Unveiling the orbital-selective electronic band reconstruction through the structural phase transition in TaTe$_2$

TL;DR

This study investigates the electronic structure changes in TaTe$_2$ during its structural phase transition, revealing orbital-dependent band reconstruction that cannot be explained by traditional nesting mechanisms.

Contribution

It uncovers the orbital-specific electronic state reconstruction in TaTe$_2$ associated with its phase transition, combining spectroscopy and first-principles calculations.

Findings

Core-level spectroscopy shows Ta 4f splitting across the transition.

Unusual kink-like band reconstruction at the Brillouin zone boundary.

Reconstruction mainly involves Ta $d_{XY}$ orbitals at central Ta sites.

Abstract

Tantalum ditelluride TaTe$_2$ belongs to the family of layered transition metal dichalcogenides but exhibits a unique structural phase transition at around 170 K that accompanies the rearrangement of the Ta atomic network from a "ribbon chain" to a "butterfly-like" pattern. While multiple mechanisms including Fermi surface nesting and chemical bonding instabilities have been intensively discussed, the origin of this transition remains elusive. Here we investigate the electronic structure of single-crystalline TaTe$_2$ with a particular focus on its modifications through the phase transition, by employing core-level and angle-resolved photoemission spectroscopy combined with first-principles calculations. Temperature-dependent core-level spectroscopy demonstrates a splitting of the Ta $4f$ core-level spectra through the phase transition indicative of the Ta-dominated electronic state reconstruction. Low-energy electronic state measurements further reveal an unusual kink-like band reconstruction occurring at the Brillouin zone boundary, which cannot be explained by Fermi surface nesting or band folding effects. On the basis of the orbital-projected band calculations, this band reconstruction is mainly attributed to the modifications of specific Ta $5d$ states, namely the $d_{XY}$ orbitals (the ones elongating along the ribbon chains) at the center Ta sites of the ribbon chains. The present results highlight the strong orbital-dependent electronic state reconstruction through the phase transition in this system and provide fundamental insights towards understanding complex electron-lattice-bond coupled phenomena.