Abstract
We investigate the intrinsic magnon spin current in a noncollinear antiferromagnetic insulator. We introduce a definition of the magnon spin current in a noncollinear antiferromagnet and find that it is in general non-conserved, but for certain symmetries and spin polarizations the averaged effect of non-conserving terms can vanish. We formulate a general linear response theory for magnons in noncollinear antiferromagnets subject to a temperature gradient and analyze the effect of symmetries on the response tensor. We apply this theory to single-layer potassium iron jarosite KFe$_3$(OH)$_6$(SO$_4$)$_2$ and predict a measurable spin current response.
Highlights
In recent years, advances in research on topological properties of electron systems [1] have encouraged explorations of manifestations of topology in many other systems, e.g., magnonic [2,3,4,5,6,7,8,9,10,11,12,13,14], acoustic [15,16], photonic [17], etc
The possibility of coupling between various degrees of freedom has led to new visions for spintronics [18,19] and resulted in new subfields such as spin caloritronics [20], in which spin carriers are manipulated by exciting heat flows
Magnons exhibit rich and fascinating physics associated with the topology of magnonic bands, e.g., the thermal Hall effect has been observed in collinear ferromagent Lu2V2O7 [21]
Summary
Advances in research on topological properties of electron systems [1] have encouraged explorations of manifestations of topology in many other systems, e.g., magnonic [2,3,4,5,6,7,8,9,10,11,12,13,14], acoustic [15,16], photonic [17], etc. Studies of spin currents in such systems can provide a new venue for probing these materials [49] Motivated by these interesting possibilities, we initiate a discussion on the magnon-mediated spin current physics in noncollinear antiferromagnets and hope to stimulate subsequent research on, e.g., spin transport in topological magnon insulators [50], optical generation of magnon-mediated spin currents [51,52], and many others, as has been discussed above. We develop a linear response theory to temperature gradients for a general observable, i.e., the source term (torque) or spin current, and discuss the symmetry constraints. Our study opens a way for future studies of fascinating physics related to spin flows in noncollinear antiferromagnets, e.g., in the context of different magnetic orders and material realizations
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