Add this to your routes.rb
devise_scope :user do
root :to => 'devise/sessions#new'
end
but on doing this, after sign in you might get stuck in infinite loop error, so its better to add after sign in and after sign out path in your application controller by overriding the devise methods
def after_sign_in_path_for(resource_or_scope)
# your_path
end
def after_sign_out_path_for(resource_or_scope)
# your_path
end
This will work!