向列超导体NbxBi2Se3的应力调控及弹性模量研究

Nematic superconductivity is a new type of unconventional superconductivity. In addition to the spontaneous U(1) symmetry breaking, nematic superconducting sate spontaneously breaks rotational symmetry in the superconducting gap amplitude or(and) spin degrees of freedom. Such a spontaneous rotational symmetry broken but translational invariant nematic state has been generally found in other unconventional superconducting systems including cuprates, iron-based and heavy fermion superconductors. The interplay between nematicity and unconventional superconductivity may be universal in these systems. The discovery of nematic superconductors provides a new playground for exploring the possible universality of the underlying interaction between superconductivity and nematicity. Despite years of study, many crucial issues including the coupling between symmetry breaking field and nematic superconductivity, possible emergence of preemptive nematic phase, the nematic superconductivity has an intrinsic origin or caused by trivial lattice distortion, are, however, still elusive. In this project, the following experiments are scheduled on the nematic superconducting candidate NbxBi2Se3 to search answers for the above mentioned questions:(1)Studying the coupling between nematic superconductivity and uni-axial strain as well as the possibility of manipulating nematic superconductivity by uni-aixal strain.(2)Searching for the possible stand alone nematic phase using elastic modulus experiments.(3)Investigating the origin of nematic superconductivity by detailed high resolution structural measurements at low temperatures.Realization of this project could fill the bank of this field and provide clues for the above mentioned issues, which could promote the development of this area.

向列超导是一种新的非传统超导态，不仅破坏了U(1)电荷守恒，其超导序参量或(及)自旋自由度也体现出自发的旋转对称性破缺。旋转对称性自发破缺但保持平移不变性的向列电子态普遍存在于铜氧化物、铁基及重费米子等非传统超导体系中，向列性与非传统超导的相互作用或存在普适性。因此，向列超导的发现为研究超导与向列性的相互作用规律提供了新阵地，该领域也成为了超导界十分重要的研究方向。虽经过数年研究，但诸多关键问题依然存疑，例如向列超导与对称性破缺场的耦合关系仍属未知、向列相能否独立于超导相而单独存在、向列超导的根源是本征的抑或来自于晶格畸变等问题。因此，本项目拟选取向列超导候选材料NbxBi2Se3体系，开展以下研究：（1）向列超导与单轴应力的耦合关系及可调控性；（2）搜寻独立于超导相而存在的向列相；（3）精细测量低温晶体结构以探究向列超导的根源。项目的顺利实施将填补相关研究空白及有助于解答上述科学问题。

向列超导是一种本征拓扑超导态，其超导序参量呈现出自发旋转对称性破缺，可涌现出非平庸拓扑激发。探索向列超导的材料体系，以及探究向列超导的机制是凝聚态物理研究的前沿方向。本项目以向列超导候选材料NbxBi2Se3及SrxBi2Se3为研究对象，通过样品制备、电学输运、磁性测量及热膨胀等技术，并结合应力调控的实验手段，对影响向列超导面内各向异性的外在因素，以及向列超导与应力的耦合关系进行了研究，主要取得了以下研究进展：1. 制备出了超导体积分数约70%的SrxBi2Se3样品，并成功搭建了高精度电容热膨胀测试系统；2. 发现样品形状各向异性及样品不均匀性等外在因素对向列超导面内各向异性有明显影响，须仔细排除这些外在因素，才能更好的对向列超导的本征行为进行研究；3. 发现了磁通涡旋与向列畴的相互作用规律，理解了应力调控向列超导的过程。本项目的相关研究，为进一步探究向列超导的根源提供了重要实验线索。