Are multiphase competition & order-by-disorder the keys to understanding Yb2Ti2O7?

TL;DR

This paper investigates how multiphase competition and order-by-disorder mechanisms explain the complex magnetic behavior of Yb2Ti2O7, revealing multiple phase transitions and expanding the understanding of frustration in quantum spin ice materials.

Contribution

It introduces a minimal model showing how thermal and quantum fluctuations stabilize a U(1) manifold, elucidating the phase competition in Yb2Ti2O7 through numerical analysis.

Findings

Multiple phase transitions observed in Yb2Ti2O7

Order-by-disorder stabilizes a U(1) symmetry

Chemical pressure influences magnetic phases

Abstract

If magnetic frustration is most commonly known for undermining long-range order, as famously illustrated by spin liquids, the ability of matter to develop new collective mechanisms in order to fight frustration is no less fascinating, providing an avenue for the exploration and discovery of unconventional properties of matter. Here we study an ideal minimal model of such mechanisms which, incidentally, pertains to the perplexing quantum spin ice candidate Yb2Ti2O7. Specifically, we explain how thermal and quantum fluctuations, optimized by order-by-disorder selection, conspire to expand the stability region of an accidentally degenerate continuous symmetry U(1) manifold against the classical splayed ferromagnetic ground state that is displayed by the sister compound Yb2Sn2O7. The resulting competition gives rise to multiple phase transitions, in striking similitude with recent experiments on Yb2Ti2O7 [Lhotel et al., Phys. Rev. B 89 224419 (2014)]. Considering the effective Hamiltonian determined for Yb2Ti2O7, we provide, by combining a gamut of numerical techniques, compelling evidence that such multiphase competition is the long-sought missing key to understanding the intrinsic properties of this material. As a corollary, our work offers a pertinent illustration of the influence of chemical pressure in rare-earth pyrochlores.