Population inversion and Dirac fermion cooling in 3D Dirac semimetal Cd${}_3$As${}_2$

Abstract

Revealing the ultrafast dynamics of three-dimensional (3D) Dirac fermions upon photoexcitation is critical for both fundamental science and device applications. So far, how the cooling of 3D Dirac fermions differs from that of two-dimensional (2D) Dirac fermions and whether there is population inversion are fundamental questions that remain to be answered. Here we reveal the ultrafast dynamics of Dirac fermions in a model 3D Dirac semimetal Cd${}_3$As${}_2$ by ultrafast time- and angle-resolved photoemission spectroscopy (TrARPES) with a tunable probe photon energy from 5.3 - 6.9 eV. The energy- and momentum-resolved relaxation rate shows a linear dependence on the energy, suggesting Dirac fermion cooling through intraband relaxation. Moreover, a population inversion is reported based on the observation of accumulated photoexcited carriers in the conduction band with a lifetime of ${\tau }_n$ = 3.0 ps. Our work provides direct experimental evidence for a long-lived population inversion in a 3D Dirac semimetal, which is in contrast to 2D graphene where the interband relaxation occurs on a much faster timescale.

References in corpus (8)

• The electronic properties of graphene
• Ultrafast Optical Excitation of a Persistent Surface-State Population in the Topological Insulator Bi2Se3
• Ultrafast Broadband Photodetectors based on Three-dimensional Dirac Semimetal Cd3As2
• Ultrafast Angle-Resolved Photoemission Spectroscopy of Quantum Materials
• Ultrafast electron calorimetry uncovers a new long-lived metastable state in 1T-TaSe${}_2$ mediated by mode-selective electron-phonon coupling
• Ultrafast Relaxation Dynamics of Photoexcited Dirac Fermion in The Three Dimensional Dirac Semimetal Cadmium Arsenide
• Transient reflectance of photoexcited Cd${}_3$As${}_2$
• Ultrafast time- and angle-resolved photoemission spectroscopy with widely tunable probe photon energy of 5.3-7.0 eV for investigating dynamics of three-dimensional materials

Cited by in corpus (2)

• Angle-resolved photoemission spectroscopy
• Ultrafast photothermoelectric effect in Dirac semimetallic Cd3As2 revealed by terahertz emission