Spin-dependent processes at the crystalline<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>Si-SiO</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>interface at high magnetic fields

We experimentally demonstrate a method for obtaining nuclear spin hyperpolarization, that is, polarization significantly in excess of that expected for a thermal equilibrium. By exploiting a modified Overhauser process, we obtain more than 68% nuclear anti-polarization of phosphorus donors in silicon. This polarization is reached with a time constant of ∼ 150 seconds, at a temperature of 1.37 K and a magnetic field of 8.5 T. The ability to obtain such large polarizations is discussed with regards to its significance for quantum information processing and magnetic resonance imaging. Phosphorus doped crystalline silicon (Si:P) is a model system for investigating spin effects in the solid state and at the same time is a point defect with great technological importance. Si:P has been used since the beginning of the semiconductor industry in the early 1950's for applications ranging from the ubiquitous (thin film transistors) to the conceptual (single electron transistors). The ability to hyperpolarize the spins in this material is important for a number of its applications. Utilizing the nuclear spin of phosphorus donors as quantum bits 1,2 relies on the ability to obtain a well characterized initial state 3 , which can be obtained by hyperpolarization. Spin polarized silicon microparticles may also have applications for magnetic resonance imaging techniques 4 , similar to other hyperpolarized systems, such as xenon 5 . Whilst it is reasonably simple to obtain large electron spin polarization, for example by using moderate magnetic fields at liquid 4 He temperatures, doing the same with nuclear spins is difficult due to their much smaller Zeeman splitting. There are a number of schemes used to obtain nuclear spin polarization in excess of the thermal polarization. Dynamic nuclear polarization using off-resonance radiation has been studied extensively 4,6 . Complex pulses or adiabatic passage effects may be used to manipulate spin states, leading to large polarizations 7,8 . Electrical injection of hot carriers has been used to obtain positive polarizations 9 , however this requires electrical contact to the sample. Optical excitation with linearly polarized sub-bandgap light has given small (∼ 2.5%) polarization of 29 Si nuclei in silicon with a natural isotopic abundance 10 .In this letter, we demonstrate anti-polarization of phosphorus donor nuclei in silicon of up to P = −68%. The scheme used is simple, fast and does not involve resonant manipulation of either the nuclear or electronic spin. Instead, the relative populations are modified using photoexcited carriers, generated using white light, at low temperatures (about 4 He temperature) and in magnetic fields (∼ 8.5 T) significantly smaller than those required to obtain an equivalent thermal nuclear spin polarization.Phosphorus in silicon can be described by the spin (S = 1/2) of its donor electron that is coupled to the spin (I = 1/2) of the 31 P nucleus. This model provides a system with four energy levels, as shown in Fig. 1 for the presence of strong magnet...

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“…Similar experiments have been described by us elsewhere 18,19 . The samples used in this study were similar to those described in reference 18 .…”

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confidence: 70%

Fast Nuclear Spin Hyperpolarization of Phosphorus in Silicon

et al. 2009

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“…This observation, however, does not prove that the observed recombination transitions take place between these different states. While the spin-dependency of transitions through localized states requires the existence of pairs of paramagnetic states 44 , there are examples of spin-dependent transitions which produce only a single resonance line in EDMR experiments 28,39 when transitions occur between identical centers or when the paramagnetic pairs are strongly coupled. Therefore, the detection of multiple EDMR lines (as in Figs.…”

Section: Experimental Datamentioning

confidence: 99%

T1andT2spin relaxation time limitations of phosphorous donor electrons near crystalline silicon to silicon dioxide interface defects

et al. 2010

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A study of donor electron spins and spin-dependent electronic transitions involving phosphorous ( 31 P) atoms in proximity of the (111) oriented crystalline silicon (c-Si) to silicon dioxide (SiO 2 ) interface is presented for [ 31 P] = 10 15 cm −3 and [ 31 P] = 10 16 cm −3 at about liquid 4 He temperatures (T = 5 K − 15 K). Using pulsed electrically detected magnetic resonance (pEDMR), spin-dependent transitions between the 31 P donor state and two distinguishable interface states are observed, namely (i) P b centers which can be identified by their characteristic anisotropy and (ii) a more isotropic center which is attributed to E ′ defects of the SiO 2 bulk close to the interface. Correlation measurements of the dynamics of spin-dependent recombination confirm that previously proposed transitions between 31 P and the interface defects take place. The influence of these electronic near-interface transitions on the 31 P donor spin coherence time T 2 as well as the donor spin-lattice relaxation time T 1 is then investigated by comparison of spin Hahn-echo decay measurements obtained from conventional bulk sensitive pulsed electron paramagnetic resonance and surface sensitive pEDMR, as well as surface sensitive electrically detected inversion recovery experiments. The measurements reveal that both T 2 and T 1 of 31 P donor electrons spins in proximity of energetically lower interface states at T ≤ 13 K are reduced by several orders of magnitude.

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“…So far, high-field EDMR has been carried out at 8.50 T on Si:P [15][16][17] with a multimode (Fabry-Pérot) cavity only, which requires comparatively long pulse duration times of the order of a few hundred nanoseconds for a π-pulse [15,16]. The sensitivity in those experiments was limited to ∼ 5 × 10 7 spins in the sample [15].…”

Section: Electron Paramagnetic Resonance [1] (Epr) Is An Important Spmentioning

confidence: 99%

Electrically detected magnetic resonance in a W-band microwave cavity

Lang

George

et al. 2011

Review of Scientific Instruments

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We describe a low-temperature sample probe for the electrical detection of magnetic resonance in a resonant W-band (94 GHz) microwave cavity. The advantages of this approach are demonstrated by experiments on silicon field-effect transistors. A comparison with conventional low-frequency measurements at X-band (9.7 GHz) on the same devices reveals an up to 100-fold enhancement of the signal intensity. In addition, resonance lines that are unresolved at X-band are clearly separated in the W-band measurements. Electrically detected magnetic resonance at high magnetic fields and high microwave frequencies is therefore a very sensitive technique for studying electron spins with an enhanced spectral resolution and sensitivity.

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Spin-dependent processes at the crystallineSi-SiO2interface at high magnetic fields

Cited by 28 publications

References 20 publications

Fast Nuclear Spin Hyperpolarization of Phosphorus in Silicon

Fast Nuclear Spin Hyperpolarization of Phosphorus in Silicon

T1andT2spin relaxation time limitations of phosphorous donor electrons near crystalline silicon to silicon dioxide interface defects

Electrically detected magnetic resonance in a W-band microwave cavity

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