Both Sony A7R and Nikon D810A have 36.0 MP resolution sensors but Sony A7R's sensor is Full frame (35.9 x 24 mm ) and Nikon D810A's sensor is Full frame (35.9 x 24 mm ).
Since Nikon D810A's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Sony A7R.
Another difference between these two cameras is that Sony A7R's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the A7R and D810A sensor size comparison.
Sony A7R and Nikon D810A have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.