Polaronic pseudogap in the metallic phase of La<SUB>0.625</SUB>Ca<SUB>0.375</SUB>MnO<SUB>3</SUB> thin films

The electronic density of states (DOS) of La<SUB>0.625</SUB>Ca<SUB>0.375</SUB>MnO<SUB>3</SUB> (LCMO) strain-free epitaxial thin films with an insulator-metal transition temperature (T<SUB>IM</SUB>) of 250 K was probed using variable-temperature scanning tunneling microscopy and spectroscopy. We find a depression in the DOS with a finite zero bias conductance (ZBC) signifying a pseudogap in the 78-310 &#954;temperature range. With cooling, the ZBC is found to increase, indicating an increased DOS near E<SUB>F</SUB>. We interpret the pseudogap as a signature of Jahn-Teller polarons while the ZBC change, in agreement with the bulk insulator-metal transition, optical Drude peak and photoemission experiments, indicates the presence of free carriers at the Fermi energy in the metallic phase. The free carriers are discussed in terms of correlated polaronic states