Date: 2024-11-19
Time: 15:00
Venue: M234
Speaker: Professor J.C. Séamus Davis
               University of Oxford

报告人简介:

Davis’active research interests are in the macroscopic quantum physics of quantum matter including studies of superconductors, superfluids and supersolids; Kondo, Weyl and Hund metals; magnetic and Kondo topological condensates; spin & monopole liquids. A specialty is development of innovative instrumentation to allow direct atomic-scale visualization or perception of the macroscopic quantum phenomena that are characteristic of these states. His honors include the Outstanding Performance Award of Berkeley National Lab, the Science and Technology Award of Brookhaven National Lab., the Fritz London Memorial Prize, the H. Kamerlingh-Onnes Memorial Prize, the O.V. Lounasmaa Memorial Prize and the O.E. Buckley Memorial Prize. Davis is a Fellow of the Institute of Physics (UK), the American Physical Society (USA), the Royal Irish Academy (Ireland), the America Assoc. for Advancement of Science (USA) , and a Member of the US National Academy of Sciences (USA).

报告摘要：

Magnetic monopoles are hypothetical elementary particles predicted by Dirac to exhibit quantized magnetic-charge m_D =±(h/μ₀e) and quantized magnetic flux Φ_D=±h/e .None have ever been detected.However,a thermally activated fluid of emergent magnetic monopoles exists in several lanthanide-pyrochlore spin-ices including Dy₂Ti₂O₇.Theory indicates that their magnetic-charge is |m|=4.24×10^-13[AM]=1.28×10^-4m_D ,and that opposite magnetic-charges ±m mayseparate freely while remaining connected by a quantized Dirac-string of polarized spins.

Yet for these monopole fluids,a microscopic transport theory is only now emerging (Hallén Science 378,1218(2022)),the phase diagram remains quite mysterious,simple electrodynamics such as monopole conductivity are unknown,and even the magnetic-charge has never been determined experimentally.To address these lacunae we have developed exceptional experimental devices,including a 'voltmeter','ammeter',flux meter and noise spectrometer,specifically for studying monopole fluids.

Using these new experimental techniques,we have discovered:the microscopictransport dynamics and conductivity for monopole currents (PNAS 121,2320384121(2023)); the characteristic monopole noise spectrum (Nature 571,234 (2019)); that monopole fluids are supercooled magneticliquids (PNAS 112,8549(2015)); the dynamical heterogeneity characteristic of supercooling monopole fluids(arXiv:2408.00460); and the precise magnetic-charge of monopoles in Dy₂Ti₂O₇ where |m|=4.36×10^-13±2.7%[AM].The fundamental physics of emergentmagnetic monopoles is now coming clearly into focus.

联系人：胡江平 研究员（8264 9818）
　　　　汪自强 教授