3 research outputs found
Phase transition in the majority rule model with the nonconformist agents
Independence and anticonformity are two types of social behaviors known in
social psychology literature and the most studied parameters in the opinion
dynamics model. These parameters are responsible for continuous (second-order)
and discontinuous (first-order) phase transition phenomena. Here, we
investigate the majority rule model in which the agents adopt independence and
anticonformity behaviors. We define the model on several types of graphs:
complete graph, two-dimensional (2D) square lattice, and one-dimensional (1D)
chain. By defining as a probability of independence (or anticonformity), we
observe the model on the complete graph undergoes a continuous phase transition
where the critical points are () for the
model with independent (anticonformist) agents. On the 2D square lattice, the
model also undergoes a continuous phase transition with critical points at () for the model with independent
(anticonformist) agents. On the 1D chain, there is no phase transition either
with independence or anticonformity. Furthermore, with the aid of finite-size
scaling analysis, we obtain the same sets of critical exponents for both models
involving independent and anticonformist agents on the complete graph.
Therefore they are identical to the mean-field Ising model. However, in the
case of the 2D square lattice, the models with independent and anticonformist
agents have different sets of critical exponents and are not identical to the
2D Ising model. Our work implies that the existence of independence behavior in
a society makes it more challenging to achieve consensus compared to the same
society with anticonformists
Electronic, Optical, and Thermoelectric Properties of Bulk and Monolayer Germanium Tellurides
Electronic, optical, and thermoelectric properties of germanium tellurides (GeTe) were investigated through a series of first-principles calculations of band structures, absorption coefficients, and thermoelectric transport coefficients. We consider bulk GeTe to consist of cubic and rhombohedral phases, while the two-dimensional (2D) GeTe monolayers can form as a 2D puckered or buckled honeycomb crystals. All of the GeTe variants in the bulk and monolayer shapes are excellent light absorbers in a wide frequency range: (1) bulk cubic GeTe in the near-infrared regime, (2) bulk rhombohedral GeTe and puckered monolayer GeTe in the visible-light regime, and (3) buckled monolayer GeTe in the ultraviolet regime. We also found specifically that the buckled monolayer GeTe exhibits remarkable thermoelectric performance compared to the other GeTe phases due to a combination of electronic band convergence, a moderately wide band gap, and unique 2D density of states from the quantum confinement effect
Spin-tunable thermoelectric performance in monolayer chromium pnictides
Historically, finding two-dimensional (2D) magnets is well known to be a
difficult task due to instability against thermal spin fluctuations. Metals are
also normally considered poor thermoelectric (TE) materials. Combining
intrinsic magnetism in two dimensions with conducting properties, one may
expect to get the worst for thermoelectrics. However, we will show this is not
always the case. Here, we investigate spin-dependent TE properties of monolayer
chromium pnictides (CrX, where X = P, As, Sb, and Bi) using first-principles
calculations of electrons and phonons, along with Boltzmann transport formalism
under energy-dependent relaxation time approximation. All the CrX monolayers
are dynamically stable and they also exhibit half metallicity with
ferromagnetic ordering. Using the spin-valve setup with antiparallel spin
configuration, the half metallicity and ferromagnetism in monolayer CrX enable
manipulation of spin degrees of freedom to tune the TE figure of merit (ZT). At
optimized chemical potential and operating temperature of 500 K, the maximum ZT
values (= 0.22, 0.12, and 0.09) with the antiparallel spin-valve setup in CrAs,
CrSb, and CrBi improve up to almost twice the original values (ZT = 0.12, 0.08,
and 0.05) without the spin-valve configuration. Only in CrP, which is the
lightest species and less spin-polarized among CrX, the maximum ZT (= 0.34)
without the spin-valve configuration is larger than that (= 0.19) with the
spin-valve one. We also find that, at 500 K, all the CrX monolayers possess
exceptional TE power factors of about 0.02-0.08 W/m.K2, which could be one of
the best values among 2D conductors.Comment: 7 pages, 6 figure