Quantum Spin Liquid in Quantum Spin Ice

In this project, we study the most general model for spins 1/2 on the pyrochlore lattice governed by nearest-neighbor exchange interactions, and show that the (ground state) phase diagram of our model contains the U(1) Quantum Spin Liquid described by Hermele, Fisher and Balents [Phys. Rev. B. 69 064404 (2004)]. We also exhibit and characterize a novel phase of matter, which we call U(1) Coulomb Ferromagnet. The latter is best seen to be a magnetized version of the U(1) Quantum Spin Liquid, and occupies a large part of the phase diagram of spin-1/2 pyrochlores.

We also make the connection with experiment by comparing our theory with inelastic neutron scattering data in high field of a single crystal of Yb₂Ti₂O₇. The comparison is based on spin wave theory in high field and fits to the data remarkably well. Moreover the exchange coupling constants we get from our fits place Yb₂Ti₂O₇ in a region where a so-called U(1) quantum spin liquid can be expected.

In the theory paper, we develop a novel non-perturbative slave particle approach and make use of a "gauge Mean Field Theory". In the "temperature paper" we extend this analysis to nonzero temperature. The "joint paper" describes the perturbative limit of our theory, the experiments, spin wave theory, and the fits.

Facts and FAQs

• Yb₂Ti₂O₇ is the first and only spin liquid candidate where the Hamiltonian is known quantitatively.
• The Coulomb Ferromagnet (CFM) is a new phase of matter, so far never predicted. It contains all the exotic excitations of the U(1) Quantum Spin Liquids.
• The U(1) Quantum Spin Liquid and Coulomb Ferromagnet described here are very promising in terms of future conclusive experimental discovery: many rare-earth pyrochlore materials (A₂B₂O₇ and B-site spinels AB₂X₄) can be grown in large single crystals, high field inelastic neutron scattering can be performed, allowing to determine the Hamiltonian parameters, the theoretical understanding is detailed, many experiments can be performed...
• The slave particle theory introduced here is quite different from the usual slave particle theories: here our spinons (slave bosons) have a very physical interpretation.