Abstract
Using thermal tensor-network approach, we investigate the spin Seebeck effect (SSE) of the triangular lattice quantum antiferromagnet hosting spin supersolid phase. We focus on the low-temperature scaling behaviors of the normalized spin current across the interface. For the 1D Heisenberg chain, we find a negative spinon spin current in the bulk with algebraic temperature scaling; at low fields, boundary effects induce a second sign reversal at lower temperatures. These benchmark results are consistent with field- theoretical analysis. On the triangular lattice, spin frustration dramatically enhances the low-temperature SSE, with distinct spin-current signatures—particularly the sign reversal and characteristic temperature dependence—distinguishing different spin states. Remarkably, we discover a persistent, negative spin current in the spin supersolid phase, which saturates to a nonzero value in the low-temperature limit and can be ascribed to the Goldstone-mode-mediated spin supercurrent. Moreover, a universal scaling T^{d/z} is found at the U(1)-symmetric polarization quantum critical points. These distinct quantum spin transport traits provide sensitive spin current probes for spin supersolid states in quantum magnets such as Na2BaCo(PO4)2. Furthermore, our results also establish spin supersolids as a promising quantum platform for spin caloritronics in the ultralow-temperature regime.