Linear scaling calculation of a n-type GaAs quantum dot

A linear scale method for calculating electronic properties of large and complex systems is introduced within a local density approximation. The method is based on the Chebyshev polynomial expansion and the time-dependent method, which is tested in calculating the electronic structure of a model n-type GaAs quantum dot.Comment: 5 pages, 3 figure

Long-range orders and spin/orbital freezing in the two-band Hubbard model

We solve the orbitally degenerate two-band Hubbard model within dynamical mean field theory and map out the instabilities to various symmetry-broken phases based on an analysis of the corresponding lattice susceptibilities. Phase diagrams as a function of the Hund coupling parameter J are obtained both for the model with rotationally invariant interaction and for the model with Ising-type anisotropy. For negative J, an intraorbital spin-singlet superconducting phase appears at low temperatures, while the normal state properties are characterized by an orbital-freezing phenomenon. This is the negative-J analog of the recently discovered fluctuating-moment induced s-wave spin-triplet superconductivity in the spin-freezing regime of multiorbital models with J>0

Aharonov-Bohm Oscillations in Photoluminescence from Charged Exciton in Quantum Tubes

The oscillation of photoluminescence peak energies is observed in InAs quantum tubes depending on the magnetic flux through the tube. The oscillation is shown to be due to the Aharonov-Bohm effect of a charged exciton in a quantum tube. No quadratic shift in photoluminescence peak energies is observed, which is a characteristic feature of a thin quantum tube with a single channel surrounding the magnetic flux through the tube.Comment: 14 pages, 4 figure

Fabrication of Highly Ordered Arrays of Nanoparticles by Mechanical Process

We have developed a new method of fabricating nanoparticles utilizing a mechanical rubbing process. Highly ordered arraysof Au nanoparticles with a diameter of 60 nm have been fabricated on a porous anodic alumina template. Pressuremeasurements during the mechanical rubbing process confirmed that these nanoparticles were formed only by a mechanicalseparation process. Our method can be applied to fabricate nanocapsules and has a wide range of applicability to materials thathave never been controlled in the nanoscale

Study on non-contact measurement method of resistance spot weld nugget diameter using laser ultrasonic technique

Resistance spot welding can instantaneously join two or more plates by the resistance heating of the metal and is in high demand owing to its high productivity and high-work efficiency. For the quality control of resistance spot welding, the size and quality of the welded part, called the nugget, are important. Therefore, this study aims to establish a highly efficient and high-speed resistance spot-weld inspection method that can be applied to whole-lot inspection, which is currently a difficult process. The objective of this study is to measure the nugget diameter using laser ultrasonic technique that enable remote, non-contact ultrasonic inspection. An investigation of the available ultrasonic waves using simulated test specimens demonstrated the feasibility of estimating the distance from the generation/detection point to the joint using the diffraction of the Lamb wave, which can propagate long distances in a thin plate. By measuring the actual resistance spot welding specimens, it was determined that differences in the nugget diameter of approximately 0.5 mm could be clearly distinguished from the arrival time of the diffraction waves. It was also inferred that the nugget diameter could be calculated by determining the propagation velocity of the diffraction wave with a similar accuracy to that of the measurement using a contact-type probe.Nomura K., Mishima S., Deno S., et al. Study on non-contact measurement method of resistance spot weld nugget diameter using laser ultrasonic technique. NDT and E International 140, 102973 (2023); https://doi.org/10.1016/j.ndteint.2023.102973

Frequency modulation technique for wide-field imaging of magnetic field with nitrogen-vacancy ensembles

We report on the application of a frequency modulation technique to wide-field magnetic field imaging of nitrogen-vacancy centers in diamond at room temperature. We use a scientific CMOS (sCMOS) camera to collect photoluminescence images from a large number of nitrogen-vacancy center ensembles in parallel. This technique allows a significant reduction in the measurement time required to obtain a magnetic field image compared with a scanning probe approach at a comparable magnetic field sensitivity

Polarization envelope helicity dependent photovoltage in GaAs/Al03Ga07As modulation-doped quantum well

In this study, we demonstrate the switching of the direction of the photocurrent in an n-type GaAs/Al0.3Ga0.7As modulation-doped quantum well using a polarization pulse-shaping apparatus containing a 4f setup. The right- and left-polarization-twisting pulses with a polarization rotation frequency in the THz-regime are incident on a modulation-doped quantum well. The results show that the sign of the photovoltage is dependent on the direction of rotation of the polarization-twisting pulses, which can be explained by the circular photogalvanic effect combined with the production of a classical edge photocurrent from the acceleration of free electrons in the vicinity of the sample edge by the incident optical electric field. The wide range over which the polarization-rotation frequency may be tuned makes this method a powerful tool to investigate the response of an extensive variety of materials in the THz-regime