Laser-induced thermomagnetic detection of a metastable band in bismuth

Thermal gradients were induced in bismuth films (5.5 μm thick) by ≃5-nsec laser pulses of moderate intensity (≤3×${10}^9$ W/${\mathrm{m}}^2$) under an applied magnetic field. The temporal evolution of the thermal gradient, when predicted by the heat-diffusion equation, does not correlate with the observed temporal evolution of the laser-induced thermomagnetic potential in the films. A new source term is introduced into the equation given by the electrons optically pumped to a metastable band. Agreement between experimental results and theoretical prediction is obtained. Estimations of the lifetime and the energy of the metastable band are given as well.