Absence of Magnetic Thermal Conductivity in the Quantum Spin Liquid Candidate EtMe3Sb[Pd(dmit)2]2

We present the ultralow-temperature specific heat and thermal conductivity measurements on single crystals of triangular-lattice compound EtMe3Sb[Pd(dmit)2]2, which has long been considered as a gapless quantum spin liquid candidate. In specific heat measurements, a finite linear term is observed, consistent with the previous work [S. Yamashita et al., Nat. Commun. 2, 275 (2011)]. However, we do not observe a finite residual linear term in the thermal conductivity measurements, and the thermal conductivity does not change in a magnetic field of 6 T. These results are in sharp contrast to previous thermal conductivity measurements on EtMe3Sb[Pd(dmit)2]2 [M. Yamashita et al., Science 328, 1246 (2010)], in which a huge residual linear term was observed and attributed to highly mobile gapless excitations, likely the spinons of a quantum spin liquid. In this context, the true ground state of EtMe3Sb[Pd(dmit)2]2 has to be reconsidered.