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Physical mechanism of superconductivity

IP.com Disclosure Number: IPCOM000198142D
Publication Date: 2010-Jul-26
Document File: 59 page(s) / 3M

Publishing Venue

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Abstract

The physical mechanism of superconductivity is proposed on the basis of carrier-induced dynamic strain effect. By this new model, superconducting state consists of the dynamic bound state of superconducting electrons, which is formed by the high-energy nonbonding electrons through dynamic interaction with their surrounding lattice to trap themselves into the three - dimensional potential wells lying in energy at above the Fermi level of the material. The binding energy of superconducting electrons dominates the superconducting transition temperature in the corresponding material. Under an electric field, superconducting electrons move coherently with lattice distortion wave and periodically exchange their excitation energy with chain lattice, that is, the superconducting electrons transfer periodically between their dynamic bound state and conducting state, so the superconducting electrons cannot be scattered by the chain lattice, and supercurrent persists in time. Thus, the intrinsic feature of superconductivity is to generate an oscillating current under a dc voltage. The wave length of an oscillating current equals the coherence length of superconducting electrons. The coherence lengths in cuprates must have the value equal to an even number times the lattice constant. A superconducting material must simultaneously satisfy the following three criteria required by superconductivity. First, the superconducting materials must possess high – energy nonbonding electrons with the certain concentrations required by their coherence lengths. Second, there must exist three – dimensional potential wells lying in energy at above the Fermi level of the material. Finally, the band structure of a superconducting material should have a widely dispersive antibonding band, which crosses the Fermi level and runs over the height of the potential wells to ensure the normal state of the material being metallic. According to the types of potential wells, the superconductors as a whole can be divided into two groups: the conventional and high temperature superconductors. The puzzling behavior of the cuprates, such as the complex phase diagrams, the linear dependence of resistivity with temperature in their normal states, the pseudogap, the transition temperature increasing with the number of the CuO2 planes in the unit cell of Bi(Tl)-based compounds, the lattice instabilities and hardening in superconducting state, and the symmetries of superconducting waves, etc. all can be uniquely understood under this new model. In addition, the effects of strain and pressure, hole and electron doping, the replacement of trivalent rare-earth elements, and oxygen concentration on the superconducting properties of cuprates can be consistently explained by this physical mechanism. We demonstrate that the factor 2 in Josephson current equation, in fact, is resulting from 2V, the voltage drops across the two superconductor sections on both sides of a junction, not from the Cooper pair, and the magnetic flux is quantized in units of h/e, postulated by London, not in units of h/2e. The central features of superconductivity, such as Josephson effect, the tunneling mechanism in multijunction systems, and the origin of the superconducting tunneling phenomena, as well as the magnetic flux quantization in a superconducting hollow cylinder are all physically reconsidered under this superconductivity model. Following this unified superconductivity model, one will certainly know where to find the new materials with much higher Tc, even room temperatures superconductivity, and how to make high quality superconductor devices. Keywords: mechanism (model) of superconductivity, high-Tc superconductors, Josephson effect, tunneling mechanism, unit of magnetic flux quantization

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Physical  mechanism of superconductivity

Xue-Shu Zhao, Yu-Ru Ge, Xin Zhao, Hong Zhao

ABSTRACT

The physical mechanism of superconductivity is proposed on the basis of carrier-induced dynamic strain effect. By this new model, superconducting state consists of the dynamic bound state of superconducting electrons, which is formed by the high-energy nonbonding electrons through dynamic interaction with their surrounding lattice to trap themselves into the three - dimensional potential wells lying in energy at above the Fermi level of the material.  The binding energy of superconducting electrons dominates the superconducting transition temperature in the corresponding material. Under an electric field, superconducting electrons move coherently with lattice distortion wave and periodically exchange their excitation energy with chain lattice, that is, the superconducting electrons transfer periodically between their dynamic bound state and conducting state, so the superconducting electrons cannot be scattered by the chain lattice, and supercurrent persists in time.  Thus, the intrinsic feature of superconductivity is to generate an oscillating current under a dc voltage. The wave length of an oscillating current equals the coherence length of superconducting electrons. The coherence lengths in cuprates must have the value equal to an even number times the lattice constant. A superconducting material must simultaneously satisfy the following three criteria required by superconductivity. First, the superconducting materials must possess high – energy nonbonding electrons with the certain concentrations required by their coherence lengths. Second, there must exist three – dimensional potential wells lying in energy at above the Fermi level of the material. Finally, the band structure of a superconducting material should have a widely dispersive antibonding band, which crosses the Fermi level and runs over the height of the potential wells to ensure the normal state of the material being metallic. According to the types of potential wells, the superconductors as a whole can be divided into two groups: the conventional and high temperature superconductors. The puzzling behavior of the cuprates, such as the complex phase diagrams, the linear dependence of resistivity with temperature in their normal states, the pseudogap, the transition temperature increasing with the number of the CuO2 planes in the unit cell of Bi(Tl)-based compounds, the lattice instabilities and hardening in superconducting state, and the symmetries of superconducting waves, etc. all can be uniquely understood under this new model. In addition, the effects of strain and pressure, hole and electron doping, the replacement of trivalent rare-earth elements, and oxygen concentration on the superconducting properties of cuprates can be consistently explained by this physical mechanism. We demonstrate that the factor 2 in Josephson current equation, in fact, is resulting from 2V, the...