Abstract
The ground states of the frustrated pyrochlore oxide Tb2+xTi2-xO7+y, sensitively depending on the small off-stoichiometry parameter x, have been studied by specific heat measurements using well characterized samples. Single crystal Tb2+xTi2-xO7+y boules grown by the standard floating zone technique are shown to exhibit concentration (x) gradient. This off-stoichiometry parameter is determined by precisely measuring the lattice constant of small samples cut from a crystal boule. Specific heat shows that the phase boundary of the electric quadrupolar state has a dome structure in the x-T phase diagram with the highest Tc ≃ 0.5 K at about x = 0.01. This phase diagram suggests that the putative U(1) quantum spin-liquid state of Tb2+xTi2-xO7+y exists in the range x < xc ≃ –0.0025, which is separated from the quadrupolar state via a first-order phase-transition line x = xc.
Highlights
Magnetic systems with geometric frustration have been intensively studied experimentally and theoretically for decades [1]
Among frustrated magnetic pyrochlore oxides [4], Tb2Ti2O7 (TTO) has attracted much attention because it does not show any conventional long-range orders (LRO) down to 50 mK [7], suggesting that it is a candidate for a quantum spin liquid (QSL) state
The x-T phase diagram shows that around x = xc ≃ −0.0025 the transition temperature Tc of the quadrupolar state [12] disappears abruptly in a small x range. This suggests that the neighboring putative QSL state is separated by a first-order phase-transition line x = xc [11, 12]
Summary
Magnetic systems with geometric frustration have been intensively studied experimentally and theoretically for decades [1]. Among frustrated magnetic pyrochlore oxides [4], Tb2Ti2O7 (TTO) has attracted much attention because it does not show any conventional LRO down to 50 mK [7], suggesting that it is a candidate for a QSL state. Many experimental studies of TTO have been performed to date, the problem why TTO does not show any magnetic LRO remains very difficult [8, 9]. This is partly because TTO shows strong sample dependence [10], extremely strong for single crystals.
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