Structural Contribution to Light-Induced Gap Suppression in Ta_{2}NiSe_{5}

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Excitonic insulators feature an energy gap from bound electron-hole pairs.
• Ta2NiSe5 is a candidate excitonic insulator, but its insulating gap origin is debated due to a concurrent structural phase transition.
• Previous studies overlooked atomic displacements during photoexcitation.

Purpose of the Study:

• To investigate the role of atomic displacements in Ta2NiSe5's photoinduced gap changes.
• To resolve the long-standing debate on the origin of the insulating gap in Ta2NiSe5.
• To understand the influence of lattice dynamics on nonequilibrium phase transitions in correlated materials.

Main Methods:

• Utilized MeV ultrafast electron diffraction to quantitatively measure atomic displacements in Ta2NiSe5 after photoexcitation.
• Performed first-principles calculations informed by the experimentally determined atomic displacements.
• Combined time-resolved structural dynamics with theoretical modeling.

Main Results:

• Photoexcitation induces significant atomic displacements in Ta2NiSe5.
• The observed structural changes largely explain the photoinduced reduction of the energy gap.
• Excitonic effects are not the primary driver of the observed gap reduction.

Conclusions:

• The insulating gap in Ta2NiSe5 is predominantly driven by structural phase transitions, not excitonic condensation.
• Quantitative reconstruction of atomic pathways is crucial for understanding photoinduced phase transitions.
• Lattice dynamics play a pivotal role in the behavior of correlated materials.