AngularJS evaluate $rootScope variable in directive template

I have a directive that creates an input field.
I need to set the ng-model attribute of this input field to the value of a $rootScope
variable.
The reason behind this is that I want the input field to be in the layout, and bind to different models depending on what page is loaded.
I thought I'd set this global variable in each controller and access it in the Directive.

ATM the variable is hard coded

App.run(function($rootScope){

    $rootScope.mymodel = 'search.name';

})

And the Directive

Directives.directive('inputFilter', function(){

    return{

        restrict: 'E',

        replace:true,

        controller: function($scope, $rootScope){

            console.log($scope.mymodel);

            console.log($rootScope.mymodel)



        },

        template: '<input class="filter" type="text" ng-model="mymodel" placeholder="Nach filtern">'

    }



});

It gets rendered as

<input class="filter ng-pristine ng-valid" type="text" ng-model="mymodel" placeholder="Filter">

and the text inside the input field is the value of mymodel variable. The console.log shows

search.name

search.name  

Could anyone please shed some light on this issue?