2024 IoP Seminar Series: Chirality, Topology, and Magnetism in Quantum Systems

14 Mar 2024, 10:00 → 18 Mar 2024, 17:00 Asia/Taipei

P7F Seminar Room (IoP Building)

Chen-Hsuan Hsu (Institute of Physics, Academia Sinica, Taiwan)

Welcome to the 2024 Institute of Physics (IoP) Seminar Series. The topics will be focusing on chirality, topology, and magnetism in various quantum material systems. This series will include four seminars presented by our visitors from Japan: 

• Prof. Yusuke Kato, University of Tokyo
• Prof. Jun-Ichiro Kishine, Open University
• Prof. Hiroaki Kusunose, Meiji University 
• Prof. Yoshihiko Togawa, Osaka Metropolitan university 

The event will be hosted at the IoP, Academia Sinica, Taiwan and is designed to facilitate direct, in-person interactions between attendees and speakers. There is no need for pre-registration to attend these seminars. 

In addition to the seminars, visitors will have the opportunity to engage in further discussions on additional days. For those interested in scheduling private discussions with any of the speakers, please contact Dr. Chen-Hsuan Hsu at chenhsuan[at]gate.sinica.edu.tw. 

Thursday, 14 March

10:00 → 11:30 Seminar by Prof. Yusuke Kato

10:00 Topological defects in superconductors and chiral magnets: Vortex and Quantum Solitons

Topological defects such as domain walls, dislocations, disclinations, and vortices play crucial roles in low energy physics in order states in condensed matters. In this talk, I will discuss three topics related to defects in superconductors and chiral magnets; (1) driving forces on vortex in type II superconductors [1,2], (2) intrinsic hysteresis due to chiral solitons in classical monoaxial chiral magnets [3], and (3) quantum effect in chiral solitons in quantum spin chain [4,5].

(1) There has been a long-term controversial issue on the driving force on vortices in type II superconductors -Hydrodynamic force (Magnus force) or electromagnetic Lorentz force drives vortices-. We show a combination of the two forces is the only well-defined force on the vortex as a consequence of the path-independency of the London fluxoid [1,2].

(2) We refer to the monoaxial chiral magnets as magnets with the Dzyalonshinskii-Moriya interaction with strong monoaxial anisotropy [6,7]. In these magnets, large hysteresis has been experimentally observed in a magnetic loop between H_small and H_large [8], and the ratio of the two fields is found to be H_small/H_large close to 0.4 in most samples of CrNb3S6. We showed theoretically that H_small/H_large is 4/π^2, which agrees quantitatively with experimental observations. The hysteresis is caused by the surface barrier for chiral solitons, and thus this phenomenon is analogous to the Bean-Livingston barrier in superconductors.

(3) Quantum spin chains of monoaxial chiral ferromagnet exhibit different magnetization processes for half-integer spin and integer spin, which is often referred to as the “spin parity effect”. i.e., different behaviors between even 2S and odd 2S. We show this spin parity effect in the chiral magnetic spin chain without relying on the Berry phase [4].

References:
[1] S. Sugai, N. Kurosawa, and Y. Kato, PRB 104 064516 (2021).
[2] Y. Kato and C-K. Chung, J. Phys. Soc. Jpn. 85 033703 (2016).
[3] M. Shinozaki, Y. Masaki, R. Aoki, Y. Togawa and Y. Kato, PRB 97, 214413 (2018).
[4] S. Kodama, A. Tanaka, and Y. Kato, PRB 107, 024403 (2023).
[5] M. Kunimi, T. Tomita, H. Katsura, and Y. Kato, "Proposal for realizing quantum spin models with Dzyaloshinskii-Moriya interaction using Rydberg atoms" [arxiv2306.05591].
[6] J. Kishine and A.S. Ovchinnikov, Solid State Physics 66, 1 (2015).
[7] Y. Togawa et al., J. Phys. Soc. Jpn. 85, 112001 (2016).
[8] Y. Togawa et al. PRB 92, 220412(R) (2015).

Speaker: Prof. Yusuke Kato (University of Tokyo, Japan)

The downloadable abstract can be found at this link. 

11:00 Q&A

12:00 → 14:00 Lunch break

14:00 → 15:30 Seminar by Prof. Hiroaki Kusunose

14:00 Spin splitting and cross-correlated responses in antiferromagnets - View from symmetry-adapted multipole basis

Recently, emergent spin-orbit couplings (SOCs) arising from antiferromagnetic orderings have been attracted much attention, as an alternative source of spin-orbit physics other than the relativistic SOC. The realization of such emergent SOCs and corresponding (anit-)symmetric spin splitting in (non-)collinear magnetic orderings have been discussed extensively [1-4] ([5,6]). In this presentation, I will discuss that effective coupling between magnetic order parameter and the electric (magnetic-toroidal) multipole is essential for the (anti-)symmetric spin splitting. From the coupling we can predict related cross-correlated responses, based on the representation theory with the symmetry-adapted (SA) complete basis [7,8]. I will also touch on topics conceived by this view of the SA representation [9-11].

References:
[1] M. Naka et al., Nat. Commun. 10, 4305 (2019).
[2] S. Hayami, Y. Yanagi, and HK, JPSJ 88, 123702 (2019).
[3] L. Yuan et al., PRB 102, 014422 (2020); PRM 5, 014409 (2021).
[4] L. Šmejkal et al., Sci. Adv. 6, eaaz8809 (2020); PRX 12, 031042 (2022); PRX 12, 040501 (2022).
[5] S. Hayami, Y. Yanagi, and HK, PRB 101, 220403(R) (2020); PRB 102, 144441 (2020).
[6] A. Hellenes et al., arXiv:2309.01607.
[7] HK, R. Oiwa, and S. Hayami, JPSJ 89, 104704 (2020); PRB 107, 195118 (2023).
[8] HK and S. Hayami, J. Phys.: Condens. Matter, 34, 464002 (2022).
[9] S. Hayami, R. Oiwa, and HK, JPSJ 91, 113702 (2022).
[10] R. Oiwa, and HK, PRL 129, 116401 (2022).
[11] S. Hayami, and HK, PRB 108, L140409 (2023).

Speaker: Prof. Hiroaki Kusunose (Meiji University, Japan)

15:00 Q&A

16:00 → 17:00 Private discussion

Friday, 15 March

09:00 → 12:00 Private discussion

12:00 → 14:00 Lunch break

14:00 → 15:30 Seminar by Prof. Jun-Ichiro Kishine

14:00 Chirality-Induced Phenomena in Chiral Crystals: Magnetic Soliton Lattice and Chiral Phonon

Chirality is a common feature in nature, observed from elementary particles to macroscopic crystals, where mirror-reflection symmetry is broken. This absence leads to polarization/spin-dependent behaviors in particles like electrons, photons, magnons, and phonons, illustrating how chirality impacts physical processes.

In this seminar, I will discuss recent progress in understanding the magnetic, electronic, spintronic, and phononic properties of chiral crystals [1-4]. I will focus on explaining how chirality-induced interactions, like the mono-axial Dzyaloshinskii-Moriya interaction (DMI), influence physical responses.

A notable example is the emergence of a chiral spin soliton lattice (CSL) in chiral helimagnets [5]. CSLs have unique properties, affecting magnetic transport and contributing to new magnetic phases [1,3,4]. They also serve as platforms for studying exotic quantum phenomena, making them valuable for research and potential applications in spintronics and magnetic data storage.

Additionally, I will explore the connection between lattice-vibration/phonon behavior and chirality. Recent experiments using Raman scattering [6] in chiral crystals have revealed insights into the relationship between crystal chirality and phonon angular momentum [7,8]. I will define chiral phonons and show how their pseudo-angular momentum relates to photon spin in Raman scattering. This investigation will enhance our understanding of how chirality influences the vibrational properties of materials and could lead to new applications in the future.

References:
[1] Y. Togawa, A. S. Ovchinnikov, and J. Kishine, J. Phys. Soc. Jpn., 92, 081006 (2023).
[2] J. Kishine, H. Kusunose, and H.M. Yamamoto, Isr. J. Chem., 62, e202200049 (2022).
[3] Y Togawa, Y Kousaka, K Inoue, and J Kishine, J. Phys. Soc. Jpn., 85 (11), 112001 (2016).
[4] J. Kishine and A.S. Ovchinnikov, Solid State Physics, 66, 1-130 (2015).
[5] Y. Togawa, T. Koyama, K. Takayanagi, S. Mori, Y. Kousaka, J. Akimitsu, S. Nishihara, K. Inoue, A.S. Ovchinnikov, and J. Kishine, Phys. Rev. Lett. 108, 107202 (2012).
[6] K. Ishito, H. Mao, Y. Kousaka, Y. Togawa, S. Iwasaki, T. Zhang, S. Murakami, J. Kishine, and T. Satoh, Nature Physics, 19, 35–39 (2023).
[7] J. Kishine, A.S. Ovchinnikov, and A.A. Tereshchenko, Phys. Rev. Lett. 125, 245302 (2020).
[8] A. Kato and J. Kishine, J. Phys. Soc. Jpn., 92, 075002 (2023).

Speaker: Prof. Jun-Ichiro Kishine (Open University, Japan)

The downloadable abstract can be found at this link.

 

15:00 Q&A

16:00 → 17:00 Private discussion

Monday, 18 March

09:00 → 12:00 Private discussion

12:00 → 13:30 Lunch break

13:30 → 15:00 Seminar by Prof. Yoshihiko Togawa

13:30 Chirality-induced selectivity and polarization in chiral inorganic materials

A role of chirality in materials is discussed, being inspired by recent studies on chirality-induced selectivity and polarization of spin angular momenta and angular momenta with chiral materials. We demonstrate that chiral materials exhibit a spin-polarized state when the charge current is injected into them [1-6]. Importantly, a robust protection of the spin polarization enables a nonlocal spin detection over micrometers or longer [7]. The influence of dynamical fluctuations, which are characteristic of chiral materials and known as chiral phonon [8], is also argued in terms of spin detection from chiral materials [9]. A comprehensive understanding of these nontrivial responses may clarify the interplay between structural and dynamical chirality.

References:
[1] A. Inui et al., PRL 124, 166602 (2020).
[2] Y. Nabei et al., APL 117, 052408 (2020).
[3] K. Shiota et al., PRL 127, 126602 (2021), featured in Physics 14, s113.
[4] H. Shishido et al., APL 119, 182403 (2021).
[5] Y. Kousaka et al., JJAP 62, 015506 (2023).
[6] H. Shishido et al., APL 119, 182403 (2021).
[7] Y. Togawa et al., JPSJ 92, 081006 (2023), Special Topics DMI.
[8] K. Ishito et al., Nat. Phys. 19, 35 (2023); Chirality 35, 338-345 (2023).
[9] K. Ohe et al., PRL 132, 056302 (2024).

Speaker: Prof. Yoshihiko Togawa (Osaka Metropolitan university, Japan)

14:30 Q&A

15:00 → 17:00 Private discussion