Error Can not read property 'then' of undefined in md-autocomplete of Angular-material

Good afternoon. I want to use md-autocoplete of angular-material but it throws me the following error:

  

angular.js: 13920 TypeError: Can not read property 'then' of undefined   at fetchResults (angular-material.js: 23331)
  at handleQuery (angular-material.js: 23437)
      at MdAutocompleteCtrl.focus (angular-material.js: 23022)
      at fn (eval at compile (angular.js: 14817),: 4: 415)
      at expensiveCheckFn (angular.js: 15906)
      at callback (angular.js: 25885)
      at ChildScope. $ eval (angular.js: 17682)
      at ChildScope. $ apply (angular.js: 17782)
      at HTMLInputElement. (angular.js: 25890)
      at HTMLInputElement.dispatch (jquery.js: 5110)

the autocomplete code is this:

<md-autocomplete md-selected-item="selectedItem" md-search-text="searchText" md-items="item in getMatches(searchText)" md-item-text="tickets.rut"> <span md-highlight-text="searchText">{{tickets.rut}}</span> </md-autocomplete>

and that of my controller is this:

$http({
    method: 'POST',
    url: 'http://localhost/Paneldetencion/app/php/consulta.php',
    headers: {
        'Content-Type': 'application/json',
        'Accept': 'application/json'
    }
})

  .then(function(data) {
     var dat = data.data;
     $scope.tickets= [];
     for (var i = 0; i < dat.length; i++) {
      var ticket = {numero : dat[i].numero,
                    rut : dat[i].rut,
                    servicio_id : dat[i].servicio_id};

     $scope.tickets.push(ticket);
  }
  });

Here when doing a console.log($scope.tickets); the data shows them like this:

How can I solve it?