| 51. |
- Kadigrobov, Anatoli M., 1937, et al.
(författare)
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Novel laser based on magnetic tunneling
- 2005
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 31:3, s. 352-357
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Tidskriftsartikel (refereegranskat)abstract
- A new principle for a compact spin-based solid-state laser is proposed. It operates in the 1-100 THz regime, which is difficult to reach with small size lasers. Spin-flip processes in ferromagnetic conductors form a basis-the mechanism is due to a coupling of light to the exchange interaction in magnetically ordered conductors via the dependence of the exchange constant on the conduction electron momenta. The interaction strength is proportional to the large exchange energy and exceeds the Zeeman interaction by orders of magnitude. A giant lasing effect is predicted in a system where a population inversion has been created by injection of spin-polarized electrons from one ferromagnetic conductor into another through an intermediate tunnel region or weak link; the magnetizations of the two ferromagnets have different orientations. We show that the laser frequency will be in the range 1-100 THz if the experimental data for ferromagnetic manganese perovskites with nearly 100% spin polarization are used. The optical gain is estimated to be gopt~107 cm-1. This exceeds the gain of conventional semiconductor lasers by 3 or 4 orders of magnitude. An experimental configuration is proposed in order to solve heating problems at a relatively high threshold current density
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| 52. |
- Kadigrobov, Anatoli M., 1937, et al.
(författare)
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Photon generation in ferromagnetic point contacts
- 2012
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Ingår i: Low temperature physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 38:12, s. 1133-1138
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Tidskriftsartikel (refereegranskat)abstract
- We show theoretically that a significant spin accumulation can occur in electric point contacts between two ferromagnetic electrodes with different magnetizations. Under appropriate conditions an inverse population of spin-split electronic levels results in stimulated emission of photons in the presence of a resonant electromagnetic field. The intensity of the emitted radiation can be several orders of magnitude higher than in typical semiconductor laser materials for two reasons. (1) The density of conduction electrons in a metal point contact is much larger than in semiconductors. (2) The strength of the coupling between the electron spins and the electromagnetic field that is responsible for the radiative spin-flip transitions is set by the magnetic exchange energy and can therefore be very large, as suggested by Kadigrobov et al. [Europhys. Lett. 67, 948 (2004)].
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| 53. |
- Krive, Ilya V., et al.
(författare)
-
Carbon "peapods" - a new tunable nanoscale graphitic structure (Review)
- 2006
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 32:10, s. 887-905
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Tidskriftsartikel (refereegranskat)abstract
- We consider the electronic properties of empty single-wall nanotubes (SWNT) and SWNT filled with fullerene molecules (carbon "nano-peapods"). The first part of the review (See. 11) is devoted mostly to the Luttinger liqued properties of individual metallic SWNT coupled to metallic electrodes or to superconducting leads. The discovery of carbon "nano-peapods" and their elastic, electric and thermal properties are reviewed in the second part of the paper (See. 111). We suggest in particular how fullerene and metallofullerene molecules can be released from a "nano-peapod" by a purely electrostatic method. (c) 2006 American Institute of Physics.
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| 54. |
- 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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| 55. |
- Krive, Ilya V., et al.
(författare)
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Resonant tunneling of electrons in quantum wires
- 2010
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 36:2, s. 119-141
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Forskningsöversikt (refereegranskat)abstract
- We consider resonant electron tunneling in various nanostructures, including single-wall carbon nanotubes, molecular transistors, and quantum wires, formed in two-dimensional electron gas. The review starts with a textbook description of resonant tunneling of noninteracting electrons through a double-barrier structure. The effects of electron-electron interaction in sequential and resonant electron tunneling are studied by using the Luttinger liquid model of electron transport in quantum wires. The experimental aspects of the problem (fabrication of quantum wires and transport measurements) are also considered. The influence of vibrational and electromechanical effects on resonant electron tunneling in molecular transistors is discussed.
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| 56. |
- Kroon, Lars, et al.
(författare)
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Bifurcation picture and stability of the gap and out-gap discrete solitons
- 2007
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Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 33:5, s. 481-483
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of a quaternary fragment of a discrete system of coupled nonlinear oscillators with modulated frequency parameters is investigated, and the stability of its gap and out-gap soliton-like excitations is studied.
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| 57. |
- Kulinich, S.I., et al.
(författare)
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Cooling of mechanical vibrations by heat flow
- 2018
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 44:12, s. 1232-1232
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Tidskriftsartikel (refereegranskat)abstract
- We theoretically consider a nanomechanical link between two metallic leads subject to a temperature drop. It is shown that mechanical dynamics of such system can be strongly affected by a heat flow through it via the position dependent electron-electron interaction, even though the electronic transport between leads is blocked. In particular, it is demonstrated that, under certain conditions, the stationary distribution of the excitations in the mechanical subsystem has a Boltzmann form with an effective temperature, which is much lower than the temperature of the environment; this seems rather counterintuitive. We also find that a change in the direction of the temperature gradient can result in the generation of mechanical vibrations rather than the heating of the mechanical subsystem.
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| 58. |
- Kulinich, S. I., et al.
(författare)
-
Nanomechanical pumping of Cooper pairs through NS junction
- 2023
-
Ingår i: Low Temperature Physics. - 1063-777X. ; 49:10, s. 1105-1110
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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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| 59. |
- 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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| 60. |
- Kulyk, Mykola, et al.
(författare)
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Magnetotransport properties of nanogranular composites with low-field positive magnetoresistance
- 2020
-
Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : American Institute of Physics (AIP). - 1063-777X .- 1090-6517. ; 46:8, s. 792-797
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Tidskriftsartikel (refereegranskat)abstract
- A low-temperature feature is detected in nanogranular magnetic films with perpendicular anisotropy that have a low-field positive magnetoresistance: positive magnetoresistance is observed during the initial magnetization of the demagnetized sample, but is absent when the magnetic field is removed and/or during subsequent magnetizations. This effect is studied using a Co-x(Al2On)(1-x)film withx = 0.60, consisting of Co metal nanogranules in an Al(2)O(n)insulating matrix withnclose to 3. It is found that together with perpendicular anisotropy, the film has local in-plane anisotropy with randomly oriented easy axes, which prevents the reorientation of the granules' magnetic moment projections in the film plane below a certain blocking temperature. The restoration of the local short-range order in the orientation of the magnetic moments of the demagnetized film's neighboring granules, which is optimal for conductivity and is destroyed by the introduction of a magnetic field, is prevented at temperatures below the blocking temperature and is not restored during subsequent cycles of introducing/removing the magnetic field without heating to temperatures above the blocking temperature.
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