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[Fizinfo] BME Fizika Tanszékének szeminárium

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  • From: Karlo Penc <penc.karlo AT>
  • To: fizinfo AT
  • Subject: [Fizinfo] BME Fizika Tanszékének szeminárium
  • Date: Tue, 20 Feb 2018 16:28:16 +0100
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Kedves Kollégák!

Szeretném a figyelmükbe ajánlani a BME Fizika Tanszékének szemináriumát.

2018. február 26., hétfő 10
BME F épület I. lh. I. em. Schay terem

prof. Shuichi Murakami
Tokyo Institute of Technology

Topological bands and topological phase transitions in magnonic systems

In electronic systems, various interesting phenomena such as spin Hall effect
and topological insulators originate from Berry curvature of Bloch
wavefunctions. We theoretically study analogous phenomena for magnons (spin
waves). We propose that the dipolar interaction gives rise to nonzero Berry
curvature [1-3]. In a thin-film ferromagnet in a long-wavelength regime, we
can calculate the Berry curvature for each magnonic band, and only when the
magnetic field is out-of-plane, the Berry curvature is nonzero. When the
exchange coupling is included, the magnonic bands are modified, and there
appear a number of band anticrossing points. Around such an anticrossing
point, the Berry curvature is enhanced. This Berry curvature gives rise to
thermal Hall effect of magnons [1,2], and it also gives rise to a shift of
wavepackets in reflection or refraction [3]. Furthermore, in analogy to the
quantum Hall effect for electrons, we can design topological magnon band
structure. By introducing artificial spatial periodicity into the magnet, for
example by fabricating nanostructures with two different magnets in a
periodic structure or by making a periodic array of nanomagnets, we
theoretically propose emergence of topological edge modes, analogous to those
in electronic quantum Hall effect. The edge modes are chiral, and propagate
along the edge of the magnet in one way. We call this a topological magnonic
crystal [4,5].

[1] R. Matsumoto and S. Murakami, Phys. Rev. Lett. 106, 197202 (2011); Phys.
Rev. B 84, 184406 (2011).
[2] R. Matsumoto, R. Shindou, and S. Murakami, Phys. Rev. B 89, 054420 (2014).
[3] A. Okamoto, S. Murakami, Phys. Rev. B 96, 174437 (2017); S. Murakami and
A. Okamoto, J. Phys. Soc. Jpn. 86, 011010 (2017).
[4] R. Shindou, R. Matsumoto, S. Murakami, and J. Ohe, Phys. Rev. B 87,
174427 (2013).
[5] R. Shindou, J. Ohe, R. Matsumoto, S. Murakami, and E. Saitoh, Phys. Rev.
B 87, 174402 (2013).

Bordács Sándor

  • [Fizinfo] BME Fizika Tanszékének szeminárium, Karlo Penc, 02/20/2018

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