| 1. |
- Aleksandrovskii, A. N., et al.
(författare)
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Low-temperature thermal expansion of pure and inert gas-doped fullerite C60
- 2003
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Ingår i: Fizika Nizkikh Temperatur (Kharkov). - : AIP Publishing. - 0132-6414 .- 1816-0328. ; 29:4, s. 432-442
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Tidskriftsartikel (refereegranskat)abstract
- The low temperature (2–24 K) thermal expansion of pure (single-crystal and polycrystalline) C60 and polycrystalline C60 intercalated with He, Ne, Ar, and Kr has been investigated using the high-resolution capacitance dilatometer. The investigation of the time dependence of the sample length variations deltaL(t) on heating by deltaT shows that the thermal expansion is determined by the sum of positive and negative contributions, which have different relaxation times. The negative thermal expansion usually prevails at helium temperatures. The positive expansion is connected with the phonon thermalization of the system. The negative expansion is caused by reorientation of the C60 molecules. It is assumed that the reorientation is of a quantum character. The inert gas impurities affect the reorientation of the C60 molecules very strongly, especially at liquid helium temperatures. A temperature hysteresis of the thermal expansion coefficient of Kr– and He–C60 solutions has been revealed. The hysteresis is attributed to orientational polyamorphous transformation in these systems.
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| 2. |
- Balkashin, O. P., et al.
(författare)
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Ferromagnetic resonance in copper-permalloy point contacts
- 2014
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Ingår i: Fizika Nizkih Temperatur. - 0132-6414 .- 1816-0328. ; 40:10, s. 1187-1197
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Tidskriftsartikel (refereegranskat)abstract
- The systematic investigations of the response signal of Copper-Permalloy (Ni80Fe20) point contacts to microwave irradiation (8-12 GHz) are performed. The influence of external magnetic field strength, transport current flowing through the contact, the intensity and frequency of the RF exposure on the measured signal is studied. The contributions to the contacts resistance from the effects of giant and anisotropic magnetoresistance are analyzed. It is established experimentally that the position of resonance features is in good agreement with the Kittel formula calculation for FMR in the film at a parallel H field. The resonance signal was observed on the background of an additional contribution due to the rectification of RF current on the nonlinear contact IV-curve. It is found that there are two mechanisms for the resonant response are revealed: a synchronous self-detection by means of mixing of RF current with temporal variations of resistance and a bolometric mechanism associated with a steady-state change of contact resistance under excitation of magnetization precession (a bolometric response). It is found that the resonance signal amplitude is linearly proportional to transport current through the contact and microwave irradiation intensity.
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| 3. |
- Balkashin, O. P., et al.
(författare)
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Spin-valve effects in point contacts to exchange biased Сo 40Fe 40B 20 films
- 2014
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Ingår i: Fizika Nizkih Temperatur. - 0132-6414 .- 1816-0328. ; 40:10, s. 1170-1174
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Tidskriftsartikel (refereegranskat)abstract
- Nonlinear current-voltage characteristics and magnetoresistance of point contacts between a normal metal (N) and films of amorphous ferromagnet (F) Co40Fe40B20 of different thickness, exchange-biased by antiferromagnetic Mn80Ir20 are studied. A surface spin valve effect in the conductance of such F-N contacts is observed. The effect of exchange bias is found to be inversely proportional to the Co40Fe40B20 film thickness. This behavior as well as other magneto-transport effects we observe on single exchange-pinned ferromagnetic films are similar in nature to those found in conventional three-layer spin-valves.
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| 4. |
- Chung, Sunjae, et al.
(författare)
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Magnetic droplet solitons in orthogonal spin valves
- 2015
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Ingår i: Fizika Nizkih Temperatur. - : American Institute of Physics (AIP). - 0132-6414 .- 1816-0328. ; 41:10, s. 833-837
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Tidskriftsartikel (refereegranskat)abstract
- We review the recent experimental advancements in the realization and understanding of magnetic droplet solitons generated by spin transfer torque in orthogonal nanocontact based spin torque nanooscillators (STNOs) fabricated on extended spin valves and spin valve nanowires. The magnetic droplets are detected and studied using the STNO microwave signal and its resistance, the latter both quasistatically and time-resolved. The droplet nucleation current is found to have a minimum at intermediate magnetic field strengths and the nature of the nucleation changes gradually from a single sharp step well above this field, mode-hopping around the minimum, and continuous at low fields. The mode-hopping and continuous transitions are ascribed to droplet drift instability and re-nucleation at different time scales, which is corroborated by time-resolved measurements. We argue that the use of tilted anisotropy fixed layers could reduce the nucleation current further, move the nucleation current minimum to lower fields, and potentially remove the need for an applied magnetic field altogether. Finally, evidence of an edge mode droplet in a nanowire is presented.
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| 5. |
- Ilinskaya, O. A., et al.
(författare)
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Polaronic suppression of shuttle vibrations
- 2023
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 49:1, s. 75-80
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Tidskriftsartikel (refereegranskat)abstract
- A re-entrant behavior of electron shuttling is shown to occur in a nanoelectromechanical transistor made of magnetic material where spin-polarized electrons are injected into a quantum dot with a single electron level split into two by an external magnetic field. A suppression of shuttle vibrations occurs at a certain value of a bias voltage that starts to allow for transport also through the upper energy level of the dot, while for a further increase of the voltage shuttling recovers. The effect is due to a time-dependent polaronic shift of the dot energy level, which results in a reduction of the supply of electric power to the mechanical motion.
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| 6. |
- Krive, Ilya V., et al.
(författare)
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Chiral symmetry breaking and the Josephson current in a ballistic superconductor-quantum wire-superconductor junction
- 2004
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Ingår i: Fizika Nizkikh Temperatur. - : AIP Publishing. - 0132-6414 .- 1816-0328. ; 30:5, s. 398-404
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Tidskriftsartikel (refereegranskat)abstract
- We evaluate the Josephson current through a quasi-1D quantum wire coupled to bulk superconductors. It Is shown that the interplay of Rashba spin-orbit interaction and Zeeman splitting results in the appearence of a Josephson current even in the absence of any phase difference between the superconductors. In a transparent junction (D [asymptotically equal to] 1) at low temperatures this anomalous supercurrent Jan appears abruptly for a Zeeman splitting of the order of the Andreev level spacing as the magnetic field is varied. In a low transparency (D very much less than 1) junction one has Jan α root D under special (resonance) conditions. In the absence of Zeeman splitting the anomalous supercurrent disappears. We have investigated the influence of dispersion asymmetry induced by the Rashba interaction in quasi-1D quantum wires on the critical Josephson current and have shown that the breakdown of chiral symmetry enhances the supercurrent.
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| 7. |
- Kulinich, S. I., et al.
(författare)
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Nanomechanical pumping of Cooper pairs through NS junction
- 2023
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Ingår i: Low Temperature Physics. - 1063-777X. ; 49:10, s. 1219-1224
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Tidskriftsartikel (refereegranskat)abstract
- We consider a system consisting of a single-level quantum dot that performs mechanical periodic oscillations between spatially distant normal and superconducting electrodes, approaching them at a distance that allows the exchange of electrons through the vacuum tunnel barrier. Considering that the distance between the electrodes is much greater than the tunneling length, we show that charge pumping occurs in such a nanosystem even when the electrochemical potentials of the electrodes coincide. In this case, the direction of the electron flow is determined by the position of the quantum dot level relative to the electrochemical potential in bulk electrodes. The latter can be controlled by applying a voltage between the ground and the electrodes. It is also shown that the value of the average current is critically sensitive to the strength of the tunnel coupling between the quantum dot and the superconducting electrode, which, in turn, is controlled by the amplitude of mechanical oscillations.
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| 8. |
- Kulinich, Sergeij I., et al.
(författare)
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Nanomechanics of a magnetic shuttle device
- 2014
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Ingår i: Low temperature physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 40:10, s. 1161-1169
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Tidskriftsartikel (refereegranskat)abstract
- We show that self sustained mechanical vibrations in a model magnetic shuttle device can be driven by both the charge and the spin accumulated on the movable central island of the device. Different scenarios for how spin- and charge-induced shuttle instabilities may develop are discussed and shown to depend on whether there is a Coulomb blockade of tunneling or not. The crucial role of electronic spin flips in a magnetically driven shuttle is established and shown to cause giant magnetoresistance and dynamic magnetostriction effects.
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| 9. |
- Massarotti, D., et al.
(författare)
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What happens in Josephson junctions at high critical current densities
- 2017
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Ingår i: Fizika Nizkih Temperatur. - : AIP Publishing. - 1816-0328 .- 0132-6414. ; 43:7, s. 816-823
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Tidskriftsartikel (refereegranskat)abstract
- The impressive advances in material science and nanotechnology are more and more promoting the use of exotic barriers and/or superconductors, thus paving the way to new families of Josephson junctions. Semiconducting, ferromagnetic, topological insulator and graphene barriers are leading to unconventional and anomalous aspects of the Josephson coupling, which might be useful to respond to some issues on key problems of solid state physics. However, the complexity of the layout and of the competing physical processes occurring in the junctions is posing novel questions on the interpretation of their phenomenology. We classify some significant behaviors of hybrid and unconventional junctions in terms of their first imprinting, i.e. current-voltage curves, and propose a phenomenological approach to describe some features of junctions characterized by relatively high critical current densities Jc. Accurate arguments on the distribution of switching currents will provide quantitative criteria to understand physical processes occurring in high-Jc junctions. These notions are universal and apply to all kinds of junctions. PACS: 74.72.-h Cuprate superconductors; 85.25.Cp Josephson devices; 74.50.+r Tunneling phenomena; Josephson effects.
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| 10. |
- Ovsyannikov, Gennady, 1948, et al.
(författare)
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Magnetic proximity effect and superconducting triplet correlations at the interface of cuprate superconductor and an oxide spin-valve
- 2016
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Ingår i: Fizika Nizkih Temperatur. - 1816-0328 .- 0132-6414. ; 42:10, s. 1115-1128
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Tidskriftsartikel (refereegranskat)abstract
- The heterostructure comprising a cuprate superconductor YBa2Cu3O7-? and a spin-valve of ruthenate/ manganite (SrRuO3/La0.7Sr0.3MnO3) has been studied by SQUID magnetometry, ferromagnetic resonance, and neutron reflectometry. It was shown that magnetic moment arises in a superconducting part of heterostructure while in spin-valve magnetic moment is suppressed. The obtained experimental value of characteristic penetration depth of magnetic moment into superconductor greatly exceeds the superconductor coherence length the cuprate superconductor indicating the dominance of mechanism of induced magnetic moment from Cu atoms. The mesa-structures made with an addition niobium superconducting electrode deposited on top of heterostructure showed superconducting current (dc Josephson effect) when thickness of interlayer was much greater than the coherence lengths of ferromagnetic materials of spin-valve. The maximum of the dependence of critical current density vs. thicknesses of magnetic materials corresponds to their coherence lengths, that is consistent with the theoretical predictions for the case of spin-triplet pairing. The superconducting current is observed at magnetic fields by two orders greater than the value of magnetic field corresponding to the occurrence of one magnetic flux quantum in the mesa-structure. The ratio of the second harmonic in current-phase relation of the superconducting current of mesa structure to the first harmonic, obtained from measurements of Shapiro step amplitudes under microwaves did not exceed 50%.
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