arXiv subjects

S S Kubakaddi

Publications and source records attributed to S S Kubakaddi.

3 recordsLinked to original sources

arXiv2019

Phonon limited mobility of the Dirac-Fermions in a three-dimensional Dirac semimetal Cd$_3$As$_2$

A theoretical model is presented for the phonon limited mobility of the Dirac-Fermion gas in a three-dimensional (3D) Dirac semimetal Cd$_3$As$_2$ considering scattering from both the acoustic and the optical phonons. Screening effects are taken into account and it is found that they lead to a significant enhancement of the mobility. Simple analytical equations and power laws are obtained in both the Bloch-Gruneisen and equipartition regimes. The dependence of mobility on the temperature $T$ and the electron density $n_e$ is investigated. It is found that optical phonon limited mobility $μ_{op}$ dominates over the acoustic phonon limited mobility $μ_{ap}$ in the higher temperature region. There is a crossover of $μ_{ap}$ and $μ_{op}$ and the crossover temperature $T_c$ shifts to higher value with increasing $n_e$. Our calculations of the mobility are in good agreement with the recent experimental data. Comparison is also made with the results in the conventional 3D electron gas in a degenerate semiconductor.

cond-mat.mtrl-sci↗

arXiv2017

Effect of piezoelectric substrate on phonon-drag thermopower in monolayer graphene

The phonon-drag thermopower is studied in monolayer graphene on a piezoelectric substrate. The phonon-drag contribution S^g_PA from the extrinsic potential of piezoelectric surface acoustic (PA) phonons of a piezoelectric substrate (GaAs) is calculated as a function of temperature T and electron concentration n_s. At very low temperature, S^g_PA is found to be much greater than S^g_DA of the intrinsic deformation potential of acoustic (DA) phonons of the graphene. There is a crossover of S^g_PA and S^g_DA at around ~5 K. In graphene samples of about >10 um size, we predict S_g ~20 uV at 10 K, which is much greater than the diffusion component of the thermopower and can be experimentally observed. In the Bloch-Gruneisen (BG) regime T and n_s dependence are, respectively, given by the power laws S^g_PA (S^g_DA) ~ T^2(T^3) and S^g_PA, S^g_DA ~ n_s^(-1/2). The T (n_s) dependence is the manifestation of the two-dimensional phonons (Dirac phase of the electrons). The effect of the screening is discussed. Analogous to Herring's law (S_g mu_p ~T^-1), we predict a new relation S_g mu_p ~n_s^0, where mu_p is the phonon-limited mobility. We suggest that n_s dependent measurements will play a more significant role in identifying the Dirac phase and the effect of screening.

cond-mat.mes-hall↗

arXiv2015

Hot electron cooling in three-dimensional Dirac fermion systems at low temperature: effect of screening

Hot electron cooling rate P, due to acoustic phonons, is investigated in three-dimensional Dirac fermion systems at low temperature taking account of screening of electron-acoustic phonon interaction. P is studied as a function of electron temperature T_e and electron concentration n_e. Screening is found to suppress P very significantly for about T_e < 0.5 K and its effect reduces considerably for about T_e > 1K in Cd_3As_2 . In Bloch-Gruniesen (BG) regime, for screened (unscreened) case T_e dependence is P ~ T_e^ 9 (T_e^ 5) and ne dependence gives P ~ n_e ^-5/3(n_e^-1/3). The T_e dependence is characteristics of 3D phonons and n_e dependence is characteristics of 3D Dirac fermions. In BG regime, screening effect is found to enhance for larger n_e. Screening is found to reduce the range of validity of BG regime temperature. Plot of P / T_e^ 4 vs T_e shows a maximum at temperature T_e m which shifts to higher values for larger n_e. Interesting observation is that maximum of P / T_e^4 is nearly same for different n_e and T_em / n_e^ 1/3 appears to be nearly constant. More importantly, we propose, the n_e dependent measurements of P would provide a clearer signature to identify 3D Dirac semimetal phase.

cond-mat.mtrl-sci↗