Unconventional Magnetic Ground State in Yb$_2$Ti$_2$O$_7$

TL;DR

This study investigates the low temperature magnetic properties of Yb$_2$Ti$_2$O$_7$, revealing a disordered state with signs of a hidden order below 265 mK, challenging previous claims of ferromagnetic order.

Contribution

The paper provides evidence for a novel hidden order ground state in Yb$_2$Ti$_2$O$_7$, contrasting prior reports of ferromagnetic order and highlighting the role of sample variation.

Findings

Disordered low temperature state persists down to 16 mK.

No evidence of ferromagnetic order in measurements.

Signs of a hidden order below 265 mK.

Abstract

We report low temperature specific heat and muon spin relaxation/rotation ($\mu$SR) measurements on both polycrystalline and single crystal samples of the pyrochlore magnet Yb$_2$Ti$_2$O$_7$. This system is believed to possess a spin Hamiltonian supporting a Quantum Spin Ice (QSI) ground state and to display sample variation in its low temperature heat capacity. Our two samples exhibit extremes of this sample variation, yet our $\mu$SR measurements indicate a similar disordered low temperature state down to 16 mK in both. We report little temperature dependence to the spin relaxation and no evidence for ferromagnetic order, in contrast to recent reports by Chang \emph{et al.} (Nat. Comm. {\bf 3}, 992 (2012)). Transverse field (TF) $\mu$SR measurements show changes in the temperature dependence of the muon Knight shift which coincide with heat capacity anomalies. We are therefore led to propose that Yb$_2$Ti$_2$O$_7$ enters a hidden order ground state below $T_c\sim265$ mK where the nature of the ordered state is unknown but distinct from simple long range order.