User:Bv.vasiliev/Superconductivity, superfluidity and zero-point oscillations
Superfluidity and superconductivity, which can be regarded as the superfluidity of the electron gas, are related phenomena. The main feature of these phenomena can be imagined, if to assume that into superconductors as well as into superfluid helium a special condensate is formed from particles which are interconnected by an attraction energy. This mutual attraction does not allow a scattering of individual particles on defects and walls, if the energy of this scattering is less than the energy of the attraction. Due to the lack of scattering condensate acquires the ability to move without a friction.
The discovery of superconductivity has been made more than a hundred years, but until now there is no clarity in the physics of this phenomenon. This problem has long been surrounded by some mystery.
Superconductivity was discovered over the century ago, and the superfluidity of about thirty years later. However, despite the attention of many scientists to the study of these phenomena, they was long been the most mysterious in condensed matter physics. This mystery was attracting for the best minds of the last century. About it V.Ginzburg said directly in his Nobel speech.
The mystery of the superconductivity phenomenon has begun to drop in the middle of the last century when the effect of magnetic flux quantization in superconducting cylinders was studied. This phenomenon was predicted even before the war by brothers F.London and H.London, but its measurements were made only after two decades.
It became clear that for the appearance of the superconducting state the carriers should be attracted to each other so as to form an ensemble of particles, which can not lose energy on lattice defects (and phonons), if portions of losing energy are smaller than the energy of their mutual attraction.
Around the same time, it was observed that the substitution of one isotope of the superconducting element to another leads to a changing of the critical temperature of superconductors - the so-called isotope-effect. This effect was interpreted as the direct proof of the key role of phonons in the formation of the superconducting state.
Coming from it, L.Cooper proposed the phonon mechanism of electron pairing and on this base the microscopic theory of superconductivity (so called BCS-theory) was built by N.Bogolyubov and J.Bardin, L.Cooper and J.Shriffer (probably more true it must be called as the Bogolyubov-BCS-theory).
However at this, a hypothetic link between superconductivity and superfluidity was disrupted - there are no phonons into liquid helium for a combining of its atoms.
Something similar happened with the description of superfluidity. Soon after its opening, L.D.Landau in his first papers immediately showed that this phenomenon should be considered as a result of formation of a condensate, which consists of a macroscopic number of atoms in the same quantum state and obeys quantum laws. It gives the possibility to describe the main features of this phenomenon - the temperature dependence of the superfluid phase density, the speed of sound, etc. -but it does not give an answer to the question of which physical mechanism leads to the unification of the atoms in the superfluid condensate and what is the critical temperature of the condensate, i.e. why the ratio of the temperature of transition to the superfluid state to the boiling point is almost exactly equal to 1/2 for helium-4, while for helium-3, it is about a thousand times smaller.
On the whole the description of both super-phenomena - superconductivity and superfluidity - in their condition to the beginning of the XXI century induced a some feeling of dissatisfaction primarily due to the fact that there was not assumed a common mechanism of their occurrence.
More than fifty years of a study of the BCS has shown that this theory successfully describes the general features of the phenomenon, but it can not be developed in the theory of superconductors. It explains general laws as the emergence of the energy gap, the behavior of specific heat capacity, the flux quantization, etc., but it can not predict the main parameters of the individual superconductors - their critical temperatures and critical magnetic fields. More precisely in the BCS, the expression for the critical temperature of superconductor obtains an exponential form the exponent of which contains the intractable in measurement factors, and this formula has no a practical interest.
With regard to the proposition which was accepted in the last century that the phonon mechanism is the only possible mechanism of superconductivity, more recent experiments have shown that this proposition is incorrect. Experiments have shown that the zero-point oscillations of ions into lattices of superconducting metals are anharmonic. As a result, the replacement of one isotope to another leads to a change in the amplitude of these oscillations, ie there is a influence of isotope mass on the interatomic distances in a metal lattice. As a consequence, the change of the isotope has a direct impact on the Fermi energy of a metal, ie directly on its electronic system, and phonons do not play any role in this effect.
Furthermore, a closer look reveals that the B-BCS describes the mechanism of electron pairing, but in it there is no mechanism of combining pairs in the single super-ensemble. Only an arising of energy of formation of a unified ensemble of particles is a necessary condition for the existence of superconductivity. At this the mechanism combines in super-ensemble a very small number of electrons - on the level 10 in minus fifth power from full number of free electrons. This fact can not be understood too in the framework of the B-BCS theory.
At very low temperatures, in which there is superfluidity in helium and superconductivity in metals, all movements of particles are freezed except their zero-point oscillations. Therefore, as an alternative, we should consider the interaction of super-particles through electro-magnetic fields of zero-point oscillations. This approach proves fruitful. At the consideration of super-phenomena as consequences of the zero-point oscillations ordering, one can construct theoretical mechanisms enabling to give estimations for the critical parameters of these phenomena which are in satisfactory agreement with measurements.
In a result, one can see that the critical temperatures of superconductors as I-type, well as II-type are equal to about 10 in minus 6-th degrees from the Fermi temperature superconducting metal, which is consistent with data of measurements.
At this the destruction of superconductivity by application of critical magnetic field occurs when the field destroys the coherence of zero-point oscillations of electron pairs. This is in good agreement with measurements also.
A suchlike mechanism works in superfluid liquid helium. The problem of the interaction of zero-point oscillations of the electron shells of neutral atoms in the s-state, was considered yet before the war by F.London. He has shown that this interaction is responsible for the liquefaction of helium. The closer analysis of interactions of zero-point oscillations of helium atoms shells shows that at first at the temperature of about 4K only one of the oscillation mode becomes ordered. As a result, attraction forces appear between atoms which are need for helium liquefaction. To create a single quantum ensemble it is necessary to reach the complete ordering of atom oscillations. At the complete ordering of oscillations at about 2K, the additional energy of the mutual attraction appears and the system of helium-4 atoms transits in superfluid state. In helium-3 for the forming of the superfluid quantum ensemble, not only the zero-point oscillations should be ordered, but the magnetic moments of the nuclei should be ordered too. For this is necessary to lower the temperature below 0.001K. This is also in agreement with experiment.
- B.V.Vasiliev (2011). "Superconductivity as a consequence of an ordering of the electron gas zero-point oscillations". Physica C Superconductivity and its applications. 471: 277-284.
- B.V.Vasiliev (2012). "Superconductivity and condensation of ordered zero-point oscillations". Physica C Superconductivity and its applications. 483: 233-246.
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