QSI Topical Seminar: Paula Giraldo Gallo (Univ. de Los Andes, Bogata)
Host: Daniel Saurez
TITLE: Defect-induced ferroic states in solid solutions of layered transition metal dichalcogenides
ABSTRACT: Solid solutions of transition-metal dichalcogenides (TMDs), a family of quasi-2D van der Waals materials, provide a powerful platform to explore how composition, structural symmetry, and defect chemistry collectively determine electronic and ferroic properties in layered materials. In this seminar I will discuss how alloying different TMDs can be a general strategy to control structural symmetry and electronic instabilities that give rise to multiple ferroic orders. Within this framework, chemical substitution primarily modifies lattice parameters, bonding geometry, and spin-orbit coupling. Deviations from ideal stoichiometry, in turn, introduce defect populations that can locally break inversion symmetry and generate magnetic moments or electric dipoles. The ability to independently tune these two control parameters offers a pathway to stabilize magnetic, polar, and multiferroic states that are absent in stoichiometric, otherwise non-ferroic layered compounds.
I will illustrate these ideas with experimental examples from the alloy families WSe2-WTe2 and WS2-WTe2, synthesized as bulk single crystals and characterized through structural, magnetic, piezoresponse and transport measurements. Both alloy systems reveal a systematic evolution of lattice symmetry and unit cell volume with tellurium substitution and the emergence of defect-stabilized magnetic and polar responses as the chalcogen vacancy density increases. By correlating substitution and defect concentration in WSe2-WTe2, a configurational ferroic phase diagram can be constructed that separates paramagnetic–ferromagnetic, paraelectric-ferroelectric, and multiferroic regimes. These results highlight how solid-solution engineering in layered van der Waals materials provides a general route to stabilize emergent ferroic phases through the coupled control of composition and defects [1,2].
[1] H. Rojas-Páez et al., arXiv:2603.08515 (2026).
[2] G. Cardenas-Chirivi et al., npj 2D Mat. and Appl. 7 (2023) 54.
Time/Location: 11:00am, Physics Bldg. Room 401. Coffee/Cookies at 10:45 am.