Light-induced Knight shifts in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Ga</mml:mi><mml:mi mathvariant="normal">As</mml:mi><mml:mo>∕</mml:mo><mml:msub><mml:mi mathvariant="normal">Al</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:msub><mml:mi mathvariant="normal">Ga</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:mi mathvariant="normal">As</mml:mi></mml:mrow></mml:math>quantum wells

Eickhoff, Marcus; Fustmann, Stefanie; Suter, Dieter

doi:10.1103/physrevb.71.195332

Cited by 7 publications

(8 citation statements)

References 25 publications

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“…This introduces hyperfine interactions, which report on spin-polarized electron density, as the measured perturbation. By modifying the sample orientation and the timing of the optical pulses within the rf sequence, this approach was adapted to a second end, revealing the distribution of E field in the same electronic states via a linear quadrupolar Stark effect (LQSE).The utility of ONMR in probing excited states has been long noted (3)(4)(5)13) and used to explore electrostatics in quantum wells (16,17), dots (10), and bulk materials (14, 15), but at a spectral resolution of no better than several kilohertz, set by many-body dipolar coupling between spins. Here, achieving resolution down to a few hertz, we demonstrate separate isolation of single-nucleus properties as the source of coherent spin evolution.…”

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confidence: 99%

“…The utility of ONMR in probing excited states has been long noted (3)(4)(5)13) and used to explore electrostatics in quantum wells (16,17), dots (10), and bulk materials (14, 15), but at a spectral resolution of no better than several kilohertz, set by many-body dipolar coupling between spins. Here, achieving resolution down to a few hertz, we demonstrate separate isolation of single-nucleus properties as the source of coherent spin evolution.…”

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confidence: 99%

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Imaging quantum confinement with optical and POWER (perturbations observed with enhanced resolution) NMR

Kempf

Miller

Weitekamp

2008

Proc. Natl. Acad. Sci. U.S.A.

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The nanoscale distributions of electron density and electric fields in GaAs semiconductor devices are displayed with NMR experiments. The spectra are sensitive to the changes to the nuclear-spin Hamiltonian that are induced by perturbations delivered in synchrony with a line-narrowing pulse sequence. This POWER (perturbations observed with enhanced resolution) method enhanced resolution up to 10 3 -fold, revealing the distribution of perturbations over nuclear sites. Combining this method with optical NMR, we imaged quantum-confined electron density in an individual AlGaAs/GaAs heterojunction via hyperfine shifts. Fits to the coherent evolution and relaxation of nuclei within a hydrogenic state established one-to-one correspondence of radial position to frequency. Further experiments displayed the distribution of photoinduced electric field within the same states via a quadrupolar Stark effect. These unprecedented high-resolution distributions discriminate between competing models for the luminescence and support an excitonic state, perturbed by the interface, as the dominant source of the magnetically modulated luminescence.GaAs ͉ hyperfine or Knight shift ͉ Stark effect ͉ H-band photoluminescence I maging electron distributions and the electrostatic potentials that govern their transfer is a longstanding goal in diverse fields. Spin or charge transfer defines function in systems for photovoltaic and photosynthetic energy capture, ion channels, enzyme catalysis, spintronics, and molecular and nanoscale electronics. Success in imaging nanoscale electronic properties can lead to mechanistic understanding and provide guidelines to tune device performance or to modify natural systems for specialized applications. With its atomic-scale capabilities for nondestructive, noninvasive spectroscopy and imaging, NMR seems well suited to such characterization. However, NMR of solids is hampered by broad spectral lines because of static interactions that prevent measurement of small differences between sites that might otherwise reveal local electronic features with atomic detail.Here, we present a general method whereby solid-state NMR surmounts this challenge and then apply it to image distributions of spin density and electric (E) field within an electronic state with dimensions (Ϸ10 nm) distributed over Ϸ10 5 nuclei. The POWER (perturbations observed with enhanced resolution) NMR approach, encodes small responses to a sample perturbation that is switched in synchrony with an NMR multiple-pulse line-narrowing sequence. The sequence removes the otherwise obscuring clutter of static spin interactions to yield a spectrum dominated by the desired perturbation with up to 3 orders-ofmagnitude resolution enhancement. To further obtain the sensitivity and selectivity needed to isolate signals of local, nanoscale features from the bulk signal of a macroscopic sample, we combined the POWER approach with methods for optical NMR (ONMR). By using both optical nuclear polarization (ONP) (1-15) and optical detection (2-4, 6, 7, 9-13), O...

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confidence: 99%

mentioning

confidence: 99%

Imaging quantum confinement with optical and POWER (perturbations observed with enhanced resolution) NMR

Kempf

Miller

Weitekamp

2008

Proc. Natl. Acad. Sci. U.S.A.

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“…Variation of the optical power (and therefore the relative occupation numbers of the two states) allows one, to some degree, to extract the individual parameters. In particular, the observed Knight shift is a direct measure of the electronic spin polarization, the lifetime of the electron spin, and the electronic excitation (26).…”

Section: Resultsmentioning

confidence: 99%

“…All three spectra show a splitting due to quadrupole coupling (resulting from strain), which does not change under the effect of the optical irradiation. The light does, however, cause a shift of all three lines by an amount that is proportional to the intensity of the optical irradiation and thus of the excited state population and electron spin density (26). Inverting the polarization of the light from right to left circular polarization inverted the sign of the Knight shift.…”

Section: Experimental Examplementioning

confidence: 95%

Spins as probes of different electronic states

Suter

Klieber

2007

Concepts Magnetic Resonance

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Nuclear spins are efficient probes of electronic states. Because most NMR experiments are performed in thermal equilibrium, they probe the electronic ground state - the only state that is significantly populated under ambient conditions. Probing electronically excited states becomes possible, if magnetic resonance techniques are combined with optical (laser) excitation. Depending on the nature of the electronic state, drastic changes of the magnetic resonance parameters may be observed. We discuss the basic principles of this type of investigation. Depending on the lifetime of the electronically excited state, it is possible to measure separate spectra of ground and excited state if the lifetime is long on the NMR timescale, or an averaged spectrum if the lifetime is short. We present examples for both limiting cases using rare earth ions and semiconductor heterostructures

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“…Direct control of nuclear spins by resonant techniques such as NMR is highly desirable for both electron and nuclear spin manipulation experiments. In the past NMR methods have been widely applied to large area semiconductor structures (heterojunctions, quantum wells etc) containing very large number of nuclei in the range 10 8 or more [4,[9][10][11]. Further refinement of these methods has made it possible to detect magnetic resonance of as few as 10 4 nuclei in otherwise abundant spin environments by detecting the optical response from individual GaAs quantum dot nano-structures [12,13].…”

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Optically tunable nuclear magnetic resonance in a single quantum dot

Makhonin

Chekhovich

Senellart³

et al. 2010

Phys. Rev. B

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We report optically detected nuclear magnetic resonance (ODNMR) measurements on small ensembles of nuclear spins in single GaAs quantum dots. Using ODNMR we make direct measurements of the inhomogeneous Knight field from a photo-excited electron which acts on the nuclei in the dot. The resulting shifts of the NMR peak can be optically controlled by varying the electron occupancy and its spin orientation, and lead to strongly asymmetric lineshapes at high optical excitation. The all-optical control of the NMR lineshape will enable position-selective control of small groups of nuclear spins in a dot. Our calculations also show that the asymmetric NMR peak lineshapes can provide information on the volume of the electron wave-function, and may be used for measurements of non-uniform distributions of atoms in nano-structures.Nuclear spins offer a nano-scale resource with extended spin life-times and coherence, leading to proposals to use nuclei for quantum computation [1][2][3][4] and coherent spin-memories [5]. Strong interest in nuclear spin effects in semiconductors has also been recently stimulated by research into manipulation of single spins in nano-structures, where the electron-nuclear (hyperfine) interaction plays an important role [6][7][8]. Direct control of nuclear spins by resonant techniques such as NMR is highly desirable for both electron and nuclear spin manipulation experiments. In the past NMR methods have been widely applied to large area semiconductor structures (heterojunctions, quantum wells etc) containing very large number of nuclei in the range 10 8 or more [4,[9][10][11]. Further refinement of these methods has made it possible to detect magnetic resonance of as few as 10 4 nuclei in otherwise abundant spin environments by detecting the optical response from individual GaAs quantum dot nano-structures [12,13]. These micro-ODNMR experiments revealed strong dot-to-dot variation of resonant frequencies [14], arising from interaction of small nuclear spin ensembles with random Knight fields from single spins of localized electrons [15].In this work we take advantage of the strong gradients of the Knight field inside a quantum dot produced by the localized electron spin and enter a new regime of nano-ODNMR. By employing ODNMR techniques first reported in Refs. [12,13], we measure with high precision the Knight shifts in the resonant frequencies of each individual isotope spin sub-system in individual GaAs/AlGaAs interface dots and find their dependence on the polarization and power of optical excitation. By varying the optical power, we find striking modifications of the lineshape of the NMR spectrum of the dot. These arise from the Knight field variation across the dot which in turn is determined by the spatial distribution of the electron wave-function. The interpretations are supported by calculations, which further demonstrate that by employing the inhomogeneities of the Knight shifts, it becomes possible to access selectively, by appropriate resonant frequencies, small groups of nuclear spi...

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Light-induced Knight shifts inGaAs∕AlxGa1−xAsquantum wells

Cited by 7 publications

References 25 publications

Imaging quantum confinement with optical and POWER (perturbations observed with enhanced resolution) NMR

Imaging quantum confinement with optical and POWER (perturbations observed with enhanced resolution) NMR

Spins as probes of different electronic states

Optically tunable nuclear magnetic resonance in a single quantum dot

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