AbstractsPhysics

Quantum magnetic materials provide pathways to exotic spin-disordered phases. We study two broad classes of quantum spin systems and their ground states. The first class is that of spin-dimer systems, which form valence-bond-solid states. In such systems, competition between interactions among the dimers can lead to interesting magnetization behaviour. We explain the magnetization of Ba3Cr2O8 as a Bose-Einstein condensate of spin-carrying excitations. Furthermore, we investigate possible dimerized and nearby magnetically ordered states in the Shastry-Sutherland compound (CuCl)LaNb2O7. The second class of spin systems feature geometric frustration, which may stabilize spin-liquid states without any order or particular dimerization. We argue the proximity of the face-centred-cubic double perovskite La2LiMoO6 to such a phase, to explain its lack of long-range order. We argue for the coexistence of such a state, along with spiral magnetic order, to explain the anomalous thermodynamic measurements in the spin-density-wave phase of powder samples of Volborthite, a distorted kagome-lattice spin system. Finally, we study spin liquid phases that have spin correlations consistent with those found from inelastic neutron scattering of the disordered kagome-lattice material Herbertsmithite. We predict electron spin resonance absorption lineshapes associated with these phases.