Magnetoabsorption of Indirect Exciton in AgCl and AgBr

Magnetoabsorption of indirect exciton has been studied in AgCl and AgBr at 4.2 K. A new absorption appears on the lower energy side of the zerofield absorption edge when a magnetic field is applied. Kinks are observed in this absorption curve in a high magnetic field. Their dependences on the magnetic field are analysed by taking an electron-hole exchange interaction into consideration. It is concluded that the new absorption is due to a triplet exciton, and the highest tops of the valence bands in both AgCl and AgBr are at the L -point in the Brillouin zone, their states being ( L 4 - , L 5 - ). Exchange energy Δ and effective g -values are estimated as Δ =0.79 meV, g c =1.9, g // υ =0.7 and Δ =0.33 meV, g c =2.5, g // υ =0.5 for AgCl and AgBr, respectively.