报告题目：Visualizing polarons on a metal oxide surface and Spin-split surface states at the twin boundaries of non-centrosymmetric BiPd
In this talk, I will first present my work on studying the behavior of electron small polarons at rutile TiO2(110). Then, I will present my study of the surface electronic structure of non-centrosymmetric BiPd.
Polarons in metal oxides play a crucial role in processes such as catalysis, high Tc superconductivity, and dielectric breakdown in nano-electronics. Using low temperature STM in combination with density functional theory, we study the behavior of electron small polarons associated with oxygen vacancies (VO) at rutile TiO2(110). We observe that the electrons are symmetrically distributed around isolated VO at 78 K, but as the temperature is reduced, their distributions become increasing asymmetric, confirming their polaronic nature. By manipulating isolated VO with the STM tip, we show that particular configurations of polarons are preferred for given locations of the vacancies, which we ascribe to small residual electric fields in the surface. We also form a series of VO-complexes and study their associated electronic distribution.
In non-magnetic bulk materials lacking inversion symmetry, spin-orbit interactions can lift the spin degeneracy, resulting in Rashba metals whose Fermi surfaces exhibit an intricate spin texture. Using scanning tunneling spectroscopy (STS), we study the surface electronic structure in the superconducting state of BiPd, previously reported to exhibit a Dirac-like surface state with a non-trivial spin texture. In STM, both domains of (0-10) and (010) terminations of the crystal structure are present, and separated by twin boundaries (TB). By performing STS, we find that the electronic structure of these non-equivalent domains are characterised by a surface state peak at ~0.4 eV above the Fermi level, and slightly distinct from one another. Intriguingly, we find an additional bound state localized at the TB, the energy of which depends on its orientation at the surface.
严智明博士，2012年毕业于英国伦敦大学学院化学系，获博士学位，导师Geoff Thornton教授。2012 年 ～ 2016 年，继续于Thornton组从事其对金属氧化物的表面研究。现于英国圣安德鲁斯大学物理系Peter Wahl 组担任博士后研究员，主攻超低温扫描隧道显微镜，研究方向包括：非中心对称超导材料，铁基超导体，自旋阀系统等。以第一作者在PNAS和PRL等期刊上发表多篇论文。