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1,090 results on '"Foxon, C. T."'

51. The Hall effect and hole densities in high Tc GaMnAs thin films

Author

Edmonds, K. W., Wang, K. Y., Campion, R. P., Neumann, A. C., Foxon, C. T., Gallagher, B. L., and Main, P. C.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

By studying the Hall effect in a series of low resistivity Ga1-xMnxAs samples, accurate values for the hole density p, Mn concentration x, and Curie temperature Tc are obtained over the range 0.015=

Published
2002

52. Phonon drag thermopower and weak localization

Author

Miele, A., Fletcher, R., Zaremba, E., Feng, Y., Foxon, C. T., and Harris, J. J.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Previous experimental work on a two-dimensional (2D) electron gas in a Si-on-sapphire device led to the conclusion that both conductivity and phonon drag thermopower $S^g$ are affected to the same relative extent by weak localization. The present paper presents further experimental and theoretical results on these transport coefficients for two very low mobility 2D electron gases in $\delta-$doped GaAs/Ga$_x$Al$_{1-x}$As quantum wells. The experiments were carried out in the temperature range 3-7K where phonon drag dominates the thermopower and, contrary to the previous work, the changes observed in the thermopower due to weak localization were found to be an order of magnitude less than those in the conductivity. A theoretical framework for phonon drag thermopower in 2D and 3D semiconductors is presented which accounts for this insensitivity of $S^g$ to weak localization. It also provides transparent physical explanations of many previous experimental and theoretical results., Comment: 19 page Revtex file, 3 Postscript figure

Published
1998
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53. Searches for Skyrmions in the Limit of Zero g-Factor

Author

Leadley, D. R., Nicholas, R. J., Maude, D. K., Utjuzh, A. N., Portal, J. C., Harris, J. J., and Foxon, C. T.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons
Abstract

Energy gaps have been measured for the ferromagnetic quantum Hall effect states at v=1 and 3 in GaAs/GaAlAs heterojunctions as a function of Zeeman energy, which is reduced to zero by applying hydrostatic pressures of up to 20kbar. At large Zeeman energy the gaps are consistent with spin wave excitations. For a low density sample the gap at v=1 decreases with increasing pressure and reaches a minimum when the g-factor vanishes. At small Zeeman energy the excitation appears to consist of a large number of reversed spins and may be interpreted as a Skyrmion. The data also suggest Skyrmionic excitations take place at v=3. The width of the minimum at v=1 is found to decrease as the g-factor is reduced in a similar way for all samples., Comment: 14 pages, 9 figures. To appear in Semiconductor Science and Technology

Published
1998
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54. Critical Collapse of the Exchange Enhanced Spin Splitting in 2-D Systems

Author

Leadley, D. R., Nicholas, R. J., Harris, J. J., and Foxon, C. T.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons
Abstract

The critical filling factor v_c where Shubnikov-de Haas oscillations become spin split is investigated for a set of GaAs-GaAlAs heterojunctions. Finite temperature magnetoresistance measurements are used to extract the value of v_c at zero temperature. The critically point is where the disorder potential has the same magnitude as the exchange energy, leading to the empirical relationship v_c = g* n t h / 2 m_0. This is valid for all the samples studied, where the density n and single particle lifetime t both vary by more than an order of magnitude and g* the exchange enhanced g-factor has a weak dependence on density. For each sample the spin gap energy shows a linear increase with magnetic field. Experiments in tilted magnetic field show the spin gap is the sum of the bare Zeeman energy and an exchange term. This explains why measurements of the enhanced g-factor from activation energy studies in perpendicular field and the coincidence method in tilted fields have previously disagreed., Comment: 16 pages, 18 figures. Submitted to Phys. Rev. B

Published
1998
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55. Fractional Quantum Hall Effect Measurements at Zero g-Factor

Author

Leadley, D. R., Nicholas, R. J., Maude, D. K., Utjuzh, A. N., Portal, J. C., Harris, J. J., and Foxon, C. T.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Fractional quantum Hall effect energy gaps have been measured in GaAs/GaAlAs heterojunctions as a function of Zeeman energy, which is varied by applying hydrostatic pressure up to 20 kbar. The gap at v=1/3 decreases with pressure until the g-factor changes sign when it again increases. The behavior is similar to that seen at v=1 and shows that excitations from the 1/3 ground state can be spin-like in character. At small Zeeman energy, the excitation appears to consist of 3 spins and may be interpreted as a small composite skyrmion., Comment: 7 pages retex + 4 ps figs

Published
1997
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56. Pulsed Magnetic Field Measurements of the Composite Fermion Effective Mass

Author

Leadley, D. R., van der Burgt, M., Nicholas, R. J., Foxon, C. T., and Harris, J. J.

Subjects
Condensed Matter
Abstract

Magnetotransport measurements of Composite Fermions (CF) are reported in 50 T pulsed magnetic fields. The CF effective mass is found to increase approximately linearly with the effective field $B^*$, in agreement with our earlier work at lower fields. For a $B^*$ of 14 T it reaches $1.6m_e$, over 20 times the band edge electron mass. Data from all fractions are unified by the single parameter $B^*$ for all the samples studied over a wide range of electron densities. The energy gap is found to increase like $\sqrt{B^*}$ at high fields., Comment: Has final table, will LaTeX without errors

Published
1995
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61. Exciton and Phonon Radiative Linewidths in Monolayer Boron Nitride

Author

Cassabois, G., primary, Fugallo, G., additional, Elias, C., additional, Valvin, P., additional, Rousseau, A., additional, Gil, B., additional, Summerfield, A., additional, Mellor, C. J., additional, Cheng, T. S., additional, Eaves, L., additional, Foxon, C. T., additional, Beton, P. H., additional, Lazzeri, M., additional, Segura, A., additional, and Novikov, S. V., additional

Published
2022
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71. Optically Detected Magnetophonon Resonance in GaAs-GaAlAs Heterojunctions

Author

Barnes, D. J., Nicholas, R. J., Watts, M., Peeters, F. M., Wu, X., Devreese, J. T., Langerak, C. J. G. M., Singleton, J., Harris, J. J., Foxon, C. T., Cardona, Manuel, editor, Fulde, Peter, editor, von Klitzing, Klaus, editor, Queisser, Hans-Joachim, editor, Lotsch, Helmut K. V., editor, and Landwehr, Gottfried, editor

Published
1992
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79. Effects of High Frequency Delocalization on the Quantum Hall Effect

Author

Meisels, R., Lim, K. Y., Kuchar, F., Weimann, G., Schlapp, W., Rampton, V., Beton, P., Eaves, L., Harris, J. J., Foxon, C. T., Cardona, Manuel, editor, Fulde, Peter, editor, von Klitzing, Klaus, editor, Queisser, Hans-Joachim, editor, Lotsch, Helmut K. V., editor, and Landwehr, Gottfried, editor

Published
1992
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84. Charging effects in quantum dots

Author

Kouwenhoven, L. P., van der Vaart, N. C., Johnson, A. T., Harmans, C. J. P. M., Williamson, J. G., Staring, A. A. M., Foxon, C. T., and Rössler, Ulrich, editor

Published
1991
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