The Mao group’s research centers on the synthesis and study of quantum materials, including topological Dirac and Weyl semimetals, magnetic topological materials, high-entropy materials, strongly correlated oxides, novel superconductors, multiferroic and nonlinear optical materials. Our team not only specializes in growing bulk single crystals of various quantum materials but also conducts extensive measurements to explore the underlying physics of these materials. For crystal growth, we primarily employ the optical floating-zone, flux, chemical vapor transport, and Bridgman methods. Beyond material synthesis, we engage in electronic transport, magnetization, and specific heat measurements to characterize and understand the electronic, magnetic, and thermodynamic properties of quantum materials. Additionally, our group conducts high-field measurements at the National High Magnetic Field Laboratory to investigate new quantum phenomena under extreme magnetic fields. Prof. Mao has also established robust collaborations with researchers at other institutions and National Laboratories to study quantum materials using advanced techniques such as neutron scattering and photoemission spectroscopy.
Recently, our research has increasingly focused on topological and high-entropy materials. In our studies of topological materials, we explore magnetic topological insulators, Dirac, and Weyl semimetals. These new classes of quantum materials exhibit relativistic fermions with linear energy dispersion, describable by the Dirac or Weyl equations. The distinctive topological properties of their electronic band structures result in unique transport characteristics, such as high carrier mobility and large magnetoresistance. Furthermore, these materials offer access to fascinating quantum states with significant technological potential, including the quantum anomalous Hall insulator, capable of supporting dissipationless currents. Consequently, topological materials hold great promise for applications in information technology. Our objective in this area is to discover novel topological materials and understand their exotic quantum transport properties through bulk single crystal growth, magnetotransport, and quantum oscillation measurements.
In the realm of high-entropy materials, our research aims to discover and understand novel electronic and magnetic states through high-entropy engineering. Our current studies have shown that the competition between parent phases in crystal structure and magnetic coupling can generate new electronic and magnetic states, offering a new avenue for discovering materials with functional properties absent in the parent phases. For instance, we have engineered a small-gap semiconductor with ultra-low thermal conductivity by leveraging configuration entropy in large-gap insulators. Our future research will further demonstrate these novel material design principles across various material systems. Additionally, we are developing research avenues to discover new nonlinear optical materials, novel superconductors, and multiferroic materials. Our work on nonlinear optical crystals is being advanced through collaborations with Prof. Gopalan in Materials Science and Engineering.
Recent achievements of our research group include the discovery of the colossal room-temperature nonreciprocal Hall effect (Nature Materials, 2024), high-entropy-protected sharp magnetic transitions (J. Am. Chem. Soc., 2024), high-entropy engineering of electronic states (Nature Communications, 2024), the demonstration of a long-sought ideal time-reversal symmetry-breaking type-II Weyl semimetal (Physical Review X, 2021), spin-valley locking and nonlinear Hall effect in a non-centrosymmetric Dirac semimetal BaMnSb2 (Nature Communications, 2021, 2023), a ferromagnetic Weyl semimetal Co2MnAl (Nature Communications, 2020), a noncollinear spin structure-induced intrinsic anomalous Hall effect in the antiferromagnetic topological insulator MnBi2Te4 (Phys. Rev. Research, 2019), unusual interlayer quantum transport behavior caused by the zeroth Landau level in a Weyl semimetal YbMnBi2 (Nature Communications, 2017), topological nodal-line fermions in ZrSiSe and ZrSiTe (Phys. Rev. Lett., 2016), the demonstration of quantum confinement effects on electron-phonon interactions in 2D materials (Nature Physics, 2015), and the discovery of a magnetic topological semimetal Sr1-yMn1-zSb2 (Nature Materials, 2017).