React JS Web App Enhancement

I'm seeking a skilled React JS developer to enhance my existing web application. The project involves adding new features, improving performance, and updating the UI/UX design.

Key tasks include:
- Implementing a new user authentication system
- Integrating custom data visualization dashboards
- Performance optimization
- UI/UX design overhaul

Ideal candidates should have:
- Proven experience with React JS
- Strong background in UI/UX design principles
- Expertise in performance tuning of web applications
- Familiarity with authentication systems and data visualization tools

Please provide a portfolio showcasing similar projects.