Magneto-optical Faraday effect probed in a scanning tunneling microscope

Prins, Mwj Menno; Wielen, M.C.M.M. van der; Abraham, D. L.; Kempen, H. van; Kesteren, H.W. van

doi:10.1109/20.334117

Cited by 6 publications

(11 citation statements)

References 4 publications

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“…Magnetic imaging can be achieved in two distinct ways, namely, by magneto-optical near-field imaging 8 and by spin-polarized tunneling due to optical spin-orientation. [9][10][11] In magnetooptical imaging, the semiconductor tip operates as a local photodetector that maps the polarization-dependent optical properties of a magnetic material. This implies that the main interest is directed toward a small collection volume for photocarriers and a high sensitivity to variations of the optical intensity.…”

Section: Discussionmentioning

confidence: 99%

“…9,10 However, because a STM is normally operated in the constant-current mode, the frequency band between zero and about 2 kHz is used for stabilization of the tip-to-sample distance. Hence, additional signals have to be detected at frequencies higher than the bandwidth of the constant-current feedback system.…”

Section: Modulated Photoexcitationmentioning

confidence: 99%

“…5 Ϫ7 These tips hold special attraction with regard to near-field optical imaging 8 and as sources of optically oriented spin-polarized electrons. [9][10][11] In this paper, we intend to develop a thorough understanding of the current transport properties of photoexcited semiconductor materials in the STM. The outline is as follows.…”

Section: Introductionmentioning

confidence: 99%

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Photoelectrical properties of semiconductor tips in scanning tunneling microscopy

Prins¹,

Jansen²,

Groeneveld³

et al. 1996

Phys. Rev. B

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We describe a model as well as experiments on the electrical properties of a photoexcited tunnel junction between a metal and a semiconductor material, as is established in a scanning tunneling microscope. The model treats the case in which carrier transport is mediated by capture and relaxation in the semiconductor surface states. In the semiconductor, majority carrier transport is determined by thermionic emission over the Schottky barrier and subsequent surface recombination. By optical excitation an additional minority carrier current is generated. The voltage that develops on the semiconductor surface is determined by the balance between majority and minority carrier current in the semiconductor, and the current across the tunnel barrier. We present model calculations of the ͑nonplanar͒ band-bending profile in the semiconductor, which indicate that the subsurface electric field operates as an electrical lens that can focus or defocus the current. Measurements were performed with moderately doped GaAs tips or samples prepared by cleavage. Continuous as well as modulated photoexcitation was used. Relationships are determined between tunnel current, applied voltage, incident optical power, and tip-sample distance. The experimental results are well described by the model that includes carrier capture in the semiconductor surface states. It is shown that the sensitivity of the tunnel current to small variations in optical power is determined by the ratio of the tunnel barrier conductance to the Schottky barrier conductance. The implications for near-field optical imaging and spin-polarized tunneling with semiconductor tips are discussed.

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Section: Discussionmentioning

confidence: 99%

Section: Modulated Photoexcitationmentioning

confidence: 99%

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Photoelectrical properties of semiconductor tips in scanning tunneling microscopy

Prins¹,

Jansen²,

Groeneveld³

et al. 1996

Phys. Rev. B

Self Cite

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“…In previously reported experiments with planar junctions, 15 a variation of photon energy and sample magnetization were employed in order to separate the spinaveraged and spin-selective signals. However, in a STM experiment, it is not trivial to employ these techniques without disturbing the critical optical alignment or the tunnel junction itself.…”

Section: A Introductionmentioning

confidence: 99%

“…14 In planar Co/Al 2 O 3 /GaAs junctions, evidence for spin-polarized tunneling of optically excited electrons was already reported. 15,16 The application of GaAs for magnetic imaging has become a hot issue with the development of cleaved GaAs tips for STM operation, under ultrahigh vacuum conditions, 17 as well as under ambient conditions. 18,19 In the latter studies, optical excitation was already included, but the spin sensitivity of GaAs tips was not yet demonstrated.…”

Section: Introductionmentioning

confidence: 99%

Spin-polarized tunneling with GaAs tips in scanning tunneling microscopy

1996

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We describe a model as well as experiments on spin-polarized tunneling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide ͑GaAs͒, where the latter is optically excited with circularly polarized light in order to generate spin-polarized carriers. We present a transport model that takes account of carrier capture in the semiconductor surface states, and describes the semiconductor surface in terms of a spin-dependent energy distribution function. The so-called surface spin splitting can be calculated from the balance of the polarized electron and hole flow in the semiconductor subsurface region, the polarized tunneling current across the tunnel barrier between the magnetic material and the semiconductor surface, and the spin relaxation at the semiconductor surface. We present experimental data obtained in a scanning tunneling microscope with a GaAs tip and a Pt/Co multilayer sample under ambient conditions. A helicity asymmetry of tunnel current ͑i.e., a circular-polarization-dependent tunnel current͒ was found with a magnitude of 4 pA , which was verified not to be due to variations of the optical power. According to our model and estimations, this observation can be explained by spin-polarized tunneling, with a lower limit to the semiconductor surface spin splitting and spin lifetime of 4 mV and 0.4 ns, respectively.

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