Thermal expansion of UCu2Sn in the basal plane

We reported from elastic moduli experiments that the hexagonal uranium compound UCu2Sn undergoes a ferroquadrupolar ordering of non-Kramers doublet *G5 at TQ = 16 K. However, a macroscopic strain has not been measured by an X-ray diffraction experiment because the strain is expected to be smaller than the experimental resolution due to the weak coupling between the strain and order parameters. To detect the spontaneous strain, we have carried out a thermal expansion measurement by a capacitance method with higher resolution from 4.2 to 40 K. The thermal expansion in the basal plane shows a remarkable change below TQ, suggesting the emergence of the *e*G5 strain which couples to the ground state *G5.