철계열 초전도체의 가변 온도/자기장 spin-polarized STM 연구
- Speaker: Prof. Jhinhwan Lee (KAIST)
- Date: Wed Nov 18, 2015 17:00
- Place: Jeongho Seminar Room
Bipartite bosonic modes and spin memory effect in superconducting Sr4V2O6Fe2As2
The role of magnetism, antiferromagnetic spin fluctuations, or phonons on superconductivity in iron-based superconductors have been a long debated issue. With a recent discovery of high Tc near 100 K on monolayer FeSe on a perovskite substrate, understanding the possible roles of enhancing the Fe-based superconductivity by the supporting layers in contact with the Fe-pnictide or Fe-chalcogenide layers is getting an ever-increased attention. Using a homemade variable temperature-magnetic field spin-polarized STM, we have performed spectroscopic-imaging STM measurement on the parent-state superconductor Sr4V2O6Fe2As2 with each unit cell composed of superconducting FeAs layer sandwiched by two Sr2VO3 layers. The hybridization between the localized V electrons and the itinerant Fe electrons causes electron transfer to the FeAs bands and generates a Gamma-centered electron pocket leading to a relatively high critical temperature near 30 K, as well as a ubiquitous Fano resonance with a signature of Fano lattice. In the QPI measurement, we observed the kinks and the partial replicas of the QPI dispersion due to bipartite bosonic modes with characteristic mode energies near 14 meV and 20 meV, whose characteristics agree excellently with the two distinct electron-boson coupling-induced self-energies in Migdal’s approximation. By a comparative study with spin-polarized and normal STM tips, we also observed atomic scale magnetic memory effect of the V atoms controlled with low energy spin-polarized tunneling current and used it to reveal underlying magnetic domains in the FeAs layer. The magnetic and nematic phase transitions near 50 K and 150 K respectively revealed by this technique favorably agrees with the phase transitions detected by bulk and transport measurements. The variable temperature-magnetic field spin-polarized STM offers a novel atomic-scale insight to the roles of the spin, charge, lattice and orbital degrees of freedom in unconventional superconductors and emergent quantum materials.