Magnetic and non-magnetic phases of a quantum spin liquid

Characterization of a quantum spin liquid Theoretical predictions of the existence of an exotic state of matter called a quantum spin liquid have been supported by experimental evidence, but many fundamental questions about this novel state remain unanswered. Quantum spin liquids can occur in an insulator with strongly interacting magnetic units when the usual symmetry-breaking magnetically ordered state at low temperatures is avoided as a result of quantum fluctuations. An advanced magnetic probing technique, called muon spin relaxation, has now been used to study the molecular layered system κ-(BEDT-TTF) 2 Cu 2 (CN) 3 , widely regarded as a prime example of a quantum spin liquid. Using implanted muons as a sensitive local magnetic probe, the authors show that magnetic order can be recovered in this system by applying a very small magnetic field. A complex phase diagram is revealed for the spin liquid, which demonstrates the delicate balance between the spin liquid and magnetic phases. A quantum spin liquid is an intriguing exotic state of matter involving a magnetic system in which a magnetically ordered ground state at low temperatures is avoided despite strong interactions between magnetic units, due to quantum fluctuations. Experimental evidence for the existence of such a state has become available, but there are many fundamental questions about this novel state. This study uses an advanced magnetic probing technique, called muon spin rotation, to study a molecular layered system that is widely regarded as a prime candidate for quantum spin liquid. A complex magnetic phase diagram for this system is determined and characteristic critical properties of the spin liquid are measured, thereby providing important new insights into this exotic state of matter. A quantum spin-liquid phase is an intriguing possibility for a system of strongly interacting magnetic units in which the usual magnetically ordered ground state is avoided owing to strong quantum fluctuations. It was first predicted theoretically for a triangular-lattice model with antiferromagnetically coupled S = 1/2 spins 1 . Recently, materials have become available showing persuasive experimental evidence for such a state 2 . Although many studies show that the ideal triangular lattice of S = 1/2 Heisenberg spins actually orders magnetically into a three-sublattice, non-collinear 120° arrangement, quantum fluctuations significantly reduce the size of the ordered moment 3 . This residual orderin