Polarized Low-Energy Positrons: A New Probe of Surface Magnetism

Gidley, David W.; Köymen, A. R.; Capehart, T. W.

doi:10.1103/physrevlett.49.1779

Cited by 102 publications

(42 citation statements)

References 26 publications

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“…The asymmetry of AR that is induced by the spin flip of the outermost electrons (+P_-o--P_) can be written as [11] AR(+P_) -AR(-P_) _ 2e(l) -c(0) AR(+P_) + AR(-P_) 2e(l)+e(0) + 1 '…”

mentioning

confidence: 99%

Charge-to-Spin Conversion and Spin Diffusion in Bi/Ag Bilayers Observed by Spin-Polarized Positron Beam

Zhang

Yamamoto

et al. 2015

Phys. Rev. Lett.

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Charge-to-spin conversion induced by the Rashba-Edelstein effect was directly observed for the first time in samples with no magnetic layer. A spin-polarized positron beam was used to probe the spin polarization of the outermost surface electrons of Bi/Ag/Al2O3 and Ag/Bi/Al2O3 when charge currents were only associated with the Ag layers. An opposite surface spin polarization was found between Bi/Ag/Al2O3 and Ag/Bi/Al2O3 samples with the application of a charge current in the same direction. The surface spin polarizations of both systems decreased exponentially with the outermost layer thickness, suggesting the occurrence of spin diffusion from the Bi/Ag interface to the outermost surfaces. This work provides a new technique to measure spin diffusion length.

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“…The asymmetry of AR that is induced by the spin flip of the outermost electrons (+P_-o--P_) can be written as [11] AR(+P_) -AR(-P_) _ 2e(l) -c(0) AR(+P_) + AR(-P_) 2e(l)+e(0) + 1 '…”

mentioning

confidence: 99%

Charge-to-Spin Conversion and Spin Diffusion in Bi/Ag Bilayers Observed by Spin-Polarized Positron Beam

Zhang

Yamamoto

et al. 2015

Phys. Rev. Lett.

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“…Spin-polarized positron sources and beams have been used for 50 yr to measure electron spin momentum distributions in ferromagnets [6], observe surface magnetism [7], search for the origin of optical activity in biological molecules [8], and study fundamental interactions [9,10]. With the advent of high density positron pulse techniques, the possibility of producing a Bose-Einstein condensate (BEC) of spin-polarized Ps atoms [11] has made it imperative to demonstrate some means of forming a fully spinpolarized collection of Ps.…”

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confidence: 99%

Production of a Fully Spin-Polarized Ensemble of Positronium Atoms

2010

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Long-lived |m|=1 positronium (Ps) atoms are produced in vacuum when high density bursts of positrons with net polarization p{0} are implanted into a porous silica film in a 2.3 T magnetic field. We observe a decrease in the |m|=1 population as the density of the incident positron beam is increased due to quenching interactions between oppositely polarized Ps atoms within the target. Saturation of this density dependent quenching indicates that the initial positron spin polarization p{0}=28+/-1%, and demonstrates the long term (10{2} s) survival of positron polarization in a Surko-type buffer gas trap. We conclude that, at high Ps densities, the minority spin component is essentially eliminated and the remaining Ps is almost entirely (approximately 96%) polarized, as required for the formation of a Ps Bose-Einstein condensate.

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“…For positronium in its ground state, the annihilation rate depends on the relative spin states of the electron and positron: if the spins are parallel (triplet states) the mean lifetime is relatively long (142 ns) whereas the antiparallel (singlet) configuration is short lived (0.125 ns). Despite its relatively short lifetime, Ps can still be used in a wide array of experiments, including precision laser spectroscopy [4], Ps ion [5] or molecule [6] formation, Psatom scattering cross section measurements [7], studies of defects [8], thin film polymers [9], surface magnetism [10], electronic densities of states [11], quantum sticking [12], and fundamental symmetry tests [13].…”

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confidence: 99%

Positronium formation via excitonlike states on Si and Ge surfaces

et al. 2011

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Recent experiments combining lifetime and laser spectroscopy of positronium (Ps) show that these atoms are emitted from p-Si(100) at a rate that depends on the sample temperature, suggesting a thermal activation process, but with an energy that does not, precluding direct thermal activation as the emission mechanism. Moreover, the amount of Ps emitted is substantially increased if the target is irradiated with 532 nm laser light just prior to the implantation of the positrons. Our interpretation of these data was that the Ps was emitted via an exciton-like positron-electron surface state, not dissimilar to an electronic surface exciton observed on Si in two-photon photoemission measurements. The hypothesis that this state may be populated by electrons from one of the occupied electronic surface states, either thermally or by laser excitation, is consistent with our observations and suggests that one should expect a high Ps yield at room temperature from an n-doped Si(100) sample, since in this case the same surface states will already be occupied. Here we present data obtained with an n-Si(100) target that supports our model, and also reveals the unexpected result that the kinetic energy of Ps emitted from this material actually decreases when it is heated, an effect we attribute to shifts in the surface energy levels due to the presence of a high density of thermally generated electrons. We show data obtained with a Ge(100) sample that corroborate the idea that the effects we observe are related to surface electron states, and hence should occur for any indirect band gap semiconductor with dangling bond states. Our model is further confirmed by the observation that the Ps yield from p-Si depends linearly on the surface density of the implanted positrons due to the effects of electron-hole pairs created as the positrons slow down.

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Polarized Low-Energy Positrons: A New Probe of Surface Magnetism

Cited by 102 publications

References 26 publications

Charge-to-Spin Conversion and Spin Diffusion in Bi/Ag Bilayers Observed by Spin-Polarized Positron Beam

Charge-to-Spin Conversion and Spin Diffusion in Bi/Ag Bilayers Observed by Spin-Polarized Positron Beam

Production of a Fully Spin-Polarized Ensemble of Positronium Atoms

Positronium formation via excitonlike states on Si and Ge surfaces

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