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Numerical verification of random phase-and-amplitude formalism of weak turbulence
The Random Phase and Amplitude Formalism (RPA) has significantly extended the
scope of weak turbulence studies. Because RPA does not assume any proximity to
the Gaussianity in the wavenumber space, it can predict, for example, how the
fluctuation of the complex amplitude of each wave mode grows through nonlinear
interactions with other modes, and how it approaches the Gaussianity. Thus, RPA
has a great potential capability, but its validity has been assessed neither
numerically nor experimentally. We compare the theoretical predictions given by
RPA with the results of direct numerical simulation (DNS) for a three-wave
Hamiltonian system, thereby assess the validity of RPA. The predictions of RPA
agree quite well with the results of DNS in all the aspects of statistical
characteristics of mode amplitudes studied here
Interplay between Superconductivity and Ferromagnetism on a Topological Insulator
We study theoretically proximity-induced superconductivity and ferromagnetism
on the surface of a topological insulator. In particular, we investigate how
the Andreev-bound states are influenced by the interplay between these
phenomena, taking also into account the possibility of unconventional pairing.
We find a qualitative difference in the excitation spectrum when comparing
spin-singlet and spin-triplet pairing, leading to non-gapped excitations in the
latter case. The formation of surface-states and their dependence on the
magnetization orientation is investigated, and it is found that these states
are Majorana fermions in the -wave case in stark contrast to the
topologically trivial high- cuprates. The signature of such states in the
conductance spectra is studied, and we also compute the supercurrent which
flows on the surface of the topological insulator when a Josephson junction is
deposited on top of it. It is found that the current exhibits an anomalous
current-phase relation when the region separating the superconducting banks is
ferromagnetic, and we also show that in contrast to the metallic case the
exchange field in such a scenario does not induce 0- oscillations in the
critical current. Similarly to the high- cuprates, the presence of
zero-energy surface states on the topological surface leads to a strong
low-temperature enhancement of the critical current.Comment: 12 pages, 11 figures
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