Temperature Dependence Of Chemical Potential Research Articles

High-temperature transport properties of a two-dimensional weakly doped parabolic semiconductor

A version of the Mexican-hat Hamiltonian is used to study high-temperature transport properties of a two-dimensional weakly doped semiconductor with electron-hole symmetric bands. For a finite doping level and a temperature-dependent band gap, we find a closed analytical form of the temperature-dependent chemical potential. The effective concentrations of charge carriers participating in transport coefficients are analyzed in the space spanned by the total electron concentration and temperature. It is shown that these concentrations are the sum of a residual contribution and two thermally activated contributions, with a complicated dependence on temperature. The analytical expression for the Hall coefficient RHis also found. It is argued that it is a non-monotonic function of the doping level with the maximum at the doping nmax that is a linear function of temperature at high enough temperatures. The analysis of the real part of the interband conductivity shows that it is inversely proportional to incoming photon energy at low temperatures and that it is nearly constant over a wide energy range at high temperatures. This results are expected to be of significant importance in understanding transport and optical properties of weakly doped two-dimensional semiconductors with nearly symmetric parabolic bands.&#xD.

Exploring the effect of strong electronic correlations in Seebeck Coefficient of the NdCoO3 compound : Using experimental and DFT+U approach

The presence of complexity in the electronic structure of strongly correlated electron system NdCoO3 (NCO) have sparked interest in the investigation of its physical properties. Here, we study the Seebeck coefficient (α) of NCO by using the combined experimental and DFT+U based methods. The experimentally measured Seebeck coefficient is found to be ∼444 μ V/K at 300 K, which decreases to 109.8 μ V/K at 600 K. In order to understand the measured Seebeck coefficient, we have calculated the PDOS and band structure of the NCO. Furthermore, the calculated occupancy of 6.4 for Co 3d orbitals and presence of large unoccupied O 2p states indicate the covalent nature of the bonding. Apart from this, the maximum effective mass is found to be 36.75 (28.13) me for the spin-up (dn) channel in conduction band indicates the n-type behaviour of the compound in contrast to our experimentally observed p-type behaviour. While, the calculated Seebeck coefficient at the temperature-dependent chemical potential (μ) at 300 K shows the p-type behaviour of the compound. Fairly good agreement is seen between the calculated and measured values of α at U ff = 5.5 eV and U dd = 2.7 eV. The maximum power factor (PF) is found to be 47.6 (114.4)×1014 μW K −2cm−1 s −1 at 1100 K, which corresponds to p (n)-type doping of ∼1.4 (0.7)×1021 cm−3. This study suggests the importance of strong on-site electron correlation in understanding the thermoelectric property of the compound

Adsorption behavior of benzene on clay mineral surfaces at different temperatures and air humidity based on molecular simulation

Benzene poses a severe threat to human health due to its prevalence and carcinogenicity. The adsorption behavior of benzene on clay mineral surfaces is significant to its migration and retention in soils. Therefore, it is crucial to understand the mechanism of benzene adsorption behavior under different environmental conditions. In this study, a series of Grand Monte Carlo (GCMC) simulations were performed to obtain benzene isotherms on clay under various temperatures and air humidity. The adsorption mechanisms were investigated via analysis of the distribution of interaction energy, density, and orientation of adsorbed benzene and water. Results show that benzene form multiple layers on mineral surfaces, and surfaces have a great impact on the first layer of adsorbed benzene. The impedance effect of temperature on benzene adsorption is attributed to the temperature-dependent chemical potential of benzene, but not the interaction between benzene and surfaces, which is slightly temperature-reliant. Humidity shows different inhibition effects on benzene adsorption due to different surface hydration behavior and competitive adsorption between water and benzene. Benzene tends to be adsorbed on hollow sites on kaolinite surfaces, which is the same as water. The surface cations on montmorillonite and mica are significant to benzene and water adsorption, and their density distribution causes different competitive adsorption behavior.

Thermochemical process and compact apparatus for concentrating oxygen in extraterrestrial atmospheres: a feasibility study

The Martian atmosphere contains 0.16% oxygen, which is an example of an in-situ resource that can be used as precursor or oxidant for propellants, for life support systems and potentially for scientific experiments. Thus, the present work is related to the invention of a process to concentrate oxygen in the oxygen-deficient extraterrestrial atmosphere by means of a thermochemical process and the determination of a suitable best-case apparatus design to carry out the process. The perovskite oxygen pumping (POP) system uses the underlying chemical process, which is based on the temperature-dependent chemical potential of oxygen on multivalent metal oxide, to release and absorb oxygen in response to temperature swings. The primary goal of this work is therefore to identify suitable materials for the oxygen pumping system and to optimize the oxidation–reduction temperature and time, required to operate the system, to produce 2.25 kg of oxygen per hour under the Martian most-extreme environmental conditions and based on the thermochemical process concept. Radioactive materials such as 244Cm, 238Pu and 90Sr are analyzed as a heating source for the operation of the POP system, and critical aspects of the technology as well as weaknesses and uncertainties related to the operational concept are identified.

Doping as a tuning mechanism for magnetothermoelectric effects to improve zT in polycrystalline NbP

Weyl semimetals combine topological and semimetallic effects, making them candidates for interesting and effective thermoelectric transport properties. Here, we present experimental results on polycrystalline NbP, demonstrating the simultaneous existence of a large Nernst effect and a large magneto-Seebeck effect, which is typically not observed in a single material at the same temperature. We compare transport results from two polycrystalline samples of NbP with previously published work, observing a shift in the temperature at which the maximum Nernst and magneto-Seebeck thermopowers occur, while still maintaining thermopowers of similar magnitude. Theoretical modeling shows how doping strongly alters both the Seebeck and Nernst magnetothermopowers by shifting the temperature-dependent chemical potential, and the corresponding calculations provide a consistent interpretation of our results. Thus, we offer doping as a tuning mechanism for shifting magnetothermoelectric effects to temperatures appropriate for device applications, improving $zT$ at desirable operating temperatures. Furthermore, the simultaneous presence of both a large Nernst and magneto-Seebeck thermopower is uncommon and offers unique device advantages if the thermopowers are used additively. Here, we also propose a unique thermoelectric device that would collectively harness the large Nernst and magneto-Seebeck thermopowers to greatly enhance the output and $zT$ of conventional thermoelectric devices.

Chemical potential influence on the condensation energy from a Boson–Fermion model of superconductivity

Influence of the temperature dependent chemical potential on the condensation energy from a ternary Boson–Fermion model of superconductivity is reported, it consist of unbound electrons/holes which are fermions plus two-electron and two-hole Cooper pairs which are bosons. When solving simultaneously the set of equations of the mixture (two gap-like equations, one for electron pairs and another one for hole pairs, plus the particle number conservation equation) within the weak-coupling (BCS regime), the resulting superconducting chemical potential shows a shift from its normal state counterpart, which is related to both the magnitude of the temperature-dependent superconducting gap and to the Fermi energy of the superconductor. As predicted by van der Marel in the early 1990s we also find that the superconducting chemical potential has a prominent kink at critical temperature Tc, which in turn coincides with the normal state chemical potential. Also there is a discontinuity in its first derivative which directly affects the magnitude in the specific heat jump. We show that the difference between the superconducting and normal state chemical potentials is of the same order of magnitude as the corresponding difference between the thermodynamic potentials for the mixture, and must therefore be accounted for in the condensation energy calculations instead of ignoring it as is done often. The condensation energy obtained here shows very good agreement with experimental data for elemental superconductors.

Expansive Growth vs. pH Reflects a Poisson Point Process of Binding/Unbinding Events in Plant Cell Walls

The paramount role of mathrm{pH} and temperature left(Tright) in the expansive growth of a plant coleoptile/hypocotyl non-meristematic zone or plant and fungal cells was examined within the framework of the underlying chemical bond statistics in order to reproduce an experimental plot of growth vs. mathrm{pH}. Here, according to the definition, mathrm{pH}=mathrm{pH}left({mu }_{{mathrm{H}}^{+}}left(Tright), Tright) is considered as a function of the chemical potential of the H+ (hydronium) ions ({mu }_{{mathrm{H}}^{+}}), as well as an implicit and explicit function of T. The derivation of the mathrm{pH} and T dependent expansive growth distribution from the Poisson statistics of the “tethers” that reproduce the chemical bonds between microfibrils was determined. The probability distribution for the attachment/detachment/reattachment events of the tethers that are connected to the microfibrils in the elongation zone was obtained. The two distinct but interrelated modes of the expansive growth, which are known as “acid growth” and “auxin growth” were distinguished in the analytic model, while the acid growth hypothesis was verified and confirmed at the semi-empirical and microscopic levels for the first time. Moreover, further perspectives, in which the macroscopic variables left(P, V, Tright) with P standing for the turgor pressure and V for the cell volume, and the microscopic variables, {E}^{{varvec{d}},{varvec{r}}}, which represent the binding energies of the detachment/reattachment events at the expense of ATP energy, and {mu }_{{mathrm{H}}^{+}} can occur simultaneously, were identified. With a few assumptions that are partly based on experimental data it was possible to synthesise a link between the microscopic, explicit statistical explanation of bond dynamics and the macroscopic rheological properties of the cell wall at a given mathrm{pH} and temperature. A statistical description that predicted the importance of mathrm{pH} and temperature-dependent chemical potential of the H+ ions in microscopic events that result in growth would be supposedly applicable across scales.

Transport signatures of temperature-induced chemical potential shift and Lifshitz transition in layered type-II Weyl semimetal TaIrTe4

Temperature-induced Lifshitz transitions have been identified in several materials. Their chemical potential shows a substantial shift with changing temperature. The common feature of these materials is the coexistence of electron and hole pockets in the vicinity of the chemical potential. Here, we report the observation of temperature-induced chemical potential shift and Lifshitz transition in a layered type-II Weyl semimetal, TaIrTe4. The reversal of the polarity of the Hall resistivity and thermoelectric power (TEP) as the temperature increases clearly signal an appreciable shift of the chemical potential and change of the Fermi surface. It is corroborated by the improving agreement between the experimental TEP and the one calculated with temperature-dependent chemical potential. The complete disappearance of an electron pocket, consistent with the change of the Fermi surface when the chemical potential moves downwards, provides an evident signature of a temperature-induced Lifshitz transition in TaIrTe4.

Nernst thermopower of time-reversal breaking type-II Weyl semimetals

Weyl semimetals host linear energy dispersions around Weyl nodes, as well as monopoles of Berry curvature in momentum space around these points. These features give rise to unique transport signatures in a Weyl semimetal, such as transverse transport without an applied magnetic field, known as anomalous transport. The type-II Weyl semimetal, recently experimentally demonstrated in several materials, is classified by a tilting of the Weyl nodes. This paper provides a theoretical study on thermoelectric transport in time-reversal breaking type-II Weyl semimetals. Our results examine the balance between anomalous and non-anomalous contributions to the Nernst effect when subject to an external magnetic field. We also show how increasing scattering times have on enhancing effect on thermoelectric transport in these materials. Since a temperature-dependent chemical potential has been theoretically shown to be paramount when considering anomalous transport, we also study how similar considerations impact the Nernst thermopower in the non-anomalous case.

Nuclear spin-lattice relaxation time in TaP and the Knight shift of Weyl semimetals

We first analyze the recent experimental data on the nuclear spin-lattice relaxation rate of the Weyl semimetal TaP. We argue that its non-monotonic temperature dependence is explained by the temperature dependent chemical potential of Weyl fermions. We also develop the theory of the Knight shift in Weyl semimetals, which contains two counteracting terms. The diamagnetic term follows $-\ln[W/\max(|\mu|,k_BT)]$ with $W$, $\mu$ and $T$ being the high energy cutoff, chemical potential and temperature, respectively, and is always negative. The paramagnetic term scales with $\mu$ and changes sign depending on the doping level. Altogether, the Knight shift is predicted to vanish or even change sign upon changing the doping or the temperature, making it a sensitive tool to identify Weyl points. We also calculate the Korringa relation for Weyl semimetals which shows an unusual energy dependence rather than being constant as expected for a non-interacting Fermi system.

Study for material analogs of FeSb2 : Material design for thermoelectric materials

Using the ab initio evolutionary algorithm (implemented in uspex) and electronic structure calculations we investigate the properties of a new thermoelectric material FeSbAs, which is a material analog of the enigmatic thermoelectric ${\mathrm{FeSb}}_{2}$. We utilize the density functional theory and the Gutzwiller method to check the energetics. We find that FeSbAs can be made thermodynamically stable above $\ensuremath{\sim}30$ GPa. We investigate the electronic structure and thermoelectric properties of FeSbAs based on the density functional theory and compare with those of ${\mathrm{FeSb}}_{2}$. Above 50 K, FeSbAs has higher Seebeck coefficients than ${\mathrm{FeSb}}_{2}$. Upon doping, the figure of merit becomes larger for FeSbAs than for ${\mathrm{FeSb}}_{2}$. Another material analog FeSbP, was also investigated, and found thermodynamically unstable even at very high pressure. Regarding ${\mathrm{FeSb}}_{2}$ as a member of a family of compounds $({\mathrm{FeSb}}_{2}$, FeSbAs, and FeSbP) we elucidate what are the chemical handles that control the gaps in this series. We also investigate solubility (As or P for Sb in ${\mathrm{FeSb}}_{2})$ we found As to be more soluble. Finally, we study a two-band model for thermoelectric properties and find that the temperature dependent chemical potential and the presence of the ionized impurities are important to explain the extremum in the Seebeck coefficient exhibited in experiments for ${\mathrm{FeSb}}_{2}$.

Dilepton production as a useful probe of quark gluon plasma with temperature dependent chemical potential quark mass

We extend the previous study of dilepton production using [S. Somorendro Singh and Y. Kumar, Can. J. Phys. 92 (2014) 31] based on a simple quasiparticle model of quark–gluon plasma (QGP). In this model, finite value of quark mass uses temperature dependent chemical potential the so-called Temperature Dependent Chemical Potential Quark Mass (TDCPQM). We calculate dilepton production in the relevant range of mass region. It is observed that the production rate is marginally enhanced from the earlier work. This is due to the effect of TDCPQM and its effect is highly significant in the production of dilepton.

Rate of tunneling nonequilibrium quasiparticles in superconducting qubits

In superconducting qubits the lifetime of quantum states cannot be prolonged arbitrarily by decreasing temperature. At low temperature quasiparticles tunneling between the electromagnetic environment and superconducting islands takes the condensate state out of equilibrium due to charge imbalance. We obtain the tunneling rate from a phenomenological model of non-equilibrium, where nonequilibrium quasiparticle tunnelling stimulates a temperature-dependent chemical potential shift in the superconductor. As a result we obtain a non-monotonic behavior for relaxation rate as a function of temperature. Depending on the fabrication parameters for some qubits, the lowest tunneling rate of nonequilibrium quasiparticles can take place only near the onset temperature below which nonequilibrium quasiparticles dominate over equilibrium one. Our theory also indicates that such tunnelings can influence the probability of transitions in qubits through a coupling to the zero-point energy of phase fluctuations.

Interpretation of thermal dependence of magnetic aftereffect for magnetic nanocomposite with slow decay rates

A new experimental characterization is presented of time-, field-, and temperature-dependent dynamic effects in magnetization of a nanocomposite which displays slow decay. Field and temperature variations of irreversible susceptibility, χ irr , decay coefficient, S, fluctuation field, hf , and activation volume, V, have been calculated for the nanocomposite sample (Co80Ni20) using a recently developed modified Preisach–Arrhenius (MPA) model. The sample is composed of non-interacting nanoparticles having negligible reversible magnetization. Non-Arrhenius behavior is observed in both the maximum decay coefficient, S max, and the fluctuation field, hf , as a function of temperature T. The peak of both temperature curves are identical and occur at a critical temperature Tk of ∼50 K, which agrees with our experimental results. Based on the effect of a temperature-dependent chemical potential on energy barrier, hf is studied for T < Tk and T ≥ Tk , respectively. A more complete MPA model that can predict the magnetization as function of time, field and temperature for a magnetic material with slow decay rates is proposed. This model uses a multi-variable analytical formula, , which incorporates the characteristic parameters.

Dilepton Emission at Temperature Dependent Baryonic Quark-Gluon Plasma

Dilepton emission is calculated from quark-gluon plasma (QGP) with the consideration of temperature dependent chemical potential (TDCP). The model is considered to be quasi-model and hence take the dynamical quark mass as a finite value dependence on temperature. The temperature in quark mass enhances in the growth of dilepton emission rates. The emission rate of dilepton spectrum is shown in the intermediate mass region (IMR) of 1.0 - 4.0 GeV and its rate is observed to be a strong increasing function of the temperature dependent chemical potential for quark and anti-quark annihilation.

Effects of temperature dependent chemical potential on the Seebeck coefficient of TiS2 thermoelectric material

ABSTRACTThe relation between chemical potential and Seebeck coefficient was investigated by using high-resolution angle resolved photoemission spectroscopy. The temperature dependence of chemical potential was experimentally determined for the n-type TiS2 thermoelectric material and compared with the measured Seebeck coefficient. We found that the temperature dependence of chemical potential of TiS2 is significantly large, and its effect on Seebeck coefficient is not negligible. This fact strongly indicates that the temperature dependence of chemical potential has to be properly understood to construct the guiding principle for developing new, practical thermoelectric materials.

Effect of Chemical Potential on Thermoelectric Power of Bi&lt;SUB&gt;2&lt;/SUB&gt;Te&lt;SUB&gt;3&lt;/SUB&gt; and Bi&lt;SUB&gt;2&lt;/SUB&gt;Se&lt;SUB&gt;3&lt;/SUB&gt;

Temperature dependence of chemical potential was determined for n-type Bi2Se3 and p-type Bi2Te3 thermoelectric materials by means of angle resolved photoemission spectroscopy, and the determined chemical potential was compared with the measured thermoelectric power. We found that the temperature dependence of chemical potential is significantly large for the present materials and the large thermoelectric power is mainly caused by the chemical potential effect. This fact strongly indicates that the temperature dependence of chemical potential has to be properly understood to construct a guiding principle for developing new, practical thermoelectric materials. [doi:10.2320/matertrans.E-M2011809]

Role of Temperature Dependent Chemical Potential on Thermoelectric Power

In this paper, the relation between chemical potential and thermoelectric power is investigated by using the linear response theory, possible models of electronic structure, the consequently obtained spectral conductivities, and high-resolution photoemission spectroscopy. We revealed that the effect of temperature dependent chemical potential on thermoelectric power S(T) is negligibly small when its magnitude is limited below 100 μV/K, but becomes nontrivial with increasing S(T). The validity of this argument we proposed on the basis of theoretical calculation was experimentally confirmed using the high-resolution photoemission spectra of the materials possessing a large magnitude in thermoelectric power.

Photoemission Study of Perovskite-Type Manganites with Stripe Ordering

We have studied the chemical potential shift and changes in the electronic density of states near the Fermi level (EF) as functions of temperature and carrier concentration in Pr1−xCaxMnO3 (PCMO) and Nd1−xSrxMnO3 (NSMO) by measurements of photoemission spectra. Suppression of the chemical potential shift as a function of carrier concentration has been observed in PCMO and NSMO near and in the composition range where the CE-type antiferromagnetic charge-ordered (CO) phase appears at low temperatures. This result indicates that there is charge self-organization on a microscopic scale such as stripe formation in this composition range. In the ferromagnetic metallic phase of NSMO, we found a large temperature-dependent chemical potential shift at low temperatures and attributed this to double-exchange mechanism. Suppression of the temperature-dependent chemical potential shift near Curie temperature was observed, possibly associated with the formation of correlated polarons. In the valence band near the EF of PCMO, spectral weight was transferred with hole doping, leading to a finite intensity at EF even in the paramagnetic insulating phase above the CO phase for x≳0.3, and as the temperature was lowered, a clear gap opening was observed in the CO phase.

Strong Correlations Produce the Curie-Weiss Phase ofNaxCoO2

Within the t-J model we study several experimentally accessible properties of the 2D-triangular lattice system NaxCoO2, using a numerically exact canonical ensemble study of 12 to 18 site triangular toroidal clusters as well as the icosahedron. Focusing on the doping regime of x approximately 0.7, we study the temperature dependent specific heat, magnetic susceptibility, and the dynamic Hall coefficient R_{H}(T,omega) as well as the magnetic field dependent thermopower. We find a crossover between two phases near x approximately 0.75 in susceptibility and field suppression of the thermopower arising from strong correlations. An interesting connection is found between the temperature dependence of the diamagnetic susceptibility and the Hall coefficient. We predict a large thermopower enhancement, arising from transport corrections to the Heikes-Mott formula, in a model situation where the sign of hopping is reversed from that applicable to NaxCoO2.