How can I create the notched corner look of the logs on the LEGO IDEAS: Log Cabin
First of all, that's a digital model. This means it may use parts in colors we don't have. It looks like Reddish Brown is used here, so the part choice is rather limited.
Upon closer inspection of the model it looks like each corner has 2x2 column with round 2x2 bricks attached from each side as seen here:
I find using Brick, Modified 1 x 1 x 1 2/3 with Studs on 1 Side (which is available in Reddish Brown) in alternating manner to be the solution here. These bricks are exactly the size of 2x2 plate placed vertically, so no tiny gaps. And it also allows you to have as musch studs as possible on all sides.
I may be misreading the question, but to answer what I think you're asking: They have used Tile, Round 2 x 2 with Bottom Stud Holder with Tree Stump / Wood Grain Pattern, which has a printed pattern that looks like the end of a wood log with notches
Given the color, I would think it's Brick, Modified 1 x 1 with Stud on 1 Side, which (unlike many other similar bricks) is available in Reddish Brown. If you put two side-by-side, then you can hang the decorated round tile off it, and then put two more side-by-side, but pointing the other way to hang the next decorated round tile. You may need to add plates to space everything just right.