  We investigate the orbit-to-charge conversion in YIG/Pt/nonmagnetic material
(NM) trilayer heterostructures. With the additional Ru layer on the top of
YIG/Pt stacks, the charge current signal increases nearly an order of magnitude
in both longitudinal spin Seebeck effect (SSE) and spin pumping (SP)
measurements. Through thickness dependence studies of the Ru metal layer and
theoretical model, we quantitatively clarify different contributions of the
increased SSE signal that mainly comes from the inverse orbital Hall effect
(IOHE) of Ru, and partially comes from the orbital sink effect in the Ru layer.
A similar enhancement of SSE(SP) signals is also observed when Ru is replaced
by other materials (Ta, W, and Cu), implying the universality of the IOHE in
transition metals. Our findings not only suggest a more efficient generation of
the charge current via the orbital angular moment channel but also provides
crucial insights into the interplay among charge, spin, and orbit.
