Express - Trying to imitate controllers. Got Router.use() requires callback functions but got a [object String] error

I'm trying to create controller in Node.js and Express framework. I've created app.js, routes/index.js and controller/index.js.

Here's each file code:

var express = require("express"),
    path = require("path"),
    indexRoutes = require("./routes/index");

var app = express();

app.use("view engine", "ejs");
app.use("views", path.join(__dirname, "views"));

app.use("/", indexRoutes);

var port = process.env.PORT || 3000;
app.listen(port, function() {
    console.log("listening to port " + port);
});

And routes/index.js:

var express = require("express");
var controller = require("../controller/index");

var router = express.Router();

router.get("/", controller.index);
router.get("/list", controller.list);

module.exports = router;

And controller/index.js:

var indexController = {
    index: function(req, res) {
        res.send("index action");
    }, 
    list: function(req, res) {
        res.send("list action");
    }
}

module.exports = indexController;

When I run the server. I get this error in my terminal:

Error: Router.use() requires callback functions but got a [object String]
    at Function.proto.use (/media/misc/www/expself/node_modules/express/lib/router/index.js:327:11)
    at Function.app.use (/media/misc/www/expself/node_modules/express/lib/application.js:195:16)
    at Object.<anonymous> (/media/misc/www/expself/app.js:7:5)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:906:3

Any help ? I'm quite a beginner to node.js