Theory of Ca10Cr7O28 as a bilayer breathing-kagome magnet: Classical thermodynamics and semiclassical dynamics

[摘要] Ca10Cr7O28 is a novel spin-1/2 magnet exhibiting spin liquid behavior, which sets it apart from any previously studied model or material. However, understanding Ca10Cr7O28 presents a significant challenge, because the low symmetry of the crystal structure leads to very complex interactions, with up to seven inequivalent coupling parameters in the unit cell. Here we explore the origin of the spin-liquid behavior in Ca10Cr7O28, starting from the simplest microscopic model consistent with experiment-a Heisenberg model on a single bilayer of the breathing-kagome (BBK) lattice. We use a combination of classical Monte Carlo (MC) simulation and (semi)classical molecular dynamics (MD) simulation to explore the thermodynamic and dynamic properties of this model and compare these with experimental results for Ca10Cr7O28. We uncover qualitatively different behaviors on different timescales, and argue that the ground state of Ca10Cr7O28 is born out of a slowly fluctuating spiral spin liquid, while faster fluctuations echo the U(1) spin liquid found in the kagome antiferromagnet. We also identify key differences between longitudinal and transverse spin excitations in applied magnetic field, and argue that these are a distinguishing feature of the spin liquid in the BBK model.

[关键词] SPIN-LIQUID;GAUGE-THEORY;ORDER;MODEL;STATE;FRACTIONALIZATION;IMPLEMENTATION;SIMULATION;CHROMIUM;FERMIONS