Mechanism of excitonic dephasing in layered InSe crystals

P. Dey, J. Paul, N. Glikin, Z. D. Kovalyuk, Z. R. Kudrynskyi, A. H. Romero, and D. Karaiskaj

Phys. Rev. B 89, 125128 – Published 31 March 2014

Abstract

The dephasing and lifetime of excitons in InSe layered crystals are carefully measured using three-pulse, four-wave mixing and two-dimensional Fourier transform (2DFT) spectroscopy. We obtain a detailed picture of the mechanism of excitonic dephasing in this layered material. The 2DFT spectra reveal contributions from the coherent excitation of continuum states, whereas the temperature dependence provides a detailed description of the phonon-exciton interactions and the low temperature limit of the homogeneous linewidth. The excitation density dependence reveals excitation-induced dephasing due to exciton-exciton scattering. The temperature-dependent homogeneous linewidth is dominated by the interaction of excitons with the $\sim$ 113 cm $^{- 1}$ out-of-plane phonon mode.

Received 12 November 2013
Revised 3 March 2014

DOI:https://doi.org/10.1103/PhysRevB.89.125128

Authors & Affiliations

P. Dey¹, J. Paul¹, N. Glikin¹, Z. D. Kovalyuk², Z. R. Kudrynskyi², A. H. Romero³, and D. Karaiskaj^1,*

¹Department of Physics, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, USA
²Frantsevich Institute of Material Sciences Problems, National Academy of Sciences of Ukraine, Chernivtsi Department, 5 Iryna Vilde Str., 58001 Chernivtsi, Ukraine
³Physics Department, West Virginia University, Morgantown, West Virginia 26506-6315, USA

^*karaiskaj@usf.edu

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 89, Iss. 12 — 15 March 2014

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a) Four-phase stabilized linearly polarized beams obtained from the MONSTR instrument described in Ref. [14] are focused on the sample, which is held in the cryostat at 5 K. A portion of the laser pulse has been split off and colinearly recombined with the FWM signal for heterodyne detection. The combined beams are dispersed in the spectrometer, resulting in the spectral interferogram. (b) The sequence of laser pulses used in the experiments, where A $^{*}$ corresponds to the phase conjugate pulse. The time delay $τ$ corresponds to the time between pulse A $^{*}$ and pulse B, T is the time delay between pulse B and pulse C, and $t$ is the evolution of the FWM in “real time.” (c) Crystal structure of $γ$ -rhombohedral InSe, where the unit cell extends over three layers bound through van der Waals interaction along the $c$ axis. The laser excitation shown is perpendicular to the covalently bound layers or parallel to the $c$ axis.
Reuse & Permissions
Figure 2
(a) Time-integrated FWM data at 5 K. (b) Population decay of excitons at 5 K. Filled (blue) circles and squares are experimental data, whereas the solid (red) line is the exponential fit, respectively.
Reuse & Permissions
Figure 3
(a–c) 2DFT spectra from the $\sim$ 0.6- $μ$ m-thick InSe crystal for resonant, high-energy, and low-energy excitation, respectively. Bottom left: Amplitudes. Bottom right: Real part of the complex amplitude. Peak A corresponds to the 1 $s$ exciton resonance, whereas peak B is stronger for high-energy excitation. Top left: 1 $s$ exciton absorption peak [dashed (red) line] as obtained from the entire sample, 1 $s$ exciton peak [solid (blue) line] obtained from the region of the sample where 2DFT experiments were performed, and laser excitation spectra (solid black line). Top right: Corresponding spectrally resolved FWM data. (d) Spectrally resolved FWM for all three excitations are shown together for comparison.
Reuse & Permissions
Figure 4
(a) Temperature dependence of the excitonic homogeneous linewidth. Filled (blue) squares are the experimentally measured linewidths, whereas the solid (red) line is the fitting using Eq. (1). (b) The calculated phonon mode corresponding to the out-of-plane vibration, where In and Se atoms vibrate against each other. (c) Partial phonon density of states calculated ab initio, showing that the low-frequency phonons originate predominantly from the heavier In atom, whereas the higher frequency phonons originate from the lighter Se atom. Between 14 and 18 meV the contributions to the phonons from both atoms are almost equal. The out-of-plane phonon mode thought to efficiently scatter excitons in InSe is denoted by the (blue) arrow. (d) Excitation density dependence of the homogeneous linewidth. Filled (blue) squares are the experimentally measured linewidths, whereas the solid (red) line is the linear fit.
Reuse & Permissions

Physical Review B

covering condensed matter and materials physics