$ionicHistory: Prevent Back Button

The first active controller in my app is ‘AppCtrl’ which checks if the user is already logged in (via localstorage property). If not I’ll call the login view with $state.go('login').
Obviously it should not be possible to navigate back with the back button from the login view to the main view. I use the following code in the ‘AppCtrl’:

         disableAnimate: true,
         disableBack: true

Of course $ionicHistory is injected into the controller:

.controller('AppCtrl', function($scope, $state, $http, $ionicHistory) {..}

Unfortunately this is not working, it’s still possible to navigate back to the main view… I tried also $ionicHistory.clearHistory(), same result…
Any ideas?