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 CsCuCl3. 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 TN 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 Hc and the IC5 phase for Hb∗. We also found the large reduction of the magnetization both below and above TN and the enhancement of TN by pressure. dTN/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 TN 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 CsCuCl3, we propose that the ab plane shrinks spontaneously so as to enhance TN and the quantum spin fluctuation in high field quantum phases under pressure.