Low-Temperature Low-Field Phases of the Pyrochlore Quantum Magnet Tb$_2$Ti$_2$O$_7$

TL;DR

This study uncovers a new low-temperature magnetic phase in Tb$_2$Ti$_2$O$_7$ with slow spin dynamics and a potential quantum spin ice ground state, revealed through ac susceptibility measurements.

Contribution

It provides experimental evidence for a novel magnetic phase and supports the quantum spin ice model in Tb$_2$Ti$_2$O$_7$ at ultra-low temperatures.

Findings

Discovery of a new magnetic phase below 140 mK

Observation of a weak magnetization plateau below 50 mK

Evidence supporting the quantum spin ice ground state

Abstract

By means of ac magnetic-susceptibility measurements, we find evidence for a new magnetic phase of Tb$_2$Ti$_2$O$_7$ below about 140 mK in zero magnetic field. In magnetic fields parallel to [111], this phase---exhibiting frequency- and amplitude-dependent susceptibility and an extremely slow spin dynamics---extends to about 70 mT, at which it gives way to another phase. The field dependence of the susceptibility of this second phase, which extends to about 0.6 T, indicates the presence of a weak magnetization plateau below 50 mK, as has been predicted by a single-tetrahedron four-spin model, giving support to the underlying proposal that the disordered low-field ground state of Tb$_2$Ti$_2$O$_7$ is a quantum spin ice.