Study of New Condensed State in Quantum Paraelectric Regime

在量子准电体中，介电常数epsilon急剧增加，并在低温t下达到高饱和值，它们不能成为铁电体（FE），迄今为止人们认为这是由软极性to声子的零点运动引起的。然而，一种新的相变可能正在发生，这是目前的兴趣所在。考虑到巨大的epsilon，在SrTiO_3中首次发现异常的T_q= 37 K以下的“新相干低t态”（称为Muller态）与大极化实体的发展有关是合理的。因此，我们通过超拉曼（HR）和非弹性中子散射（INS）光谱研究了假设的穆勒态，以及如果存在的话它的性质。用INS测定了SrTiO_3中低q区各种声子的色散关系。发现TA声子在特定方向上与软极声子强耦合，这是问题中一些异常的原因。对单取向SrTiO_3样品成功地进行了高分辨率的HR测量。结果发现，相关TO声子的频率受到T_q= 105k时结构相变引起的应变的高度影响，这表明除了量子效应外，早期铁电态（IFR）主要是由应变引起的。虽然HR没有观测到相关声子频率t依赖性的异常，但仍然发现了一些异常行为，包括光谱宽度的异常，HR选择规则的破坏，以及INP中也观测到异常的非极性Eg声子的意外观测。综上所述，我们在SrTiO_3的IFR中获得了一些重要的结果，其中一些结果被认为与Muller态有关。然而，要对这个国家的存在做出决定性的结论，还需要更多的研究和分析。

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.