 In 1926, at the recommendation of Abram Ioffe, he was sent to the Leiden cryogenic laboratory of Wander Johannes de Haas in the Netherlands; he worked there until 1930.Shubnikov studied bismuth crystals with low impurity concentrations, and in cooperation with de Haas he discovered magnetoresistance oscillations at low temperatures in magnetic fields (the Shubnikov–de Haas effect).The importance of this effect for condensed state physics became completely clear only much later.