Kavli Affiliate: Mamoru Matsuo
| First 5 Authors: Yuta Sekino, Yuya Ominato, Hiroyuki Tajima, Shun Uchino, Mamoru Matsuo
| Summary:
We study magnon-driven spin and heat transport in a magnetic linear junction
(MLJ) formed by two ferromagnets in optical lattices linked via linearly
aligned bonds. Using the Schwinger-Keldysh formalism, we uncover that under
weak effective Zeeman fields, where Bose-Einstein statistics of magnons
dominate, magnonic criticality dramatically enhances spin and thermal
conductances. These singular transport properties depend on the junction
geometry, and the transport properties qualitatively differ between the linear
junction in this study and the point contact in our previous work. The
quantum-enhanced conductances result in the breakdown of the magnonic
Wiedemann-Franz (WF) law. In the classical regime at temperatures much lower
than magnon energy gaps, we find that a magnonic Lorenz number becomes
independent of temperature yet dependent on junction geometry, sharply
contrasting with the universal WF law for Fermi liquids. We also find that the
interface geometry of MLJ decouples spin and heat relaxations between
ferromagnets with decay times insensitive to temperature and effective Zeeman
fields. These dynamics reveal junction-geometry-sensitive magnon transport
distinct from Fermi liquids, paving the way for new avenues in thermomagnetic
research leveraging the tunability of cold atomic systems.
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