Spin dynamics of individual molecules probed with electron paramagnetic resonance in a scanning tunneling microscope
ORAL · Invited
Abstract
Individual spins on surfaces offer a promising platform for understanding quantum coherence and spin–environment interactions at the atomic scale – an essential step towards the rational design of surface-based quantum systems. By combining scanning tunnelling microscopy (STM) with electron paramagnetic resonance (EPR) [1, 2], we can directly image and manipulate atomic-scale environments of individual spins while probing spin dynamics with high energy and temporal resolution.
We study the dynamics of individual molecular adsorbates on a decoupling layer formed by ultrathin insulators. We have investigated covalently bound metal dimers [3], compact organic molecules [4], and graphene nanoribbons weakly adsorbed on the substrate. The weak molecule-substrate interaction gives rise to well-preserved molecular states with a high degree of spin polarization. These states also enable a sensitive readout of the molecular spin via tunnelling magnetoresistance and offer a means to control the interaction between the molecule and the magnetic tip of the STM with applied bias voltage.
Our work focuses on charge and spin transport through molecular orbitals, as well as the impact of spin-polarized electron transport on molecular spin dynamics. We present a novel approach to the resonant excitation of individual spins in a magnetic field that relies on the spin transfer torque induced by the tunnelling of spin-polarized electrons from the tip of an STM into the molecular orbital [4]. The nonlinear nature of the tunnelling process enables higher harmonic excitation. This nonlinearity can be used to excite transitions that match the integer multiples of the excitation frequency. This overcomes the bandwidth limitation of the experimental setup.
Our theoretical and experimental investigations suggest that the injection of time-dependent spin-polarized current is a convenient mechanism for the manipulation of the magnetic state of individual atoms and molecules.
References
[1] S. Baumann, W. Paul et al., Science 350 (2015), 417.
[2] T. S. Seifert et al., Phys. Rev. Res. 2 (2020), 013032.
[3] S. Kovarik et al., Nano Lett. 22, (2022), 4176.
[4] S. Kovarik, R. Schlitz et al. Science 384, (2024), 1368.
We study the dynamics of individual molecular adsorbates on a decoupling layer formed by ultrathin insulators. We have investigated covalently bound metal dimers [3], compact organic molecules [4], and graphene nanoribbons weakly adsorbed on the substrate. The weak molecule-substrate interaction gives rise to well-preserved molecular states with a high degree of spin polarization. These states also enable a sensitive readout of the molecular spin via tunnelling magnetoresistance and offer a means to control the interaction between the molecule and the magnetic tip of the STM with applied bias voltage.
Our work focuses on charge and spin transport through molecular orbitals, as well as the impact of spin-polarized electron transport on molecular spin dynamics. We present a novel approach to the resonant excitation of individual spins in a magnetic field that relies on the spin transfer torque induced by the tunnelling of spin-polarized electrons from the tip of an STM into the molecular orbital [4]. The nonlinear nature of the tunnelling process enables higher harmonic excitation. This nonlinearity can be used to excite transitions that match the integer multiples of the excitation frequency. This overcomes the bandwidth limitation of the experimental setup.
Our theoretical and experimental investigations suggest that the injection of time-dependent spin-polarized current is a convenient mechanism for the manipulation of the magnetic state of individual atoms and molecules.
References
[1] S. Baumann, W. Paul et al., Science 350 (2015), 417.
[2] T. S. Seifert et al., Phys. Rev. Res. 2 (2020), 013032.
[3] S. Kovarik et al., Nano Lett. 22, (2022), 4176.
[4] S. Kovarik, R. Schlitz et al. Science 384, (2024), 1368.
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Publication: T. S. Seifert et al., Phys. Rev. Res. 2 (2020), 013032.
S. Kovarik et al., Nano Lett. 22, (2022), 4176.
S. Kovarik, R. Schlitz et al. Science 384, (2024), 1368.
R. Schlitz, S. Kovarik, J Reina Gálvez et al., "High-Harmonic Spin Resonance in a Single Molecule Driven by Quantum Spin Torques" (manuscript in preparation)
Presenters
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Stepan Kovarik
- Empa, Swiss Federal Laboratories for Materials Science and Technology, nanotech@surfaces Laboratory