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تسجيل مستخدم جديدSET based experiments for HTSC materials
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Sher Alam
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The cuprates seem to exhibit statistics, dimensionality and phase transitions in novel ways. The nature of excitations [i.e. quasiparticle or collective], spin-charge separation, stripes [static and dynamics], inhomogeneities, psuedogap, effect of impurity dopings [e.g. Zn, Ni] and any other phenomenon in these materials must be consistently understood. In this note we suggest Single Electron Tunneling Transistor [SET] based experiments to understand the role of charge dynamics in these systems. Assuming that SET operates as an efficient charge detection system we can expect to understand the underlying physics of charge transport and charge fluctuations in these materials for a range of doping. Experiments such as these can be classed in a general sense as mesoscopic and nano characterization of cuprates and related materials.
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The cuprates seem to exhibit statistics, dimensionality and phase transitions in novel ways. The nature of excitations [i.e. quasiparticle or collective], spin-charge separation, stripes [static and dynamics], inhomogeneities, psuedogap, effect of
impurity dopings [e.g. Zn, Ni] and any other phenomenon in these materials must be consistently understood. In this note we further discuss our original suggestion of using Single Electron Tunneling Transistor [SET] based experiments to understand the role of charge dynamics in these systems. Assuming that SET operates as an efficient charge detection system we can expect to understand the underlying physics of charge transport and charge fluctuations in these materials for a range of doping. Experiments such as these can be classed in a general sense as mesoscopic and nano characterization of cuprates and related materials. In principle such experiments can show if electron is fractionalized in cuprates as indicated by ARPES data. In contrast to flux trapping experiments SET based experiments are more direct in providing evidence about spin-charge separation. In addition a detailed picture of nano charge dynamics in cuprates may be obtained.
Previously we have indicated the relationship between quantum groups [Phys. Lett A272, (2000)] and strings via WZWN models in the context of applications to cuprates and related materials.The connection between quantum groups and strings is one way o
f seeing the validity of our previous conjecture [i.e. that a theory for cuprates may be constructed on the basis of quantum groups]. The cuprates seems to exhibit statistics, dimensionality and phase transitions in novel ways. The nature of excitations [i.e. quasiparticle or collective] must be understood. The Hubbard model captures some of the behaviour of the phase transitions in these materials. On the other hand the phases such as stripes in these materials bear relationship to quantum group or string-like solutions. One thus expects that the relevant solutions of Hubbard model may thus be written in terms of stringy solutions. In short this approach may lead to the non-perturbative formualtion of Hubbard and other condensed matter Hamiltonians. The question arises that how a 1-d based symmetry such as quantum groups can be relevant in describing a 3-d [spatial dimensions] system such as cuprates. The answer lies in the key observation that strings which are 1-d objects can be used to describe physics in $d$ dimensions. For example gravity [which is a 3-d [spatial] plus time] phenomenon can be understood in terms of 1-d strings. Thus we expect that 1-d quantum group object induces physics in 2-d and 3-d which may be relevant to the cuprates. We present support for our contention using [numerical] variational Monte-Carlo [MC] applied to 2d d-p model. We also briefly discuss others ways to formulate a string picture for cuprates, namely by exploiting connection between gauge theories and strings and tHooft picture of quark confinement.
We examine experiments on energy gaps in high temperature superconductors (HTSC) in terms of experimental probes that utilize momentum, position, or neither. Experiments on very high quality mechanical tunnel junctions show a sharp energy gap with a
maximum anisotropy of ~ 10%, while ultrahigh precision ARPES experiments show 100% anisotropy (d-wave pairing). We resolve this conbflict by showing that the latter result is caused by the momentum-projective nature of ARPES and glassy orthorhombic dopant correlations. The latter appear to be a universal feature of the intermediate phase tha is responsible for HTSC. Apparent large inconsistencies between position-projective STM gap data and tunnel junction data on severely underdoped BSCCO are also resolved.
The temperature and field dependences of the trapped magnetic fields and of the frozen magnetoresistance of (Pb)Bi-Sr-Ca-Cu-O ceramics and Bi-based magnetron films are investigated. It is found that in the resistive transition region of granular Bi-H
TSC the trapped magnetic fields become highly inhomogeneous and alternating in sign at scale of less than 50 microns. Unlike ceramic the films have critical temperature of trapping lower than the upper temperature of magnetoresistance disappearance. The experimental results are explained by a model in which the magnetic fields are trapped in superconducting loops embedded in Josephson weak links medium. The loops nature which is essentially different for films and ceramics is discussed. Observed temperature and field dependences of trapped field are in good agreement with those calculated for normal law of the loops distribution on critical fields.
Magnetoresistive properties of granular Bi-based HTSC with trapped magnetic fields are investigated in the temperature region near superconducting transition . The effect of trapped field and transport current values and orientations on the field dep
endence of magnetoresistance is studied. It is found that for the magnetic field parallel and the current perpendicular to trapping inducing field the field dependence of magnetoresistance is nonmonotonic and magnetoresistance turns out to be negative for small fields. The magnetoresistance sign inversion field increases roughly linear with the trapped magnetic field and slightly decrease with transport current. The results are explained in the framework of model of magnetic flux trapping in granules or superconducting loops embedded in weak links matrix.
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