Study of New Condensed State in Quantum Paraelectric Regime

在量子顺电材料中，介电常数epsilon急剧增加，并在较低的温度T下饱和，但未能转变为铁电(FE)，这被认为是由软极性对声子的零点运动引起的。目前人们感兴趣的是，一种新型的相变可能正在发生。考虑到巨大的Esisilon，在电子顺磁共振首次发现反常的SrTiO3Tq=37K以下称为Muller态的“新的相干低T态”是合理的，它与大偏振体的发展有关。因此，我们用超拉曼(HR)和非弹性中子散射(INS)光谱研究了假设的米勒态，以及它的性质(如果存在的话)。用INS测定了SrTiO_3中低Q区各声子的色散关系，发现在特定方向上的TA声子与软极性声子强耦合，这是问题中某些反常现象的原因。对单取向的SrTiO_3样品成功地进行了高分辨率的HR测量。结果表明，在T_q=105K时，结构相变引起的应变对声子的相关频率有很大的影响，表明初始铁电域(IFR)除了量子效应外，主要是由应变引起的。虽然HR没有观察到相关声子频率的T依赖关系的反常现象，但仍然发现了一些反常行为，包括光谱宽度的反常，HR选择规则的崩溃，以及意外观察到在INP中也异常观察到的非极性例如声子。综上所述，我们在SrTiO_3的IFR中获得了一些重要的结果，其中一些被认为与Muller态有关。然而，还需要更多的研究和分析，才能对国家的存在做出决定性的结论。

In quantum paraelectrics dielectric constant epsilon increases strongly and saturates at a high value at low temperatures T.They fail to become ferroelectric (FE), which is believed up until now to be caused by the zero-point motion of the soft polar TO phonon. It is current interest that a new type of phase transition could nevertheless be occurring. Given the huge epsilon, it is reasonable that the "new coherent low-T state" called the Muller state below T_q= 37 K in SrTiO_3 where an anomaly was first revealed in EPR, is connected with the development of large polarization entities. So, we studied the hypothetical Muller state, and the nature, if it exists, by hyper-Raman (HR) and inelastic neutron scattering (INS) spectroscopies.1. The dispersion relations of various phonons in the low q region in SrTiO_3 were determined by INS.It is found that a TA phonon in the specific direction is strongly coupled to the soft polar phonon, which is responsible for some of the anomalies under problem.2. HR measurements were successfully made with a high resolution for a singly-oriented sample of SrTiO_3. As a result, the frequencies of the relevant TO phonons are found to be highly influenced by strains induced by the structural phase transition at T_q=1O5 K, indicating that the incipient ferroelectric regime (IFR) is primarily caused by the strains, in addition to the quantum effect.3. Although no anomaly of the T-dependencies of the relevant phonon frequencies has been observed by HR, a few anomalous behaviors are nevertheless found, which include those of the spectral widths, breakdown of the HR selection rules, and unexpected observation of a non-polar Eg phonon that was also observed anomalously in INP.In summary, we have obtained a few important outcomes in IFR of SrTiO_3, some of which are thought to be related to the Muller state. More studies and analyses are, however, needed to have a decisive conclusion of the existence of the state.