  In this study, a novel material from the rare-earth based breathing
pyrochlore family, Ba3Tm2Zn5O11, was successfully synthesized. Powder X-ray
diffraction and high-resolution powder neutron diffraction confirmed phase
purity and crystal structure, while thermogravimetric analysis revealed
incongruent melting behavior compared to its counterpart, Ba3Yb2Zn5O11.
High-quality single crystals of Ba3Tm2Zn5O11 were grown using the traveling
solvent floating zone technique and assessed using Laue diffractometer and
single crystal X-ray diffraction. Thermodynamic characterization indicated
paramagnetic behavior down to 0.05 K, and inelastic neutron scattering
measurements identified distinct crystal electric field bands. Additional
low-energy excitation studies on single crystals revealed dispersionless bands
at 0.8 and 1 meV. Computed phonon dispersions from first principles
calculations ruled out phonons as the source of these modes, further
illustrating the puzzling and unique properties of Ba3Tm2Zn5O11.
