Pressure-induced quantum phase transitions in the S=12 triangular lattice antiferromagnet CsCuCl3

We investigated the pressure effect on the magnetization of the soft material ${\mathrm{CsCuCl}}₃$. We also measured the lattice distortion under the longitudinal magnetic fields at the ambient pressure. While the $ab$ plane shrinks in all the quantum phases below ${T}_{\mathrm{N}}$ at the ambient pressure, its magnitude is much larger in the intermediate 2-1-coplanar or the IC3 phase with a large quantum spin fluctuation than in the low field phase. We found the pressure induced quantum phases; the uud phase for $H\ensuremath{\parallel}c$ and the IC5 phase for $H\ensuremath{\parallel}{b}^*$. We also found the large reduction of the magnetization both below and above ${T}_{\mathrm{N}}$ and the enhancement of ${T}_{\mathrm{N}}$ by pressure. $d{T}_{\mathrm{N}}/dP$ is much larger in the intermediate field phase than in the low field phase. From these results, we could draw the rough magnetic phase diagram under pressure in a high field region. While all the quantum phases below ${T}_{\mathrm{N}}$ are stabilized by pressure, the degree of the stability by pressure is much larger in the quantum phase with a large quantum spin fluctuation than in the low field phase. In the soft material such as ${\mathrm{CsCuCl}}₃$, we propose that the $ab$ plane shrinks spontaneously so as to enhance ${T}_{\mathrm{N}}$ and the quantum spin fluctuation in high field quantum phases under pressure.