Charge density wave instability below the semimetal to semiconductor transition in Mo8O23
The semimetallic to semiconductor transition of a complex oxide, Mo8O23, remains a mysterious process among low-dimensional conductors. Although a general agreement was reached that the transition originates from a purely structural tilt instability related to the M3 instability of perovskites, rec...
| Autores: | , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión aceptada para publicación |
| Fecha de publicación: | 2025 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/394433 |
| Acceso en línea: | http://hdl.handle.net/10261/394433 |
| Access Level: | acceso abierto |
| Palabra clave: | Charge density waves Electrical conductivity Electronic structure Fermi surface Peierls transition |
| Sumario: | The semimetallic to semiconductor transition of a complex oxide, Mo8O23, remains a mysterious process among low-dimensional conductors. Although a general agreement was reached that the transition originates from a purely structural tilt instability related to the M3 instability of perovskites, recent scanning tunneling microscopy as well as Raman/IR reflectivity measurements have cast doubt about this scenario. We report an in-depth analysis of the density functional theory electron-hole response of this material, showing that a consistent scenario for the evolution of its structural and physical properties can not be put forward without taking into account an electron-hole instability at Γ of the perovskite fragment of the structure. We propose that the mechanism of the semimetallic to semiconductor transition involves several order parameters: (i) an octahedral tilt instability (tilt) driving the incommensurate and later commensurate modulations, and (ii) a Γ electron-hole instability coupled with the lattice via a low-frequency Raman mode. The latter induces the uniform deformation (i.e., tetramerization) of a group of four corner-sharing MoO6 octahedra (unif) repeating along one of the directions of the lattice. The two order parameters are of different symmetries and are independent in the semimetallic state but couple when the inversion symmetry is lost in the semiconducting state and the Raman mode becomes polar. The development of the uniform order of octahedral tetramers competes with the electronic and structural degrees of freedom of the high-temperature staggered tilt wave and induces a disorder of tetramer orientations stopping the growth of the charge density wave (CDW) coherence below 200 K. It is proposed that the generated polar orientation disorder can be explained by the formation of a series of solitons and antisolitons in the CDW, evidenced by a strong optical response. |
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