ui-router nested route controller isn't being called

I am trying to call a controller which should be linked with the home.category route but it isn't being called. What's wrong in it?

$stateProvider    
  .state("home", {
    // Use a url of "/" to set a states as the "index".
    url: "/",
    templateUrl: APP_CONFIG.baseUrl +
      'partials/layouts/home.html',
    controller: 'MainCtrl'
  })
  .state("home.category", {
    // Use a url of "/" to set a states as the "index".
    url: "c/:categoryId/:categorySlug",
    controller: function($stateParams) {
      alert($stateParams.categoryId);
    }
  })