Charge Chemical Potential Research Articles

Charge transfer and chemical potential in 1,3-dipolar cycloadditions

We revisit the role of the electronic chemical potential as the indicator for the tendency of chemical species to attract or donate electrons. Studying a set of 1,3-dipolar cycloadditions shows that the classical Mulliken expression is insufficient in some cases to accurately predict the direction of electron transfer. Agreement with experimental results can be achieved by including the effects of interactions between the reacting partners in the working equation used to calculate the chemical potential. We present a simple revision of the Mulliken expression, inspired by previous work from Gazquez, Cedillo, and Vela, that incorporates the interactions between the reagents in an approximate manner. The revised formula adequately describes the experimental data. We also explore how different methods for computing the ionization potential and electron affinity affect our results.

Competition and duality correspondence between inhomogeneous fermion-antifermion and fermion-fermion condensations in theNJL2model

We investigate the possibility of spatially homogeneous and inhomogeneous chiral fermion-antifermion condensation and superconducting fermion-fermion pairing in the ($1+1$)-dimensional model by Chodos et al. [Phys. Rev. D 61, 045011 (2000)] generalized to continuous chiral invariance. The consideration is performed at nonzero values of temperature $T$, electric charge chemical potential $\ensuremath{\mu}$ and chiral charge chemical potential ${\ensuremath{\mu}}_{5}$. It is shown that at ${G}_{1}<{G}_{2}$, where ${G}_{1}$ and ${G}_{2}$ are the coupling constants in the fermion-antifermion and fermion-fermion channels, the $(\ensuremath{\mu},{\ensuremath{\mu}}_{5})$-phase structure of the model is in a one-to-one correspondence with the phase structure at ${G}_{1}>{G}_{2}$ (called duality correspondence). Under the duality transformation the (inhomogeneous) chiral symmetry breaking (CSB) phase is mapped into the (inhomogeneous) superconducting (SC) phase and vice versa. If ${G}_{1}={G}_{2}$, then the phase structure of the model is self-dual. Nevertheless, the degeneracy between the CSB and SC phases is possible in this case only when there is a spatial inhomogeneity of condensates.

Striped phases in the holographic insulator/superconductor transition

We study striped phases in holographic insulator/superconductor transition by considering a spatially modulated chemical potential in AdS soliton background. Generally striped phases can develop above a critical chemical potential. When the constant leading term in the chemical potential is set to zero, a discontinuity in the plot of charge density versus chemical potential is observed in the limit of large wave vector. We explain this discontinuity using an analytical approach. When the constant leading term in the chemical potential is present, the critical chemical potential is larger than in the case of a homogeneous chemical potential, which indicates that the spatially modulated chemical potential disfavors the phase transition. This behavior is also confirmed qualitatively by analytical calculations. We also calculate the grand canonical potential and find that the striped phase is favored.

Density versus chemical potential in holographic probe theories

We study the relationship between charge density ($\ensuremath{\rho}$) and chemical potential ($\ensuremath{\mu}$) for an array of Lorentz-invariant $3+1$-dimensional holographic field theories with the minimal structure of a conserved charge. In all cases, at large density, the relationship is well-modeled by a power-law behavior of the form $\ensuremath{\rho}\ensuremath{\propto}{\ensuremath{\mu}}^{\ensuremath{\alpha}}$. For the minimal ingredients of a gravitational field and a probe $U(1)$ gauge field in the bulk, we find general constraints $\ensuremath{\alpha}=1$ for the Maxwell action and $\ensuremath{\alpha}>1$ for the Born-Infeld case, for general background metrics. We show that the constraint $\ensuremath{\alpha}\ensuremath{\ge}1$ can also be understood directly in the field theory from thermodynamic stability and causality. We then determine which values of $\ensuremath{\alpha}$ are realized in a large range of example systems, including $\mathrm{D}p\mathrm{\text{\ensuremath{-}}}\mathrm{D}q$ probe brane constructions and ``bottom-up'' models with gauge and scalar fields.

Quasi-transverse electromagnetic modes supported by a graphene parallel-plate waveguide

A model is developed for a parallel-plate waveguide formed by graphene. The graphene is represented by an infinitesimally thin, local two-sided surface characterized by a surface conductivity obtained from the Kubo formula. Maxwell’s equations are solved for the model fields guided by the graphene layers. It is shown that despite the extreme thinness of its walls, a graphene parallel-plate waveguide can guide quasi-transverse electromagnetic modes with attenuation similar to structures composed of metals, while providing some control over propagation characteristics via the charge density or chemical potential. Given the interest in developing graphene electronics, such waveguides may be of interest in future applications.

Gauged supergravity from type IIB string theory on [formula omitted] manifolds

We first construct a consistent Kaluza–Klein reduction ansatz for type IIB theory compactified on Sasaki–Einstein manifolds Y p , q with Freund–Rubin 5-form flux giving rise to minimal N = 2 gauged supergravity in five dimensions. We then investigate the R-charged black hole solution in this gauged supergravity, and in particular study its thermodynamics. Based on the gauge theory/string theory correspondence, this non-extremal geometry is dual to finite temperature strongly coupled four-dimensional conformal gauge theory plasma with a U ( 1 ) R -symmetry charge chemical potential. We study transport properties of the gauge theory plasma and show that the ratio of shear viscosity to entropy density in this plasma is universal. We further conjecture that the universality of shear viscosity of strongly coupled gauge theory plasma extends to non-zero R-charge chemical potential.

Higher derivative corrections to near-extremal black holes in type IIB supergravity

We discuss string theory α ′ corrections to charged near-extremal black 3-branes/black holes in type IIB supergravity. We find that supersymmetric global AdS 5 × S 5 geometry is not corrected to leading order in α ′ , while charged or non-extremal black 3-branes/black hole geometries receive α ′ corrections. Following gauge theory-string theory correspondence the thermodynamics of these geometries is mapped to the thermodynamics of large- n c N = 4 supersymmetric Yang–Mills theory at finite (large) 't Hooft coupling with the U ( 1 ) R -charge chemical potential. We use holographic renormalization to compute the Gibbs free energy and the ADM mass of the near-extremal solutions. The remaining thermodynamic potentials are evaluated enforcing the first law of thermodynamics. We present analytic expressions for the α ′ corrected thermodynamics of black holes in AdS 5 × S 5 and the thermodynamics of charged black 3-branes with identical chemical potentials for [ U ( 1 ) R ] 3 charges and large (compare to chemical potential) temperature. We compute α ′ corrections to Hawking–Page phase transition. We find that for nonzero chemical potential thermodynamics of near-extremal black 3-brane solution receives ln T correction to leading order in α ′ .

Charge ordering and chemical potential shift inLa2−xSrxNiO4studied by photoemission spectroscopy

We have studied the chemical potential shift in La$_{2-x}$Sr$_x$NiO$_4$ and the charge ordering transition in La$_{1.67}$Sr$_{0.33}$NiO$_4$ by photoemission spectroscopy. The result shows a large ($\sim$ 1 eV/hole) downward shift of the chemical potential with hole doping in the high-doping regime ($\delta \gtrsim$ 0.33) while the shift is suppressed in the low-doping regime ($\delta \lesssim$ 0.33). This suppression is attributed to a segregation of doped holes on a microscopic scale when the hole concentration is lower than $\delta \simeq 1/3$. In the $\delta = 1/3$ sample, the photoemission intensity at the chemical potential vanishes below the charge ordering transition temperature $T_{\rm CO}=$ 240 K.

Molecular dynamics simulations in the grand canonical ensemble: Formulation of a bias potential for umbrella sampling

An extended Hamiltonian technique for performing grand canonical ensemble molecular dynamics simulations has been reformulated to include umbrella sampling, thus improving the efficiency of particle creation and annihilation processes. This was accomplished through incorporation of a bias potential in the Hamiltonian that modifies the free energy contour between integer particle number states. The extended Hamiltonian includes a continuous particle number variable that is the sum of the integer particle number and a coupling parameter, the latter being used in a scaling function for a fractional molecule’s interactions with the rest of the system. Equations of motion for the coupling parameter, derived from the Hamiltonian, integrate to yield density fluctuations at constant chemical potential. This new method may be adapted to a wide range of potential scaling functions. The technique was applied to calculations of extended simple point charge water density versus chemical potential, using both linear and nonlinear scaling. For each scaling function, a bias potential was constructed using a thermodynamic integration technique. Grand canonical ensemble simulations then yielded results in agreement with independent calculations.

Kaon zero-point fluctuations in neutron star matter

We investigate the contribution of zero-point motion, arising from fluctuations in kaon modes, to the ground state properties of neutron star matter containing a Bose condensate of kaons. The zero-point energy is derived via the thermodynamic partition function, by integrating out fluctuations for an arbitrary value of the condensate field. It is shown that the vacuum counterterms of the chiral Lagrangian ensure the cancellation of divergences dependent on $\mu$, the charge chemical potential, which may be regarded as an external vector potential. The total grand potential, consisting of the tree-level potential, the zero-point contribution, and the counterterm potential, is extremized to yield a locally charge neutral, beta-equilibrated and minimum energy ground state. In some regions of parameter space we encounter the well-known problem of a complex effective potential. Where the potential is real and solutions can be obtained, the contributions from fluctuations are found to be small in comparison with tree-level contributions.

Quantum fluid density functional theory of time-dependent phenomena: Ion-atom collisions

Using a recently proposed kinetic energy density functional and an amalgamation of density functional theory with quantum fluid dynamics, a time-dependent Kohn-Sham-type equation in three-dimensional space, which is a new non-linear Schrödinger equation, has been derived. The equation is also derived through the stochastic interpretation of quantum mechanics. A molecular “thermodynamic” viewpoint is suggested in terms of space-time-dependent quantities. Numerical solution of the above equation yields the time-dependent charge density, current density, effective potential and chemical potential. Perspective plots of these quantities for the proton-neon 25 keV head-on collision are presented.