2D quantum materials | Qimin Yan Group

Discovery and design of quantum materials using 2D materials and heterojunctions

Funded by the DOE Quantum Information Science Program and the DOE EFRC center, my research greatly extended the use of data-driven approaches in the field of quantum materials guided by symmetry-based physical principles. With the support from the DOE EFRC center, my group has constructed a material database with more than 2000 2D materials with symmetry-incorporated electronic band structure information. This materials database together with the combination of orbital-symmetry-based physical principles and data-driven approaches led to the predictions of 2D magnetic heterojunctions that host quantum anomalous Hall states and novel 2D quantum spin Hall systems. This set of research demonstrates how data-driven materials science can be combined with symmetry-based physical principles to guide the search for novel 2D and 2D heterojunction-based quantum materials hosting exotic quantum states for quantum information sciences.

Quantum anomalous Hall effects in 2D magnetic heterojunctions

The discovery of magnetic topological phases that break time-reversal symmetry is challenging and limited to several exemplary materials because the coexistence of magnetism and topological electronic band structure is rare in a single compound. To overcome this challenge, we propose an alternative approach to realize the quantum anomalous Hall (QAH) effect, a typical example of magnetic topological phase, via engineering two-dimensional (2D) magnetic van der Waals heterojunctions. Instead of a single magnetic topological material, we search for the combinations of two 2D (typically trivial) magnetic insulator compounds with specific band alignment so that they can together form a type-III broken-gap heterojunction with a topologically non-trivial band structure. By combining the data-driven materials search, first-principles calculations, and the symmetry-based analytical models, we identify eight type-III broken-gap heterojunctions consisting of 2D ferromagnetic insulators in the MXY compound family as a set of candidates for the QAH effect. This work illustrates how data-driven material science can be combined with symmetry-based physical principles to guide the search for heterojunction-based quantum materials hosting the QAH effect and other exotic quantum states in general.

J. Pan, J. B. Yu, Y. F. Zhang, S. Du, A. Janotti, C. X. Liu, Q. Yan, “Quantum anomalous Hall effect in two-dimensional magnetic insulator heterojunctions” npj Comput. Mater. 6, 152 (2020)

2D Dirac materials and quantum spin Hall effects in the MX compound family

We propose a novel class of two-dimensional (2D) Dirac materials in the MX family (M = Be, Mg, Zn and Cd, X = Cl, Br and I), which exhibit graphene-like band structures with linearly-dispersing Dirac-cone states over large energy scales (0.8–1.8 eV) and ultra-high Fermi velocities comparable to graphene. Spin-orbit coupling opens sizable topological band gaps so that these compounds can be effectively classified as quantum spin Hall insulators. The electronic and topological properties are found to be highly tunable and amenable to modulation via anion-layer substitution and vertical electric field. The presence of sizable band gaps, ultra-high carrier mobilities, and small effective masses makes the MX family promising for electronics and spintronics applications.

Y. F. Zhang, J. Pan, H. Banjade, J. Yu, H. Lin, A. Bansil, S. Du, Q. Yan, “Two-dimensional MX Dirac materials and quantum spin Hall insulators with tunable electronic and topological properties”, Nano Res. 14, 584 (2021) Selected as Cover Article (March 2021).