Mesoscale And Nanoscale Physics
Catalogue of Andreev spectra and Josephson effects in structures with time-reversal-invariant topological superconductor wires (1812.09678v2)
Liliana Arrachea, Alberto Camjayi, Armando A. Aligia, Leonel Gruñeiro
2018-12-23
We study all the possible different two terminal configurations of Josephson junctions containing wires of time-reversal invariant topological superconductors (TRITOPS) and ordinary superconductors, including combinations with an interacting quantum dot between both wires in the junction. We introduce simple effective Hamiltonians which explain the different qualitative behaviors obtained. We analyze a wide range of phenomena, including occurrence and quenching of the so called
transition, anomalous periodicity and jumps of the Josephson current as a function of the phase difference, and finite Josephson current in the absence of magnetic flux.
Switching on superferromagnetism (1902.03728v2)
A. Arora, L. C. Phillips, P. Nukala, M. Ben Hassine, A. A. Ünal, B. Dkhil, Ll. Balcells, O. Iglesias, A. Barthélémy, F. Kronast, M. Bibes, S. Valencia
2019-02-11
Recent results in electric-field control of magnetism have paved the way for the design of alternative magnetic and spintronic devices with enhanced functionalities and low power consumption. Among the diversity of reported magnetoelectric effects, the possibility of switching on and off long-range ferromagnetic ordering close to room temperature stands out. Its binary character opens up the avenue for its implementation in magnetoelectric data storage devices. Here we show the possibility to locally switch on superferromagnetism in a wedge-shaped polycrystalline Fe thin film deposited on top of a ferroelectric and ferroelastic BaTiO3 substrate. A superparamagnetic to superferromagnetic transition is observed for confined regions for which a voltage applied to the ferroelectric substrate induces a sizable strain. We argue that electric-field-induced changes of magnetic anisotropy lead to an increase of the critical temperature separating the two regimes so that superparamagnetic regions develop collective long-range superferromagnetic behavior.
Segmental front line dynamics of randomly pinned ferroelastic domain walls (1902.04449v1)
S. Puchberger, V. Soprunyuk, W. Schranz, M. A. Carpenter
2019-02-12
Dynamic mechanical analysis (DMA) measurements as a function of temperature, frequency, and dynamic force amplitude are used to perform a detailed study of the domain wall motion in LaAlO3. In previous DMA measurements Harrison et al.[Phys. Rev. B69,144101(2004)] found evidence for dynamic phase transitions of ferroelastic domain walls in LaAlO3. In the present work we focus on the creep-to-relaxation region of domain wall motion using two complementary methods. We determine, in addition to dynamic susceptibility data, waiting time distributions of strain jerks during slowly increasing stress. The present dynamic susceptibility data can be well fitted with a power law, where a crossover from stochastic DW motion to the pinned regime is well described using the scaling function of Fedorenko et al.[Phys. Rev. B70, 224104(2004)].
Thermal fluctuations in antiferromagnetic nanostructures (1806.11130v2)
Yuriy G. Semenov, Xiniy Xu, Ki Wook Kim
2018-06-28
A theoretical model is developed that can accurately analyze the effects of thermal fluctuations in antiferromagnetic (AFM) nano-particles. The approach is based on Fourier series representation of the random effective field with cut-off frequencies of physical origin at low and high limits while satisfying the fluctuation-dissipation theorem at the same time. When coupled with the formalism of a Langevin dynamical equation, it can describe the stochastic N'eel vector dynamics with the AFM parameters, circumventing the arbitrariness of the commonly used treatments in the micro-magnetic simulations. Subsequent application of the model to spontaneous N'eel vector switching provides a thermal stability analysis of the AFM states. The numerical simulation shows that the AFM states are much less prone to the thermally induced accidental flips than the ferromagnetic counterparts, suggesting a longer retention time for the former.
A study of the nonlinear optical response of the plain graphene and gapped graphene monolayers beyond the Dirac approximation (1902.04438v1)
G. B. Ventura, D. J. Passos, J. M. Viana Parente Lopes, J. M. B. Lopes dos Santos
2019-02-12
In this work, we present numerical results for the second and third order conductivities of the plain graphene and gapped graphene monolayers associated with the second and third harmonic generation, the optical rectification and the optical Kerr effect. The frequencies considered here range from the microwave to the ultraviolet portion of the spectrum, the latter end of which had not yet been studied. These calculations, performed in the velocity gauge, involve some particular points concerning tight binding Hamiltonians, which will also be presented.
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