Ferroaxial and nematic transitions in the charge density wave phase of 1T-TiSe2
Year: 2026
Type: article
Abstract: Charge density waves (CDWs) with multi-component order parameters can break unexpected symmetries through the interplay of nearly degenerate instabilities. In the widely investigated material 1T-TiSe$_2$, a central question is whether the observed CDW has a chiral character, which would manifest as the spontaneous breaking of mirror and inversion symmetries. Previous experiments have reported conflicting results about the broken symmetries in the CDW phase of 1T-TiSe$_2$. Here, we resolve this controversy by identifying the bulk broken symmetry as ferroaxial, corresponding to the breaking of vertical mirrors while preserving inversion symmetry. Using symmetry-resolved elastoresistivity, we detect the spontaneous emergence of intrinsic off-diagonal elastoresistivity coefficients that satisfy an antisymmetric relation ($m_{xx-yy,xy} \approx -m_{xy,xx-yy}$), providing an unambiguous bulk transport signature of a macroscopic electric toroidal moment. Simultaneous elastocaloric measurements reveal that the onset of ferroaxial order occurs just below the CDW transition. As the temperature is lowered further, a diverging nematic susceptibility signals a distinct rotational symmetry-breaking instability inside the ferroaxial CDW state. Our findings demonstrate that the proposed ``chiral'' CDW in 1T-TiSe$_2$ is actually a centrosymmetric ferroaxial state, reconciling previous surface-sensitive observations with bulk symmetry constraints.
Source: Physical Review X
DOI: 10.1103/x2k1-7dst
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,200
Funders: National Science Foundation, U.S. Department of Energy, Gordon and Betty Moore Foundation, Fundación BBVA, University of Washington, European Commission, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Office of Science, Agencia Estatal de Investigación, Division of Materials Research, Argonne National Laboratory, NextGenerationEU
Awards: G102163711, G107546177, G1145126297, G1313983767, G1420670123, G1664757510, G1739289980, G2287611682, G262962599, G3075337988, Probing and Controlling Unconventional Electronic Order with Multi-Component Strain Fields, G3589692066, G4515799968, G498139845, G513797252, MRSEC: UW Molecular Engineering Materials Center, G5917724123, G6256534168, Nonunitary superconducting states in multiorbital systems., G6918803902, G8874625583, G993149817
OpenAlex ID: W7138780735