講師：Dr. Rico Pohle 氏（The University of Tokyo）
タイトル：Dynamical signatures of spin liquids and spin nematic states
In magnets, unconventional states of matter can emerge from complex interaction mechanisms (e.g. frustration induced spin liquids) or from higher-order spin degree of freedom (e.g. multipole fluctuations in spin nematic states). Such unconventional phases can be found hard to probe experimentally, and therefore require new theoretical tools to describe and interpret their ground state and excitation properties.
In the first half of this talk I will focus on thermodynamic and dynamic signatures seen in a spin liquid on the spin–1/2 bilayer breathing-kagome (BBK) lattice, Ca10Cr7O28 , a spiral spin liquid, celebrated for its complex frustration mechanism. We find that excitations encode not one, but two distinct types of spin liquids at different time scales, a “coulombic spin liquid” at finite frequencies, and a “spiral spin liquid” at zero frequencies.
In the second half of my talk I will concentrate on signatures in magnets made of higher-order moments, in particular, magnets made of spin-1, which allow for dipolar and quadrupolar fluctuations on a single site. By taking the example of Ferroquadrupolar order, I will show that our new Monte Carlo and molecular dynamics method is well suited to study quadrupole excitations at finite temperatures, certainly helpful to identify and characterize spin-1 magnets in experiments. C. Balz et al., Nat. Phys. 12, 942 (2016)
 R. Pohle et al. PRB 104, 024426 (2021)
 H. Tsunetsugu and M. Arikawa, J. Phys. Soc. Jpn 75, 083701 (2006)
 K. Remund, R. Pohle, Y. Akagi, J Romhányi, N. Shannon (in preparation)