Ian image for editors suggestionsThe electronic structure of crystalline materials reflects the influence of underlying discrete symmetries of the atomic lattice. When these symmetries are broken, associated degeneracies in the spectrum of states often split, with important consequences for potential electronic and spintronic applications. The mathematical language of group theory can be used to capture the effect of these symmetries and provide insight into the origins of spectrum features obtained from essentially empirical ab initio numerical calculations such as density functional theory. A salient example comes from the unusual electronic structure of atomically thin two-dimensional "four-six-ene" semiconductors such as tin sulfide, germanium telluride, etc. (related to group-V phosphorene but formed from group IV and VI). In this case, group theoretic methods provide a straightforward framework for understanding the consequences of inversion symmetry breaking due to inequivalent sublattice atomic identity. In particular, the quantum states at the edge of the fundamental band gap – relevant to all transport, optoelectronic, and spintronic properties – are shown to directly inherit their character from nearby points of high symmetry in the reciprocal lattice, where the form of allowable energetic interactions is constrained.

Abstract: Band-edge states in the indirect-gap group-IV metal monochalcogenide monolayers (four-six-enes such as SnS, GeTe, etc.) inherit the properties of nearby reciprocal space points of high symmetry at the Brillouin zone edge. We employ group theory and the method of invariants to capture these essential symmetries in effective Hamiltonians including spin-orbit coupling, and use perturbation theory to shed light on the nature of the band-edge states. In particular, we show how the structure of derived wave functions leads to specific dominant momentum and spin scattering mechanisms for both valence holes and conduction electrons, we analyze the direct optical transitions across the band gap, and expose the interactions responsible for subtle features of the local dispersion relations. 

PDF

Condensed Matter Experiment News

  • Distinguished University Professor Ellen Williams Retires

      Ellen D. Williams, a Distinguished University Professor in the Department of Physics and the Institute for Physical Science and Technology at the University of Maryland and director of the university’s Earth System Science Interdisciplinary Center (ESSIC), retired on December 30, 2023, after 42 years at the university. Following her official retirement, Williams is now a research professor

    Read More
  • Department Rated Highly by US News

    The Department of Physics received high ratings in the U.S. News & World Report’s 2024 Best Graduate Schools lists released on April 25. .Eleven programs and specialties in the University of Maryland’s College of Computer, Mathematical, and Natural Sciences (CMNS) earned top-25 accolades. The college’s graduate rankings are: Physics at No. 17 (No.

    Read More
  • Twisting Up Atoms Through Space and Time

    One of the most exciting applications of quantum computers will be to direct their gaze inwards, at the very quantum rules that make them tick. Quantum computers can be used to simulate quantum physics itself, and perhaps even explore realms that don’t exist anywhere in nature. But even in the

    Read More
  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7