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 G44: 2D Materials: Advanced Characterization IFocus
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Sponsoring Units: DMP Chair: Ramakanta Chapai, Argonne National Laboratory Room: Room 316 |
Tuesday, March 7, 2023 11:30AM - 12:06PM |
G44.00001: Multiscale imaging of interfacial slip, heterostrain, and phase changes in deformed 2D heterostructures Invited Speaker: Arend van der Zande Mechanical strain and deformation offer an unprecedented ability to tailor the symmetry and structure of 2D materials, enabling a host of quantum phenomena like electronic and ferroic phase transitions, exciton trapping, pseudomagnetic fields, and moire engineering. We utilize atomic to microscale imaging to unravel the breakdown of continuum mechanics and new scaling laws of 2D materials under deformations including in-plane heterostrain and 3D bending. |
Tuesday, March 7, 2023 12:06PM - 12:18PM |
G44.00002: Sensing quasi-local Coulomb screening in moiré materials with planar scanning probes Laurel E Anderson, Chadwick Evans, Jordan M Fonseca, Jiaqi Cai, Andrew M Vincent, Takashi Taniguchi, Kenji Watanabe, Xiaodong Xu, Arthur W Barnard The extent to which Coulomb interactions contribute to novel emergent behavior, such as correlated insulating states, superconductivity, and linear-in-T resistivity, is a key question in studies of moiré flat band systems. Global electronic transport or compressibility measurements of mesoscopic moiré devices are highly impacted by variations in twist angle in different regions of the sample, impeding the systematic investigation of its effect on electronic behavior. Using a scanning probe terminated by a few-micron diameter metallic plane parallel to a moiré heterostructure, we can measure the electronic compressibility with scanning capacitance microscopy. Examining small regions of a large-area device, we can determine the local twist angle and compressibility in each region. As the probe is lowered toward the moiré heterostructure, image charges in the tip begin to screen Coulomb interactions in the device region below. Tuning the voltages on the tip, sample and a graphite gate beneath the device enables inquiry into how states in the moiré system are affected by changes in electron-electron interactions. We report advances in development of this novel experimental system and in our understanding of Coulomb screening in 2D heterostructures. |
Tuesday, March 7, 2023 12:18PM - 12:30PM |
G44.00003: Cooled scanning probe microscope to image electronic interactions in graphene Sagar Bhandari, Joseph D Lydon, Cody Graves, Miguel A Moya, Alexander Kanell, Samuel Lowery Scanning probe techniques such as scanning SQUID, diamond nitrogen-vacanacy magnetometry and Scanning Gate Microscopes (SGM) have revealed spatial distribution of electronic behavior indicating laminar Poiseuille flow in graphene, vortex sheets in WTe2, insulating and superconducting states in twisted bilayer graphene (tBLGs), viscous flow in GaAs heterostructures. However, a direct imaging of electron interaction and spatial features such as whirlpools, eddies, vortex sheets and insulating localized states in electronic flow in graphene is yet to be observed. In this talk, I will present our work on directly imaging such behavior of electrons in graphene. We propose to use combination of scanning NV center diamond magnetometry and scanning gate microscopy to image carrier collisions in graphene to explore the role they place in the Dirac fluid, Fermi liquid, and hydrodynamic flow regimes. We present our progress in building the apparatus, fabricating graphene devices and preliminary transport measurements on graphene devices. In our imaging experiment, we anticipate directly observing electrons, hydrodynamic effects such as whirlpools and vortex sheets in electron flow, and localized states related to Mott-like insulator in tBLG. |
Tuesday, March 7, 2023 12:30PM - 12:42PM |
G44.00004: Imaging nanoscale photocurrent in the twisted bilayer graphene by magneto-scanning near-field optical microscopy Zengyi Du, Makoto Tsuneto, Yinan Dong, Baichang Li, Zijian Zhou, Micheal Dapolito, Wenjun Zheng, Lukas Wehmeier, Xu Du, James C Hone, Dmitri N Basov, Mengkun Liu In graphene, one main mechanism for generating photocurrent is the thermoelectric effect. For the twisted bilayer graphene (TBG), photocurrent induced by optical thermoelectric effect has been used to probe the local superlattice structure and electronic structure in nanoscales1,2, while the effect of high magnetic field on nano-photocurrent has never been explored. Here in this talk, using the newly developed magneto-scanning near field optical microscopy (m-SNOM), we will show nano-photocurrent measurements in TBG samples under high magnetic field up to 7T and discuss these magneto-photocurrent phenomena in terms of thermal Nernst effect. |
Tuesday, March 7, 2023 12:42PM - 12:54PM |
G44.00005: Two-dimensional Spin Waves in CrI3 Atomic and Moiré Crystals Xiangpeng Luo, Zeliang Sun, Hongchao Xie, Gaihua Ye, Zhipeng Ye, Shaohua Yan, Yang Fu, Shangjie Tian, Hechang Lei, Kai Sun, Rui He, Liuyan Zhao Van der Waals magnets can not only host distinctive spin physics on their own, but also harbor the unprecedented tunability of magnetism and magnetic excitations. Very recent progress has been made to understand the magnetic ground states in atomically thin CrI3 samples, both in the form of natural few-layers and twisted moiré superlattices. However, the exploration of spin waves–collective magnetic excitations–has been limited to natural bilayer CrI3, more specifically, in the ferromagnetic phase above the spin flip transition at BC = 0.6 T. In this talk, we present a comprehensive polarization-resolved magneto-Raman study of spin waves in natural few-layer (monolayer to four-layer) and twisted double bilayer CrI3. We will pay particular attention to the spin waves in the antiferromagnetic phase in natural few-layer CrI3, and compare them to those in the twisted double bilayer CrI3. We will then move onwards to discuss the magnetic field dependence of spin waves in both types of systems. And finally, we will comment on the spin wave behaviors in twisted double bilayer CrI3 in the context of their reported magnetic ground states. |
Tuesday, March 7, 2023 12:54PM - 1:06PM |
G44.00006: Investigation of moiré inhomogeneity in twisted transition metal dichalcogenide bilayers June Ho Yeo, Liuyan Zhao Twist angle is an important design parameter in two-dimensional (2D) moiré materials. Much of the novel physical phenomena found in twisted homobilayers of 2D atomic crystals are highly sensitive to the twist angle, or equivalently, the moiré superlattice periodicity. It has been suggested that local variations of twist angle may be introduced in moiré materials due to factors including anisotropy inherent in the fabrication process and structural distortion due to the interaction between constituent monolayers. As a result, moiré inhomogeneity is introduced in moiré crystals, in analogy to atomic inhomogeneity in regular crystals. In this talk, we will report our investigation of moiré inhomogeneity at mesoscopic scales in twisted transition metal dichalcogenide (TMD) homobilayers probed by scanning rotational anisotropy second harmonic generation (RA-SHG) microscopy. We will leverage the high angular resolution and the intensity sensitivity of our RA-SHG microscopy to map out the twist angle variations and interlayer coupling of the twisted TMD bilayers. Furthermore, we will compare this moiré inhomogeneity mapping with the spatially dependent exciton landscape. Finally, we will comment on frequency-resolved SHG in conjunction with moiré electronic band structures. |
Tuesday, March 7, 2023 1:06PM - 1:18PM |
G44.00007: Abstract Withdrawn
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Tuesday, March 7, 2023 1:18PM - 1:30PM |
G44.00008: Structural characterization of few-layer chromium trihalides using 4D-STEM Hem Prasad Bhusal, Koichi Tanaka, Colin Ophus, Karen Bustillo, Jim Ciston, Carlos Gonzalez, Samuel Mcnair, Maximo Rocha, Aiming Yan The recent discovery of long-range magnetic ordering in atomically thin chromium trihalides (CrX3; X = Cl, Br, I) have attracted significant interest due to having the tremendous opportunities for exploring novel magnetic phenomena at the two-dimensional (2D) limit [1]. In this study, we characterize the crystal structure including various stacking sequences of few-layer chromium trichlorides using a four-dimensional scanning transmission electron microscopy (4D-STEM). 4D-STEM allows us to directly quantify local structure, deformation, and different stacking sequences [2]. In order to make a chromium trichloride TEM sample, we exfoliate bilayer or trilayer chromium trichloride flakes and encapsulate them with two few-layer graphene sheets inside the glovebox. The encapsulation is necessary because chromium trichlorides are sensitive to air and moisture. The 2D heterostructure is then transferred onto a quantifoil TEM substrate and studied under TEM. By using 4D-STEM, we are able to identify different stacking orders based on crystallographic symmetry in our bilayer and trilayer chromium trichloride samples. In CrX3, the stacking sequence dictates the magnetic ordering [3]. Therefore, our study is a crucial step toward controlling the magnetic properties of few-layer chromium trichlorides.
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Tuesday, March 7, 2023 1:30PM - 2:06PM |
G44.00009: Impact of strong quantum spin fluctuations on the magnetism, the excitons, and the spin waves in a two-dimensional XY-type magnetic system Invited Speaker: Zeliang Sun The newly emergent two-dimensional (2D) van der Waals (vdW) magnets provide an ideal platform to understand the interplay between quantum fluctuations and symmetry breaking orders. Among them, the antiferromagnet NiPS3 has drawn tremendous attention due to the possible realization of 2D XY model in its 2D limit, as well as its exceptionally sharp exciton mode. In this talk, I will show our recent optical spectroscopy results on bulk and few-layer NiPS3. First, I will use Raman signatures of spin fluctuations, magnetism-induced broken translational symmetry and broken rotational symmetry to show the dimensionality crossover of the magnetic state in NiPS3 from the long-range antiferromagnetic order in bulk to the spin-induced nematic order in few-layers. Second, I will correlate the thickness, temperature, and spatial dependencies of magnetism to the evolution of the intriguing excitons in NiPS3. Finally, I will comment on the spin waves in NiPS3 and their thickness dependence. |
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