Kyun Nahm

Band structure of ternary compound semiconductors beyond the virtual crystal approximation

A simple pseudopotential scheme, which incorporates compositional disorder as an effective potential, is proposed for calculation of the band structure of ternary compound semiconductors. It is shown that the present theory, which is free from any additional parameter, satisfactorily produces the band-gap bowings of ternary compounds when the lattice mismatch is small.

Acoustic wave propagation in one-dimensional phononic crystals containing Helmholtz resonators

One-dimensional acoustic waveguide containing subwavelength-sized Helmholtz resonators is known to exhibit novel physical phenomena. However, no systematic theoretical study on this system has been carried out so far except on a few limited cases. We present a thorough theoretical calculation on the acoustic wave propagation in phononic crystals containing Helmholtz resonators without any geometrical size restrictions. The band structures, transmission spectra, and defect states are studied for diverse geometries using the interface response theory. It is shown that the acoustic band structure of the model is fundamentally different from the conventional acoustic–elastic cases and richer due to the coexistence of the resonant and the Bragg gaps. It is also shown that the presence of a defect resonator in the system can give rise to a localized mode inside the resonance gaps. The results clearly show that the presence of the Helmholtz resonators singly or periodically can play a prominent role in designing...

Fano resonance in electron transport through parallel double quantum dots in the Kondo regime

Electron transport through parallel double quantum dot system with interdot tunneling and strong on-site Coulomb interaction is studied in the Kondo regime by using the finite-

Effective medium theory of the one-dimensional resonance phononic crystal

U

An EPM calculation of band structure of zincblende semiconductor alloys

slave boson technique. For a system of quantum dots with degenerate energy levels, the linear conductance reaches the unitary limit

A new approximation scheme in quantum mechanics

(2{e}^{2}∕h)

Thermopower behavior for the shape memory alloy NiTi

due to the Kondo effect at low temperature when interdot tunneling is absent. As the interdot tunneling amplitude increases, the conductance decreases in the singly occupied regime and a conductance plateau structure appears. In the crossover to the doubly occupied regime, the conductance increases to reach a maximum value of

Specific heat of YCo12B6 and GdCo12B6 intermetallics

G=2{e}^{2}∕h

A variational expansion for the free energy of a bosonic system

. For parallel double dots with different energy levels, we show that the interference effect plays an important role in electron transport. The linear conductance is shown to have an asymmetric line shape of the Fano resonance as a function of gate voltage.

The ideal Bose gas in non-integer dimensions and liquid 4He in porous media

A general theoretical scheme to describe the effective modulus and mass density for acoustic metamaterials is presented. For such a purpose, an effective medium theory of a one-dimensional acoustic waveguide containing subwavelength-sized Helmholtz resonators is formulated. It is shown that, when the wavelength is much larger than the periodic length and the size of the resonators, the whole composite structure can be treated as an effective homogeneous medium in accounting for its acoustic properties. It is also shown that the acoustic characteristics, such as the effective modulus and the effective mass density, can be determined precisely from the transmission and the reflection data. The calculated effective modulus and effective mass density confirm that this structure behaves as a homogeneous metamaterial with a negative effective modulus in a frequency range just above the resonant frequency.