Jens Brede

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Soon after the discovery of superconductivity in CuxBi2Se3 [Hor2010], this compound has been predicted to be a topological superconductor (TSC) [Fu2010]. Recently, spontaneous symmetry breaking of the SC state in the bulk as well as on the surface of CuxBi2Se3 was demonstrated experimentally [Matano2016, Yonezawa2017, Tao2018]. The observed nematic SC state is in agreement with the proposed odd-parity two-component superconducting order parameter [Fu2010] and confirms the topological nature of the SC state. In the first part of this talk, I will present preliminary results recently obtained in the M-STM lab on the surface of CuxBi2Se3 crystals grown in-house. In particular, scanning tunneling spectroscopy performed at 400 mK shows that the three-fold symmetry of the underlying lattice is broken in the nematic SC state. Specifically, the SC density of states measured as a function of the azimuthal angle between the external magnetic field (|B|=0.5 T ) direction and the sample surface shows a characteristic two-fold symmetry. Taking advantage of the atomic resolution capabilities of the STM we can deduce the nematic axis with respect to the crystal lattice locally on the sample surface. Going beyond pervious work [Tao2018], we were able to find all three symmetry related nematic domains on the same sample thus offering the prospect to study the physics at the boundary of the nematic SC domains in the future. In the second part, I will discuss possible future research to be performed in the M-STM lab. The long-term goal could be to bridge the gap between clean-room based (nano)device-fabrication and characterization of such devices with the STM on the atomic scale. In order to achieve this goal several obstacles have to be overcome. Specifically, I will propose an approach which allows (i) identification (and positioning) of nano-devices on mm sized sample carriers and (ii) realization of ultra-clean surfaces. [Hor2010] Hor et al. Phys. Rev. Lett. 104, 057001 (2010) [Fu2010] Fu and Berg, Phys. Rev. Lett. 105, 097001 (2010) [Yonezawa2017] Yonezawa et al. Nat. Phys. 13, 123 (2017) [Tao2018] Tao et al. Phys. Rev. X 8, 041024 (2018)

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Institute of physics 2
Seminar Room of the Institute of Physics II
Contact: Y. Ando