Letter reSeArCH
Extended Data Fig. 5 | Magnon thermal conductivity in La 2 CuO 4.
Thermal conductivity of magnons in La 2 CuO 4 , plotted as κmag/T versus
T (blue data points, right axis; ref.^37 ). The solid blue line is a fit to the
data using the standard calculation for two magnon branches in 2D, with
gaps as measured by neutron inelastic scattering^36 , namely Δ 1 = 26 K and
Δ 2 = 58 K. Below T ≈ 5 K, thermally excited magnons are exponentially
rare and κmag/T ≈ 0. In sharp contrast, the thermal Hall conductivity of
La 2 CuO 4 , |κxy/T| (red data points, left axis; the red line is a guide to the
eye; Fig. 1b), is largest at T ≈ 5 K. This comparison shows that the κxy
signal in La 2 CuO 4 cannot come from magnon transport.