Investigating the Ground States of Triangular Antiferromagnet Quantum Spin Liquid Candidates

Abstract

The pursuit of the quantum spin liquid (QSL) state has been at the fore of condensed matter physics for several decades. In this exotic state of matter, spins remain dynamic in the zero temperature limit while retaining a high degree of entanglement. QSLs may play a role in quantum computing and high temperature conductivity, and are predicted to host exotic quasiparticle excitations. The first system proposed to host the QSL state was a triangular antiferromagnet, and variations of these materials are still being proposed as candidate systems decades later. Here I present work aimed at shedding light on the ground states of two closely related spin S=1/2 triangular antiferromagnets, YbMgGaO4 and YbZnGaO4. These materials garnered great interest in recent years for showing many experimental signatures associated with QSL phenomena in a variety of measurements. However, both possess a high degree of disorder due to nominally perfect site mixing between the non-magnetic cations, and there is an ongoing debate about the role of this disorder in the spin liquid features. We used a combination of inelastic and diffuse neutron scattering, and tunnel diode oscillator, cantilever torque, and SQUID magnetometry measurements that seek to advance our understanding of the possible spin liquid behaviors in these materials by constraining the exchange parameters of their Hamiltonians. These measurements have further served as a guide for theoretical studies performed by our collaborators. Plausible ground states are suggested for these materials in the disorder-free limit, and efforts are made to address nuances with respect to the role of frustration, disorder, and thermal and quantum mechanical fluctuations that all play important roles in the spin liquid phenomena in these and other QSL candidates, as well as the rich phase diagram of anisotropic triangular antiferromagnets.