（Center for Electronic Correlations and Magnetism, University of Augsburg, Germany）

报告摘要：Strongly-correlated-electronic magnetism is the most fantastic field with surprises and challenges, in condensed matter physics. Exotic ground states and excitations have been discovered and proposed, such as classical spin liquids with zero-point entropy, quantum spin liquids without symmetry breaking, fractionalized spinon excitations with intrinsic topological order, and the high-temperature superconductivity [1, 2]. The essential physics of these fantastic phenomenon is the many-body problem, which is hardly exactly resolved to date except in very rare and special cases. In this talk, the speaker will present his relevant experimental results, including new high-quality strongly-correlated and spin frustrated materials, milli-Kelvin Faraday-force magnetization, heat capacity, adiabatic magnetocaloric effect measurements, muon spin relaxation/rotation, electron spin resonance, neutron scattering and diffraction, as well as modelling. He is trying to answer the following basic and interesting questions, by employing the studies on the novel magnets: YbMgGaO4 [3-8] and TmMgGaO4 [9].

1. What is the classical spin liquid? Can it exist in a real material? Shall we throw the third law of thermodynamics into the trash? Can we really realize the absolute zero temperature?

2. What is the quantum spin liquid? How can we characterize it in a real material by experiments? What it looks like?

References:

[1] L. Balents, Nature 464, 199 (2010).

[2] P. W. Anderson, Science 235, 1196 (1987).

[3] Y. Li*, et al. “Rearrangement of uncorrelated valence bonds evidenced by low-energy spin excitations in YbMgGaO4”, accepted in Phys. Rev. Lett. (2019).

[4] Y. Li*, et al. “Nearest-neighbor resonating valence bonds inYbMgGaO4”, Nat. Commun. 8, 15814 (2017).

[5] Y. Li*, et al. “Crystalline electric-field randomness in the triangular lattice spin-liquid YbMgGaO4”, Phys. Rev. Lett.118, 107202 (2017).

[6] Y. Li*, et al. “Muon spin relaxation evidence for the U(1) quantum spin-liquid ground state in the triangular antiferromagnet YbMgGaO4”, Phys. Rev. Lett.117, 097201 (2016).

[7] Y. Li, et al. “Rare-earth triangular lattice spin liquid: a single-crystal study of YbMgGaO4”, Phys. Rev. Lett.115, 167203 (2015).

[8] Y. Li, et al. “Gapless quantum spin liquid ground state in the two-dimensional spin-1/2 triangular antiferromagnet YbMgGaO4”, Sci. Rep. 5, 16419 (2015).

[9] Y. Li, et al. “Absence of zero-point entropy in a triangular Ising antiferromagnet”, arXiv:1804.00696.

报告人简介：See enclosed CV.

邀请人：孙培杰

联系电话：82648081