Electron spin resonance-scanning tunneling microscopy

Abstract

Electron spin resonance-scanning tunneling microscopy (ESR-STM) is a rapidly developing surface-science technique that is sensitive to a single spin existing on or nearby a solid surface. The single spin is detected through elevated noise at the Larmor frequency that appears when the single spin participates in the tunneling process between the tip and the surface. In this review, experimental and theoretical works which have been performed up to date on ESR-STM are reviewed. The remaining experimental problems which have to be solved, possible approaches to differentiate between different mechanisms and the future of ESR-STM are discussed.\ PACS: 72.25.Dc Spin polarized transport in semiconductors, 72.70.+m Noise processes and phenomena, 73.20.Hb Impurity and defect levels; energy states of adsorbed species, 73.40.Gk Tunneling, 75.70.Rf Surface magnetism, 75.76.+j Spin transport effects, 76.30.-v Electron paramagnetic resonance and relaxation, 78.47.-p Spectroscopy of solid state dynamics

Keywords:

• scanning tunneling microscopy
• electron spin resonance
• spin precession
• noise
• spectroscopy
• single spin detection
• rf signal

Acknowledgements

We are grateful to L. Bulaevskii, M. Crommie, S. Crooker, J.C. Davis, J. Fransson, D. Eigler, A. Heinrich, W. Ho, H. Manoharan, I. Martin, D. Mozyrsky, R. Moerner, K. Schwab, D. Smith, B. Spivak, Z. Nussinov, R. Wiesendanger, A. Yazdani, J.X. Zhu, Y. Imry, O. Entin-Wohlman, B Horovitz, T. Komeda, H. Ohya-Nishiguchi, A. Yoshimori, C. Ascoli, A. Caneschi, D. Gatteschi, P. Messina, M. Fabrizioli and P. Pittana for useful discussions over the years. The work presented in Figure 13 is part of the PhD work of M. Averbukh 27. This work was performed, in part, at the Center for Integrated Nanotechnologies, a US Department of Energy, Office of Basic Energy Sciences, user facility. Los Alamos National Laboratory, an affirmative action equal opportunity employer, is operated by Los Alamos National Security, LLC, for the National Nuclear Security Administration of the US Department of Energy under contract DE-AC52-06NA25396. This work was supported by the USA–Israel Binational Science Foundation (BSF). Additional support from the Israeli Ministry of Science and the Wolfson Foundation and from the Israeli Ministry of Science is acknowledged.

Notes

The experimental technique is also called electron spin noise-scanning tunneling microscopy (ESN-STM), electron spin precession-scanning tunneling microscopy (ESP-STM), etc. This technique may also be called dynamic spin-polarized STM, if the direct exchange mechanism discussed in Section 4.1 (Figure 15) is indeed the most dominant.

The spin-orbit interaction is given by from the Dirac's wave equation the potential energy, the Pauli matrix vector and p the momentum operator]. If the potential slope is structurally asymmetric with respect to the symmetry inversion as in the case of the solid surface, it is called the Rashba spin-orbit interaction, and expressed as .

According to the Nyquist sampling theorem, if the signal is a periodic function with the period T, then the signal detection is not possible if the signal sampling period τ is larger than T/2; if the dc tunneling current is 1 nA, the average signal sampling period τ is . Thus, from τ>(=) T/2, the detection of the Larmor frequency larger than is impossible.

In metal, if a localized magnetic moment exists, it induces the spin polarization of the surrounding conduction electrons, which spatially decays away from the localized moment with oscillatory behavior. This kind of long-range interaction through the spin polarization works between the two localized magnetic moments in metal (–Kittel–Kasuya–Yoshida) 2.

IETS and the noise spectroscopy are quite different spectroscopic methods, but both give similar information. The former is related with the energy dissipation of the linear response theory and the latter with the correlation function which determines the corresponding displacement of the fluctuations at the thermal equilibrium. Kubo's fluctuation-dissipation theorem is the equation relating the two (see 4).