Thomas Sakwa

• BSc, MPhil, DPhil
• Professor at Masinde Muliro University of Science and Technology

Spin fluctuation in strong correlated systems give rise to superconductivity in cuprate superconductors. The correlation effects in copper oxide layers give rise to collective excitations in high-cuprates.

Strongly correlated electronic models such as the Hubbard, are often used to describe the properties of cuprates. In most cases, the projected Hubbard operators are normally used to study this models. The Hubbard operators normally give rise to a specific kinematical interaction of electrons with spin and charge fluctuations. These interaction is i...

In the original version of article [1], the lists of authors and affiliations, and the Acknowledgements and Author Contributions were incomplete [...]

The first truly high temperature ceramic superconductor is composed of Yttrium, Barium, Copper and Oxygen (YBCO).The copper oxide networks play a major role for the occurrence of superconductivity. We present a possible pairing mechanism in YBCO-123 materials. Different models like; Resonance valence bond ,spin fluctuation and t-j models have been...

Studies have shown that perovskites have a high potential of outdoing silicon based solar cells in terms of solar energy conversion, but their rate of degradation is also high. This study reports on improvement on the stability of CH3NH3PbI3 by passivating it with polymethylmethacrylate (PMMA). Structural and electronic properties of CH3NH3PbI3 sta...

Superconductivity with simple s-wave pairing symmetry is another intriguing phenomenon in heavy-fermion systems. Heavy-fermion superconductors favor the nodal pairing states, such as the d-wave and p-wave states, rather than the s-wave state. The s-wave Cooper pairing in Uranium and Cerium based HF systems has been studied by analyzing the periodic...

We have studied the thermodynamic properties of electron doped Niodium Cellenium Copper Oxide (Nd 2-x Ce x CuO 4-NCCO) and Praseodymium Cellenium Copper Oxide (Pr 2-x Ce x CuO 4-PCCO) and hole doped Yitrium Barium Copper Oxide (YBa 2 CuO 7-YBCO) and Lanthanum Strontium Copper Oxide (La 2-x Sr x CuO 4-LSCO) within the framework of modified Bose-Ferm...

The s-wave and p-wave Cooper pairing in Uranium and Cerium based HF systems has been studied by analyzing the periodic Anderson model by means of the Bogoliubov-Valatin approach (BVT) while focusing on the interorbital Cooper pairing between a conduction electron (c electron) and an f electron, called the "c-f pairing." It is shown that the s-wave...

Studies on superconductivity arising from doping a Mott insulator have become critical in the area of superconductivity. Within the framework of the Bose-Fermi-Hubbard model, we discuss the thermodynamic phase transition via specific heat in hole and electron doped high-T C cuprate superconductors. By considering the interplay between the electrons...

Studies on superconductivity arising from doping a Mott insulator have become critical in the area of superconductivity. Within the framework of the Bose-Fermi-Hubbard model, we discuss the thermodynamic phase transition via specific heat in hole and electron doped high-T C cuprate superconductors. By considering the interplay between the electrons...

Cubic Scandium Triflouride (ScF3) is a material that contracts when exposed to heat. Not many materials are known to behave this way. Such a material has many interesting technological applications yet some of its properties are yet to be fully explored using ab initio methods. This paper engaged the state-of-the-art ab initio methods to study the...

A study has been done using generalized coordinates system with the application of the Lagrangian formalism for n mass units linearly connected to move in space. Lagrangian equations have been developed and used throughout the research to determine the equations of motion for multi-pendula system for several as well as many mass units involved. The...

There are compounds whose structures support superconductivity at high temperatures. They have intra and inter-band interactions which occur within their bands. However there has been no hybrid Hamiltonian developed so far for a lattice structure that can support conduction by both D-waves and other waves on the same Fermi surface. These waves inte...

Interaction between electrons at the critical temperature that culminates into formation of Cooper pair holds the key in explaining cuprates high temperature superconductivity. We study the effects of the number of copper oxide planes on thermodynamic properties of Mercury based high temperature superconductivity due to an interaction between coope...

Cobalt doped TiO2 thin films (CTF) deposited by spray pyrolysis has been studied. The compositional analysis has been done using RBS method, while optical spectroscopy has been done by measuring the transmittance and reflectance of the films. The CTF thin films were prepared by doping TiO2 at different concentration levels of Co which was varied be...

Surface photovoltage (SPV) spectroscopy is a powerful tool for studying electronic defects on semiconductor surfaces, at interfaces, and in bulk for a wide range of materials. Undoped and Cobalt-doped TiO2 (CTO) thin films were deposited on Crystalline Silicon (c-Si) and Flourine doped Tin oxide (SnO2:F) substrates by chemical spray pyrolysis at a...

Computational methods have been widely applied in studying material properties. In this paper, we give an introduction to density functional theory (DFT), how it works and how it is able to predict the ground state properties of a material accurately. As an example, we have studied ScF3 with a simple cubic structure and space group P 2 3 (#195). Th...

Electron interaction near the critical temperature is viewed as a contributor to the establishment of the energy gap which of late is projected to be a harbinger to explaining microscopic mechanism behind High temperature superconductivity. This study investigated the effects of the number of planes of CuO2 on the thermodynamic properties of double...

Developed countries have appreciated the importance of Science, Technology, Engineering and Mathematics (STEM) for scientific and technological development. STEM subjects have been posting low results in the Kenya Certificate of Secondary Examinations over the years and we have linked the deteriorating standards to the inappropriate teaching approa...

The t-J model has been modified for a dipole mediated t-J Hamiltonian and used to study the thermodynamic properties of high-T c superconductivity. In point of fact, we looked at the system energy, specific heat capacity, and entropy and transition temperature. The effective Hamiltonian of this model is obtained from the sum of the separately diago...

Bose-Einstein Condensation, BEC, of an ideal gas is investigated for a finite number of particles trapped in a harmonic potential. The values of the critical temperature for Rb-87, its condensate fraction and the energy per particle are determined. The maxima appear to increase with the number of particles due to the fact that a smaller system has...

The thermodynamic properties of in commensurate quantum crystal at low temperature are studied using commensurability count. Permutation of the sites and atoms is done in the system of bosons where exclusion is done due to identity among the bosons. The count of the whole system is made and by use of starling approximation, the equation is simplifi...

Certain types of interactions can lead to massive quasi-particles such that the resulting effective masses of the electrons may reach values between 100 and 1000 times the mass of the free electrons. The interactions between such heavy electrons are assumed to be singlet s-wave and triplet s-wave, and their contribution to s-wave superconductivity...

The thermodynamic properties of in commensurate quantum crystal at low temperature are studied using commensurability count. Permutation of the sites and atoms is done in the system of bosons where exclusion is done due to identity among the bosons. The count of the whole system is made and by use of starling approximation, the equation is simplifi...

Ion layer gas reaction (ILGAR) method allows for deposition of Cl-containing and Cl-free In2S3 layers from InCl3 and In(OCCH3CHOCCH3)3 precursor salts, respectively. A comparative study was performed to investigate the role of Cl on the diffusion of Cu from CuSCN source layer into ILGAR deposited In2S3 layers. The Cl concentration was varied betwee...

Kenya has over six million active mobile subscribers who may at some point want to replace or get rid of old mobile phones. A big number of the mobile phones were recently switched off for not being genuine without a prober mechanism being put in place for the disposal. If every affected individual or otherwise disposed off phones by throwing it aw...

The ground state properties of trapped atomic Boson-Fermion mixture at near absolute zero temperature Kelvin is studied using second quantization techniques. An effective Hamiltonian for the Binary system is developed in terms of the magnitude of fluctuations to bring out the interplay between boson-boson, boson-fermion & fermion-fermion interactio...

A four and five-tupple chain pendulum system constrained to move in a plane(X, Y,0) has been studied within the framework of a generalized coordinate system by using an abridged Lagrangian formalism. The Lagrangian is developed and used to get the equations of motion which are further solved using eigenvalue relations. In an ideal case of a non-vis...

A multiple chain pendula system constrained to move in a plane has been studied further within the framework of a generalized coordinate system by using Lagrangian formalism. Equations of motions for many body pendula systems have been derived. These equations concur very well with known data for m≤5. We confirm that equations of motion for any val...

The properties of crystalline quantum hard-sphere systems of bosons at low and high densities have been studied. At very high density, the hard-sphere system approaches close packing (CP) structure. Ground state energy per particle of a many-boson system of particles has been calculated for close-packing densities. For a hard-sphere diameter fixed...

The low-temperature thermodynamic variables of entropy, internal energy and specific heat capacity of a liquid 3He- 4He binary system have been studied. The system showed a remarkable discontinuity in internal energy at about 2.14 K. In the binary mixtures, the bosonic components have been studied by means of modified Gross-Pitaevskii (GP) approxim...

Elastic scattering of 4He atoms when they approach the surface of 4He liquid, has been studied. The liquid surface is assumed to be uniform and the density profile is the same along and perpendicular to the surface. The incident 4He atom will interact with a large number of 4He atoms in the liquid near the surface of liquid 4He. Hence, the effectiv...

The pair distribution function g(r) for a system of bosons interacting through a two-body potential composed of a hard core followed by a square well has been obtained using the reaction matrix formalism for the energy excitation spectrum Ek and the fundamental definition relating the structure factor S(k) and g(r) . This has been used in obtaining...

Under very high pressure, pockets of vacuum may be created around super solid 4He crystals. Crystals of 4He may flow through pockets of vacuum, one behind the other, and since the flow in vacuum will be frictionless and 4He atoms being bosons can swap positions, the flow may appear to be superfluid. Thus, the crystals will not be flowing into each...

Under very high pressure, pockets of vacuum may be created around super solid He-4 crystals. Crystals of He-4 may flow through pockets of vacuum, one behind the other, and since the flow in vacuum will be frictionless and He-4 atoms being bosons can swap positions, the flow may appear to be superfluid. Thus, the crystals will not be flowing into ea...

Using the exotic pairing model, the jump in the specific heat ΔC/Tc in YBa 2Cu 307-δ, for both breathing mode and buckling mode has been calculated. Its value was compared with the experimental values and it has been found that the specific heat jump in superconductor and the density of states were one fifth of the earlier reported values. This is...

A micro-canonical ensemble for an assembly of bosons and fermions is considered in which the number of particles, internal energy and volume are kept constant. A statistical distribution model, which is fermion dominated and where bosons and fermions interact in pairs, is developed. The partition function is derived. Macroscopic thermodynamic quant...

The correlation amplitude for the quasi-particles in high Tc superconductors has been deduced. From this amplitude, the maximum critical transition temperature has been calculated. The assumption, which has been made is that, the superconductivity is due to condensation of electron pairs, which may be in a parallel spin-state, an antiparallel spin-...

The adsorption of superfluid 4 He into a disordered medium, the disappearance of superfluidity due to adsorption, and the subsequent appearance of superfluidity when more 4 He flows into the disordered medium have been described by the four-level approximation. The adsorption of superfluid 4 He into a disordered medium depletes the ZMS as the parti...

For pure 4 He liquid the superfluid fraction starts having a finite value at and below the λ-transition temperature 2.176K, whereas for 4 He in a disordered media the superfluid fraction starts having a finite value at 2.168K, a temperature that is lower compared to the temperature at which superfluidity appears in pure 4 He. Relations for transiti...

Radial breathing mode oscillation of 87Rb Condensate. [Myatt C J et al., Phys Rev Lett. 78 (1997) 586] has been obtained in the time range of 5 to 50 milliseconds. The authors have computed the temporal variations of the condensate fraction of bosons using Fourier transform. The authors found that there is an increase in the condensate fraction wit...

The variation of the occupation number of the zero momentum states (Z-M-S) with the momentum vector k and that of the condensate fraction with k for adsorption of Liquid Helium (He-4) in a porous medium has been studied theoretically.

Experimental observations show that superfluidity is destroyed when He-4 is adsorbed in Vycor glass, and He-4 in aerogel is superfluid at T-e = 2.168K which is lower than the corresponding temperature T-e = 2.172K for pure He-4. A simple theoretical explanation of why this happens is outlined in this note.

The critical properties of the superfluid-insulator transition have been studied using the reaction matrix formalism instead of the conventional Bogoliubov approximation that is unable to capture even the roton minimum found in real strongly interacting Bose fluids. Although the inert phase is described as disordered Bose condensate, its spatial or...