Electronic nematicity without charge density waves in titanium-based kagome metal

TL;DR

This study demonstrates the existence of electronic nematic order in the titanium-based kagome metal CsTi3Bi5 without accompanying charge density waves, highlighting the role of electronic orbitals in symmetry breaking.

Contribution

It reveals electronic nematicity in CsTi3Bi5 without charge density waves, contrasting with other kagome materials, and emphasizes the importance of orbital effects in symmetry breaking.

Findings

No detectable charge density wave in CsTi3Bi5.

Electronic anisotropy breaks six-fold lattice symmetry.

Orbital effects contribute to nematic order.

Abstract

Layered crystalline materials that consist of transition metal atoms on a kagome network have emerged as a versatile platform to study unusual electronic phenomena. For example, in the vanadium-based kagome superconductors AV3Sb5 (where A can stand for K, Cs, or Rb) there is a parent charge density wave phase that appears to simultaneously break both the translational and the rotational symmetry of the lattice. Here, we show a contrasting situation where electronic nematic order - the breaking of rotational symmetry without the breaking of translational symmetry - can occur without a corresponding charge density wave. We use spectroscopic-imaging scanning tunneling microscopy to study the kagome metal CsTi3Bi5 that is isostructural to AV3Sb5 but with a titanium atom kagome network. CsTi3Bi5 does not exhibit any detectable charge density wave state, but comparison to density functional theory calculations reveals substantial electronic correlation effects at low energies. Comparing the amplitudes of scattering wave vectors along different directions, we discover an electronic anisotropy that breaks the six-fold symmetry of the lattice, arising from both in-plane and out-of-plane titanium-derived d orbitals. Our work uncovers the role of electronic orbitals in CsTi3Bi5, suggestive of a hexagonal analogue of the nematic bond order in Fe-based superconductors.