| 1. |
- Alekseeva, L. A., et al.
(författare)
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Determination of the low-temperature self-diffusion coefficient in solid p-H-2 from creep experiments
- 2018
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Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : American Institute of Physics (AIP). - 1063-777X .- 1090-6517. ; 44:9, s. 946-951
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Tidskriftsartikel (refereegranskat)abstract
- Dependencies of the relative elongation epsilon under the constantly applied stress at T = 1.8 K on the endurance time t of polycrystalline parahydrogen (p-H-2, similar to 0.2% of o-H-2) of high purity (99.9999 mol.%), with varying deuterium content, were measured. The region of linear dependence between the measured creep rates (epsilon) over dot of samples and the applied stress s was revealed. The conclusion that the low-temperature creep of the studied p-H-2 possesses a vacancy-type diffusion character was made on the basis of linear dependence (epsilon) over dot similar to s. Determination of the low-temperature self-diffusion coefficient of vacancies D in solid p-H-2, which characterizes the rate of low-temperature mass transfer, was performed. The cases of migration of vacancies in the crystal bulk, along boundaries separating individual crystallites, as well as between dislocations existing in crystals, are considered. A significant decrease in the (epsilon) over dot and D values with an increase in the isotope concentration in the samples was observed, while maintaining the linear relationship between (epsilon) over dot and s for the studied p-H-2. Published by AIP Publishing.
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| 2. |
- Alekseeva, L.A., et al.
(författare)
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Unusual changes in the shape of solid parahydrogen with higher than natural isotope content
- 2016
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Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 42:6, s. 484-490
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Tidskriftsartikel (refereegranskat)abstract
- The relative elongation epsilon of samples of high purity (99.9999 mol. % with respect to nonhydrogenic impurities) parahydrogen (p-H-2, similar to 0.2% o-H-2) with different amounts of the stable hydrogen isotope deuterium is measured as a function of applied stress sigma at temperatures of 1.8-4.2 K. The samples were subjected to uniaxial tension by stepwise loading. The ratio [D]/[H] of the number [D] of deuterium atoms to the number [H] of p-H-2 hydrogen atoms ranged from 0.0055 +/- 0.0005 at. % up to 0.07 at. %. For deuterium enriched p-H-2, the easy slip dislocation stage vanished from the sigma(epsilon) curves and there was a significant reduction in the total relative elongation of the samples, as well as a substantial increase in the hardening coefficient d sigma/d epsilon. Deformation of samples of p-H-2 with deuterium contents higher than the natural amount produces an unusual change in their shape owing to the appearance of a rotational component of the low-temperature plastic mass transfer
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| 3. |
- Bagatskii, M.I., et al.
(författare)
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The low-temperature heat capacity of fullerite C60
- 2015
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Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : American Institute of Physics (AIP). - 1063-777X .- 1090-6517. ; 41:8, s. 630-636
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Tidskriftsartikel (refereegranskat)abstract
- The heat capacity at constant pressure of fullerite C60 has been investigated using an adiabatic calorimeter in a temperature range from 1.2 to 120 K. Our results and literature data have been analyzed in a temperature interval from 0.2 to 300 K. The contributions of the intramolecular and lattice vibrations into the heat capacity of C60 have been separated. The contribution of the intramolecular vibration becomes significant above 50 K. Below 2.3K the experimental temperature dependence of the heat capacity of C60 is described by the linear and cubic terms. The limiting Debye temperature at T → 0 K has been estimated (Θ0=84.4 K). In the interval from 1.2 to 30K the experimental curve of the heat capacity of C60 describes the contributions of rotational tunnel levels, translational vibrations (in the Debye model with Θ0=84.4 K), and librations (in the Einstein model with ΘE,lib=32.5 K). It is shown that the experimental temperature dependences of heat capacity and thermal expansion are proportional in the region from 5 to 60K. The contribution of the cooperative processes of orientational disordering becomes appreciable above 180 K. In the high-temperature phase the lattice heat capacity at constant volume is close to 4.5 R, which corresponds to the high-temperature limit of translational vibrations (3 R) and the near-free rotational motion of C60 molecules (1.5 R).
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| 4. |
- Bocharov, D., et al.
(författare)
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Electronic structure of cubic ScF3 from first-principles calculations
- 2016
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Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 42:7, s. 556-560
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Tidskriftsartikel (refereegranskat)abstract
- The ground state properties of cubic scandium trifluoride (ScF3) perovskite were studied using first-principles calculations. The electronic structure of ScF3 was determined by linear combination of atomic orbital (LCAO) and plane wave projector augmented-wave (PAW) methods using modified hybrid exchange-correlation functionals within the density functional theory (DFT). The comprehensive comparison of the results obtained by two methods is presented. Both methods allowed us to reproduce the lattice constant found experimentally in ScF3 at low temperatures and to predict its electronic structure in good agreement with known experimental valence-band photoelectron and F 1s x-ray absorption spectra.
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| 5. |
- 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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| 6. |
- Entin-Wohlman, O., et al.
(författare)
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Rashba proximity states in superconducting tunnel junctions
- 2018
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 44:6, s. 543-551
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Tidskriftsartikel (refereegranskat)abstract
- We consider a new kind of superconducting proximity effect created by the tunneling of "spin split" Cooper pairs between two conventional superconductors connected by a normal conductor containing a quantum dot. The difference compared to the usual superconducting proximity effect is that the spin states of the tunneling Cooper pairs are split into singlet and triplet components by the electron spin-orbit coupling, which is assumed to be active in the normal conductor only. We demonstrate that the supercurrent carried by the spin-split Cooper pairs can be manipulated both mechanically and electrically for strengths of the spin-orbit coupling that can realistically be achieved by electrostatic gates. Published by AIP Publishing.
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| 7. |
- Ilinskaya, O. A., et al.
(författare)
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Coulomb effects on thermally induced shuttling of spin-polarized electrons
- 2019
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 45:9, s. 1032-1040
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Tidskriftsartikel (refereegranskat)abstract
- A thermally driven single-electron transistor with magnetic leads and a movable central island (a quantum dot) subject to an external magnetic field is considered. The possibility of a mechanical instability caused by magnetic exchange interactions between spin-polarized electrons in this system was studied by the density matrix method. We proved analytically that for noninteracting electrons in the dot there is no such mechanical instability. However, for finite strengths of the Coulomb correlations in the dot we numerically found critical magnetic fields separating regimes of mechanical instability and electron shuttling on the one hand and damped mechanical oscillations on the other. It was shown that thermally induced magnetic shuttling of spin-polarized electrons is a threshold phenomenon, and the dependence of the threshold bias temperature on model parameters was calculated.
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| 8. |
- Ilinskaya, O. A., et al.
(författare)
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Magnetically controlled single-electron shuttle
- 2015
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Ingår i: Low temperature physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 41:1, s. 70-74
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Tidskriftsartikel (refereegranskat)abstract
- A theory of single-electron shuttling in an external magnetic field in nanoelectromechanical system with magnetic leads is presented. We consider partially spin-polarized electrons in the leads and electron transport in both the Coulomb blockade regime and in the limit of large bias voltages when the Coulomb blockade is lifted. The influence of the degree of spin polarization on shuttle instability is considered. It is shown that there is certain degree of spin polarization above which the magnetic field ceases to control electron transport. In the Coulomb blockade regime the depend- ence of the threshold magnetic field, which separates the “shuttle” and vibron regimes, on the degree of polarization is evaluated. The possibility of re-entrant transitions to the shuttle phase is discussed.
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| 9. |
- Jonson, Mats, 1947, et al.
(författare)
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Mechanically driven spin-orbit-active weak links
- 2018
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Ingår i: Fizika Nizkikh Temperatur. - : AIP Publishing. - 0132-6414. ; 44:12, s. 1577-1581
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Tidskriftsartikel (refereegranskat)abstract
- We show that new functionality of spin-orbit-active electronic weak links can be achieved by their time-dependent mechanical deformation. As an illustration we use a simple model to calculate the electronic spin current generated by rotating a bent spin-orbit-active nanowire coupled to bulk metallic leads. © Institute for Low Temperature Physics and Engineering. All rights reserved.
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| 10. |
- 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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