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Register a new userElectrically detected magnetic resonance of neutral donors interacting with a two-dimensional electron gas
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We have measured the electrically detected magnetic resonance of channel-implanted donors in silicon field-effect transistors in resonant X- ($9.7:$GHz) and W-band ($94:$GHz) microwave cavities, with corresponding Zeeman fields of $0.35:$T and $3.36:$T, respectively. It is found that the conduction electron resonance signal increases by two orders of magnitude from X- to W-band, while the hyperfine-split donor resonance signals are enhanced by over one order of magnitude. We rule out a bolometric origin of the resonance signals, and find that direct spin-dependent scattering between the two-dimensional electron gas and neutral donors is inconsistent with the experimental observations. We propose a new polarization transfer model from the donor to the conduction electrons as the main contributer to the spin resonance signals observed.
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We report on the demonstration of the resistively detected nuclear magnetic resonance (RDNMR) of a single InSb two-dimensional electron gas (2DEG) at elevated temperatures up to 4 K. The RDNMR signal of 115In in the simplest pseudospin quantum Hall ferromagnet triggered by a large direct current shows a peak-dip line shape, where the nuclear relaxation time T1 at the peak and the dip is different but almost temperature independent. The large Zeeman, cyclotron, and exchange energy scales of the InSb 2DEG contribute to the persistence of the RDNMR signal at high temperatures.
In an ultrahigh mobility 2D electron gas, even a weak nonparabolicity of the electron dispersion, by violating Kohns theorem, can have a drastic effect on dc magnetotransport under ac drive. We study theoretically the manifestation of this effect in the dc response to the combined action of two driving ac-fields (bichromatic irradiation). Compared to the case of monochromatic irradiation, which is currently intensively studied both experimentally and theoretically, the presence of a second microwave source provides additional insight into the properties of an ac-driven 2D electron gas. In particular, we find that nonparabolicity, being the simplest cause for a violation of Kohns theorem, gives rise to new qualitative effects specific to bichromatic irradiation. Namely, when the frequencies $omega_1$ and $omega_2$ are well away from the cyclotron frequency, $omega_c$, our simple classical considerations demonstrate that the system becomes parametrically unstable with respect to fluctuations with frequency $(omega_1+omega_2)/2$. As an additional effect of nonparabolicity, this parametric instability can manifest itself in the dc properties of the system. This happens when $omega_1$, $omega_2$ and $omega_c$ are related as 3:1:2, respectively. Even for weak detuning between $omega_1$ and $omega_2$, the effect of the bichromatic irradiation on the dc response in the presence of nonparabolicity can differ dramatically from the monochromatic case. In particular, the equations of motion can acquire multistable solutions. As a result, the diagonal dc-conductivity can assume several stable negative values at the same magnetic field.
Electrically-detected magnetic resonance (EDMR) provides a highly sensitive method for reading out the state of donor spins in silicon. The technique relies on a spin-dependent recombination (SDR) process involving dopant spins that are coupled to interfacial defect spins near the Si/SiO$_2$ interface. To prevent ionization of the donors, the experiments are performed at cryogenic temperatures and the mobile charge carriers needed are generated via optical excitation. The influence of this optical excitation on the SDR process and the resulting EDMR signal is still not well understood. Here, we use EDMR to characterize changes to both phosphorus and defect spin readout as a function of optical excitation using: a 980 nm laser with energy just above the silicon band edge at cryogenic temperatures; a 405 nm laser to generate hot surface-carriers; and a broadband white light source. EDMR signals are observed from the phosphorus donor and two distinct defect species in all the experiments. With near-infrared excitation, we find that the EDMR signal primarily arises from donor-defect pairs, while at higher photon energies there are significant additional contributions from defect-defect pairs. The optical penetration depth into silicon is also known to be strongly wavelength dependent at cryogenic temperatures. The energy of the optical excitation is observed to strongly modulate the kinetics of the SDR process. Careful tuning of the optical photon energy could therefore be used to control both the subset of spin pairs contributing to the EDMR signal as well as the dynamics of the SDR process.
We study the coupling of Pb0 dangling bond defects at the Si/SiO2 interface and 31P donors in an epitaxial layer directly underneath using electrically detected double electron-electron resonance (EDDEER). An exponential decay of the EDDEER signal is observed, which is attributed to a broad distribution of exchange coupling strengths J/2pi from 25 kHz to 3 MHz. Comparison of the experimental data with a numerical simulation of the exchange coupling shows that this range of coupling strengths corresponds to 31P-Pb0 distances ranging from 14 nm to 20 nm.
We compute the single-particle states of a two-dimensional electron gas confined to the surface of a cylinder immersed in a magnetic field. The envelope-function equation has been solved exactly for both an homogeneous and a periodically modulated magnetic field perpendicular to the cylinder axis. The nature and energy dispersion of the quantum states reflects the interplay between different lengthscales, namely, the cylinder diameter, the magnetic length, and, possibly, the wavelength of the field modulation. We show that a transverse homogeneous magnetic field drives carrier states from a quasi-2D (cylindrical) regime to a quasi-1D regime where carriers form channels along the cylinder surface. Furthermore, a magnetic field which is periodically modulated along the cylinder axis may confine the carriers to tunnel-coupled stripes, rings or dots on the cylinder surface, depending on the ratio between the the field periodicity and the cylinder radius. Results in different regimes are traced to either incipient Landau levels formation or Aharonov-Bohm behaviour.
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