Electron-Hole Asymmetry Observed in Photoinduced Phase Transition of Excitonic Insulators
© The Physical Society of Japan
This article is on
Temporal Evolution and Fluence Dependence of Band Structure in Photoexcited Ta2Ni0.9Co0.1Se5 Probed by Time- and Angle-Resolved Photoemission Spectroscopy
(JPSJ Editors' Choice)
J. Phys. Soc. Jpn. 92, 064706 (2023).
During a photoinduced phase transition from an excitonic insulator to a semimetal, photoinduced energy shift of its hole band is delayed than that of its electron band indicating electron-hole asymmetry.
Existence of excitonic insulators was theoretically predicted in 1960s. They can be realized if conduction and valence bands in a semiconductor or semimetal are hybridized by the electron-hole attractive Coulomb interaction. The electron-hole hybridization by the attractive Coulomb interaction can be viewed as a Bose-Einstein condensation of bounded electron-hole pairs or excitons. In 2009, a layered transition-metal chalcogenide Ta2NiSe5 was proposed to be an excitonic insulator. This has been confirmed by various experimental techniques. In particular, a photoinduced phase transition with 100 fs time scale from the excitonic insulating state to a semimetal state is one strongest proof. In the present study, the photoinduced energy shift of conduction and valence bands (electron and hole bands) of Ta2Ni0.9Co0.1Se5 (which is also an excitonic insulator) is investigated by time-resolved angle-resolved photoemission spectroscopy. In a canonical excitonic insulator, valence and conduction bands are expected to shift simultaneously to close the energy gap between them owing to the screening effect of the photoinduced carriers. However, in Ta2Ni0.9Co0.1Se5, the energy shift of the valence band is delayed than that of the conduction band. This observation indicates that the electron-hole symmetry (which is assumed in the canonical theory for excitonic insulators) is broken and that the mechanism of the electron-hole hybridization is complicated in the layered transition-metal chalcogenide. We speculate that the electron-lattice interaction and electronic correlation in the valence band of Ni 3d and Se 4p orbitals provide the residual and transient energy gap during the photoinduced phase transition to the semimetal state.
(written by T. Mizokawa on behalf of all authors.)
Temporal Evolution and Fluence Dependence of Band Structure in Photoexcited Ta2Ni0.9Co0.1Se5 Probed by Time- and Angle-Resolved Photoemission Spectroscopy
(JPSJ Editors' Choice)
J. Phys. Soc. Jpn. 92, 064706 (2023).
Share this topic
Fields
Related Articles
-
How Many Excitons Can Combine?
Dielectric, optical, and other properties in condensed matter
Electronic structure and electrical properties of surfaces and nanostructures
2023-8-31
Quantum diffusion Monte Carlo simulation demonstrated the formation of polyexcitons in two-dimensional multi-valley semiconductor systems, where all exciton pairs were energetically bound by equal-strength “chemical bonds.”
-
Toward Accurate Diamond Quantum Sensing
Dielectric, optical, and other properties in condensed matter
2023-8-16
A systematic investigation of the optical power dependence of the response of diamond quantum sensors provides valuable guidelines for accurate magnetic field measurements.
-
Topological Properties of the Periodic Toda Lattice: Analogy with the Thouless Pump
Mathematical methods, classical and quantum physics, relativity, gravitation, numerical simulation, computational modeling
Electronic structure and electrical properties of surfaces and nanostructures
2023-8-8
We find that the periodic Toda lattice belongs to the same topological class as the Thouless pump.
-
Double Superconductivity in Nodal Line Material NaAlSi; Coexistence of Bulk and 2D Superconductivities
Superconductivity
Electronic structure and electrical properties of surfaces and nanostructures
2023-7-26
Unique diamagnetic torque signals are found in the nodal line material NaAlSi, which suggests the presence of double superconductivity; i.e., bulk superconductivity and 2D superconductivity on the crystal surface.
-
Geometry-Based Nonlinear and Nonequilibrium Phenomena in Solids
Electronic structure and electrical properties of surfaces and nanostructures
Dielectric, optical, and other properties in condensed matter
Electronic transport in condensed matter
2023-7-10
Researchers from The University of Tokyo have recently reviewed geometric aspects of nonlinear and nonequilibrium optical phenomena for advanced materials applications in novel solar panels, photodetectors, diodes, and quantum computing.