报告题目：Discrete scale invariance in topological semimetal and theory of type-I and type-II Ising superconductivity
报告人：刘海文 北京师范大学
报告时间：2019年 5月 21 日 晚 8:00-9:00
邀请人： 江华
报告地点：致远楼 304室
报告摘要：In this talk, I will talk about two issues of my recent interest. The first topic is the discrete scale invariance in topological semimetal systems. I will discuss that the two-body Weyl Hamiltonian with supercritical Coulomb attraction can give rise to Efimovian quasi-bound states with discrete scale invariance. Moreover, the magnetic field introduces a new length scale and breaks the discrete scale invariance of the system down to approximate discrete scale invariance. The resonate scattering between the Efimovian bound states and the mobile carriers around the Fermi surface gives rise to a novel type of log-B periodic magneto-resistance oscillations in Dirac materials [1], which goes beyond the Landau level physics scenario. This phenomenon has been justified in topological materials ZrTe5 and HfTe5 by magneto-transport results [2,3].
The second topic is on the microscopic theory of type-I and type-II Ising superconductivity. Spin-orbit coupling (SOC), which is indispensable for realizing topological materials, is the key ingredient for the so-called Ising pairing in two-dimensional (2D) superconductors. Although the phenomenological theory of type-I Ising superconductivity has been formulated and attract a lot of attention in the related field, a concrete microscopic theory, which properly handles the topological correction and the impurity scattering on same footing, is still lacking. Moreover, the present theory only focuses on the 2D transition metal dichalcogenides systems with spin splitting around the K point, but wholly neglect the large class of 2D topological insulator system with spin degeneracy around the Gamma point. Here, based on the Gor’kov Green function technique, we give the microscopic theory of both type-I (applied to 2D supconducting transition metal dichalcogenides systems) and type-II (applied to 2D supconducting topological insulator system) Ising superconductivity [4]. Our microscopic theory returns to the Ginzburg-Landau theory and the well-known Klemm-Luther-Beasley theory in the relatively small field region [4]. Our microscopic theory can give quantitatively explanation for measurements in 2D superconducting Pb ultrathin films [5] and 2D superconducting Stanene ultrathin films [6], which are not consistent with the Ginzburg-Landau theory and the Klemm-Luther-Beasley theory.
References:
[1] H. Liu, et al., arXiv:1807.02459.
[2] H. Wang, et al., Sci. Adv. 4, eaau5096 (2018).
[3] H. Wang, et al., arXiv:1810.03109.
[4] H.C. Liu, et al., under construction.
[5] Y. Liu, et al., Phys. Rev. X 8, 021002 (2018).
[6] J. Falson, et al., arXiv:1903.07627.
