Author

# John K Liakos

Other affiliations: University of Southampton, York University, University of Bath

Bio: John K Liakos is an academic researcher from Kettering University. The author has contributed to research in topics: Schrödinger equation & Wave packet. The author has an hindex of 5, co-authored 12 publications receiving 108 citations. Previous affiliations of John K Liakos include University of Southampton & York University.

##### Papers

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TL;DR: In this paper, the authors applied the Landau theory of phase transitions to elastic phase transitions pertaining to crystals belonging to each of the 32 crystallographic point groups and found the form of third-order invariants (the fourth-order terms also have been obtained for cubic crystals).

Abstract: The Landau theory of phase transitions has been applied to elastic phase transitions pertaining to crystals belonging to each of the 32 crystallographic point groups. Investigation of the Landau free-energy expansions provides information about: (i) the order of the possible transitions, (ii) the associated acoustic mode (which for a second-order transition should soften completely at the transition temperature) and (iii) the higher-order elastic constant contributions to thermal expansion only. Emphasis has been placed on finding the form of third-order invariants (the fourth-order terms also have been obtained for cubic crystals), which are needed in any quantitative assessment of the applicability of the Landau theory to elastic phase transitions in which the order parameter is just a strain tensor component. Application of the theory to the f.c.c. to f.c.t., transition in In-TI alloys is discussed.

54 citations

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TL;DR: In this article, the effect of band-band impact ionization, band band Auger recombination, and p-n junction structure on heterojunction solar cell efficiencies is investigated.

Abstract: This paper reports a theoretical study of heterojunction solar cell efficiencies to include the effect of band - band impact ionization, the band - band Auger recombination and the p - n junction structure. We also study conditions under which configuration A (light encounters the large energy gap first) or configuration B (light encounters the small energy gap first) is the optimal heterojunction configuration for a solar cell, other conditions being kept fixed. Constant efficiency contour diagrams having the energy gaps as axes show that, subject to our assumptions, the best efficiencies are only of order 38% for a black body equivalent to one sun. The higher efficiencies are favoured by the smaller semiconductor widths. Open-circuit voltage, short-circuit current density and fill factor are also calculated for several sets of cell parameters.

13 citations

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York University

^{1}TL;DR: In this article, a time-dependent variational method for the timedependent Schrodinger equation (TDSE) is presented for the study of multiphoton ionization of one-electron atoms.

Abstract: A time-dependent variational method for the time-dependent Schrodinger equation (TDSE) is presented for the study of multiphoton ionization of one-electron atoms. An isotropic Gaussian wave packet with variable width parameter was chosen as a trial function. The calculated ionization rates are compared with accurate nonperturbative results from Floquet theory and numerical integration of the TDSE.

7 citations

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York University

^{1}TL;DR: In this article, a variational principle for the time-dependent Schrodinger equation with an anisotropic Gaussian wave packet as a trial wave function is used to calculate the nonperturbative response of a hydrogen atom to a strong linearly polarized laser field.

Abstract: A variational principle for the time-dependent Schr\"odinger equation with an anisotropic Gaussian wave packet as a trial wave function is used to calculate the nonperturbative response of a hydrogen atom to a strong linearly polarized laser field. This method leads to equations of motion for the position expectation value and allows one to study a classical (\ensuremath{\Elzxh}=0) limit as well as the first quantum corrections. These corrections are shown to be responsible for a strong enhancement in the generation of the third and fifth harmonic by the bound-state part of the electronic wave function for field intensities of the order of ${10}^{14}$ W/${\mathrm{cm}}^{2}$ and a laser frequency corresponding to three-photon ionization. For a low-frequency field a strong nonperturbative enhancement of harmonics of orders 9 to 15 is observed. It is concluded that the plateau at even higher harmonics observed recently in experiment and in numerical calculations is caused by the ionizing parts of the wave function that are not represented in the present calculation.

6 citations

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TL;DR: In this article, the authors generalized the usual Shockley - Read - Hall statistics to involve recombination between two different traps A and B in distributed non-interacting trap-pairs.

Abstract: The usual Shockley - Read - Hall statistics is generalized to involve recombination between two different traps A and B in distributed non-interacting trap-pairs. Characteristics of inter-trap (A to B) and band-to-trap recombinations are numerically surveyed as regards their dependence on the thermal equilibrium Fermi level, the excitation intensity and the interaction between A and B. The inter-trap A to B recombination rate peaks if the Fermi level is near the energy level of trap A or B in the case of moderate excitation and moderate interaction. The inter-trap recombination rate saturates at characteristic values when these parameters become large. We find that for strong interaction between the traps the inter-trap recombination saturates. The reason is that the recombination between the upper trap and the valence band as well as the recombination between the lower trap and the conduction band can then be neglected. Saturation occurs also for strong excitation since then the occupation probabilities approach unity for the upper trap and zero for the lower trap.

5 citations

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299 citations

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TL;DR: In the case of ferromagnetic Heusler alloys Ni2+xMn1-xGa single crystals, a reversible strain of 6% was obtained in fields of 1 T.

Abstract: In ferromagnetic alloys with shape memory large reversible strains can be obtained by rearranging the martensitic domain structure by a magnetic field. Magnetization through displacement of domain walls is possible in the presence of high magnetocrystalline anisotropy, when martensitic structure rearrangement is energetically favorable compared to the reorientation of magnetic moments. In ferromagnetic Heusler alloys Ni2+xMn1–xGa the Curie temperature exceeds the martensitic transformation temperature. The fact that these two temperatures are close to room temperature offers the possibility of magnetically controlling the shape and size of ferromagnets in the martensitic state. In Ni2+xMn1–xGa single crystals, a reversible strain of ~6% is obtained in fields of ~1 T.

265 citations

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TL;DR: In this paper, a brief review of the effect of temperature and pressure on Raman spectra is given, with some basic concepts in a tutorial way before showing how intricated are these manifestations of anharmonicity.

Abstract: This paper gives a brief review of the effect of temperature and pressure on Raman spectra. Anharmonicity, defined by the cubic, quartic and higher terms in the potential expansion, is shown to be responsible for various properties such as dilatation or for variations of wavenumber and half-width of Raman bands with temperature and pressure, or may be strongly involved in phase transitions. This contribution does not pretend to be an exhaustive review on the subject but aims to introduce some basic concepts in a tutorial way before showing how intricated are these manifestations of anharmonicity. Copyright © 2003 John Wiley & Sons, Ltd.

246 citations

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TL;DR: In this article, the authors investigated the recombination processes in antimonide-based materials for thermophotovoltaic (TPV) devices using a radiofrequency photoreflectance technique, in which a Nd-YAG pulsed laser is used to excite excess carriers, and the short-pulse response and photoconductivity decay are monitored with an inductively coupled noncontacting rf probe.

Abstract: Recombination processes in antimonide-based materials for thermophotovoltaic (TPV) devices have been investigated using a radio-frequency (rf) photoreflectance technique, in which a Nd–YAG pulsed laser is used to excite excess carriers, and the short-pulse response and photoconductivity decay are monitored with an inductively coupled noncontacting rf probe. Both lattice-matched AlGaAsSb and GaSb have been used to double cap InGaAsSb active layers to evaluate bulk lifetime and surface recombination velocity with different active layer thicknesses. With an active layer doping of 2×1017 cm−3, effective bulk lifetimes of 95 ns and surface recombination velocities of 1900 cm/s have been obtained. As the laser intensity is increased the lifetime decreases, which is attributed to radiative recombination under these high-level injection conditions. Similar measurements have been taken on both TPV device structures and starting substrate materials for comparison purposes.

168 citations

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TL;DR: In this paper, a more precise definition of the Keldysh gamma parameter ( gamma (0.5) and of the laser field F (F(FBSI) is proposed, where FBSI is the barrier suppression ionization field.

Abstract: Some 'Keldysh-like' theories are analysed leading to a more pragmatic definition of the tunnelling regime of ionization of atoms. Rather than using the more extreme definition of tunnelling (i.e. gamma <<1, F<

167 citations