Prof. Long Ju

Professor Long Ju's group is within the Condensed Matter Experiment group at MIT Physics. Condensed matter physics (previously known as solid state physics) studies the properties of all kinds of solid and liquid materials. It is an extremely important research area of physics and it has direct and far-reaching impact on technological applications in various industries. For example, the whole electronic industry, which is based on the understanding and engineering properties of semiconductors, is the derivative of condensed matter research. Condensed matter physics has a wide overlap with chemistry, chemical engineering, materials science and engineering, as well as electrical engineering, which makes it the branch of physics that is most close to technological applications.

We study the fundamental physical properties of novel Nano and Quantum materials using electric and optical probes. Of particular interest are atomically thin materials and van der Waals hetero-structures of them. These materials host a variety of fascinating electronic and optical properties individually, and they offer exciting opportunities to explore possibilities enabled by controlling the stacking order and electrically tuning the band structure and charge doping. We make great efforts in engineering their optical, electrical and magnetic properties for novel device applications. Specifically, we are working on three topics that are directly related to industrial applications:

(1) Developing materials for quantum information and quantum computing applications. Materials are the basis of conventional electronics and the booming applications in quantum science and engineering. While most of quantum devices are built upon conventional materials such as metal superconductors, such devices tend to be vulnerable to the perturbations of the environment. We focus on a class of materials that encode the principle of topology into the physics, so that their quantum properties are more robust against environmental perturbations. Such topological materials promise topological quantum computation applications, but have been rare to find. We explore novel 2D materials and heterostructures that are protected by the electron topology, and aim for demonstrating topological quantum bits based on such materials.

(2) Research on the electric and optical properties of graphene. We demonstrated AB-stacked bilayer graphene, simply two layers of carbon atoms, can be engineered into a semiconductor with tunable bandgap and unique electrical and optical properties. In conventional semiconductors, the energy bandgap is a fixed property once the material is grown. In contrast, the bandgap of bilayer graphene can be controlled by applying an electric field in situ—means we can have many different semiconductors in the same device. This material has very strong optical response in the mid infrared to Tera Hertz spectral range of light. It can be engineered into semiconductor devices such as tunable infrared detectors, tunable infrared light-emitting-diodes and lasers. Relevant industrial applications include but are not limited to thermal imaging, gas detection, chemical composition analysis and medical diagnostics.

(3) We also develop advanced experimental tools for material characterization that could be of interest for industrial applications. One of such tools is an AFM(atomic force microscope)-based near field infrared nanoscopy/spectroscopy setup. By shining infrared light at a metal coated AFM tip, which scans over the surface of materials, and collecting the back scattered light, we can understand the local structural, electronic and optical properties of materials. The spatial resolution of this microscopy technique is ~10-20 nanometers—orders magnitude smaller than conventional optical microscopy technique where the wavelength of infrared light. By combining with broadband light source, we can also study the spectroscopic properties of materials through the Nano-FTIR technique. Given the importance of infrared spectrum range, this experimental setup can be used for a wide range of applications include but are not limited to: spatially-resolved characterization of polymers, organics, biological materials; monitoring the chemical reaction process at a single metal-particle catalyst; homogeneity characterization and diagnosis of integrated circuits and micro-chips. These applications are directly related to energy, chemical, semiconductor and biomedical industries.