  Thermal conductivity, point contact spectroscopy, angle-resolved
photoemission and Raman spectroscopy measurements were performed on
BaFe1.9Pt0.1As2 single crystals obtained from the same synthesis batch in order
to investigate the superconducting energy gap structure using multiple
techniques. Low temperature thermal conductivity was measured in the
superconducting state as a function of temperature and magnetic field,
revealing an absence of quasiparticle excitations in the T=0 limit up to 15 T
applied magnetic fields. Point-contact Andreev reflection spectroscopy
measurements were performed as a function of temperature using the needle-anvil
technique, yielding features in the conductance spectra at both 2.5 meV and 7.0
meV scales consistent with a multi-gap scenario. Angle-resolved photoemission
spectroscopy probed the electronic band structure above and below the
superconducting transition temperature of T_c=23 K, revealing an isotropic gap
of magnitude ~3 meV on both electron and hole pockets. Finally, Raman
spectroscopy was used to probe quasiparticle excitations in multiple channels,
showing a threshold energy scale of 3 meV below T_c. Overall, we find strong
evidence for an isotropic gap structure with no nodes or deep minima in this
system, with a 3 meV magnitude gap consistently observed and a second, larger
gap suggested by point contact spectroscopy measurements. We discuss the
implications that the combination of these results reveal about the
superconducting order parameter in the BaFe1-xPtxAs2 system and how this
relates to similar substituted iron pnictides.
