Isotope Effect in Strongly Coupled High Temperature Superconductors in the Presence of Electron-Plasmon Interaction

Abstract

An expression for α, the exponent of the vibrating ionic mass, in a strongly coupled superconductor is derived using the expression for superconducting critical temperature, T_c, recently suggested by us, which incorporates the simultaneous presence of electron-phonon, electron-electron and electron-plasmon interactions. The dependence of α on electron-plasmon coupling constant λ_PI, is quite involved. Calculations of α with α_PI, on high temperature superconductors, both Lanthanum and Yttrium based cuprates, have been made. It turns out that it is possible to have full isotope effect (α = 0.5), fractional isotope effect (α < 0.5) and no isotope effect (α = 0.0) depending upon the interplay of the three mechanisms that bring about superconductivity.

Indexing terms:

• Superconductivity
• Superconducting critical temperature T_c
• Strongly coupled ceramic cuprate superconductors
• Phonons
• Plasmons
• Isotope effect

Additional information

Notes on contributors

S P Tewari

S P Tewari, is a Professor of Physics in the Department of Physics and Astrophysics, University of Delhi, Delhi for the last over twelve years. He has been involved in all kinds of academic activities like teaching, research, supervising research work leading to the award of PhD degrees, organizing Symposia and Conferences, presenting research work at various International and National Symposia and Conferences in the form of invited talks, presentations and chairing the sessions etc since he joined as a Faculty member of Delhi University almost thirty years ago. He has published well over hundred research papers in the top class International reputed journals of physics in different branches of Condensed Matter Physics like superconductivity: both high temperature (rare earth cuprates, Cheveral phase, heavy fermions and fullerides) and conventional, strongly coupled superconductors; density—density distinct and auto—correlation functions, in ordered (highly anisotropic crystals, proteins, bio-polymers, fullerites etc) and disordered (polymers and liquids) materials; frequency and wave—vector dependent electron dielectric functions in solid state plasma at different densities ranging from highly degenerate (metallic) to non-degenerate state (semiconductors); thermal neutron scattering, transport and production of intense beam of cold neutrons from hydrogenous condensed systems; different properties of recently discovered crystalline form of fullerene-fullerite—the third allotrope of carbon, etc.

Prof Tewari is co-editor of two research level books and has co-authored five books; two of which have been published by NCERT, New Delhi and one by CSIR New Delhi, in its Golden Jubilee series.

Prof S P Tewari was visiting Professor of Physics at Northwestern University, USA (1971–72) and Commonwealth Academic Staff Fellow at Bristol University, UK (1978–79). He has been consultant and senior participant etc in different activities of International Center for Theoretical Physics (ICTP) Trieste, Italy. He has also visited many other countries in connection with his research activities.

Poonam Silotia

Poonam Silotia, has been teaching, carrying out and supervising research work for last several years in the ‘Post-Graduate’ Department of Physics and Astrophysics, University of Delhi, Delhi. Soon after receiving her PhD degree from Delhi University in theoretical Condensed Matter Physics, she was offered a Faculty position in the Department. Her research interest spans different kinds of auto-correlation functions in condensed matter physics. She has brought out clearly the effect of two dimensions in various properties of highly anisotropic crystals like zinc and graphite. Her work on the dynamics of proteins-particularly that of myoglobin, reveals the onset of different kinds of dynamics as one approaches the temperature' where the biological activity of the protein sharply increases. Her current research interest is in the understanding of the recently discovered buck-minsterfullerenes-the third allotrope of carbon, and its crystalline form-fullerite. She has already published physical properties of fullerites. Her research work has also been presented in both National and International Symposia and Conferences.

Dr Poonam Silotia is engaged, amongst other activities, in teaching ‘Advanced Solid State Theory’—special paper at the MSc final level. At present she occupies the position of 'Senior Lecturer” in the Department of Physics and Astrophysics, University of Delhi, Delhi.

Paramjeet Kaur Gumber

Paramjeet Kaur Bedi, nee Gumber is teaching and doing research work in Delhi University at Deen Dayal Updhaya College. She obtained her PhD in 1992 in ‘Solid State Physics (Theory)’ from Delhi University. Her research interest lies essentially in the study of various aspects of superconductivity in strongly coupled highly anisotropic superconductors including highsuperconductors both Lanthanum and Yttirum based. She has published several papers in reputed International Journals of Physics like Physical Review? (USA), Journal of Physics: Condensed matter (UK), Physica C: Superconductivity (Amsteram, The Netherlands) etc. Her work on “Effect of fractons on strongly coupled superconductors” (Physical Review B 41, 2619 (1990) (Rapid Communications) has been widely acclaimed. Her work has also been presented in both National and International Symposia and Conferences.