Laravel: User Is Logged in but Only Works in My Controller

My Laravel instance doesn't remember that a user is logged in. When I type Auth::user()->accountName it tells me what I want in the LoginController, but on the site, I need it to confirm that the user is logged in, but it doesn't work.

When I return the view('neu_anmeldung') in the MainController, I can check if the user is logged in and it works. The problem is when I click on another link on the navbar it automatically logs out and the MainController doesn't work when it checks in the view. I think it only saves the Auth::user() variable locally because i can access it from the MainController but not the view.

Controller

<?php
// My Login Controller
class MainController extends Authenticate
{
    function index()
    {
        return view('home');
    }
    function checklogin(Request $request)
    {
        $user = Input::get('user');
        $pwd = Input::get('password');
        try {
            $validated = $request->validate([
                'user' => 'required',
                'password' => 'required|min:3'
            ]);
            $user = pupil::where('accountName', $user)
                ->where('password', $pwd)
                ->first();
            if ($user) {
                Auth::login($user);
                return redirect('/successlogin');
            } else {
                return redirect()->back()->withInput('email');
            }
        } catch (QueryException $e) {
            return back()->withError($e->getMessage())->withInput();
        }
    }
    function successlogin()
    {
        return redirect('/neue_anmeldung');
    }
    function logout()
    {
        Auth::logout();
        return redirect('/index');
    }
}

View

@if(isset(Auth::user()->accountName))
    <div class="alert">
        <strong>Wilkommen {{Auth::user()->accountName}}</strong>
        <br/>
        <a href="{{url('/index/logout')}}">Logout</a>
    </div>
@else
    <script>window.location = "/index";</script>
@endif

Model

namespace App;
use Illuminate\Notifications\Notifiable;
use Illuminate\Foundation\Auth\User as Authenticatable;
class pupil extends Authenticatable
{
    use Notifiable;
    protected $table = 'pupil';
    protected $fillable = [
        'name', 'email', 'password',
    ];
    protected $hidden = [
        'password', 'remember_token',
    ];
}