Research

Magnetic Topological Quantum Materials:

Crystal symmetry and magnetism are the two important tools to tailor material properties, especially in topological materials. Magnetic topological insulators (MTIs)  are mainly narrow band gap semiconductor which combine magnetic order and non-trivial  band topology together. In contrast to their nonmagnetic counterparts, MTIs have some of the surfaces gapped which allows for a variety of exotic phenomena with potential applications in spintronics such as the quantum anomalous Hall effect (QAHE), topological axion insulating states, topological Hall effect and Majorana modes etc.

Our research group focuses on the growth of single crystals using appropriate growth techniques and the investigation of magnetic and transport (electrical and thermal) properties of magnetic topological insulators. More experimental, and systematic research on magnetic topological insulators is required to discover novel fundamental phenomenon as well as making new quantum devices.

Magneto-Thermoelectrics:

The demand for clean and sustainable energy sources has driven thermoelectricity to become an integral part of the research portfolio aimed at identifying new and efficient energy materials for power generation applications. Thermoelectric (TE) materials can directly convert heat to electricity, so they are likely to play an important role in energy management in the future.

  Topological quantum materials are good candidates for thermoelectrics because both demand similar material features such as heavy constituent elements, narrow band gap, and high spin-orbit coupling. The basic requirements for the magneto-thermoelectric effect (MTE) are materials with ultrahigh carrier mobility, electron–hole compensation, and a small Fermi surface. MTE is characterized by both transverse and longitudinal properties, depending on the direction of the magnetic field (B), the temperature gradient (ΔT), and the voltage drop (ΔV).

  The Seebeck effect, S is proportional to the entropy per carrier and is therefore suppressed at lower temperatures. Therefore, current thermoelectrics are ineffective at low temperatures and there is a pressing need for thermoelectrics that can operate efficiently at room temperature and below. Therefore, it is necessary to develop new materials that can exhibit large electronic entropy at low temperatures while still maintaining significant electrical conductivity. To achieve large electronic entropy, band-structure engineering can be used in combination with low carrier density, partially filled carrier pockets.

  Chemical doping and defect manipulation are necessary for shifting the Fermi level to comprehend the Dirac/Weyl physics. By understanding the interplay between crystal symmetry and magnetic structure in topological materials, we will grow high quality single crystals of topological semimetals to achieve large thermoelectric performance.

Nernst Effect in Topological Semimetals:

Conventional thermoelectric (TE) devices use the Seebeck effect to convert heat into electrical energy. In contrast, transverse thermoelectric devices based on the Nernst effect are attracting recent attention due to their unique transverse geometry, which uses a single material to eliminate the need for a multitude of electrical connections.

In ferromagnetic materials, large anomalous Nernst effect (ANE) has been realized previously due to the presence of large Berry curvature near to the Fermi level. In contrast, research on this effect in antiferromagnets is in its infancy. At this time, only a handful of antiferromagnets (AFM) with a noncolinear magnetic structure.

We therefore would like to broaden our understanding of the material family for transverse thermoelectric energy conversion by considering: (i) topological magnets with high magnetic transition temperatures, which enable an anomalous Nernst effect signal at or near room temperature; (ii) low magnetic moment is ideal to eliminate the stray magnetic fields in devices; or (iii) hard magnets that produce anomalous Nernst effect at zero magnetic field.