Seminars

Title: Quantum Magnetism on Frustrated Six-Fold Lattices: From Valence-Bond to Simplex States
 
Abstract: Quantum magnets on lattices with six-fold symmetry, such as the kagome, maple-leaf, star, and ruby lattices, host a wide variety of exotic ground states resulting from the complex interplay between geometric frustration and quantum fluctuations. Although the kagome lattice has been studied extensively, other six-fold symmetric systems remain comparatively unexplored. In this talk, I will summarize some of the key developments in the study of quantum antiferromagnets on the maple-leaf, star, and ruby lattices, which exhibit a rich spectrum of magnetically ordered and quantum-disordered phases, including exact product singlet ground states, canted magnetic order, valence-bond states, and simplex singlet states.

I will demonstrate how our newly developed hexagonal Corner Transfer Matrix Renormalization Group (CTMRG) and infinite projected entangled pair states (iPEPS) methods offer efficient and accurate approaches for contracting infinite tensor networks, enabling the precise characterization of ground-state properties, correlation functions, and competing quantum orders in six-fold symmetric lattice systems.

 

Title: Field-driven phenomena in helimagnets
 
Abstract: Helimagnets exhibit noncollinear spin arrangements characterised by a periodic helical modulation, giving rise to emergent chiral properties. These materials have attracted significant interest due to their potential applications in spintronics, particularly for robust information storage and the realisation of topological spin textures such as skyrmions. In this talk, I will focus on Yoshimori-type helimagnets, where competing exchange interactions mediated by conduction electrons stabilise helical spin structures without requiring Dzyaloshinskii–Moriya interaction. I will introduce a minimal model describing the electronic structure of a one-dimensional helimagnet under an external magnetic field and analyse its consequences on non-linear transport [1]. I will mainly focus on how band asymmetry emerges in the conical phase, leading to a nonzero second-order electronic conductivity and injection photoconductivity. Additionally, I will discuss how to extend the model to reproduce the electronic structure of α-EuP₃obtained from density functional theory calculations and qualitatively reproduce the features observed in experimental measurements of non-reciprocal transport in this system [2]. I hope that our results provide insight into the interplay between spin texture and electronic properties, paving the way for future studies on chirality-driven transport phenomena in helimagnets.

[1] Darius-Alexandru Deaconu, Aneesh Agarwal, Rodion Vladimirovich Belosludov, Robert-Jan Slager, and Mohammad Saeed Bahramy. Field-driven band asymmetry and non-reciprocal transport in a helimagnet. Phys. Rev. Lett. (accepted July 2025): arXiv:2503.00475, 2025.

[2] Alex Hiro Mayo, Darius-Alexandru Deaconu, Hidetoshi Masuda, Yoichi Nii, Hidefumi Takahashi, Rodion Vladimirovich Belosludov, Shintaro Ishiwata, Mohammad Saeed Bahramy, and Yoshinori Onose. Band asymmetry–driven nonreciprocal electronic transport in a helimagnetic semimetal α-EuP3. Proceedings of the National Academy of Sciences, 122(4):e2405839122,2025