Research ArticlePHYSICS

Exciton control in a room temperature bulk semiconductor with coherent strain pulses

See allHide authors and affiliations

Science Advances  29 Nov 2019:
Vol. 5, no. 11, eaax2937
DOI: 10.1126/sciadv.aax2937
  • Fig. 1 Characterization of the c-axis exciton in anatase TiO2.

    (A) Calculated wave function of the c-axis exciton. The isosurface representation shows the electronic configuration when the hole of the considered excitonic pair is localized close to one oxygen atom. The colored region represents the excitonic squared modulus wave function. (B) Imaginary part of the dielectric function (blue curve) and reflectivity (red curve) of anatase TiO2 measured at RT, with the electric field polarized along the c axis. The experimental data are obtained from (7), as measured by spectroscopic ellipsometry. The pump photon energy of 4.50 eV used for the pump-probe experiment is indicated by the violet arrow, and the probed region is highlighted as a gray shaded area.

  • Fig. 2 Ultrafast broadband UV spectroscopy data.

    (A) Color-coded map of ∆R/R at RT as a function of probe photon energy and time delay between pump and probe. Both pump and probe beams are polarized along the material c axis. The pump photon energy is 4.50 eV. (B) Transient spectra of ∆R/R for different time delays during the coherent acoustic phonon evolution. The exciton peak undergoes a δE = 30-meV variation in energy and a δR/R ∼ 5% change in intensity. The low-energy tail of the exciton also reacts to the modulation, shifting by 50 meV. a.u., arbitrary units. (C) Zoom-in of the transient spectra of ∆R/R for different time delays during the first 6 ps of the response. The time-dependent variation of the exciton peak energy is also shown. (D) Temporal traces of ∆R/R for different probe photon energies (dotted lines), as indicated in the label. The solid lines are fits to the experimental data. (E) Probe photon energy dependence of the amplitude (Aph) and frequency (νph) of the coherent oscillations with a comparison between experiment and theory.

  • Fig. 3 Many-body perturbation theory calculations and simulated acoustic response.

    (A) Calculated imaginary part of the dielectric function in the BSE-GW scheme for the equilibrium unit cell (blue curve) and in the presence of a 0.2% tensile (red curve) and compressive (green curve) strain. (B) Calculated reflectivity in the BSE-GW scheme for the equilibrium unit cell (blue curve) and in the presence of tensile (red curve) and compressive (green curve) strain. (C) Calculated real (blue curve) and imaginary (red curve) parts of the photoelastic coefficient. (D) Simulated transient acoustic response at different probe photon energies (solid lines), as indicated in the labels. The dotted lines are the experimental data.

  • Table 1 Exciton shifts in different materials under distinct time-dependent perturbations.

    MaterialDimensionalityPerturbationTemperatureExciton shiftReference
    Zn1−xCdxSeQuantum wellsPulsed light field10 K4 meV(45)
    WS2, WSe2MonolayerPulsed light field295 K10–18 meV(38, 39)
    CH3NH3PbI3BulkPulsed light field295 K10 meV(40)
    GaAs/AlGaAsHeterostructurePulsed strain field1.8 K1 meV(12)
    ZnSe/ZnMgSSeQuantum wellsPulsed strain field1.8 K10 meV(13)
    CdSeQuantum dotsPulsed strain field295 K<1 meV(14)
    Anatase TiO2BulkPulsed strain field295 K30–50 meVThis work

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/11/eaax2937/DC1

    Section S1. Global fit analysis

    Section S2. Generation mechanism

    Section S3. Phenomenological description of the observed exciton renormalization

    Section S4. Perturbative model for coherent acoustic phonons

    Section S5. Additional many-body perturbation theory calculations

    Fig. S1. Traditional approach of ultrafast acoustics applied to anatase TiO2.

    Fig. S2. Simulation of the transient acoustic signal.

    Fig. S3. Many-body perturbation theory calculations on the strained unit cell.

    Fig. S4. Calculation of the photoelastic coefficients.

    Fig. S5. Comparison between the RPA-GW and BSE-GW results.

    References (46, 47)

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Global fit analysis
    • Section S2. Generation mechanism
    • Section S3. Phenomenological description of the observed exciton renormalization
    • Section S4. Perturbative model for coherent acoustic phonons
    • Section S5. Additional many-body perturbation theory calculations
    • Fig. S1. Traditional approach of ultrafast acoustics applied to anatase TiO2.
    • Fig. S2. Simulation of the transient acoustic signal.
    • Fig. S3. Many-body perturbation theory calculations on the strained unit cell.
    • Fig. S4. Calculation of the photoelastic coefficients.
    • Fig. S5. Comparison between the RPA-GW and BSE-GW results.
    • References (46, 47)

    Download PDF

    Files in this Data Supplement:

Stay Connected to Science Advances


Editor's Blog

Navigate This Article