arXiv subjects

Natalia G. Mensah

Publications and source records attributed to Natalia G. Mensah.

3 recordsLinked to original sources

arXiv2015

Amplification of Hypersound in Graphene with degenerate energy dispersion

Hypersound amplification/absorption of acoustic phonons in Graphene with degenerate energy dispersion $\varepsilon(p)$ near the Fermi level was theoretically studied. For $k_βT << 1$ and $ql >> 1$, the dependence of the absorption coefficient $Γ/Γ_0$ on ${V_D\over V_s}$ was studied where the results satisfied the Cerenkov effect. That is when ${V_D\over V_s} > 1$, an amplification was obtained but for ${V_D\over V_s} < 1$, an absorption was obtained which could lead to Acoustoelectric Effect (AE) in Graphene. A linear dependence of the $Γ/Γ_0$ on $ω_q$ was observed where the result obtianed qualitatively agreed with an experimentally observed acoustoelectric current in Graphene via the Weinrich relation. It is interesting to note from this study that, frequencies above $10THz$ can be attained for $V_D = 1.1ms^{-1}$. This study permit the use of Graphene as hypersound phonon laser (SASER).

cond-mat.mes-hall↗

arXiv2011

Amplification of acoustic phonons in superlattice

The amplification of acoustic phonons in a superlattice in the presence of an electric field $E =E_0 + E_1 cos(ωt)$ has been investigated theoretically and numerically by computational methods. The calculation is done in the hypersound regime $(ql\gg 1)$ where the attenuation coefficient depends on the phonon wave vector $ q =[-\fracπ{q} \quad \frac{2pi}{q}]$ and the frequency $ω_q = 10^{12} s^{-1}$ . An inversion is attained where amplification far exceeds absorption and the ratio $ frac\mid\frac{Γ/Γ_0\mid_{min}}{\midΓ/Γ_0\mid_{max}}\approx 3$ . A high frequency build up of acoustic energy from noise (phonon spectrum) is obtained by using specialized spectral techniques. This indicates an amplification of the phonons generated in the terahertz range leading to the possibility of obtaining a hypersound MASER.

cond-mat.mes-hall↗

arXiv2010

Amplification of Acoustic Wave in GaN in the Presence of Slowly Changing Periodic Electric Field

Acoustic wave propagation in bulk GaN Semiconductor in the presence of a slowly changing a.c electric field and a constant electric field has been studied. Analytical expression for the attenuation (amplification) coefficient has been obtained. It is shown that the a.c electric field is acting as a modulator and that the acoustoelectric gain increases to a maximum value and then fall off as the acoustic wave frequency is increased. Also for a a.c electric field of 4 x 104 V/CM the acoustoelectric gain remains zero until the acoustic wave frequency is about 5.8x1012Hz then a resonant amplification peak appears. If the a.c electric field is increased a second resonant peak accurs at 8.7x1012Hz. It is therefore suggested that the sample can be used as a maser.

cond-mat.mes-hall↗