Hi Thiago, are you looking to have your lookup to like this https://www.lightningdesignsystem.com/components/lookups/ ? If yes, then you could use the code template in the page to mockup the lookup field.
Alternatively, you can choose to embed the field in lightning:recordEditForm component. This will help to render the field in lightning experience properly.
Alternatively, you can choose to embed the field in lightning:recordEditForm component. This will help to render the field in lightning experience properly.