Searcharxiv⌕ Search

arXiv subjects

Andrew Das Arulsamy

Publications and source records attributed to Andrew Das Arulsamy.

At least 37 records · Page 2Linked to original sources
arXiv2010

Non-square-well potential profile and non-blinking effect in graded CdZnSe/ZnSe nanocrystals: An ionization-energy theoretic study

Randomly blinking nanocrystals have given rise to numerous and intense theoretical and experimental investigations recently. An experimental breakthrough was finally made by fabricating the non-blinking Cd$_{1-x}$Zn$_x$Se/ZnSe graded nanocrystal [Nature 459 (2009) 686]. Here, we report (1) an unequivocal and detailed theoretical investigation to understand the properties of the potential-well and the distribution of Zn content with respect to the nanocrystal radius and (2) develop a strategy to find the relationship between the photoluminescence (PL) energy peaks and the potential-well due to Zn distribution in nanocrystals. We found that the non-square-well potential can be varied in such a way that one can indeed control the PL intensity and the energy-level difference (PL energy peaks) in any non-free-electron nanocrystals accurately. This implies that we can either suppress the blinking altogether, or alternatively, manipulate the PL energy peaks and intensities systematically to give non-random blinking. Our theoretical strategy developed here is generic and can be applied to any non-free-electron nanocrystals.

cond-mat.str-el↗
arXiv2009

Controlling electronic and adiabatic isolation of quantum dots from the substrate: An ionization-energy theoretic study

Recent controversy on the quantum dots dephasing mechanisms (between pure and inelastic) is re-examined by isolating the quantum dots from their substrate by using the appropriate limits of the ionization energy theory and the quantum adiabatic theorem. When the phonons in the quantum dots are isolated adiabatically from the phonons in the substrate, the elastic or pure dephasing becomes the dominant mechanism. On the other hand, for the case where the phonons from the substrate are non-adiabatically coupled to the quantum dots, the inelastic dephasing process takes over. This switch-over is due to different elemental composition in quantum dots as compared to its substrate. We also provide unambiguous analyses as to understand why GaAs/AlGaAs quantum dots may only have pure dephasing while InAs/GaAs quantum dots give rise to the inelastic dephasing as the dominant mechanism. Our study accentuates the importance of the elemental composition (of both quantum dots and substrate) in evaluating the dephasing mechanisms of quantum dots.

cond-mat.mes-hall↗
arXiv2009

Diffusivity of adatoms on plasma-exposed surfaces determined from the ionization energy approximation and ionic polarizability

Microscopic surface diffusivity theory based on atomic ionization energy concept is developed to explain the variations of the atomic and displacement polarizations with respect to the surface diffusion activation energy of adatoms in the process of self-assembly of quantum dots on plasma-exposed surfaces. These polarizations are derived classically, while the atomic polarization is quantized to obtain the microscopic atomic polarizability. The surface diffusivity equation is derived as a function of the ionization energy. The results of this work can be used to fine-tune the delivery rates of different adatoms onto nanostructure growth surfaces and optimize the low-temperature plasma based nanoscale synthesis processes.

cond-mat.str-el↗
arXiv2009

Electron-conduction mechanism and specific heat above transition temperature in LaFeAsO and BaFe(2)As(2) superconductors

The ionization energy theory is used to calculate the evolution of the resistivity and specific heat curves with respect to different doping elements in the recently discovered superconducting Pnictide materials. Subsequently, the electron-conduction mechanism in the Pnictides above the structural transition temperature is explained unambiguously, which is also consistent with other strongly correlated matter, such as cuprates, manganites, titanates and magnetic semiconductors. Therefore, the superconductivity is not uniquely corresponds to the electronic properties above the structural transition temperature. Detailed prediction are given on these compounds for various doping elements, namely, La(Sm,Ce,Ba,Sr,Ca)FeAsO(F,Cl,Br) and Ba(Sr,Ca,K,Rb,Cs)Fe(2)As(2).

cond-mat.supr-con↗
arXiv2009

How do we interrogate the electrons without roughing them up?

Electrons are indistinguishable, but the energy of each electron is different in different materials and if we can exploit this energy, then we can systematically study the changes of electronic properties in non free-electron metals.

cond-mat.str-el↗
arXiv2008

Magneto-resistivity model and ionization energy approximation for ferromagnets

The evolution of resistivity versus temperature ($ρ(T)$) curve for different doping elements, and in the presence of various defects and clustering are explained for both diluted magnetic semiconductors (DMS) and manganites. Here, we provide unambiguous evidence that the concept of ionization energy ($E_I$), which is explicitly associated with the atomic energy levels, can be related quantitatively to transport measurements. The proposed ionization energy model is used to understand how the valence states of ions affect the evolution of $ρ(T)$ curves for different doping elements. We also explain how the $ρ(T)$ curves evolve in the presence of, and in the absence of defects and clustering. The model also complements the results obtained from first-principles calculations.

cond-mat.stat-mech↗
arXiv2008

Length-dependent resistance model for a single-wall Carbon nanotube

The non-linear length-dependent resistance, $\mathcal{R}(l)$ observed in single-wall Carbon nanotubes (SNTs) is explained through the recently proposed ionization energy ($E_I$) based Fermi-Dirac statistics ($i$FDS). The length here corresponds to the Carbon atoms number ($\mathcal{N}$) along the SNT. It is also shown that $\mathcal{R}_y(l_y)$ $<$ $\mathcal{R}_x(l_x)$ is associated with $E_I^y$ $<$ $E_I^x$, which can be attributed to different semiconducting properties in their respective $y$ and $x$ directions.

cond-mat.other↗
arXiv2008

Many-body Hamiltonian with screening parameter and ionization energy

We prove the existence of a new Hamiltonian that can be used to study strongly correlated matter, which consists of the total energy at temperature equals zero (E_0) and the ionization energy (ξ) as eigenvalues. We show that the existence of this total energy eigenvalue, E_0 \pm ξ, does not violate the Coulombian atomic system. Since there is no equivalent known Hamilton operator that corresponds quantitatively to ξ, we employ the screened Coulomb potential operator, which is a function of this ionization energy to analytically calculate the screening parameter (σ) of a neutral Helium atom in the ground state. In addition, we also show that the energy level splitting due to spin-orbit coupling is inversely proportional to ξeigenvalue.

physics.gen-ph↗
arXiv2007

An alternative normal state c-axis resistivity model for high-Tc superconductors

An alternative model for c-axis resistivity in layered high-Tc crystalline superconductors is proposed and has been characterized as an essentially two-dimensional Fermi liquid. Average ionization energy is included as additional parameter that determines the concentration of tunnelling electrons between Cu-O2 layers. This model agrees well quantitatively with the Bi2212 and Y123 single crystals, and qualitatively with the pure 1212 phase polycrystals.

cond-mat.supr-con↗
arXiv2005

Hall resistance and Lorenz ratio models in YBa2Cu3O7

The 2D models of heat capacity, its conductivity ($κ$), Hall resistance ($R_H$) and the Lorenz ratio ($\mathcal{L}$) have been derived using the ionization energy ($E_I$) based Fermi-Dirac statistics (iFDS). These models reproduce the experimentally measured $ρ(T)$ and $R_H(T)$. The variation of $\mathcal{L}$ is proportional to 1/T due to electron-phonon ($e$-$ph$) scattering in $κ$. However, the $e$-$ph$ coupling in the electrical resistivity has the polaronic effect that complies with iFDS, rather than the $e$-$ph$ scattering that satisfies the Bloch-Grüneisen formula. These models are purely Fermi liquid and are not associated with any microscopic theories of high-Tc superconductors.

cond-mat.supr-con↗
arXiv2005

Diagnosis of transport properties in Ferromagnets

The resistivity model as a function of temperature and ionization energy (doping) is derived with further confinements from spin-disorder scattering in ferromagnetic phase. Magnetization and polaronic effects capture the mechanism of both spin independent and spin-assisted charge transport of ferromagnets, including the newly reported Mn$_x$Ge$_{1-x}$ ferromagnetic semiconductor. The computed $T_{crossover}$ below $T_C$ and carrier density in Ga$_{1-x}$Mn$_x$As system are 8-12 K and 10$^{19}$ cm$^{-3}$, remarkably identical with the experimental values of 10-12 K and 10$^{18}-10^{20}$ cm$^{-3}$ respectively. The calculated charge carriers density for Mn$_x$Ge$_{1-x}$ is 10$^{19}$ cm$^{-3}$, which is also in the same order with the experimental values.

cond-mat.mtrl-sci↗
arXiv2005

Comments on "Thermal Conductivity of Nanotubes: Effects of Chirality and Isotope Impurity" [cond-mat/0501194]

Based on Zhang and Li's molecular dynamics calculations, the heat conductivity ($κ$) of metallic single-wall Carbon nanotubes (SNTs) was incorrectly concluded as mainly influenced by the radius. Apart from that, their isotope effect interpretation on $κ(T)$ for the metallic SNTs using solely the phonon scattering mechanism is also highlighted to be incorrect.

cond-mat.mtrl-sci↗
arXiv2005

Conductivity rules in the Fermi and charge-spin separated liquid

Ioffe-Larkin rule applies for the pure charge-spin separation regardless of its dimensionality. Here, an extension to this rule as a result of the coexistence of spinon, holon and electron as a single entity in the 2-dimensional (2D) system is derived, which is also in accordance with the original rule.

cond-mat.str-el↗
arXiv2004

Ionization energy based Fermi-Dirac statistics

Quantitative differences of Lagrange multipliers between standard Fermi-Dirac statistics (FDS) and Ionization energy ($E_I$) based FDS (iFDS) are analyzed in detail. It is shown here that iFDS is degenerate and its total energy remains the same with the standard FDS. The total energy can be obtained by recasting the $E_I$ in quantized form, as required by the restrictive condition.

cond-mat.stat-mech↗
arXiv2004

Phenomenological models of dielectric functions and screened Coulomb potential

The evolution of static dielectric constants and polarization with doping are analyzed and discussed using established experimental results. The variation of screened Coulomb potential with doping is derived theoretically to justify the said evolutions. The latter justification arises due to the influence of ionization energy ($\mathcal{E_I}$) on the static dielectric functions. The bare Coulomb potential and the Thomas-Fermi screened potential with finite carrier density were recovered when $\mathcal{E_I} \to \infty$ and $\mathcal{E_I} \to E_F^0$ respectively. Basically, these phenomenological models are associated with the ionization energy based Fermi-Dirac statistics (iFDS).

cond-mat.str-el↗
arXiv2004

Magneto-electronic transport theory in ferromagnets above the Curie temperature and in semiconductors

Quantitative differences of Lagrange multipliers between standard Fermi-Dirac statistics (FDS) and Ionization energy ($E_I$) based FDS (iFDS) are analyzed in detail to obtain reasonably accurate interpretations without violating the standard FDS. The resistivity and Hall-resistance models in 1D, 2D and 3D are also derived to illustrate the transport phenomena in semiconducting manganites. It is shown via calculation that the charge carriers in these materials seem to be strongly correlated in term of electron-ion attraction or simply, fermions in those materials are somewhat gapped due to Coulomb attraction. This Coulomb attraction naturally captures the polaronic effect in manganites. $E_I$ is found to be the only essential parameter that predicts $ρ(T,doping,pressure,magnetic field)$ quite accurately. However, this model as will be pointed out, is not suitable for metals with free-electrons and strong electron-phonon scattering. It is to be noted that iFDS and $ρ(T,doping,pressure,magnetic field)$ model are only valid in the paramagnetic region of ferromagnetic manganites and other doped-semiconductors. Recent X-ray photoemission spectroscopy (XPS) studies have indicated that there exists a critical crossover from Mn(2+) to Mn(3+) depending upon Mn's concentrations in (Ga(1-x)Mnx)As diluted magnetic semiconductors (DMS). Such phenomenon occuring at certain critical concentration directly point towards the applicability of $E_I$ based Fermi-liquid (iFLT). As such, iFDS is also discussed with respect to DMS above Curie temperature.

cond-mat.stat-mech↗
arXiv2004

Resistivity model for both paramagnetic and ferromagnetic phases

The resistivity, $ρ$ as a function of temperature and ionization energy (doping) and magnetization respectively is derived with further confinements from spin-disorder scattering. The computed $T_{crossover}$ below $T_C$ and carrier density in Ga$_{1-x}$Mn$_x$As system are 8-12 K and 10$^{19}$ cm$^{-3}$, remarkably identical with the experimental values of 10-12 K and 10$^{18}-10^{20}$ cm$^{-3}$ respectively.

cond-mat.str-el↗