Bulletin of the American Physical Society
Mid-Atlantic Section Fall Meeting 2020
Volume 65, Number 20
Friday–Sunday, December 4–6, 2020; Virtual
Session G05: Quantum Materials on Nanoscale IV (Imaging) |
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Chair: Scott A. Crooker, Los Alamos National Lab |
Saturday, December 5, 2020 4:15PM - 4:51PM |
G05.00001: Magnetic imaging of domain walls and surface magnetism in antiferromagnetic topological insulator MnBi$_2$Te$_4$ Invited Speaker: Weida Wu The control of domain walls or spin textures is crucial for spintronic applications of antiferromagnets [1,2]. Despite many efforts, it has been challenging to directly visualize antiferromagnetic domains or domain walls, especially in magnetic field [3]. In this talk, I will present our recent results of magnetic imaging of domain walls in several uniaxial antiferromagnets, including the topological insulator MnBi$_2$Te$_4$ family and topological semimetal EuMnBi$_2$, using cryogenic magnetic force microscopy (MFM) [4]. Our MFM results reveal higher magnetic susceptibility inside the domain walls due to the winding of the antiferromagnetic order parameter. Domain walls in these antiferromagnets form randomly with strong thermal and magnetic field dependence. The direct visualization of these domain walls and domain structures in magnetic field will not only facilitate the exploration of intrinsic topological phenomena in antiferromagnets [2], but will also open a new path toward control and manipulation of domain walls or spin textures in functional antiferromagnets [1]. If time allows, I will present our MFM results of the robust A-type order on the surface of MnBi$_2$Te$_4$ [5], which might shed light on the mystery of gapless topological surface states observed by angle-resolved photoemission spectroscopy [6–8]. References: [1] V. Baltz, A. Manchon, M. Tsoi, T. Moriyama, T. Ono, and Y. Tserkovnyak, Rev. Mod. Phys. 90, 15005 (2018). [2] L. Šmejkal, Y. Mokrousov, B. Yan, and A. H. Macdonald, Nat Phys 14, 242 (2018). [3] S. W. Cheong, M. Fiebig, W. Wu, L. Chapon, and V. Kiryukhin, Npj Quantum Mater. 5, 1 (2020). [4] P. M. Sass, W. Ge, J. Yan, D. Obeysekera, J. J. Yang, and W. Wu, Nano Lett. 20, 2609 (2020). [5] P. M. Sass, J. Kim, D. Vanderbilt, J. Yan, and W. Wu, Phys. Rev. Lett. 125, 037201 (2020). [6] H. Li, S.-Y. Gao, S.-F. Duan, Y.-F. Xu, K.-J. Zhu, S.-J. Tian, W.-H. Fan, Z.-C. Rao, J.-R. Huang, J.-J. Li, Z.-T. Liu, W.-L. Liu, Y.-B. Huang, Y.-L. Li, Y. Liu, G.-B. Zhang, H.-C. Lei, Y.-G. Shi, W.-T. Zhang, H.-M. Weng, T. Qian, and H. Ding, Phys. Rev. X 9, 041039 (2019). [7] Y. J. Chen, L. X. Xu, J. H. Li, Y. W. Li, C. F. Zhang, H. Li, Y. Wu, A. J. Liang, C. Chen, S. W. Jung, C. Cacho, H. Y. Wang, Y. H. Mao, S. Liu, M. X. Wang, Y. F. Guo, Y. Xu, Z. K. Liu, L. X. Yang, and Y. L. Chen, Phys. Rev. X 9, 041040 (2019). [8] Y.-J. Hao, P. Liu, Y. Feng, X.-M. Ma, E. F. Schwier, M. Arita, S. Kumar, C. Hu, R. Lu, M. Zeng, Y. Wang, Z. Hao, H. Sun, K. Zhang, J. Mei, N. Ni, L. Wu, K. Shimada, C. Chen, Q. Liu, and C. Liu, Phys. Rev. X 9, 041038 (2019). [Preview Abstract] |
Saturday, December 5, 2020 4:51PM - 5:27PM |
G05.00002: Direct imaging antiferromagnetic domain patterns using magnetic x-ray diffraction phase contrast Invited Speaker: Valery Kiryukhin We discuss a recently demonstrated domain imaging technique based on the localization of domain boundaries by resonant magnetic diffraction of coherent x rays. Contrast arises from reduction of the scattered intensity at the domain boundaries due to destructive interference effects. We demonstrate this approach by imaging antiphase domains in representative collinear antiferromagnets. Real-space imaging of the temperature-dependent development and evolution of such domains is demonstrated for the first time. Unlike the conventional coherent diffraction imaging, this technique does not involve any numerical algorithms. It is fast, sensitive, produces large-scale images in a single-exposure measurement, and is applicable to a variety of magnetic domain types. It should find various applications in the physics of antiferromagnetism, including phase transitions, topological domain textures, antiferromagnetic spintronics, topological materials, studies of nonlocal transport, and device physics. [Preview Abstract] |
Saturday, December 5, 2020 5:27PM - 6:03PM |
G05.00003: Coherent Correlation Imaging: unveiling new space and time information in dynamical mesoscopic systems. Invited Speaker: Claudio Mazzoli In experiments, time and space resolutions are typically antagonist as a certain number of particles (used as probes during a measurement, e.g. photons) can be typically used for increasing only one or the other of the two. Here we report a new method exploiting the detected particles by partially classifying the results obtained, instead of limiting the statistical improvement to blind averaging. Indeed, informed averaging (by classification) allows the resolution in time AND space to be improved. The idea behind is simple, and we report a specific application to soft x-ray holography in magnetic thin films as an example. However, we prove that the generalization to other techniques, probes and sample is trivial. Moreover, the implementation of this method naturally allows to retrieve a complete map of states explored by the sample during the measurement, together with their transitions. In short, the connectivity network of states is revealed, thus uncovering new and original information typically inaccessible by blind averaging. This opens up new possibilities in the investigation of the intimate behavior of dynamic systems at the mesoscopic scales. Some applications and implications are sketched, together with their potential impact in crucial and forefront scientific areas. [Preview Abstract] |
Saturday, December 5, 2020 6:03PM - 6:15PM |
G05.00004: Position-Sensitive Response of Single-Pixel Large-Area SNSPDs Brian Lerner Superconducting nanowire single photon detectors (SNSPDs) are typically employed as single-pixel small-area detectors. Demand for large-area detectors is building for a variety of applications including microscopy and free-space quantum communication. Using large-area SNSPDs, we examine the leading edge of the readout pulse as a function of incident spot size, bias current, and mean photon number per pulse. We show a bimodal distribution of rise times that is correlated with spot size for small photon number. In the limit of low bias current, the set of dark-count readout pulses are most similar to the bright-count pulses at large spot size and small photon number. These observations are consistent with a model of traveling microwave modes excited by single photons incident at different positions along the length of the nanowire. [Preview Abstract] |
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