Steps:

Download the Poliigon Material Converter for Maya.

To install the material converter, extract the zip folder to your desktop and then drag in the installation script from that folder into the viewport in Maya.
You will then be prompted by Maya to navigate to the extracted folder again. Once there, select the poliigon_material_converter folder and click select folder.

Click on the new Material Converter button located in the custom tab, select the location of your materials then check that Arnold is assigned as the renderer and finally click on 'Load Material'

Open the Hypershade window and you will see your imported materials, from there you can hold the right mouse button to assign the material to a selected object.