Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Directional excitation of a high-density magnon gas using coherently
  driven spin waves   Controlling magnon densities in magnetic materials enables driving spin
transport in magnonic devices. We demonstrate the creation of large,
out-of-equilibrium magnon densities in a thin-film magnetic insulator via
microwave excitation of coherent spin waves and subsequent multi-magnon
scattering. We image both the coherent spin waves and the resulting incoherent
magnon gas using scanning-probe magnetometry based on electron spins in
diamond. We find that the gas extends unidirectionally over hundreds of
micrometers from the excitation stripline. Surprisingly, the gas density far
exceeds that expected for a boson system following a Bose-Einstein distribution
with a maximum value of the chemical potential. We characterize the momentum
distribution of the gas by measuring the nanoscale spatial decay of the
magnetic stray fields. Our results show that driving coherent spin waves leads
to a strong out-of-equilibrium occupation of the spin-wave band, opening new
possibilities for controlling spin transport and magnetic dynamics in target
directions.

20
The categories of this paper are: acc-phys
22
The categories of this paper are: chao-dyn
7
The categories of this paper are: hep-th
16
The categories of this paper are: stat
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
19
The categories of this paper are: eess
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
9
The categories of this paper are: nlin