How to set MeshCollider Material to a material in Project View Materials\PhysMatRough

I added a MeshCollider Component to and object in a c# script. I have this stored in a variable called

MeshCollider mcMeshCollider

I would like to set the Material to a material in Project View Materials/PhysMatRough

I tried the following but the material part didn't work:

GameObject goCurObj;
MeshCollider mcMeshCollider  = null;
PhysicMaterial phymMaterial  = null;

//goCurObj = ... // Assigned to an object I want to attach the MeshCollider

// Add the MeshCollider - This part worked
mcMeshCollider = goCurObj.AddComponent<MeshCollider>();

// Change Material
// Set the Material to PhysMatRough
// This didn't work and it was null
phymMaterial  
   = (PhysicMaterial)Resources.Load("Materials/PhysMatRough");

// I tried both but since phymMaterial is null it had no effect.
mcMeshCollider.sharedMaterial = phymMaterial;
   or
mcMeshCollider.material = phymMaterial;

Resources is not the Assets folder. It is a folder named Resources.