Split Axis is an option available in Qlikview but not in Qlik Sense. According to Qlikview help "Splitting the y-axis into two parts creates the impression of two charts sharing a common x-axis. The Primary n % setting defines the percentage of the available axis length that will be used for the primary part of the axis."
To overcome this limitation, actually we need to make some tweaking in the min and max values of the primary and secondary Y Axis.