Spin-Polarized Scanning Tunneling Microscopy

Literature Review by Dmitri Y. Petrovykh

1. Introduction
2. SPSTM Basics
3. Spin-Polarized Tunneling
4. SPSTM with Magnetic Tips
5. Optically Pumped Tips
6. SPSTM Q&A
7. References

VI. SPSTM Questions and Answers

As it was noted repeatedly, SPSTM experiments are facing numerous technical difficulties, many of which were identified at the prototype stage¹⁶ and by various experimental groups^17,20,23,24:

• Thermal drift problems: sample and tip can be heated by the magnetic coils and illuminating laser light. Also in many cases scan speeds have to be low, which results in abnormally high thermal drifts.
• Magnetostriction of both the tip and the sample (even paramagnetic sample) can introduce significant uncertainty in tip-sample separation.
• Magnetostatic tip-sample interactions are poorly understood on nm scale.
• Stray magnetic fields, non-stable laser light, and other sources of spurious noise.
• Lack of a good test system [such as Si(111) 7x7 reconstructed surface for STM (Fig. 1)].

None of the above problems, however, appear insurmountable at this point: alternative tip materials can fight the magnetic effects; faster and smaller STM's will help with drift; dealing with noises is every experimentalist's headache, but it never stopped anybody anyway; even the test system problem may be solved by stepped surfaces, for example. There is certainly room for future developments, but the situation is far from desperate.

In addition, there are a few other alternative SPSTM techniques, such as idea of Alvarado et al. to combine the SEMPA⁶ technique and polarized fluorescence into STM-induced fluorescence with polarization analysis²⁵. These ideas are generally only on very preliminary stages right now, but so were the current favorites just a few years ago, and only the future will tell us which one them will be the first to reach the ultimate goal of magnetic microscopy with atomic resolution.

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