Optical detection of single-electron spin resonance in a quantum dot

We demonstrate optically detected spin resonance of a single electron confined to a self-assembled quantum dot. The dot is rendered dark by resonant optical pumping of the spin with a laser. Contrast is restored by applying a radio frequency (rf) magnetic field at the spin resonance. The scheme is sensitive even to rf fields of just a few microT. In one case, the spin resonance behaves as a driven 3-level lambda system with weak damping; in another one, the dot exhibits remarkably strong (67% signal recovery) and narrow (0.34 MHz) spin resonances with fluctuating resonant positions, evidence of unusual dynamic processes.     

Acoustic detection of electron spin resonance

The ESR-signal of DPPH was recorded by detecting the modulation of the absorbed microwave power with a gas-coupled microphone. This photo-acoustic detection scheme is compared with conventional ESR-detection. Applications of the acoustical detection method to other modulation spectroscopic techniques, particularly NMR, are discussed.     

Non-equilibrium spin accumulation in ferromagnetic single-electron transistors

We study transport in ferromagnetic single-electron transistors. The non-equilibrium spin accumulation on the island caused by a finite current through the system is described by a generalized theory of the Coulomb blockade. It enhances the tunnel magnetoresistance and has a drastic effect on the time-dependent transport properties. A transient decay of the spin accumulation may reverse the electric current on time scales of the order of the spin-flip relaxation time. This can be used as an experimental signature of the non-equilibrium spin accumulation. Received 6 May 1998     

Optical detection of electron spin resonance in CdTe

We report the optical detection of electron spin resonance in p-type CdTe at 1.7 K in optical pumping conditions. The Overhauser shift of the electronic resonance, of the order of 45 G, is related to the sign of the electron g-factor g¹. We measure $\text{g}{}^1\text{= -1.59±0.02}$. Using this g¹ value and the previous results on the Knight shift, we deduce the value of the electron wavefunction on Cd in CdTe, which is consistent with the value in CdS.     

A new scheme for measuring itinerant spin polarizations

An optical method for the measurement of itinerant electron spin polarization is proposed. It is based on the idea that when an itinerant electron is injected into a p-type semiconductor with a valence band spin orbit splitting ? kT, the polarization of the resulting recombination radiation is characteristic of the spin polarization. The feasibility and advantages of this technique are discussed.     

Optical detection of conduction electron spin resonance in InP

Conduction electron spin resonance is optically detected in InP at 1.7 K. The measured value |g¹| = 1.26 ± 0.05 is in very good agreement with theoretical predictions and with the only other experimental determination available.     

Measurements of Kondo and spin splitting in single-electron transistors

We measure the spin splitting in a magnetic field B of localized states in single-electron transistors using a new method, inelastic spin-flip cotunneling. Because it involves only internal excitations, this technique gives the most precise value of the Zeeman energy Delta=/g/mu(B)B. In the same devices we also measure the splitting with B of the Kondo peak in differential conductance. The Kondo splitting appears only above a threshold field as predicted by theory. However, the magnitude of the Kondo splitting at high fields exceeds 2/g/mu(B)B in disagreement with theory.     

Room temperature electrical detection of spin coherence in C60

An experimental demonstration of electrical detection of coherent spin motion of weakly coupled, localized electron spins in thin fullerene C60 films at room temperature is presented. Pulsed electrically detected magnetic resonance experiments on vertical photocurrents through Al/C(60)/ZnO samples showed that an electron spin Rabi oscillation is reflected by transient current changes. The nature of possible microscopic mechanisms responsible for this spin to charge conversion as well as its implications for the readout of endohedral fullerene (N@C(60)) spin qubits are discussed.     

Muon spin resonance — A variant of magnetic resonance

Spin polarized positive muons injected in matter serve as magnetic probes for the investigation of various properties. The evolution of muon spin polarization rests on the same basis as in conventional magnetic resonance techniques. The background of the technique, different variants of the experimental set-up, and potential and limitations of the muon as a probe are described.     

A soft-segmentation visualization scheme for magnetic resonance images

Prevalent visualization tools exploit gray value distribution in images through modified histogram equalization and matching technique, referred to as the window width/window level-based method, to improve visibility and enhance diagnostic value. The window width/window level tool is extensively used in magnetic resonance (MR) images to highlight tissue boundaries during image interpretation. However, the identification of different regions and distinct boundaries between them based on gray-level distribution and displayed intensity levels is extremely difficult because of the large dynamic range of tissue intensities inherent in MR images. We propose a soft-segmentation visualization scheme to generate pixel partitions from the histogram of MR image data using a connectionist approach and then generate selective visual depictions of pixel partitions using pseudo color based on an appropriate fuzzy membership function. By applying the display scheme in clinical examples in this study, we could demonstrate additional overlapping regions between distinct tissue types in healthy and diseased areas (in the brain) that could help improve the tissue characterization ability of MR images.     

Electron spin resonance detection and identification of nitrogen centers in nanodiamonds

Individual nitrogen centers N⁰ and nitrogen pairs N ₂ ⁺ have been detected and identified in natural diamond nanocrystals by means of the high-frequency electron spin resonance method. The N⁰ nitrogen centers have been observed in synthetic diamond nanocrystallites with a size of less than 10 nm produced by high-temperature high-pressure sintering of detonation nanodiamonds. Thus, the possibility of the stable state of impurity nitrogen atoms in diamond nanoparticles has been demonstrated.     

Low-frequency spectra of dislocation paths in NaCl crystals in the electron spin resonance scheme

It is shown that the criterion of dislocation mobility resonance in NaCl crystals in the electron spin resonance scheme in the Earth’s magnetic field depends on both the sample orientation in this field and the location of impurity atoms in the dislocation core. The measured low-frequency spectrum of dislocation paths makes it possible to resolve a series of peaks corresponding to different positions of a Ca impurity that correlate with the results from computer simulations of the dislocation core structure.     

A beam divergence correction mirror for neutron resonance spin echo

Neutron resonance spin echo (NRSE) enables us to measure neutron quasi-elastic scattering with high energy resolution. Its energy resolution is limited by a path length variation due to the beam divergence. Neutron focusing technique using a neutron supermirror can be used to overcome this problem. To investigate the effect of a cylindrical mirror on the path length variation due to the beam divergence, MIEZE (modulation of intensity by zero effort) spin echo measurement was performed. The result demonstrated that the cylindrical mirror effectively corrects the path length variation and leads to high energy resolution as well as high intensity in NRSE and MIEZE measurement.     

A novel tamper detection scheme for BTC-compressed images

A novel image authentication scheme for the compressed images of block truncation coding (BTC) is proposed in this paper. In the proposed scheme, 1-bit authentication data is generated from the quantization levels of each image block. Multiple block permutations are generated by using the random sequences induced by the selected random number seeds. Multiple copies of the authenticaiton data are embedded into the bit maps of BTC-compressed image blocks based on the block permutations. Experimental results show that the proposed scheme achieves good detecting accuracy while keeping good image quatiy of the embedded image.     

Experimental tests for detecting spin polarization pick-up of single-electron19F-ions on emergence from magnetized iron

A new method to detect polarization pick-up by ions emerging from thin polarized ferromagnetic layers has been tested. The applied technique consists in the observation of attenuated-angular correlations and atomic spin precessions for single-electron ions recoiling through vacuum in weak transverse magnetic fields. The Coulomb-excited¹⁹F(5/2⁺) state at 197 keV was used as probe. The experimental concept is described and the expected effects are discussed using the perturbed angular correlation formalism for polarized hyperfine interactions.     

A neutron resonance spin echo spectrometer for quasi-elastic and inelastic scattering

We propose a modified neutron spin echo (NSE) spectrometer using high frequency spin flippers to replace the static spin flipper and the long magnetic precession field in each arm of the classicalspin echo setup. The spectrometer is suitable for quasi-elastic as well as inelastic scattering and can work with an arbitrary magnetic field on the sample. The restrictions on sample size and scattering angle can be relaxed, in comparison with the classical NSE method.     

Development of neutron resonance spin flipper for high resolution spin echo spectrometer

A new type of neutron resonance spin flipper (RSF) with high frequency oscillating magnetic field has been developed for Modulated IntEnsity by Zero Effort (MIEZE) spectrometer at cold neutron beam line MINE1 at JRR-3M reactor in JAEA. Dipole magnets enable us to provide the strong static fields for the RSFs. MIEZE signals have been demonstrated with the effective frequency of 600 kHz by using the new RSFs. The contrast of the signals was 0.58. The MIEZE spectrometer is under final process to practical use. The spectrometers can also be applied to the pulsed neutrons like J-PARC.     

A vertical transport geometry for electrical spin injection and extraction in Si

Schottky barriers formed between ferromagnetic metal and Semiconductor are of particular interest for spin injection and detection experiments. Here, we investigate electrical spin polarized carrier injection and extraction in Si using a Co/Si/Ni vertical structure built on a 250 nm thick Si membrane. Current–voltage measurements performed on the devices at low temperatures showed evidence of the conduction being dominated by thermionic field emission, which is believed to be the key to spin injection using Schottky junctions. This, however, proved inconclusive as our devices did not show any magnetoresistance signal even at low temperatures. We attribute this partially to the high resistance-area product in our Schottky contacts at spin injection biases. We show the potential of this vertical spin-device for future experiments by numerical simulation. The results reveal that by growing a thin highly doped Ge layer at the Schottky junctions the resistance-area products could be tuned to obtain high magnetoresistance.     

Single-molecule electron spin resonance

In 1993, two collaborations independently achieved the first optical detection of a single electron spin, using paramagnetic resonance of the triplet state of a single molecule. We review the context of this work and the main later results and give a brief outlook for future experiments based on the detection and manipulation of single spins by optical methods.