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Nano Lett. 2019 Jun 12;19(6):3464-3472. doi: 10.1021/acs.nanolett.9b00144. Epub 2019 May 23.

Detection of Bosonic Mode as a Signature of Magnetic Excitation in One-Unit-Cell FeSe on SrTiO3.

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International Center for Quantum Materials, School of Physics , Peking University , Beijing 100871 , China.
Collaborative Innovation Center of Quantum Matter , Beijing 100871 , China.
CAS Center for Excellence in Topological Quantum Computation , University of Chinese Academy of Sciences , Beijing 100190 , China.
Beijing Academy of Quantum Information Sciences , Beijing 100193 , China.


A "fingerprint" of Cooper pairing mediated by collective bosonic excitation mode is the reconstruction of the quasiparticle-density-of-states (DOS) spectrum with an additional "dip-hump" structure located outside the superconducting coherence peak. Here, we report an in situ scanning tunneling spectroscopy study of one-unit-cell (1-UC) FeSe film on a SrTiO3(001) substrate. In the quasiparticle-DOS spectrum, the bosonic excitation mode characterized by the dip-hump structure is detected outside the larger superconducting gap. Statistically, the excitation mode shows an anticorrelation with pairing strength in magnitude and yields an energy scale upper-bounded by twice the superconducting gap. The observation coincides with the characteristics of magnetic resonance in cuprates and iron-based superconductors. Furthermore, the local response of superconducting spectra to magnetically distinct Se defects all exhibits the induced in-gap quasiparticle bound states, indicating an unconventional sign-reversing pairing over the Fermi surface in 1-UC FeSe. These results clarify the magnetic nature of the bosonic excitation mode and reveal a signature of electron-magnetic-excitation coupling in 1-UC FeSe/SrTiO3(001) besides the previously established pairing channel of electron-phonon interaction.


One-unit-cell FeSe/SrTiO; bosonic mode; electron‚ąímagnetic-excitation coupling; high-temperature superconductivity; scanning tunneling spectroscopy

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