Electron paramagnetic resonance and dynamic nuclear polarization via the photoexcited triplet states of radiation defects in natural and ²⁹ Si isotope enriched silicon

Abstract

Electron paramagnetic resonance (EPR) of the triplet centers and dynamic29 Si nuclear polarization was studied in irradiated naturally abounded (4.7%) and 29Si isotope enriched (99.3%) silicon crystals. Saturation of the EPR lines of the photoexcited triplet centers with nonequilibrium spin polarization between m S = +1, 0, and -1 sates leads to the nuclear polarization ≈7000 times higher than equilibrium value. It was shown that the observed dynamic nuclear polarization is a result of the "solid-effect". 1 Introduction Growing interest to the investigation of spin dependent phenomena in silicon is related to the advantages in the production of the isotope enriched silicon crystals and silicon based structures. The possible future applications of these materials in spin electronics and quantum computers require high electron and nuclear spin polarization.The photoexcited spin S = 1 centers characterized by strong nonequilibrium populations of states with different spin projections m S = +1, 0, and -1 can be used for dynamic nuclear polarization. The defects with the excited triplet states are produced by electron or γ-irradiation of silicon crystals containing oxygen and carbon impurity atoms [1][2][3][4].In the present paper we report the experimental results of electron paramagnetic resonance (EPR) and dynamic nuclear polarization (DNP) investigations in irradiated silicon crystals containing different amount of the 29 Si lattice nuclei.

Simultaneous Subsecond Hyperpolarization of the Nuclear and Electron Spins of Phosphorus in Silicon by Optical Pumping of Exciton Transitions

“…Electron and nuclear spin polarization in silicon has been studied for decades [15,16,17,18,19,20,21,22,23,24], but the nuclear polarization obtained to date has typically been less than a few percent, and requires thousands of seconds to establish. Very recently, a 31 P nuclear polarization of 68% has been reported [24] in a high magnetic field, using a variation of a mechanism first proposed in 1959 [17], and demonstrated in InSb in 1963 [18], but the time constant was still a relatively long 150 s. The method demonstrated here works at low magnetic field, and can simultaneously hyperpolarize both the electron and nuclear spins of 31 P in less than a second.…”

“…Several methods for achieving quantum logic with spin states of the shallow neutral donor (D 0 ) 31 P in 28 Si have been proposed [1,2,3] and the manipulation of electron and nuclear spin coherences have been demonstrated [4], but unsolved challenges include the measurement of single spins and the initialization, or polarization, of these spins. Fortuitously, the isotopic enrichment of 28 Si has another dramatic effect: the linewidths of many optical transitions are drastically reduced [9,10,11,12,13], including those involving 31 P. These narrow transitions have been proposed both for measurement of single spins [12,13,14] and for preferentially populating specific spin states [12,13].Electron and nuclear spin polarization in silicon has been studied for decades [15,16,17,18,19,20,21,22,23,24], but the nuclear polarization obtained to date has typically been less than a few percent, and requires thousands of seconds to establish. Very recently, a 31 P nuclear polarization of 68% has been reported [24] in a high magnetic field, using a variation of a mechanism first proposed in 1959 [17], and demonstrated in InSb in 1963 [18], but the time constant was still a relatively long 150 s. The method demonstrated here works at low magnetic field, and can simultaneously hyperpolarize both the electron and nuclear spins of 31 P in less than a second.…”

Optical and dynamic nuclear polarization of29Si nuclei via photoexcited triplet states of oxygen-vacancy complexes in isotopically controlled silicon

“…The intensity of Si-SL1 EPR lines and P N are in accordance with this picture for the temperature range 4-20 K but decreases at higher temperatures in accordance with our earlier investigations. 40 Such a decrease of P N at T >20 K is explained by the decrease in electron spin-lattice relaxation, which, in turn, decreases the electron spin polarization degree between magnetic sublevels of Si-SL1 centers. 40,61 To achieve the higher DNP degree in shorter time, we used the laser excitation at the light power up to 700 mW.…”

“…39 While the physics leading to very high 29 Si polarization in microparticles 38 and in heavily doped silicon 39 is very interesting, employment of lightly doped silicon single crystals are preferred strongly for quantum information processing in order to retain the coherence time as long as possible. The present work shows a systematic investigation of dynamic 29 Si nuclear polarization using electron spins bound to photoexcited oxygen-vacancy (O-V) spin-triplet (SL1) centers, 40,41 leading to the maximum 29 Si nuclear polarization of ∼6.4%. The concentration of SL1 is low, of the order of 10 15 cm −3 , and they exist only during the optical irradiation for initialization.…”

Dynamic nuclear polarization ofS29inuclei in isotopically controlled phosphorus doped silicon

“…34 Enhancement of nuclear polarization greater than 7000 was observed in recent DNP experiments using saturation of the EPR transitions of the photoexcited triplet states of radiation defects. 35 The present study focuses on DNP of 29 Si nuclear spins based on saturation of phosphorus donor EPR transitions. A phosphorus EPR spectrum consists of two absorption lines separated by 4.2 mT due to the isotropic hyperfine interaction with the phosphorus nuclear spin I =1/ 2.…”