IAMS Lecture on Jan 22 (Prof. Tomáš Jungwirth) & Jan 23 (Dr. You-Sheng Li 李侑昇博士)
消息來源：原分所
截止日期：2024-01-23
IAMS Lecture Announcement
中研院原分所演講公告
Title: Altermagnetism: The third magnetic class
Speaker: Prof. Tomáš Jungwirth (Institute of Physics, Czech Academy of Sciences, Czech Republic & School of Physics and Astronomy, University of Nottingham, United Kingdom)
Time: 10:30 AM, January 22 (Monday), 2024
Place: Dr. Poe Lecture Hall, IAMS (本所浦大邦講堂臺大校園內)
Contact: Dr. Cheng-Tien Chiang 江正天博士
Place: Dr. Poe Lecture Hall, IAMS (本所浦大邦講堂臺大校園內)
Contact: Dr. Cheng-Tien Chiang 江正天博士
Abstract:
Magnetically ordered crystals are traditionally divided into two basic classes – ferromagnetism and antiferromagnetism. In the first part of the talk, we will recall that the ferromagnetic order offers a range of phenomena for energy efficient IT, while the vanishing net magnetization in antiferromagnets opens a possibility of combining ultra-high energy efficiency, capacity and speed of future IT [1-4]. In the main part of the talk we will move on to our recent predictions of instances of strong time-reversal symmetry breaking and spin splitting in electronic bands, typical of ferromagnetism, in crystals with antiparallel compensated magnetic order, typical of antiferromagnetism [5-8]. We resolved this apparent fundamental conflict in magnetism by symmetry considerations that allowed us to classify and describe a third basic magnetic class [6,7]. Its alternating spin polarizations in both crystal-structure real space and electronic-structure momentum space suggested a term altermagnetism. We will discuss predictions and initial experimental verifications [9,10] in which altermagnets combine merits of ferromagnets and antiferromagnets, that were regarded as principally incompatible, and have merits unparalleled in either of the two traditional basic magnetic classes. We will introduce the broad materials landscape of altermagnetism and show how its unconventional nature enriches fundamental concepts in condensed matter physics, such as the Kramers theorem [10]. We will show that this underpins a development of a new avenue in spintronics, elusive within the two traditional magnetic classes, based on strong and conserving spin phenomena, without magnetization imposed scalability limitations.
[1] P. Wadley, T. Jungwirth et al., Science 351, 587 (2016)
[2] T. Jungwirth et al., Nature Nanotech. 11, 231 (2016)
[3] Z. Kaspar, T. Jungwirth et al., Nature Electron. 4, 30 (2021)
[4] F. Krizek T. Jungwirth et al., Science Adv. 8, eabn3535 (2022)
[5] L. Smejkal, T. Jungwirth et al., Science Adv. 6, eaaz8809 (2020)
[6] L. Smejkal, T. Jungwirth et al., Nature Rev. Mater. 7, 482 (2022)
[7] L. Smejkal, J. Sinova, T. Jungwirth, Phys. Rev. X 12, 031042 (2022)
[8] L. Smejkal, J. Sinova, T. Jungwirth, Phys. Rev X (Perspective) 12, 40501(2022)
[9] Z. Feng, T. Jungwirth et al., Nature Electron. 5, 735 (2022)
[10] J. Krempasky, T. Jungwirth et al., Nature, in press (2023) https://arxiv.org/abs/2308.10681
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Title: Thermodynamic Studies of Sr2RuO4 under Uniaxial Pressure
Speaker: Dr. You-Sheng Li 李侑昇博士 (Max Planck Institute for Chemical Physics of Solids, Dresden, Germany)
Time: 10:30 AM, January 23 (Tuesday), 2024
Place: Dr. Poe Lecture Hall, IAMS (本所浦大邦講堂臺大校園內)
Contact: Dr. Cheng-Tien Chiang 江正天博士
Place: Dr. Poe Lecture Hall, IAMS (本所浦大邦講堂臺大校園內)
Contact: Dr. Cheng-Tien Chiang 江正天博士
Abstract:
Many intriguing unconventional superconductors display a phase diagram containing strongly correlated states, which can be tuned by external parameters, such as chemical doping or pressure. In recent years, uniaxial pressure, which can break the symmetry of the crystal lattice, has shown the capabilities of tuning the electronic structures of Sr2RuO4 across a Van Hove singularity (VHS) [1, 2]. By performing high precision ac-elastocaloric effect (ECE) [3] and ac-heat capacity (HC) [4] measurements under uniaxial pressure along the [100] direction, we mapped out the phase diagram of Sr2RuO4 in detail and narrowed down possible superconducting (SC) order parameters. We summarize our main findings, as many unconventional superconductors, Sr2RuO4 has a SC dome in proximity to a magnetic phase. Both ECE and HC exhibit no signature of a second transition below Tc. Besides, we observe a strong reversal of the ECE around the VHS upon entering the SC state. Together with a model calculation, these results strongly suggest a node-less gap opening at the VHS and, thus, put a strong constraint on possible SC order parameters.
[1] A. Steppke et al. Science 355, eaaf9398 (2017).
[2] V. Sunko et al. npj Quant. Mat. 4, 2397–4648 (2019).
[3] Y.-S. Li et al. Nature 607, 276–280 (2022).
[4] Y.-S. Li et al. Proc. Natl. Acad. Sci. USA 118, e2020492118 (2021).