20, 2023 11:36AM - 11:48AM |
EE10.00007: Nanoscale Imaging of Local Vibrational States and Phonon Dynamics at Interfaces Xingxu Yan, Chaitanya A Gadre, Xiaoqing Pan As the minimization of microelectronic devices continues, nanoscale thermal interface conductance becomes increasingly important in dissipating the heat flux generated in integrated circuits and helps prolong their lifetime. Phonon transport can be greatly modulated by interfaces between two differing materials. Thus, uncovering nanoscale phonon transport mechanisms at interfaces is crucial for heat management in operating electronics. However, it is challenging to detect local phonon properties due to the lack of effective experimental tools to investigate nanoscale vibrational spectra. Recent developments in monochromated electron energy-loss spectroscopy (EELS) have enabled the acquisition of vibrational spectra with few-meV energy resolution and sub-nm spatial resolution [1]. We developed a series of novel space- and angle-resolved vibrational EELS methods [2] to probe local vibrational states and phonon dynamics at diverse interfaces. Interfacial phonon modes at around 48 meV are observed in Si-Ge heterojunctions and confined to within a few nanometers of the interface [3]. Using our differential phonon momentum mapping method, we revealed a strong specular reflection of Si optical phonons at compositionally abrupt interfaces between Si and SiGe QDs [4]. Our work charts a definitive course for investigating local phonon spectra and phonon propagation around interfaces and provides guidance for the thermal nanoengineering of electronic devices. |
Monday, March 20, 2023 11:48AM - 12:00PM |
EE10.00008: Coherent Spin-Phonon Coupling in the Layered Ferrimagnetic Crystal Mn3Si2Te6 Luis M Martinez, Prashant Padmanabhan, Srinivasa Rao SINGAMANENI, Yu Liu, Cedomir Petrovic, Marshall Campbell, Michael T Pettes, Rohit P Prasankumar Layered magnetic materials have enormous potential in enabling the next generation of high-speed nanoscale information storage and spintronic technologies. In order to realize their promise, it is of critical importance that we understand how lattice structure and magnetic order are coupled, particularly on their intrinsic ultrafast time scales. Here, we use ultrafast optical microscopy to study the coherent lattice dynamics of the pseudo-van der Waals ferrimagnet Mn3Si2Te6. Our results reveal strong coherent phonon oscillations under near-infrared pumping that persist from room temperature down to below the magnetic ordering temperature of ~75 K. An analysis of the frequency of these modes as a function of temperature highlights a significant stiffening of the oscillatory frequency across the critical temperature that cannot be explained using a thermal expansion model. Instead, we suggest that this is due to an exchange-mediated contraction of the lattice, highlighting a strong magneto-structural coupling in this material. This is mirrored in the temperature dependence of incoherent dynamics, measured across the magnetic phase transition. Our findings showcase the ultrafast dynamics in this semiconducting layered ferrimagnet and suggest a new route for their optical control through their intertwined electronic, lattice, and spin degrees of freedom. |
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