A Discrepancy in Thermal Conductivity Measurement Data of Quantum Spin Liquid $β$'-EtMe$_3$Sb[Pd(dmit)$_2$]$_2$ (dmit = 1,3-Dithiol-2-thione-4,5-dithiolate)

A molecular Mott insulator $β$'-EtMe$_3$Sb[Pd(dmit)$_2$]$_2$ is a quantum spin liquid candidate. In 2010, it was reported that thermal conductivity of $β$'-EtMe$_3$Sb[Pd(dmit)$_2$]$_2$ is characterized by its large value and gapless behavior (a finite temperature-linear term). In 2019, however, two other research groups reported opposite data (much smaller value and a vanishingly small temperature-linear term) and the discrepancy in the thermal conductivity measurement data emerges as a serious problem concerning the ground state of the quantum spin liquid. Recently, the cooling rate was proposed to be an origin of the discrepancy. We examined effects of the cooling rate on electrical resistivity, low-temperature crystal structure, and $^{13}$C-NMR measurements and could not find any significant cooling rate dependence.