@phdthesis{oai:oist.repo.nii.ac.jp:00000190,
 author = {ポーレ, リコ and Pohle, Rico},
 month = {2017-12-22, 2018-03-14},
 note = {The phenomenon of magnetism in solids aroused the curiosity of scientists already in ancient times. While quantum mechanical effects on a single–particle level are well understood, magnets offer phenomena caused by collective interactions between many electrons and provide the opportunity to find novel states of matter. In this context, frustrated magnets play a central role, since interactions between local magnetic moments on a crystallographic lattice cannot be satisfied at the same time. This can prevent the systems to order even at very low temperatures, creating a magnetic state similar to those of liquids, which gives them the name spin liquids. Within this field, the kagome lattice — a two–dimensional network of corner–sharing triangles — has played a particularly iconic role and continues to provide rich inspiration to theoreticians and experimentalists alike.
   In this thesis, we first explore the thermodynamic properties and signatures of classical spin liquids on kagome–like lattices, by the use of complementary analytical Husimi tree and numerical Monte Carlo simulation techniques. The emerging phenomenon of a Curie–law crossover, reflecting a crossover between a high–temperature paramagnet and a low–temperature collective paramagnet, turns out to be a powerful signature of exotic physics in classical spin liquids, and explains the difficulty of making a precise estimate of the Curie–Weiss temperature in experiments.
   But spin liquids do not necessarily need to show just one Curie–law crossover. The anisotropic Ising model on the shuriken, or square–kagome lattice, shows a succession of multiple Curie–law crossovers due to a rich phase diagram with many disordered ground states. Hereby, low–and high–temperature regimes are less correlated than the intervening classical spin liquid, allowing to extend the definition of reentrant phenomena to disordered systems.
   Furthermore, we also study dynamical properties of the nearest–neighbour Heisenberg model on the bilayer breathing kagome lattice, which has been motivated by recent experiments on Ca10Cr7O28. Using semi–classical molecular–dynamics simulations, we are able to reproduce many features seen by inelastic neutron scattering experiments and provide a first explanation of its spin–liquid origin. Surprisingly, we find that excitations encode not one, but two distinct types of spin liquids at different time scales. Fast fluctuations reveal a Coulombic spin liquid, as known from the classical kagome–lattice antiferromagnet, while slow fluctuations reveal a spiral spin liquid, which can be understood by a mapping onto an effective spin-3/2 honeycomb model.},
 school = {Okinawa Institute of Sciencce and Technology Graduate University},
 title = {擬カゴメ格子上で発現する新奇なスピン液体の特徴的性質},
 year = {}
}