Hyperfine spectroscopy in a quantum-limited spectrometer

Abstract

Abstract. We report measurements of electron spin echo envelope modulation (ESEEM) performed at millikelvin temperatures in a custom-built high-sensitivity spectrometer based on superconducting micro-resonators. The high quality factor and small mode volume (down to 0.2 pL) of the resonator allow to probe a small number of spins, down to 5 ⋅ 102. We measure 2-pulse ESEEM on two systems: erbium ions coupled to 183W nuclei in a natural-abundance CaWO4 crystal, and bismuth donors coupled to residual 29Si nuclei in a silicon substrate that was isotopically enriched in the 28Si isotope. We also measure 3- and 5-pulse ESEEM for the bismuth donors in silicon. Quantitative agreement is obtained for both the hyperfine coupling strength of proximal nuclei, and the nuclear spin concentration.

Electron spin resonance spectroscopy with femtoliter detection volume

“…For B 0 < 1 mT, slight oscillations are visible on top of an exponential decay with T 2 ¼ 0:85 ms. They approximately match the expected Electron Spin Echo Envelope Modulation (ESEEM) by a bath of 29 Si nuclei with the nominal relative concentration of 5 Â 10 À4 , 32 suggesting that spins are in the bulk of the sample.…”

Spin echo from erbium implanted silicon

“…Also, the large modulation index is inconsistent with the 4.67% abundance of 29 Si and a single crystallographic position. Another possibility is ν1 and ν2 originate from two crystallographic positions, one with ≈ ≈ 1 ≈ , the other with…”

“…24 Since the 4f wavefunction is highly localised, the superhyperfine coupling between a RE and a neighbouring nuclear spin is usually regarded as magnetic dipole-dipole only. 25,26 The ESEEM effect when using to a two pulse echo sequence, 2 ( 12 ), on an isolated Er 3+ ion (effective electron spin S = ½) in proximity to a 29 Si nuclei (nuclear spin I = ½) can be described as follows, 23…”

“…Also, a crystallographic position with ≈ ≈ 2 indicates strong coupling, which can be discounted for the same reasons given for the first possible origin. Given the structure of the OEr-3 centre, it is more likely that the observed ESEEM is due to weak coupling to many 29 Si nuclei, in which case each 29 Si nuclei has ≈ ≈ and ≪ 1; in this situation the overall decay profile is given by 29…”

“…The origin of the echo is an Er centre surrounded by six O atoms with monoclinic site symmetry. The spin echo decay profile had superimposed modulations due strong superhyperfine coupling with a spin bath of 29 Si nuclei. This is the author's peer reviewed, accepted manuscript.…”