models/User.php
public function getIsSuperAdmin()
	{
		if ($this->_isSuperAdmin !== null) {
			return $this->_isSuperAdmin;
		}

		$this->_isSuperAdmin = in_array($this->username, Yii::$app->getModule('auth')->superAdmins);
		return $this->_isSuperAdmin;
	}
public function getIsSuperAdmin()
	{
		if ($this->_isSuperAdmin !== null) {
			return $this->_isSuperAdmin;
		}

		$this->_isSuperAdmin = in_array($this->username, Yii::$app->getModule('auth')->superAdmins);
		return $this->_isSuperAdmin;
	}
Returns whether the logged in user is an administrator.

@return boolean the result.