Observation of a pseudogap at terahertz frequencies in the ferromagnetic metallic phase of La2-2xSr1+2xMn2O7 (x=0.3)

We have directly measured the low-energy (0.5-3 meV) complex optical spectra of magnetoresistive La2-2xSr1+2xMn2O7 (x=0.3) thin films by using THz time-domain spectroscopy. a-axis oriented thin films of La2-2xSr1+2xMn2O7 (x=0.3) were epitaxially grown on MgO(100) substrates by pulsed laser deposition technique. The films showed paramagnetic insulator to ferromagnetic metal transition at 240 K. In the ferromagnetic metallic phase, we found that the real part of the optical conductivity spectrum exhibits a clear gap signature around 2 meV, which infringes the Drude-like behavior as expected from the electronic and magnetic properties. This provides an optical identification of a pseudogap in La2-2xSr1+2xMn2O7 (x=0.3). (C) 2003 American Institute of Physics.