A. V. Nikulov

Quantum force in a superconductor

Transitions between states with continuous (called as classical state) and discrete (called as quantum state) spectrum of permitted momentum values is considered. The persistent current can exist along the ring circumference in the quantum state in contrast to the classical state. Therefore the average momentum can changes at the considered transitions. In order to describe the reiterated switching into and out the quantum state an additional term is introduced in the classical Boltzmann transport equation. The force inducing the momentum change at the appearance of the persistent current is called as quantum force. It is shown that dc potential difference is induced on ring segments by the reiterated switching if the dissipation force is not homogeneous along the ring circumference. The closing of the superconducting state in the ring is considered as real example of the transition from classical to quantum stateA contradiction of the Little-Parks experiment with the Ohms law and other fundamental laws is explained. This explanation shows that the Little-Parks oscillations of the loop resistance are an experimental evidence of a direct (non-chaotic) Brownian motion. The Langevin force is connected with a change of the momentum circulation of superconducting pairs because of the quantization. Its average value can be non-zero because of the quantization. The existence of a direct Brownian motion contradicts to the principle on which the second law of thermodynamic is based. Therefore the Little-Parks experiment is evidence of a possibility of violation of the second law. In the last years other authors have stated also violation of the second law in different quantum systems: A.E.Allahverdyan and Th.M.Nieuwenhuizen, PRL 85, 1799 (2000); cond-mat/0011389; V.Capec and J.Bok, Czech.J. of Phys. 49, 1645 (1999); cond-mat/0012056; Physica A 290, 379 (2001); P. Weiss, Science News, 158, 234 (2000).

Observation of the external-ac-current-induced dc voltage proportional to the steady current in superconducting loops

A dc voltage induced by an external ac current is observed in system of asymmetric mesoscopic superconducting loops. The value and sign of this dc voltage, like the one of the persistent current, depend in a periodical way on a magnetic field with period corresponded to the flux quantum within the loop. The amplitude of the oscillations does not depend on the frequency of the external ac current (in the investigated region 100 Hz - 1 MHz) and depends on its amplitude. The latter dependence is not monotonous. The observed phenomenon of rectification is interpreted as a consequence of a dynamic resistive state induced by superposition of the external current and the persistent current. It is shown that the dc voltage can be added in system of loops connected in series: the dc voltage oscillations with amplitude up to 0.00001 V were observed in single loop, up to 0.00004 V in a system of 3 loops and up to 0.0003 V in a system of 20 loops.A dc voltage induced by an external ac current was observed in a system of asymmetric aluminum loops at temperatures corresponding to 0.95–0.98 of the superconducting transition temperature. The voltage magnitude and sign change periodically in a magnetic field with a period corresponding to the magnetic flux quantum through the loop. The amplitude of these oscillations depends nonmonotonically on the amplitude of ac current and is almost independent of its frequency in the range from 100 Hz to 1 MHz. The observed phenomenon is interpreted as the result of displacing the loop into a dynamic resistive state by the external current, where the loop is “switched” back and forth between the closed superconducting state with a nonzero steady current and the nonclosed state with a nonzero resistance along the loop circle. It is shown that voltages are summed up in a system of loops connected in series. For systems with one, three, and twenty loops, the voltage reaches 10, 40, and 300 μ V, respectively.

Little-Parks Effect in a System of Asymmetric Superconducting Rings

Little-Parks oscillations are observed in a system of 110 series-connected aluminum rings 2 μm in diameter with the use of measuring currents from 10 nA to 1 μA. The measurements show that the amplitude and character of oscillations are independent of the relation between the measuring current and the amplitude of the persistent current. By using asymmetric rings, it is demonstrated that the persistent current has a direction. This means that, in the Little-Parks experiment, the total current in one of the half-rings may be directed against the electric field.Little-Parks oscillations are observed in a system of 110 series-connected aluminum rings 2 μm in diameter with the use of measuring currents from 10 nA to 1 μA. The measurements show that the amplitude and character of the oscillations are independent of the relation between the measuring current and the amplitude of the persistent current. By using asymmetric rings, it is demonstrated that the persistent current has clockwise or contra-clockwise direction. This means that the total current in one of the semi-rings may be directed against the electric field at measurement of the Little-Parks oscillations. The measurements at zero and low measuring current have revealed that the persistent current, like the conventional circulating current, causes a potential difference on the semi-rings with different cross sections in spite of the absence of the Faraday’s voltage.

Special Issue on Quantum Limits to the Second Law of Thermodynamics

The second law of thermodynamics holds, I think,the supreme position among the laws of Nature. If someone points out to you that your pet theory ofthe universe is in disagreement with Maxwells equations – then so much the worse for Maxwellsequations. If it is found to be contradicted by observation, well, these experimentalists do bunglethings sometimes. But if your theory is found to be against the second law of thermodynamics I cangive you no hope; there is nothing for it but to collapse in deepest humiliation

Contradiction between the Results of Observations of Resistance and Critical Current Quantum Oscillations in Asymmetric Superconducting Rings

Magnetic field dependences of critical current, resistance, and rectified voltage of asymmetric (half circles of different widths) and symmetrical (half circles of equal widths) aluminum rings close to the super-conducting transition were measured. All these dependences are periodic magnetic field functions with periods corresponding to the flux quantum in the ring. The periodic dependences of critical current measured in opposite directions were found to be close to each other for symmetrical rings and shifted with respect to each other by half the flux quantum in asymmetric rings with ratios between half circle widths of from 1.25 to 2. This shift of the dependences by a quarter of the flux quantum as the ring becomes asymmetric makes critical current anisotropic, which explains the effect of alternating current rectification observed for asymmetric rings. Shifts of the extrema of the periodic dependences of critical current by a quarter of the flux quantum directly contradict the results obtained by measuring asymmetric ring resistance oscillations, whose extrema are, as for symmetrical rings, observed at magnetic fluxes equal to an integer and a half of flux quanta.

Absence of the transition into Abrikosov vortex state of two-dimensional type-II superconductor with weak pinning.

The resistive properties of thin amorphous

The critical current of the Josephson junction with boundaries in the mixed state : application to HTSC polycrystalline materials

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Dependence of the magnitude and direction of the persistent current on the magnetic flux in superconducting rings

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Possibility of persistent voltage observation in a system of asymmetric superconducting rings

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Weak dissipation does not result in the disappearance of the persistent current

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