Se quantum well*

Large g-factors in system with strong spin-orbit coupling are ideal for spintronic and quantum computing devices. Here, we report the high g-factor of the surface state in Pb_1-xSn_xSe quantum wells. We successfully grow high quality Pb_0.85Eu_0.15Se/Pb_0.7Sn_0.3Se/ Pb_0.85Eu_0.15Se single quantum wells with mobility larger than 4000cm²V^-1s^-1.  The high carrier mobility allows us to reach the quantum limit at reasonably achievable magnetic fields. We exploit this advantage to combine magnetooptical Landau level spectroscopy, Shubnikov-de-Haas transport measurement and consistent modelling of the two experiments to precisely extract the band parameters of the topological states of this system along with their spin and orbital g-factor. The obtained effective g-factor (g~80 at 1T for index n=1) is comparable with what is found for the InSb system, and is much larger than the InAs system (~15). This information is vital to the realization and understanding of novel quantized Hall effect stemming from this material family, and also shed light onto their future applications to quantum devices utilizing topological surface states.