Topological crystalline insulators
We are currently investigating new states of matter that arise in topological crystalline insulator due their unique valley degenerate topological properties. We can synthesize high mobility epilayers of PbSnSe to observe quantum coherent phenomena and quantum oscillations in magnetooptics and magnetotransport. Our goal is to study multivalley quantized Hall phenomena in these materials. See: Phys. Rev B 102 155307 (2020)
We are also studying induced magnetism in topological crystalline insulators by bulk doping and proximity . We expect to reveal the intrinsic anomalous Hall effect resulting from the Berry curvature of gapped Dirac states in magnetic PbSnSe as well as a new phase of matter where the spin, valley and topological index are coupled. Magnetic topological crystalline superlattices can also be used to generate new quasiparticles such Weyl fermions and nodal line states.
Magnetism in the Bi2Te3 system
The Bi2Te3-Sb2Te3 system hosts the quantum anomalous Hall effect. Introducing Mn in Bi2Te3 can yield a self-assembled MnBi2Te4-MnBi2Te3 superlattice. This superlattice hosts a quantum anomalous Hall effect at elevated temperatures. We are currently working on the MBE synthesis of such superlattices to study their potential to achieve a spontaneous quantum anomalous Hall effect.
Magnetic III-V materials
The magnetism in III-Mn-V materials is mediated by mobile charge carriers that result in a finite exchange interaction between Mn atoms. The origin of anomalous Hall effect in these materials is however still debated. We are examining this specific question in the context of recent theories linking strong anomalous Hall effects to the Berry curvature of the band structure. The ability to engineer band crossings in III-Vs using broken gap heterostructures (InAs/GaSb) and strain (GaMnAsP) opens up a new horizon in the our understanding of how magnetic and band effects couple to yield novel spintronic phenomena.
MBE growth of novel thins films and heterostructures
We are also working on the MBE synthesis of new materials that host unexpected magnetic, topological and superconducting behavior. We have recent attempted the synthesis of Sr-Bi2Se3 [arxiv.2011.12755] by MBE and that of PbSe of GaAs. Both materials were characterized using a variety of structural, optical and electrical tools, providing and unprecedented and complete picture about their growth mechanism and properties.
Our method consists in a hybrid approach that combines material synthesis using MBE and CVD with electrical and optical characterization techniques. It allows us to produce, measure and identify materials with specific electronic and optical properties that can be integrated into functional devices. A list of the synthesis and characterization techniques used in our lab is given below:
- Molecular beam epitaxy (with the MBE group at Notre Dame – with Prof. Xinyu Liu)
- Chemical vapor deposition
- Infrared magnetooptical spectroscopy
- Strong magnetic fields