Search

We investigate the opinion evolution of outflow dynamics based on the Sznajd model on a complete graph involving contrarian and independence behaviors. We consider a group of four spins representing the social agents with the following scenarios: (1) scenario two-two with contrarian agents or independence agents and (2) scenario three-one with contrarian or independence agents. All of them undergo a second-order phase transition according to our simulation. The critical point decreases exponentially as $\lambda$ and $f$ increases, where $\lambda$ and $f$ are contrarian and flexibility factors, respectively. Furthermore, we find that the critical point of scenario three-one is smaller than that of scenario two-two. For the same level of $\lambda$ and $f$, the critical point of the scenario involving independence is smaller than the scenario with contrarian agents. From a sociophysics point of view, we observe that scenario three-one can likely reach a stalemate situation rather than scenario two-two. Surprisingly, the scenarios involving contrarians have a higher probability of achieving a consensus than a scenario involving independence. Our estimates of the critical exponents indicate that the model is still in the same universality class as the mean-field Ising model., Comment: 12 pages, 12 figures

We investigate thermoelectric (TE) properties of two-dimensional materials possessing two Dirac bands (a Dirac band) and a nonlinear band within the three-(two-)band model using linearized Boltzmann transport theory and relaxation time approximation. In the three-band model, we find that combinations of Dirac bands with a heavy nonlinear band, either a parabolic or a pudding-mold band, does not give much difference in their TE performance. The apparent difference only occurs in the position of the nonlinear band that leads to the maximum figure of merit ($ZT$). The optimum $ZT$ of the three-band model consisting of a nonlinear band is found when the nonlinear band intersects the Dirac bands near the Fermi level. By removing the linear conduction band, or, in other words, transforming the three-band model to the two-band model, we find better TE performance in the two-band model than in the three-band model, i.e., in terms of higher $ZT$ values

We theoretically investigate the thermoelectric properties of semiconducting (gapped) materials by varying the degrees of polynomials in their energy dispersion relations, in which either the valence or conduction energy dispersion depends on the wave vector raised to the power of two, four, and six. The thermoelectric transport coefficients such as the Seebeck coefficient, electrical conductivity, and thermal conductivity are calculated within the linearized Boltzmann transport theory combined with the relaxation time approximation. We consider various effects such as band gaps, dimensionalities, and dispersion powers to understand the conditions that can give the optimal thermoelectric efficiency or figure of merit ($ZT$). Our calculations show that the so-called pudding-mold band structure produces larger electrical and thermal conductivities than the parabolic band, but no significant difference is found in the Seebeck coefficients of the pudding-mold and parabolic bands. Furthermore, we find that a high $ZT$ can be obtained by tuning the band gap of the material to an optimum value simultaneously with breaking the band symmetry. The largest $ZT$ is found in a combination of two-contrasting polynomial powers in the dispersion relations of valence and conduction bands. This band asymmetry also shifts the charge neutrality away from the undoped level and allows optimal $ZT$ to be located at a smaller chemical potential. With some reasonable values of thermal conductivity parameters, the maximum $ZT$ for the bulk systems can be larger than 1, while for one-dimensional systems it can even reach almost 4. We expect this work to trigger high-throughput calculations for screening of potential thermoelectric materials combining various polynomial powers in the energy dispersion relations of semiconductors., Comment: 12 pages, 11 figures