Function Of Chemical Potential Research Articles

Seebeck effect in a thermal QCD medium in the presence of strong magnetic field

The strongly interacting partonic medium created post ultrarelativistic heavy ion collision experiments exhibits a significant temperature-gradient between the central and peripheral regions of the collisions, which in turn, is capable of inducing an electric field in the medium; a phenomenon known as Seebeck effect. The effect is quantified by the magnitude of the induced electric field per unit temperature-gradient - the Seebeck coefficient ($S$). We study the coefficient, $S$ in the relativistic Boltzmann transport equation in relaxation-time approximation, as a function of temperature ($T$) and chemical potential ($\mu$), wherein we find that with current quark masses, the magnitude of $S$ for individual flavours as well as that for the medium as a whole decreases with $T$ and increases with $\mu$, with the electric charge of the flavour deciding the sign of $S$. The emergence of a strong magnetic field ($B$) in the non-central collisions at heavy-ion collider experiments motivates us to study the effect of $B$ on Seebeck effect. The strong $B$ affects $S$ in multifold ways, via : a) modification of phase-space due to the dimensional reduction, b) dispersion relation in lowest Landau level (occupation probability), and c) relaxation-time. We find that a strong $B$ not only decreases the magnitudes of $S$'s of individual species, it also flips their signs. This leads to a faster reduction of the magnitude of $S$ of the medium than its counterpart at $B=0$. We then explore how the interactions among partons in perturbative thermal QCD in the quasiparticle framework affect Seebeck effect, where we find that even in strong B, there is no more a flip of the sign of $S$ for individual species and an enhancement of the magnitudes of $S$ of individual species as well as that of the medium, compared to current quark mass description at either $B=0$ or $B \neq 0$.

Duality study of the chiral Heisenberg-Gross-Neveu model in 1+1 dimensions

We consider a version of the Gross-Neveu model in 1+1 dimensions with discrete chiral and continuous flavor symmetry (isospin). In 2+1 dimensions, this model is known as chiral Heisenberg Gross-Neveu model. Spontaneous symmetry breaking and the emergence of two massless and one massive scalar bosons are shown. A duality to the Nambu--Jona-Lasinio model with isospin is exhibited, provided that the isovector pseudoscalar mean field is constrained to a plane in isospin space. This enables us to find the phase diagram as a function of temperature, chemical potential and isospin chemical potential as well as twisted kinks. A bare mass term acts quite differently when added to this model as compared to other chiral variants of the Gross-Neveu model.

Fermi seas from Bose condensates in Chern-Simons matter theories and a bosonic exclusion principle

We generalize previously obtained results for the (all orders in the ’t Hooft coupling) thermal free energy of bosonic and fermionic large N Chern-Simons theories with fundamental matter, to values of the chemical potential larger than quasiparticle thermal masses. Building on an analysis by Geracie, Goykhman and Son, we present a simple explicit formula for the occupation number for a quasiparticle state of any given energy and charge as a function of the temperature and chemical potential. This formula is a generalization to finite ’t Hooft coupling of the famous occupation number formula of Bose-Einstein statistics, and implies an exclusion principle for Chern-Simons coupled bosons: the total number of bosons occupying any particular state cannot exceed the Chern-Simons level. Specializing our results to zero temperature we construct the phase diagrams of these theories as a function of chemical potential and the UV parameters. At large enough chemical potential, all the bosonic theories we study transit into a compressible Bose condensed phase in which the runaway instability of free Bose condensates is stabilized by the bosonic exclusion principle. This novel Bose condensate is dual to — and reproduces the thermodynamics of — the fermionic Fermi sea.

Proximity effect in a superconductor–topological insulator heterostructure based on first principles

Superconductor-topological insulator (SC-TI) heterostructures were proposed to be a possible platform to realize and control Majorana zero-modes. Despite experimental signatures indicating their existence, univocal interpretation of the observed features demands theories including realistic electronic structures. To achieve this, we solve the Kohn-Sham-Dirac-Bogoliubov-de Gennes equations for ultrathin Bi$_2$Se$_3$ films on superconductor PdTe, within the fully relativistic Korringa-Kohn-Rostoker method, and investigate quasiparticle spectra as a function of chemical potential and film thickness. We find a strongly momentum-dependent proximity-induced gap feature where the gap sizes highly depend on characteristics of the TI states. The interface TI Dirac state is relevant to the induced gap only when the chemical potential is close to the Dirac-point energy. Otherwise, at a given chemical potential, the largest induced gap arises from the highest-energy quantum-well states, whereas the smallest gap arises from the TI topological surface state with its gap size depending on the TI pairing potential.

Study of optoelectronic and transport properties of MgLu2Z4 (Z=S, Se) spinels for optoelectronic and energy harvesting applications

Intense research has been done to build materials that are potential candidates for energy storage applications. Spinels are of great interest in this respect because they have vast potential to be used in Mg-based batteries. To explore their energy storage as well as transport response, we calculate Mg-based spinels, namely MgLu2Z4 (ZS, Se). The full potential linearized augmented plane wave method has been used to examine their optoelectronic and transport response. An increase in the lattice constant has been observed by replacing S with Se, and our calculated values are in good agreement with those obtained experimentally. The Tran-Blaha modified Becke-Johnson exchange potential (TB-mBJ), has been used to study the optoelectronic and thermoelectric characteristics of the respective spinels. The dependence of these properties on the bandgap has also been observed. Replacing S with Se resulted in the transformation of the electronic bandgap from near-infrared to the visible region (MgLu2S4: 2.60 eV and MgLu2Se4: 2.00 eV). These results showed that these materials have the potential to be used in optoelectronic devices. The optical properties are discussed as a function of energy. Besides, the thermal transports are discussed with the help of Seebeck coefficient and figure of merit as a function of chemical potential and temperature.

Elastic, Half-Metallicity, Thermodynamic, and Transport Properties of Ru2VGe and Ru2VSb Full-Heusler Compounds: a First-Principle Study

The aim of this work is the study of the magnetic, elastic, thermic, and thermoelectric properties of the ternary full-Heusler alloys Ru2VZ (Z = Ge and Sb) in L21 structure, using an ab initio calculation within the linearized augmented plane wave method with a full potential (FP-LAPW) based on the density functional theory (DFT). We computed these properties within the general gradient approximation (GGA). The structural parameters obtained are in favorable agreement with respect to the theoretical values found in the literature. The electronic properties studied have shown that the compounds have a half-metallic behavior. We have also computed the mechanical properties where we found that these full-Heusler compounds are mechanically stable. Furthermore, we have studied the thermal properties by the quasi-harmonic Debye model incorporated in the GIBBS code, which takes into account the lattice vibrations, pressure, and temperature effects on structural parameters. The thermoelectric properties were computed as a function of chemical potential at 300, 600, and 900 K. To our knowledge, the thermodynamic and thermoelectric characteristics have not yet been measured or calculated; hence, our results serve as a prediction for future study. Our obtained results for these quantities make these compounds attractive candidates for materials used in spintronic devices.

Density of states approach to the hexagonal Hubbard model at finite density

We apply the Linear Logarithmic Relaxation (LLR) method, which generalizes the Wang-Landau algorithm to quantum systems with continuous degrees of freedom, to the fermionic Hubbard model with repulsive interactions on the honeycomb lattice. We compute the generalized density of states of the average Hubbard field and divise two reconstruction schemes to extract physical observables from this result. By computing the particle density as a function of chemical potential we assess the utility of LLR in dealing with the sign problem of this model, which arises away from half filling. We show that the relative advantage over brute-force reweighting grows as the interaction strength is increased and discuss possible future improvements.

Structural, electronic and thermoelectric properties of topological semimetal lanthanum monopnicitide LaBi

The structural, electronic and thermoelectric properties of LaBi have been studied using density functional theory (DFT) combined with semiclassical Boltzmann transport theory. The exchange and correlation (XC) effects have been treated using local density approximation (LDA) including spin-orbit coupling (SOC). In the present work, we have determined the topological character of LaBi, which is in agreement with available theoretical and experimental studies. The elastic constants such as Bulk modulus, Young modulus, Poisson's ratio and shear anisotropy factor have been calculated to check the mechanical stability. The thermoelectric transport parameters such as Seebeck coefficient, Power factor, electrical and thermal conductivity are calculated as a function of temperature and chemical potential. The values of power factor and lattice thermal conductivity are found to be 1.34×1013 WK−2m−1sec−1 and 4.20 Wm−1K−1, respectively, at T=1000 K. The calculated value of figure of merit ZT is 0.42 at T=1000 K, suggesting that LaBi may be used as an effective thermoelectric material for high temperature applications.

Tunable Plasmonic Talbot Effect Based on Graphene Monolayer

In this article, the plasmonic Talbot effect supported by a graphene monolayer is investigated theoretically when surface plasmon polaritons (SPPs) are excited on the graphene. The Talbot effect distance is studied by varying the chemical potential, wavelength and the period of grating. The Talbot distance increases with the period in a parabolic way, and exhibits the opposite trends with respect to the chemical potential and wavelength. Moreover, the full width at half maximum (FWHM) of the Talbot image is recorded as a function of chemical potential and the wavelength. This study provides a new approach for sub-wavelength scale imaging and extends the applications of Talbot effect as well as graphene-based plasmonic devices.

Phase diagram of the Polyakov–Nambu–Jona-Lasinio approach for finite chemical potentials

We extend the SU(3) (Polyakov) Nambu Jona-Lasinio in two ways: We introduce the next to leading order contribution (in $N_c$) in the partition function. This contribution contains explicit mesonic terms. We introduce a coupling between the gluon field and the quark degrees of freedom which goes beyond a simple rescaling of the critical temperature. With both these improvements we can reproduce, for vanishing chemical potentials, the lattice results for the thermal properties of a strongly interacting system like pressure, energy density, entropy density, interaction measure and the speed of sound. Also the expansion parameter towards small but finite chemical potentials agrees with the lattice results. Extending the calculations to finite chemical potentials (what does not require any new parameter) we find a first order phase transition up to a critical end point of $T_{CEP}= 110\ MeV$ and $\mu_q = 320\ MeV$. For very large chemical potentials, we find agreement with pQCD calculations. We calculate the mass of mesons and baryons as a function of temperature and chemical potential and the transition between the hadronic and the chirally restored phase. These calculations provide an equation of state in the whole $T,\mu$ plane an essential ingredient for dynamical calculations of ultra-relativistic heavy ion collisions but also for the physics of neutron stars and neutron star collisions.

Superconducting proximity effect in flat band systems

We study theoretically proximity-induced superconductivity and its inverse effect in dice lattice flat band model by considering Josephson junction with an s-wave pairing in the superconducting leads. Using self-consistent tight-binding Bogoliubov–de Gennes method, we show that there is a critical value for chemical potential of the superconductors depending on paring interaction strength over which for undoped normal region the proximity effect is enhanced. Whereas if the supserconductor chemical potential is less than the critical one the proximity effect decreases regardless of normal region doping and in the meanwhile, the pairing amplitude of superconducting region increases significantly. Furthermore, we unveil that the supercurrent passing through the junction is large (vanishingly small) when the superconductor chemical potential is smaller (larger) than the critical value which increases as a function of normal region chemical potential.

Computational determination of structural, electronic, optical, thermoelectric and thermodynamic properties of hybrid perovskite CH3CH2NH3GeI3: An emerging material for photovoltaic cell

Owing to high power conversion efficiency and low-cost, methyl-ammonium lead-based halide (viz. CH3NH3PbI3) Perovskites have been emerging as the innovative candidate in the development of optoelectronic devices. However, the toxic lead in these materials is a major hurdle in its commercialization. Thus, there is an urgent need to replace lead with an appropriate element. Ethyl-ammonium based lead-free hybrid halide perovskites may be an alternative photovoltaic (PV) absorber material with appropriate band gap, high stability and non-toxic properties. Herein, we have investigated structural, electronic, optical, thermoelectric and thermodynamic properties of ethyl-ammonium germanium iodide (CH3CH2NH3GeI3 or EAGeI3) by full-potential augmented plane wave (FP-LAPW) method as implemented in the WIEN2k code within the density functional theory (DFT). In this paper, we have found that EAGeI3 has direct band gap of 1.3 eV and high absorption coefficient greater than 104 cm−1 indicating its suitability as PV absorber material. We have also calculated thermoelectric coefficients as a function of carrier concentration, chemical potential and temperature. The thermodynamic calculations have been done within the quasi-harmonic approximation. As EAGeI3 has been studied first time for PV applications, the present study may open a new vista for more exhaustive experimental and theoretical investigations in search of non-toxic and eco-friendly PV materials.

Investigation of structural, electronic, optical and thermoelectric properties of Ethylammonium tin iodide (CH3CH2NH3SnI3): An appropriate hybrid material for photovoltaic application

Hybrid halide Perovskites have been emerging as the innovative candidate in the development of optoelectronic devices. Ethyl-ammonium based hybrid halide perovskites have been admirable compounds regarding low band gap, high stability and non-toxic properties instead of methyl-ammonium based hybrid halide perovskites. Herein, we have investigated structural, electronic, optical and thermoelectric (TE) properties of ethyl-ammonium tin iodide (CH3CH2NH3SnI3) by full-potential linearized augmented plane wave plus local orbital (FP-LAPW + lo) method as implemented in the WIEN2k code within the density functional theory (DFT). The PBE-GGA, PBE-sol-GGA and TB-mBJ-GGA exchange-correlation potentials have been used to calculate the density of states and band structure of ethyl ammonium tin iodide (EASnI3) and found that it is a direct band gap semiconductor. We have calculated optical parameters such as dielectric function, absorption coefficient, refractive index, extinction coefficient, Eloss, optical reflectivity and optical conductivity for photon energies in the range 0–25 eV. We have also calculated transport coefficients (Seebeck coefficient, the figure of merit, power factor, electrical conductivity, thermal conductivity) as a function of carrier concentration, chemical potential and temperature. Most of the investigated parameters are being reported for the first time. The present study establishes that ethyl-ammonium tin iodide (EASnI3) offers high absorption coefficient, high Seebeck coefficient, etc. This makes it a prospective material for cost effective photovoltaic device applications to overcome environmental instabilities.

Differential entropy per particle in Dirac semimetals in external magnetic field

We obtain a general expression for the differential entropy per particle (DEP) for three-dimensional Dirac systems as a function of chemical potential, temperature and magnetic field. It is shown that in the presence of magnetic field the dependence of DEP on the chemical potential near a charge neutral point is quite different from the corresponding dependence in graphene. Specifically, we observe a flat region with almost zero DEP near the charge neutral point which grows with the increase of the magnetic field followed then by decreasing oscillations due to contributions from the Landau levels. In contrast, in graphene there is a sharp peak observed for the chemical potential in the temperature vicinity of the Dirac point.

Initial steps toward Auad island nucleation on a c(2 × 2)-Cl Au(001) surface investigated by DFT.

Density functional theory calculations are reported that elucidate the initial steps toward Au ad-island nucleation on c(2 × 2)-Cl covered Au(001) surfaces, which is relevant for Au electrodeposition in Cl- containing electrolytes. The atomic geometry of (Auad)n adatom structures for n ≤ 4, as well as their stability as a function of Cl chemical potential, has been determined. The electrolyte, however, has not been accounted for in the computation. We find a weakly bonded (AuadCl2)-chain as the most stable structure in the case of Cl chemical potentials such that Cl vacancies are suppressed. In the range of Cl chemical potential, where Cl vacancies occur in equilibrium and bind to an (modified) Auad induced ad-structure, the formation of a dimer from two monomers is accompanied by an energy gain between 0.06 and 0.23 eV. For Auad trimer and tetramer formation, the calculations suggest a similar tendency. This suggests that on c(2 × 2)-Cl covered Au(001) surfaces, the Au ad-island nucleation is supported by the presence of vacancies in the Cl adlayer.

Comparative study of the condensate fraction of balanced and imbalanced uniform fermionic systems in the BEC-BCS crossover

In this paper, we have made a comparative study of the condensate fraction of balanced and imbalanced two-component uniform fermionic systems in the Bose–Einstein condensation-Bardeen–Cooper–Schrieffer (BEC-BCS) crossover. We have used extended BCS equations to calculate the condensate fraction of Cooper pairs as a function of chemical potential and gap energy in a balanced system using a path integral approach. For an imbalanced system, the same equation has been derived as a function of average chemical potential, imbalanced chemical potential, gap energy, and temperature. The condensate fraction in a balanced fermionic system varies with the interaction parameter, whereas its behavior in an imbalanced system changes with the interaction parameter and polarization, in different regimes. In particular, the effect of polarization on the condensate fraction has been studied in an imbalanced system for odd values of polarization. We have compared the condensate fraction for both systems analytically and graphically and observed that for an imbalanced system, it decreases with increasing polarization and almost vanishes for higher values of polarization in the BEC regime.

Zeeman-splitting-induced topological nodal structure and anomalous Hall conductivity in ZrTe5

We investigate the topological nodal structure of three-dimensional (3D) ZrTe$_5$ driven by Zeeman splitting as a function of the direction of external magnetic (B) field by using a Wannier-function-based tight-binding (WFTB) model obtained from first-principles calculations. It is known that small external stimuli can drive 3D ZrTe$_5$ into different topological phases including Dirac semimetal. In order to emphasize the effect of Zeeman splitting, we consider 3D ZrTe$_5$ in a strong TI phase with a small band gap. With Zeeman splitting greater than the band gap, the WFTB model suggests that a type-I nodal ring protected by (glide) mirror symmetry is formed when the B field aligns with the crystal $a$ or $b$ axes, and that a pair of type-I Weyl nodes are formed otherwise, when conduction and valence bands touch. We show that a pair of Weyl nodes can disappear through formation of a nodal ring, rather than requiring two Weyl nodes with opposite chirality to come together. Interestingly, a type-II nodal ring appears from crossings of the top two valence bands when the B field is applied along the $c$ axis. This nodal ring gaps out to form type-II Weyl nodes when the B field rotates in the $bc$ plane. Comparing the WFTB and linearized $k \cdot p$ model, we find inadequacy of the latter at some B field directions. Further, using the WFTB model, we numerically compute the intrinsic anomalous Hall conductivity ${\sigma_{ac}}$ induced by Berry curvature as a function of chemical potential and B field direction. We find that ${\sigma_{ac}}$ increases abruptly when the B field is tilted from the $a$ axis within the $ab$ plane. Our WFTB model also shows significant anomalous Hall conductivity induced by avoided level crossings even in the absence of Weyl nodes.

Spin Hall Conductance In a Two-Dimensional Tight-Binding Model In The Presence Of Rashba Spin-Orbit Interaction And Random Impurities

The spin-Hall conductance in a two-dimensional tight-binding model is studied in the presence of Rashba spin-orbit interaction and random impurities. The conventional definition of spin current falls through for a system with Rashba spin-orbit interaction because of the non-conservation of the spin magnetic moment in the presence of Rashba coupling. Using a modified definition of spin-current operator, the relaxation time for electron-impurity scattering is calculated with the help of Matsubara Green function and the spin-Hall conductivity is determined by employing the Kubo-Greenwood formalism. Our results show the explicit behavior of the spin-Hall conductance as a function of chemical potential, Rashba spin-orbit coupling constant and the impurity strength

A hybrid model of Skyrme- and Brueckner-type interactions for neutron star matter

Abstract We suggest a hybrid model for neutron star matter to discuss the hyperon puzzle inherent in the 2.0 M$_{\odot}$ of the neutron star. For the nucleon–nucleon ($NN$) interaction, we employ the Skyrme–Hartree–Fock approach based on various Skyrme interaction parameter sets, and take the Brueckner–Hartree–Fock approach for the interactions related to hyperons. For the many-body interactions including hyperons, we make use of the multi-pomeron-exchange model, whose parameters have been adjusted to the data deduced from various hypernuclei properties. For clear understanding of the physics in the hybrid model, we discuss fractional functions of related particles, symmetry energies, and chemical potentials in dense matter. Finally, we investigate the equations of state and mass–radius relation of neutron stars, and show that the hybrid model can properly describe the 2.0 M$_{\odot}$ neutron star mass data with the many-body interaction employed in the hybrid model. Recent tidal deformability data from the gravitational wave observation are also compared to our calculations, especially in terms of the neutron skin of $^{208}$Pb and nuclear incompressibility.

Thermoelectric properties of YSb: A first-principles approach

The electronic and thermoelectric properties of YSb have been investigated using Full Potential Linearized Augmented Plane wave method (FP-LAPW) based on density functional theory (DFT) in combination with semi-classical Boltzmann transport equation. The exchange and correlation effects have been taken into account by generalized gradient approximation (GGA) within Perdew-Burke-Ernzerhof (PBE) parameterization. The calculated elastic constants such as Bulk modulus, Young modulus, Poisson’s ratio and shear anisotropy factor confirm the mechanical stability of this compound. Boltzmann transport equations were used for the calculation of electronic part of thermoelectric transport parameters such as Seebeck coefficient, Power factor, electrical conductivity and electronic part of thermal conductivity as a function of chemical potential. The temperature dependence of thermoelectric properties of this material at pressure ∼12 GPa is studied over wide range of temperature (200–1200 K). The calculated value of power factor, electrical conductivity and thermal conductivity at T = 1200 K are found to be 65.92 × 1010 W K−2 cm−1 sec−1, 2.90 × 1020 S cm−1sec−1 and 0.97 × 1016 W m−1K−1 sec−1, respectively. The large value of power factor which is due to its non-trivial topological nature strongly suggests that this material can act as a good thermoelectric material in high temperature region.