DYNAMICS OF QUANTUM FLUCTUATION STUDIED BY COHERENT PHONON EXCITATION METHOD

相干声子激发法研究量子涨落动力学

基本信息

批准号：
14204029
负责人：
YAGI Toshirou
金额：
$ 24.63万
依托单位：
HOKKAIDO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14204029/
关键词：
quantum fluctuations coherent soft mode complete freezing quantum paraelectrics inhomogeneity ferroelectrics soft phonon 相転移ダイナミクス同位元素誘起強誘電性 STO STO18 FMR

项目摘要

We concentrated to elucidate the relation between the quantum fluctuations and the macroscopic order in the quantum paraelectric and ferroelectric crystals. The specimen were the quantum paraelectric strontium titanate SrTi^<16>O_3(STO16) and its oxygen isotope exchanged crystal SrTi(^<18>O_x^<16>O_<1-x>)_3(STO18-x), where x=0.23,0.32 and 0.89. The exchange concentration of the oxygen isotope more than 33% (x_c) from ^<16>O to ^<18>O in strontium titanate induces the ferroelectric phase in the typical quantum paraelectric STO16 as discovered by Itch et al.(1999). The spectra of the ferroelectric soft Eu mode in STO16 and STO18-x have been observed in the ultra-low temperature region down to milli-Kelvin. The nominally Raman inactive Eu mode spectra in the centro-symmetric phase were observed as a function of temperature for each of the crystals.The following two conclusions are obtained ; (1)In STO-89 crystal where the quantum fluctuation is completely depressed by the mass effect of t … More he isotope oxygen, the soft Eu mode can soften completely to zero frequency (complete fireezing) at the ferioelectric phase transition point associated with the less damping vibration than the ordinary other ferroelectrics, where the heavily over-damped spectra of soft mode have been reported as a central peaks. In the case of STO-89, the role of the quantum fluctuations seems to be coherently depression of the damping of the soft mode vibration via the coupling between the soft modes and quantum fluctuations. (2)For the specimen STO-23 and STO-32, the ferroelectric phase transition does not take place because the concentration of both crystals is lower than the critical concentration x_c=0.33. In these crystal, the softening behavior of the Eu mode is confirmed by the observation of the locally symmetry breaking region caused by the inhomogeneity of the concentration of ^<18>O, though it does not show any softening to the zero frequency. In this case, the role of the quantum fluctuation is to prevent the occurrence of the long-range order even in the ultra low temperature region. Less

我们集中精力阐明了量子顺电和铁电晶体中量子涨落与宏观有序的关系，样品是量子顺电钛酸锶SrTi^<16>O_3(STO16)及其氧同位素交换晶体SrTi(^<18)。 >O_x^<16>O_<1-x>)_3(STO18-x)，其中x＝0.23、0.32和0.89，钛酸锶中从^ 16 O到^ 18 O的氧同位素交换浓度超过33％(x_c)，在典型的量子顺电STO16中诱导出铁电相。 Itch 等人 (1999) STO16 和中的铁电软 Eu 模式的光谱。在低至毫开尔文的超低温区域观察到了 STO18-x，观察到每个晶体的中心对称相中的名义拉曼非活性 Eu 模式光谱随温度的变化。以下两个结论是(1)在STO-89晶体中，量子涨落完全被同位素氧的质量效应抑制，软Eu模式在与普通其他铁电体相比，铁电相变点与较小的阻尼振动相关，其中软模式的严重过阻尼光谱已被报告为中心峰，在 STO-89 的情况下，量子涨落的作用似乎是。通过软模和量子涨落之间的耦合来相干地抑制软模振动的阻尼（2）对于样本STO-23和STO-32，没有发生铁电相变。因为两种晶体的都低于临界浓度 x_c=0.33 在这些晶体中，Eu模式的软化行为通过观察^ 18 O浓度的不均匀性引起的局部对称破缺区域得到证实。，虽然在零频率下没有表现出任何软化，但在这种情况下，量子涨落的作用是即使在超低温区域也能防止长程有序的出现。