对多铁Eu0.5Ba(Sr)TiO3于高压环境下的固有电偶极矩测量

Extensions beyond the Standard Model such as supersymmetry, grand unification and Multi-Higgs predict the existence of a permanent electron electric dipole moment (EDM) near the order of 10^-29 e-cm, here e is the charge of an electron. Existence of a permanent electron EDM gives rise to a direct violation of the charge and parity symmetries which is necessary to explain the huge disparity found between matter and anti-matter in our universe, the rapid expansion of the universe, neutrino oscillations and so on. The systematic of 10^-29 e-cm is a sensitivity resolution achievable by making use of the inherent magneto-electric (ME) coupling effect inside a multiferroic compound subjected to extreme environments of high electric field, high pressure and low temperature. 　　　Experimental verification of the electron EDM has been difficult due to the limits constrained by current laboratory means to a resolution of 1.6x10^-27 e-cm. Recent suggestions of making use of the ME coupling effect in multiferroics capable of reaching sensitivity values of 10^-28 e-cm have been proposed by Shushkov et al. The EDM of the electron points along the same direction as its spin and upon switching of the electric polarization an EDM magnetization is generated which can be measured via a SQUID magnetometer. Hence, it is critical that any background magnetization noise is kept to a minimum. Not only that, for a strong electron EDM signal, the materials should have a high concentration of magnetic ions but remain paramagnetic at low temperature while at the same time possess a large atomic number and large dielectric constant. Eu0.5Ba0.5TiO3 possesses a ferroelectric and magnetic order and fits these criteria the best. However, a large coercive electric field exists making it hard to switch the polarization without generating too much thermal noise. Doping of Sr has shown to lower the coercive field, but only by a factor of three near 11 K. Replacement of Ba by Sr is equivalent to a reduction of its chemical pressure for which the same effect can be achieved via application of pressure. 　　　For this reason, we propose to use our knowledge of multiferroic characterization in double piston cells and apply it to a diamond anvil cell on Eu0.5Ba(Sr)TiO3 to obtain pressure up to 50 GPa to dramatically suppress the coercive electric field, polarization and the anti-ferromagnetic phase to study its ferroelectric properties between 2 and 300 K. Electron EDM magnetization measurements will follow once a suitable pressure and temperature environment capable of reaching sensitivities near 10^-29 e-cm has been confirmed. We expect to enhance the current upper limit in measurement sensitivity of electron EDM detection by at least 1 to 2 orders of magnitude. A discovery or non-discovery of the electron EDM will set further constraints in existing theories of fundamental physics and help explain the mechanisms behind the ME effect present in many multiferroics not allowed by symmetry.

标准模型的衍生理论例如超对称，大一统和多粒子理论预言了电子固有电偶极矩（EDM）的存在，其值可达10^-29e-cm量级，其中e为电子电荷。由于电子EDM的存在将会直接导致电荷和宇称对称破缺，这对解释宇宙中的物质与反物质极大的失衡，宇宙的极速膨胀和中微子振荡等问题是十分必要的。由于实验手段制约，目前电子EDM的实验证明尚未实现，Shushkov等人认为利用掺杂铀和锶的钛酸钡多铁材料可有利于突破电子EDM的系统极限分辨率，但在低温环境下该材料具有多余矫顽力导致热激发而干扰电子EDM所引起的信号。因此，为了抑制该矫顽力本计划打算将在油压加压元件测量电容和电极化已有的知识应用到金刚石上,对钛酸钡铀锶绘制温度压力相图，进行滞后回线和EDM磁化率的测量。同时，为了寻找出自旋声子的直接耦合证据，也将会在高压和偏电场环境下进行拉曼散射光谱测量。无论EDM的发现与否都将进一步给现存的基本物理理论提出约束。

本人近四年主要从事氢化合物在低温下的分子力学研究，相关结果如下：..发现在118 K温度条件下六甲基苯中的氢原子相关运动具有新的一种磁性。由于质子和氘核的质量是超过电子的三个数量级，相关的慢动力学将会给研究人员提供另一个研究磁量子力学的框架。应用方面上，具有甲基基团的齿轮耦合性可实现具有更强大的量子相干量子比特存储器。同时，该发现也识别了以前未经分类的反铁磁性排列并自旋-晶格耦合。这些结果发表在化学领域顶级期刊之一Angewandte Chemie。..发现了一种能获得非掺杂H2O冰的质子有序基态的方法：从而识别了冰Ih/II/XI三相点及完成了水的低温低压区域的相图绘制；在冰中发现了一种新的质子相关穿遂宏观量子现象；发现了水在43 MPa和212 K具有第二个临界点存在的证据。..在过渡金属二硫族中发现超导体的存在：WTe2在2.5 GPa压力下具有超导基态，最高临界温度在7 K（16.8 GPa）；MoS2在90 GPa压力下具有超导基态，最高临界温度为12 K（120-220 GPa）。