# Near-commensuration from Intertwined Charge Density Waves in Single-Layer TiSe2

## TL;DR

Researchers observed a new near-commensurate state in TiSe2, revealing complex interactions between charge density waves and nematicity.

## Contribution

The study identifies a novel near-commensurate state in TiSe2 involving intertwined charge density waves and nematicity.

## Key findings

- A near-commensurate state in TiSe2 is revealed with unidirectional domain walls.
- The state involves two coupled real charge density waves of different symmetry.
- An unexpected nematic modulation is coupled to the charge density waves.

## Abstract

When the period of
an incommensurate charge density wave
(ICDW)
approaches a multiple of a lattice vector, the energy gain from locking
the period can drive a transition into an intermediate near-commensurate
(NC) state made of locally commensurate regions separated by phase
slips of a complex CDW. In TiSe2, a paradigmatic CDW system,
incommensuration is believed to be induced by carrier doping, yet
its putative NC state has never been imaged. Here we observe a striking
NC state in ultraclean, doped monolayers of TiSe2, displaying
an intricate network of unidirectional domain walls. Detailed analysis
reveals that these are not phase slips of a complex CDW, but rather
sign-changing Ising-type domain walls of two coupled real CDWs of
different symmetry. In addition, these CDWs are coupled to an unexpected
nematic modulation at the lattice Bragg peaks. TiSe2 is
thus a rare example of a NC-CDW of two intertwined real modulations
with nematicity.