Theoretical scenarios for the SIT of disordered materials

Transcription

1 Volume 119 No , ISSN: (on-line version) url: ijpam.eu Special emphasissuperconductive action of insulating Materials Abstract P.ANTONY LYLA 1,K.SEEVAKAN 2 1 AssistantProfessor,Dept. of Physics, 2 Department of Bioinformatics, 1 BIST, BIHER, Bharath university,chennai-73, antonylyla.phy@bharathuniv.ac.in The application and effects of low oxygen pressures for the growth of YBa 2 Cu 3 O 7-x films by post deposition annealing are reviewed and related to available thermodynamic data at subatmospheric oxygen pressures. Special emphasis is given to the correlation between epitaxial growth properties and high temperature annealing conditions and the effect of variable low temperature oxidation. The application of low oxygen pressures is extended to the recrystallization of ion implanted, amorphized YBa 2 Cu 3 O 7-x layers for comparison with epitaxial growth properties during initial post deposition annealing.there is a wealth of data showing the existence of important lattice effects and intrinsic inhomogeneities in 123-O x. Five phase transition mechanism The well-known T O transition at x = 6.4, which according to Kartha et al. (1995) and Krumhansl (1992) is a first-order martensitic transformation. Also a neutron diffraction refinement ( Radaelli et al. 1992) concludes that it is a first-order structural transition. The onset of superconductivity (I M transition) takes place inside the composition range of the T O transition and the latter triggers the former[1-6], as originally proposed by Cava et al. (1990). The ideas of a universal hole count for all cuprates to become superconducting are doubtful for 123-O x because their proof was based on questionable samples[7-11]. Recent structural data on very slowly cooled equilibrium samples ( Conder et al. 1999;) support clearly the abrupt change of the c-axis and apical bond found earlier by Cava et al. (1990). Charge transfer from the chains to the planes is coupled to this c-axis contraction. A giant dt c /dp effect is measured at this composition which seems to be correlated with the oxygen ordering taking place at this transition[12-19]. Raman investigations show another transition or cross-over at the Néel temperature (x = 6.22). Deconvolution of the apex-phonon width shows the coexistence of four phases in the nonstoichiometric range of 123. It is possible that physical phase separation starts at x = 6.22 with the formation of hole-doped islands in an AF matrix (sect )[20-26], the percolation to the superconducting phase taking place at x Several lattice distortions have been found in the underdoped and optimally doped fields.inthe local structure, shifts of 0.1 of the oxygen sites appear along the c-axis in domains of 10. The question arises whether this is the result of the presence of polarons or some kind of stripes, as was shown to be the case for the La cuprates[27-35]. Electron diffraction shows correlated displacements of Cu2 and O1 in the a b plane leading to local perturbation of charge density roughly parallel to the c-axis, supporting the results of PDF. 1401

2 These perturbations form a network of cells in the a b plane with nanoscopic dimensions, comparable with the coherence length[36-45]. The reason for these distortions is the strain field, which has been shown to exist also with the bond valence sum method in the 123-perovskite lattice. These results support the nanoscale phase separation model of 5 and 6. Y-EXAFS shows displacements of the O2,03 and Cu2 atoms parallel to the c-axis, inducing distortions of the dimpling. Lattice distortions appear also both at T c and the spin-gap opening temperature. Theoretical scenarios for the SIT of disordered materials Interest in SI transitions arose in the context of study of the interplay between superconductivity and disorder. Anderson [6] and Abrikosov and Gor kov[7] showed that nonmagnetic impurities do not affect the superconducting transition temperature because Cooper pairs form from extended time-reversed eigenstates, which have disorder included. On the other hand with sufficient disorder Anderson localization occurs, and superconductivity will not develop, even in the presence of an attractive electron electron attraction [8]. This leads to the question of how superconductivity disappears with increasing disorder [46-50], [10], [1], [2], [3] and [4]. At nonzero temperatures, the superconducting phase transition is a continuous phase transition, so that there are fluctuations. For a transition suppressed to zero temperature, the fluctuations become quantum in character and the transition becomes a quantum phase transition. Boson localization theories [4], [6] and [7] are closely related to models used to describe superfluid helium and Josephson junction arrays. Doniach[8] pioneered this approach, which involves phase fluctuations, in the context of Josephson junction arrays. There is a quantum critical point, and the ground state can be controlled by disorder or perpendicular magnetic field. An important prediction is that at the critical level of disorder, or magnetic field, Cooper pairs move diffusively, leading to metallic behavior in the T 0T 0 limit. This occurs only at the quantum critical point. If one assumes complete duality between Cooper pairs and vortices [4], this resistance is universal with a value given by the quantum resistance for pairs, h/4e 2 h/4e2. The physics is related to the universal jump condition in the finite temperature BKT transition [5]. 1402

3 Conclusion We have briefly reviewed the major results relating to the SIT in two dimensions, including interfacial systems as well as high temperature superconductors in addition to the consideration of nominally homogeneous disordered thin films. Despite a long history it is clear that there are many open questions relating to the SIT. These include, but are not limited to the following: What different physical models govern the various SITs of drastically different materials with different tuning parameters, which can have different exponent products and different critical resistances? Although there has been considerable progress there is still a question as to why the insulating states of various transitions are so very different. What is the correct theory of the ubiquitous large magnetoresistance peak? Is this phenomenon one in which there are localized Cooper pairs in an essentially homogenous system, or in particular is disorder on a length scale greater than atomic scales necessary for such a peak? Under what conditions is an intermediate metallic regime, or a two-phase regime a feature of a particular SIT? Finally, how does electrostatic tuning of the carrier concentration differ from chemical tuning? A comprehensive review of the SIT problem with a more detailed discussion of the theories associated with the behavior of disordered superconductors is that of Gantmakher and Dogolpolov[3]. Finally, although the work described in detail here has no direct bearing on the issue of raising the superconducting critical temperature, some of the procedures employed may have relevance. Certainly ionic liquid gating may facilitate the search for new superconductors through bypassing the complexities of chemical doping for which a separate sample is required for each doping level. Also interfacial studies may be an important route to high critical temperatures with the work on FeSe serving as an existence proof for the concept [5]. In some manner this could lead to a realization of the ideas of Ginzburg and Little in which a conductive layer derives its superconducting nature from a separate layer or layers in intimate contact with it [2]. References 1. Ongguang Qin, C.L. Vicente, JongsooYoonMagnetically induced metallic phase in superconducting tantalum filmsphys. Rev. B, 73 (2006), p (R) 1403

4 2. M.D. Stewart Jr., Aijun Yin, J.M. Xu, James M. Valles Jr.Superconducting pair correlations in an amorphous insulating nanohoneycombfilmscience, 318 (2007), p R. Crane, N.P. Armitage, A. Johansson, G. Sambandamurthy, D. Shahar, G. GrunerSurvival of superconducting correlations across the two-dimensional superconductor insulator transition: a finite-frequency studyphys. Rev. B, 75 (2007), p K.H. Sarwa, B. Tan, Kevin A. Parendo, A.M. GoldmanEvidence of spatially inhomogeneous pairing on the insulating side of a disorder-tuned superconductor insulator transitionphys. Rev. B, 78 (2008), p A. Pourret, H. Aubin, J. Lesueur, C.A. Marrache-Kikuchi, L. Berge, L. Dumoulin, K. Behnia Observation of the Nernst signal generated by fluctuating Cooper pairs Nat. Phys., 2 (2008), p. 683Ramamoorthy, R., Kanagasabai, V., Kausalya, R., Impact of celebrities' image on brand,, V- 116, I-18, PP , Ramamoorthy, R., Kanagasabai, V., Vignesh, M., Quality assurance in operation theatre withreference to fortis malar hospital, International Journal of Pure and Applied Mathematics, V-116, I-14, PP-87-93, Ramya, N., Arthy, J., Honey comb graphs and its energy, International Journal of Pure and Applied Mathematics, V-116, I-18, PP-83-86, Ramya, N., Jagadeeswari, P., Proper coloring of regular graphs, International Journal of Pure and Applied Mathematics, V-116, I-16, PP , Ramya, N., Karunagaran, K., Proper, star and acyclic coloring of some graphs,, V-116, I-16, PP , Ramya, N., Muthukumar, M., On coloring of 4-regular graphs, International Journal of Pure and Applied Mathematics, V-116, I-16, PP , Ramya, N., Muthukumar, M., On star and acyclic coloring of graphs, International Journal of Pure and Applied Mathematics, V-116, I-16, PP , Ramya, N., Pavi, J., Coloring of book and gear graphs, International Journal of Pure and Applied Mathematics, V-116, I-17, PP , Ramya, P., Hameed Hussain, J., Alteration framework for integrating quality of service in internet real-time network,, V- 116, I-8, PP-57-61, Ramya, P., Sriram, M., Tweet sarcasm: Peep, International Journal of Pure and Applied Mathematics, V-116, I-10, PP , Sabarish, R., Meenakshi, C.M., Comparision of beryllium and CI connecting rod using ansys,, V-116, I-17, PP ,

5 16. Sabarish, R., Rakesh, N.L., Outcome of inserts for enhancing the heat exchangers,, V-116, I-17, PP , Sangeetha, M., Gokul, N., Aruls, S., Estimator for control logic in high level synthesis,, V-116, I-20, PP , Sangeetha, M., Gokul, N., Aruls, S., Image steganography using a curvelet transformation,, V-116, I-20, PP , Saraswathi, P., Srinivasan, V., Peter, M., Research on financial supply chain from view of stability,, V-116, I-17 Special Issue, PP , Saravana Kumar, A., Hameed Hussain, J., Expanding the pass percentage in semester examination,, V-116, I-15 Special Issue, PP-45-48, Saravana, S., Arulselvi, S., AdaBoost SVM based brain tumour image segmentation and classification,, V-116, I-20, PP , Saravana, S., Arulselvi, S., Dynamic power management monitoring and controlling system using wireless sensor network, International Journal of Pure and Applied Mathematics, V-116, I-20, PP , Saravana, S., Arulselvi, S., Clustered morphic algorithm based medical image analysis,, V-116, I-20, PP , Saravana, S., Arulselvi, S., Networks, International Journal of Pure and Applied Mathematics, V-116, I-20, PP , Saritha, B., Chockalingam, M.P., Adsorptive removal of heavy metal chromium from aqueous medium using modified natural adsorbent, International Journal of Civil Engineering and Technology, V-8, I-8, PP , Saritha, B., Chockalingam, M.P., Adsorptive removal of brilliant green dye by modified coconut shell adsorbent,, V-116, I-13, PP , Saritha, B., Chockalingam, M.P., Photodegradation of eriochrome black-t dye from aqueous medium by photocatalysis, International Journal of Pure and Applied Mathematics, V-116, I-13, PP , Saritha, B., Chockalingam, M.P., Photodradation of malachite green DYE using TIO<inf>2</inf>/activated carbon composite, International Journal of Civil Engineering and Technology, V-8, I-8, PP , Saritha, B., Chockalingam, M.P., Synthesis of photocatalytic composite Fe-C/TiO2 for degradation of malachite green dye from aqueous medium, International Journal of Pure and Applied Mathematics, V-116, I-13, PP ,

6 30. Saritha, B., Chockalingam, M.P., Removal of heavy X`X`l from aqueous medium using modified natural adsorbent,, V- 116, I-13, PP , Saritha, B., Chockalingam, M.P., Degradation of malachite green dye using a semiconductor composite,, V- 116, I-13, PP , Sartiha, B., Chockalingam, M.P., Photocatalyticdecolourisationoftextileindustrywastewaterby TiO2, International Journal of Pure and Applied Mathematics, V-116, I-18, PP , Sartiha, B., Chockalingam, M.P., Study on photocatalytic degradation of Crystal Violet dye using a semiconductor,, V- 116, I-18, PP , Shanthi, E., Nalini, C., Rama, A., The effect of highly-available epistemologies on hardware and architecture, International Journal of Pharmacy and Technology, V-8, I-3, PP , Shanthi, E., Nalini, C., Rama, A., Drith: Autonomous,random communication, International Journal of Pharmacy and Technology, V-8, I-3, PP , Shanthi, E., Nalini, C., Rama, A., A case for replication, International Journal of Pharmacy and Technology, V-8, I-3, PP , Shanthi, E., Nalini, C., Rama, A., Elve: A methodology for the emulation of robots, International Journal of Pharmacy and Technology, V-8, I-3, PP , Shanthi, E., Nalini, C., Rama, A., Autonomous epistemologies for mesh networks, International Journal of Pharmacy and Technology, V-8, I-3, PP , Sharavanan, R., Golden Renjith, R.J., Design and analysis of fuel flow in bend pipes,, V-116, I-15, PP , Sharavanan, R., Jose Ananth Vino, V., Emission analysis of C.I engine run by diesel,sunflower oil,2 ethyl hexyl nitrate blends, International Journal of Pure and Applied Mathematics, V-116, I-14, PP , Sharavanan, R., Sabarish, R., Design of built-in hydraulic jack for light motor vehicles,, V-116, I-17, PP , Sharavanan, R., Sabarish, R., Design and fabrication of aqua silencer using charcoal and lime stone,, V-116, I-14 Special Issue, PP , Sharmila, G., Thooyamani, K.P., Kausalya, R., A schoolwork on customer relationship management with special reference to domain 2 host, International Journal of Pure and Applied Mathematics, V-116, I-20, PP , Sharmila, S., Jeyanthi Rebecca, L., Anbuselvi, S., Kowsalya, E., Kripanand, N.R., Tanty, D.S., Choudhary, P., SwathyPriya, L., GC-MS analysis of biofuel extracted from marine algae, Der Pharmacia Lettre, V-8, I-3, PP ,

7 45. Sidharth Raj, R.S., Sangeetha, M., Data embedding method using adaptive pixel pair matching method,, V-116, I-15, PP , Sidharth Raj, R.S., Sangeetha, M., Android based industrial fault monitoring,, V-116, I-15, PP , Sidharth Raj, R.S., Sangeetha, M., Mobile robot system control through an brain computer interface,, V-116, I-15, PP , Sivaraman, K., Sundarraj, B., Decisive lesion detection in digital fundus image,, V-116, I-10, PP , Sridhar, J., Sriram, M., Cloud privacy preserving for dynamic groups, International Journal of Pure and Applied Mathematics, V-116, I-8, PP ,

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