Title: A tale about discovery of quantum E₈ particles in quantum material BaCo₂V₂O₈

Speaker: Prof. Jianda Wu, Shanghai Jiao Tong University

Time&Location: 12:00 pm, Oct. 10,  Room B501, Tangzhongying Building 

Abstract:

Exotic thermodynamics and excitations can emerge in the vicinity of a quantumphase transition. In the talk, I will first detailedly discuss the unique quantum criticalityfor the Grüneisen ratio in the transverse field Ising chain (TFIC) [1]. Theunique quantum criticality of the Grüneisen ratio then serves as a smoking gunto identify the underlying TFIC universality observed in quasi-1D antiferromagneticmaterials BaCo₂V₂O₈ with transverse field applied along [110] direction [2]. From systematicquantum critical analysis for the effective model of the material SrCo₂V₂O₈[3], we confirm the material with a field applied along [100] direction can also accommodatethe TFIC universality with a much weaker magnetic field [4]. Furthermore,when the quantum critical point of the TFIC is perturbed by a longitudinal magneticfield, it was predicted that its massive excitations are precisely described by theexceptional E8 Lie algebra. Here we first discuss the non-trivial low-temperature local spin dynamics of the exotic E8 model [5]. Then we show an unambiguous experimental realizationof the E8 physics in the material BaCo₂V₂O₈, via nuclear magnetic resonanceand inelastic neutron scattering measurements, and detailed theoretical analysis [6 - 9]. The large separation between the masked 1D and 3D quantum critical pointsof the system allows us to identify, for the first time,the full 8 single-particle E₈ excitations, various multi-E8-particle states [7, 8] as well as the dispersion of E8 particles [9] in the spin excitation spectrum.Our results open new experimental and theoretical routes for exploring the dynamicsof quantum integrable systems and physics beyond integrability, and thus bridge keyphysics in condensed matter and statistical field theory.

[1] J. Wu, L. Zhu & Q. Si, Phys. Rev. B 97, 245127 (2018).

[2] Z. Wang, T. Lorenz, D. I. Gorbunov, P. T. Cong, Y. Kohama, S. Niesen, O. Breunig, J. Engelmayer, A. Herman, J. Wu, K. Kindo, J. Wosnitza, S. Zherlitsyn& A. Loidl, Phys. Rev. Lett. 120, 207205 (2018).

[3] H. Zou, R. Yu & J. Wu, J. Phys.: Condens. Matter. 32, 045602 (2020).

[4] Y. Cui, H. Zou, N. Xi, Z. He, Y. X. Yang, L. Shu, G. H. Zhang, Z. Hu, T. Chen, R. Yu, J. Wu & W. Yu, Phys. Rev. Lett. 123, 067203 (2019).

[5] J. Wu, M. Kormos, Q. Si, Phys. Rev. Lett. 113, 247201 (2014).

[6] X. Wang, H. Zou, K. Hódsági, M. Kormos, G. Takács& J. Wu, Phys. Rev. B 103, 235117 (2021).

[7] Z. Zhang, K. Amelin, X. Wang, H. Zou, J. Yang, U. Nagel, T. Rõõm, T. Dey, A. A. Nugroho, T. Lorenz, J. Wu & Z. Wang, Phys. Rev. B 101, 220411(R) (2020).

[8] H. Zou, Y. Cui, X. Wang, Z. Zhang, J. Yang, G. Xu, A. Okutani, M. Hagiwara, M. Matsuda, G. Wang, G. Mussardo, K. Hódsági, M. Kormos, Z. Z. He, S. Kimura, R. Yu, W. Yu, J. Ma & J. Wu, Phys. Rev. Lett. 127, 077201 (2021).

[9] X. Wang, K. Puzniak, K. Schmalzl, C. Balz, M. Matsuda, A. Okutani, M. Hagiwara, J. Ma, J. Wu, & B. Lake, submitted (2023).

Biography: 

Prof. Jianda Wu has long been committed to the research work in quantum phase transitions, quantum critical thermodynamics and dynamics, Bethe ansatz, and dynamics in quantum integrable systems. He obtained BS (2004) and MS (2007) degrees from University of Science and Technology of China, and got PhD (2014) from Rice University. From2014-2017 he carried out postdoc research at University of California at San Diego, then (2017-2018) became a guest scientist at Max Planck Institute for the Physics of Complex Systems. Since 2018 he became a Tsung-Dao Lee Fellow at Tsung-Dao Lee Institute and a faculty member at School of Physics and Astronomy at Shanghai Jiao Tong University. Prof. Wu has published 29 papersincludingPhys. Rev. Lett., Nature, Nature Physics, Nature Communicationsetc.So far, he has delivered more than 50 invited talks at international conferences/workshops,universities and institutes around the world.