Experimental investigation of quantum phase transition on one-dimensional spin gapped system

我们研究了一个典型的S=1/2海森堡交替自旋链系统：五氟苯基硝酰基氮氧化物（F_5PNN）和一个具有两个临界场区的新磁系统;（CH_3）_2NH_2CuCl_3（DMACuCl_3）研究了自旋能隙体系的场致相变和Tomonaga-Luttinger液相。在T= 250 mK以下，我们发现了一个在Hc_1 = 3 T和Hc_2 =6.5T之间的场致磁有序。观察到的特征行为取决于磁场Hc 2以上的H-T相边界外的场诱导相。比热随温度和磁场的变化与S=1/2自旋能隙系统的理论计算结果定性一致，DMACuCl_3在低于Hc_1 = 2 T时观察到自发磁有序，而在Hc_1 = 2 T到Hc_2 =3.5T的1/2磁化平台区没有磁有序.磁场诱导的磁有序在H_c ~ 2 =3.5T以上出现，并随着磁场的增加而增加，直到H= 8 T。

We have studied a typical S=1/2 Heisenberg alternating spin chain system ; pentafulorophenyl nitronyl nitroxide (F_5PNN) and a novel magnetic system with two critical field regios ; (CH_3)_2NH_2CuCl_3 (DMACuCl_3) to investigate field induced phase transitions and Tomonaga-Luttinger liquid phase in spin-gapped system.In F_5PNN, we found a field induced magnetic ordering between Hc1=3T and Hc2=6.5T below T=250mK. Characteristic behaviors are observed depending on the magnetic field up to above Hc2 outside of the H-T phase boundary for the field induced phase. The temperature and field dependence of the specific heat are qualitatively in good agreement with the theoretical calculation on an S=1/2 spin gapped system.In DMACuCl_3,a spontaneous magnetic ordering is observed below Hc1=2T, while no magnetic ordering is in the 1/2 magnetization plateau field region from Hc1=2T to Hc2 =3.5T. A field induced magnetic ordering emerges above Hc2=3.5T, which grows with increasing magnetic field up to H=8T.