Optically detected nuclear magnetic resonance in n-GaAs using an on-chip microcoil

Abstract

Optically detected nuclear magnetic resonance (NMR) with micrometer resolution is demonstrated in n-GaAs using an on-chip microcoil. To trace the Overhauser field, the electron Larmor frequency is monitored via time-resolved magneto-optical Kerr rotation. Sweeping the frequency of the rf magnetic field induced by an on-chip microscale current loop, nuclear spin depolarization is achieved for each isotope species. The experimental data indicate an impact of a local quadrupole field, most likely caused by ionized donors, on the amplitude and linewidth of the NMR spectrum. By applying rf pulse sequences, the Rabi oscillation of A75s nuclear spins is obtained with an effective dephasing time of ∼200 μs.

Dynamic Nuclear Spin Resonance inn-GaAs

“…The local rf field is provided by an on-chip Au microcoil with an inner diameter of about 19 m, which is realized atop the semiconductor by electron beam lithography and liftoff technique [15,16]. We use TRKR measurements to track the electron Larmor precession frequency !…”

“…We use TRKR measurements to track the electron Larmor precession frequency ! L [16] for gaining insight into the nuclear spin dynamics under rf excitation. For linear optical excitation the characteristic electron Larmor frequency is found to be $13:9 GHz (see dashed line in Fig.…”

“…To perform NMR experiments, a switchable rf field with a magnitude of $1:2 mT is generated from the on-chip microscale current loop [16]. For the NMR experiments discussed in the following, optical excitation is always on and DNP gets saturated prior to the rf excitation being switched on.…”

“…1. They can be classified as four types: (1) fundamental NMR at frequencies of f ¼ B ext [7][8][9][10][11]13,14,16,17,19], where is the nuclear gyromagnetic ratio of isotope species ; (2) two-spin NMR involving one isotope species at 2f [10,13,19]; (3) two-spin NMR involving different species of isotopes at (f 1 þ f 2 ) [19]; (4) half-harmonic NMR at 1=2f [12,19,20].…”

“…This geometry can happen in case of either strong nuclear quadrupole interaction with the crystal field if the applied rf field is perpendicular to B ext [8,12], or the applied rf field is intentionally oblique to B ext [20]. As the quadrupole field around donors is on the order of 0.1 mT [16,22], which is quite small compared with B ext ¼ 374 mT, this hardly changes the parallelism of B N and B ext . However, the transverse field component B rf-tran (parallel to B ext ) varies within the microcoil center and can achieve values on the order of 1 mT in the metal vicinity, thus resulting in B N , which is oblique to the total rf field.…”