Field induced pinch points in the quantum spin liquid Ca10Cr7O28

Ca10Cr7O28 is a quantum spin liquid – characterised by the absence of static magnetic order where the spins are in coherent dynamical motion in the ground state. This state originates from the frustrated breathing kagome bilayer lattice of spin-1/2 Cr5+ ions which hosts competing interactions. The excitations are broad and diffuse reminiscent of spinons, however in a magnetic field they sharpen into spin-waves modes. Three pairs of gapped modes exist, the lowest energy pair condenses into the ground state at low field and is responsible for the spiral spin liquid behaviour. Theory predicts that the other modes host unusual ’dynamical’ spin liquids which would give a kagome spin liquid characterised by a pinch-point pattern if they were to become gapless. The aim of this proposal is to test these ideas by measuring the gapped and dispersionless pinch point modes predicted at high fields.