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Scanning tunneling microscopy combined with high frequency : Recent developement and futur prospects - Marie Hervé - Mardi 8 septembre 2020 à 10 h 30

INSP - Sorbonne Université - 4 place Jussieu - 75005 Paris - Barre 22-32, 2e étage, salle 201

Marie Hervé - chargée de recherche dans l’équipe spectroscopie des nouveaux états quantiques de l’INSP

In condensed matter systems, the investigation of low energy magnetic excitations has been carried out using resonance method such as Electron Paramagnetic Resonance (EPR), Nuclear Magnetic resonance (NMR) or Ferromagnetic Resonance (FMR) [1]. Conventional magnetic resonance techniques are based on the inductive detection of an electromagnetic signal induced by the precession of an electron’s or nucleus’s magnetic moment and require to investigate macroscopic systems. With the development of low dimension electronic and quantum computing, one challenge in condensed matter physics is to develop radio frequency (rf)-based resonance experiments liable to sense low energy electronic, magnetic and vibronic excitations down to the single atom / molecule limit. A tool to investigate electronic, magnetic, as well as vibronic excitations of single molecules or atoms on [2-4] surfaces in the sub-meV range is scanning tunnelling microscopy (STM). Indeed, such excitation spectrum can be probe using conventional STM as long as the energy separation between the states is larger than 3.2kbT, i.e., the Fermi-Dirac broadening at finite temperature. To give an example, at a temperature of 300 mK, the STM energy resolution is about 90 µeV. It can be enhanced down to 30 µeV with the use of a superconducting tip. To go further, a possibility would be to use a resonance technique : if combined to STM, it is liable to address electronic, magnetic and vibronic excitation spectrum down to few neVs resolution at the atomic scale. Access to such an extreme energy resolution and high frequency signal in STM was a long-standing problem. Conventional STM has a natural limitation to detect high frequency signal. This is due to the bandwidth of its transimpedence amplifier used to convert tunnelling current in the pA / nA range to manageable voltage. Typical bandwidths are around several kHz which is far too low to track high frequency signal corresponding to µeV energy splitting. In this communication we will present the recent development done to improve the STM energy resolution and our future prospects at INSP. [1] C. P. Slichter Principles of Magnetic Resonance 1996).
[2] M. F. Crommie, C. P. Lutz, and D. M. Eigler, Science 262, 218 (1993).
[3] A. J. Heinrich, J. A. Gupta, C. P. Lutz, and D. M. Eigler, Science 306, 466 (2004).
[4] J. K. Gimzewski, E. Stoll, and R. R. Schlittler, Surface Science 181, 267 (1987).