| 発表者名 |
新井 敦郎 |
| 指導教員名 |
求 幸年 教授 |
| 発表題目（英語） |
Variational Monte Carlo Study of Quantum Spin Liquids and Their Nature |
| 要旨（英語） |
Quantum spin liquids (QSLs) represent a fascinating class of quantum phases that defy conventional magnetic ordering even at absolute zero temperature. They exhibit highly entangled ground states with remarkable properties such as topological order and fractionalized excitations [1]. However, the very definition of QSLs make their theoretical and numerical analyses exceptionally challenging.
Variational Monte Carlo (VMC) methods have been extensively employed in the numerical studies of QSLs [2]. These methods allow for the flexible construction of variational wavefunctions and enable the calculation of ground state energies and correlation functions with controlled approximations. This approach is particularly beneficial for large-scale systems where other numerical methods become impractical.
Despite their success in providing candidate ground states for QSLs, the VMC methods face significant limitations. There is a tradeoff between numerical precision and physical insight: more sophisticated variational wavefunctions can provide better numerical precision, but they may lack physical insights because of the large number of variational parameters. The goal of this research is to construct a VMC approach that retains physical transparency while remaining expressive enough to capture the essential features of QSLs. We aim to classify different QSL phases and extract their topological properties based on the structure of the variational wavefunction.
[1] L. Savary and L. Balents, Rep. Prog. Phys. 80, 016502 (2017)
[2] Y. Zhou et al., Rev. Mod. Phys. 89, 025003 (2017) |
| 発表言語 |
日本語 |
|
| 発表者名 |
池上 草玄 |
| 指導教員名 |
求 幸年 教授 |
| 発表題目（英語） |
Multipole orders and quantum spin liquids in spin-3/2 honeycomb models |
| 要旨（英語） |
Quantum spin liquids have been extensively studied for their remarkable properties, such as the absence of magnetic order, fractionalized excitations, and topological order [1, 2]. While most research has focused on S=1/2 systems, there have been several efforts to explore magnets with S ≥ 1. These magnets exhibit additional multipolar degrees of freedom, offering the potential for a rich variety of both ordered and disordered states with multipolar character. Indeed, in S = 1 systems with quadrupolar degrees of freedom, diverse quantum states have been realized in models with bilinear, biquadratic, and anisotropic interactions [3]. On the other hand, S = 3/2 systems additionally possess octupolar degrees of freedom and can host two different exotic states, the Kitaev spin liquid [4, 5] and the Affleck-Kennedy-Lieb-Tasaki (AKLT) state [6, 7] on a honeycomb lattice, suggesting the potential for much richer quantum phenomena. However, the effects of the biquadratic and bicubic interactions in S = 3/2 systems have not been fully clarified, and the interplay between quantum spin liquids and multipole orders remains elusive.
In this study, we investigate the ground states of two different S=3/2 quantum spin models on a honeycomb lattice. One is the “b3 model” with isotropic bilinear, biquadratic, and bicubic interactions, and the other is the Kitaev-AKLT model, which is a combination of two exactly solvable models that stabilize quantum spin liquid ground states. Using a semiclassical approach based on SU(4) spin coherent states, we show that the b3 model exhibits multipolar
ordered phases with suppressed magnetic dipole moments and that the Kitaev-AKLT model exhibits various dipolar ordered phases, including noncoplanar multiple-Q states.
[1] L. Savary and L. Balents, Rep. Progr. Phys. 80, 016502 (2016).
[2] Y. Zhou, K. Kanoda, and T.-K. Ng, Rev. Mod. Phys. 89, 025003 (2017).
[3] R. Pohle, N. Shannon, and Y. Motome, Phys. Rev. B 107, L140403 (2023).
[4] A. Kitaev, Ann. Phys. 321, 2 (2006).
[5] H.-K Jin, W. M. H. Natori, F. Pollmann, and J. Knolle, Nat. Commun. 13, 3813 (2022). [6] I. Affleck, T. Kennedy, E. H. Lieb, and H. Tasaki, Phys. Rev. Lett. 59, 799 (1987).
[7] I. Affleck, T. Kennedy, E. H. Lieb, and H. Tasaki, Commun. Math. Phys. 115, 477 (1988). |
| 発表言語 |
日本語 |
|
| 発表者名 |
LAURIENZO Joseph Thomas |
| 指導教員名 |
求 幸年 教授 |
| 発表題目（英語） |
Theoretical Study of Quantum Fluctuations in Topological Spin Textures |
| 要旨（英語） |
Topological spin textures, such as two-dimensional skyrmions and three-dimensional hopfions, are a trending front of research due to their novel physical properties stemming from the topological robustness of their particle-like nature and quantum geometric effects due to noncollinear and noncoplanar spin configurations. They have been extensively investigated using classical spin models and semi-classical approaches for quantum spins. However, effects of quantum fluctuations on these spin textures can be crucial, e.g., in the formation of their crystals and real-time dynamics, especially in low-dimensional systems. Such intriguing physics remains largely unexplored, primarily due to the lack of a suitable theoretical framework capable of adequately addressing quantum fluctuations.
The aim of this study is to elucidate the effects of quantum fluctuations on topological spin textures. By employing advanced theoretical techniques, such as the density matrix renormalization group (DMRG) and variational Monte Carlo methods, we will investigate quantum phenomena, such as melting behavior of crystals of topological spin textures and their real-time dynamics. As an initial step, we will discuss the case of one-dimensional topological spin textures, called the chiral solitons, in monoaxial chiral magnets. |
| 発表言語 |
英語 |
|
