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Четверг 6 декабря 2018 г.<br>
Теоретический семинар в ИФП, 11:30.<br>
<br>
<br>
<u>Wolfgang Belzig</u> (University of Konstanz, Germany), Akashdeep
Kamra (NTNU Trondheim, Norway)<br>
<br>
<font size="+1"><b>Unconventional Magnons and their Impact on Spin
Pumping Transport</b></font><br>
<br>
Exotic quasiparticles have been observed in complex spin systems
exhibiting spin ice rules, skyrmions and so on. Here, we discuss the
emergence of novel quasiparticles, mediated by magnetic dipolar
interactions that have been hiding in simpler spin systems with
uniformly ordered ground states. Amongst other properties, these
quasiparticles exhibit a spin ranging from zero to above 1ℏ [1]. Of
particular interest is our finding that the eigenmodes in an
easy-axis antiferromagnet are spin-zero quasiparticles instead of
the widely believed spin-1 magnons [2]. These unusual properties
originate from a competition between quantum mechanical squeezing
(increasing the spin) and hybridization (decreasing the spin).<br>
<br>
We then present a theoretical study of spin transport across a
ferrimagnet/non-magnetic conductor interface, when a magnetic
eigenmode is driven into a coherent state. In the simple case of
ferromagnets with non-integer “effective spin” above 1ℏ, we show
that spin-current noise measurement can reveal this fundamental
quantum phenomenon [1]. This is in full analogy to the effective
charge known e.g. in the fractional quantum Hall regime, which has
been experimentally determined via shot noise measurements.<br>
<br>
Furthermore, we extend our model to continuously encompasses systems
from ferromagnets to antiferromagnets [3] and include novel
dissipation terms [4], thereby allowing analytical results for the
full range of materials within a unified description. We also allow
arbitrary interfaces (disordered and asymmetric). The obtained spin
current expression includes intra- as well as cross-sublattice
terms. We find that the cross-sublattice terms, disregarded in
previous studies, play an important role and result in qualitative
changes to our understanding of spin pumping in antiferromagnets.
The dc current is found to be sensitive to the asymmetry in
interfacial coupling between the two sublattice magnetizations and
the mobile electrons, especially for antiferromagnets.<br>
<br>
[1] A. Kamra and W. Belzig, Super-Poissonian shot noise of
squeezed-magnon mediated spin transport, Phys. Rev. Lett. 116,
146601 (2016).<br>
[2] A. Kamra, U. Agrawal, and W. Belzig, Noninteger-spin magnonic
excitations in untextured magnets, Phys. Rev. B 96, 020411(R)
(2017).<br>
[3] A. Kamra and W. Belzig, Spin pumping and shot noise in
ferrimagnets: bridging ferro- and antiferromagnets, Phys. Rev. Lett.
119, 197201 (2017).<br>
[4] A. Kamra, R. E. Troncoso, W. Belzig, and A. Brataas, Gilbert
damping phenomenology for two-sublattice magnets, arXiv:1808.04385
(to appear in Phys. Rev. B).<br>
<br>
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Информация о всех запланированных семинарах:<br>
<a href="http://itp.ac.ru/ru/seminars/kapitza-institute/">http://itp.ac.ru/ru/seminars/kapitza-institute/</a><br>
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