- Quasiparticle energy, excitons, and optical spectra of nanostructures
- Doping induced renormalizations of the Band gap and excitonic effects of two-dimensional (2D) semiconductors
- Band offset and excitons in heterostructures of 2D materials
We have calculated the quasiparticle band gap and excitonic effects of black phosphorus, graphene, MoS2, ReS2, ReSe2, silicon nanowires, graphene nanoribbons, silicene, fluorographene, graphyne, and graphane.
We have predicted that the enhanced density of states (DOS) and the strong coupling between quasiparticle/exciton with 2D plasmon can induce a significant bandgap renormalization around a few hundred meV and dynamical excitonic effects in doped 2D semiconductors. An effective-mass model has been developed to substantially simplify the calcualtion of band gap renormalization.
We have provided band offsets, gate-tunable interlayer exctions, and their lifetimes of bilayer TMD heterostructures.
GW-calculated quasiparticle band gap, the optical gap (BSE) with excitonic effects included.
Band gap renormalization of doped monolayer MoS2.
The evolution of Interlayer and intralayer excitons in gated bilayer MoS2/WS2.
Polarization properties in two-dimensional materials
- Giant piezoelectric effects in 2D materials
- Robust in-plane ferroelectricity in 2D materials
- Off-plane ferroelectricity in 2D materials
- Magnetic polarization in 2D materials
We predict enormous piezoelectric effects in intrinsic monolayer group IV monochalcogenides (MX, M=Sn or Ge, X=Se or S). Their piezoelectric coefficients are about one to two orders of magnitude larger than those of other 2D materials and bulk quartz and AlN.
We predict robust in-plane ferroelectricity in monolayer group-IV monochalcogenides. The Currie temperature is higher than room temperature.
The Comparison of the piezoelectric coefficient between monolayer MXs with other typical piezoelectric materials.
Polarization vs temperature of monolayer SnSe and the Currie temperature is around 326 K.
Manipulating atomic structures, electronic structures, and transport properties
- Stark effect in 2D structures
- Strain tunable anisotropic electric conductance in black phosphorus
- Pressure-induced quantum phase transition in layered materials
- Doping manipulates phase transitions in 2D materials
We work with experimentalists to show that gate field can substantially tune the band gap and optical response of black phosphorus thin films. We also predict that the Stark effect on the band gap of doped 2D structures will be qualitatively different from the intrinsic result.
We predict the anisotropic electrical conductance can be rotated by moderate strain in black phosphorus.
We predict that small pressure can induce a Lifshitz quantum phase transition in bulk black phosphorus, converting it from a semiconductor to a nodal-line semimetal.
We predict that a low hole doping density (~ 10^12 hole/cm2) can switch monolayer antimony from the hexagonal β-phase to the orthorhombic α phase with a direct band gap and potentially better carrier mobility. We also work with experimentalists to show that electron doping can induce the phase transition of monolayer WSe2 from the semiconducting 2H phase to the metallic 1T' phase.
Band gap vs gate field in thin films of black phosphorus
The electrical conductance tensor under strain of monolayer black phosphorus.
Pressure induced topological nodal line semimetal of bulk black phosphorus.
Thermal properties and applications of nanostructures
- Anisotropic lattice thermal conductance and thermoelectric applications
- Lattice vibrbrational modes in silicon nanowires
We predict not only that black phosphorus possesses a spatially anisotropic electrical conductance, but that its lattice thermal conductance exhibits a pronounced spatial-anisotropy as well. The prominent electrical and thermal conducting directions are orthogonal to one another, enhancing thermoelectric performance.
Anisotropic and orthogonal electrical and thermal conductance in black phosphorus.
The figure of merit of the thermoelectric performance of black phosphorus.
Microscopic structures of supercooled liquids and metallic glasses
- Connectivity of icosahedral network and a dramatically growing static length scale in metallic glasses
- A locally preferred structure characterises all dynamical regimes of a supercooled liquid
We predict that a percolating icosahedral network appears in the Cu64Zr36 system as it is supercooled. This leads us to introduce a static length scale, which grows dramatically as this three-dimensional system approaches the glass transition.
Growth of network of clusters in Cu-Zr supercooled liquid.
The populations of connected and isolated icosahedra, plus their sum.
The connected-icosahedron domain sizes present at a given simulation timestep plotted versus time.
Tools under development