Intertwined chiral charge orders and topological stabilization of the light-induced state of a prototypical transition metal dichalcogenide

Abstract

The fundamental idea that the constituents of interacting many body systems in complex quantum materials may self-organise into long range order under highly non-equilibrium conditions leads to the notion that entirely new and unexpected functionalities might be artificially created. However, demonstrating new emergent order in highly non-equilibrium transitions has proven surprisingly difficult. In spite of huge recent advances in experimental ultrafast time-resolved techniques, methods that average over successive transition outcomes have so far proved incapable of elucidating the emerging spatial structure. Here, using scanning tunneling microscopy, we report for the first time the charge order emerging after a single transition outcome initiated by a single optical pulse in a prototypical two-dimensional dichalcogenide 1T-TaS 2. By mapping the vector field of charge displacements of the emergent state, we find surprisingly intricate, long-range, topologically non-trivial charge order in which chiral domain tiling is intertwined with unpaired dislocations which play a crucial role in enhancing the emergent states' remarkable stability. The discovery of the principles that lead to metastability in charge-ordered systems opens the way to designing novel emergent functionalities, particularly ultrafast all-electronic non-volatile cryo-memories.

Multivalley Free Energy Landscape and the Origin of Stripe and Quasi-Stripe CDW Structures in Monolayer MX2 Compounds

“…In our extended analysis we have used two types of free energies: the first one (type-1) uses phenomenological parameters which reproduce a ring-like diffuse scattering obtained by an electron diffraction experiment 35 (also in ref. 25 for optically excited hidden CDW states), while the second one (type-2) uses McMillan's original free energy 9 analyzed with the method of Nakanishi-Shiba (see the Method section for more detail). The type-2 free energy is important because ring-like diffuse scattering were not observed for ultra-thin sheet of 1T-TaS 2 including monolayer 22 .…”

“…Recent progress in STM technique has deepened the understanding of the CDW states 22,25,29,30 . These materials exhibit various CDW phases which are characterized by domain walls (topological defects).…”

Configurational electronic states in layered transition metal dichalcogenides

“…Simply counting sites in STM images ( figure 5) gives the doping level. Of course, one needs to take into account that diverse DW patterns are present which are both electronrich and hole rich [3,43,49].…”

“…Most of the images were obtained using an Omicron 4-probe LT STM at 5 K. The exceptions are the TaSeS image (obtained using a Specs JT-STM at 1 K), Cu intercalated TiSe 2 (images taken from [54]) and Ti doped TaSe 2 (images taken from [109]). The experimental setup and sample growth were described previously [43].…”

A time-domain phase diagram of metastable states in a charge ordered quantum material

“…Its' phase diagram includes different structural polytypes (1T-TaS 2 , 2H-TaS 2 etc) 17 , different con gurational charge-ordered states 13,[18][19][20][21] , superconductivity 22 and a quantum spin liquid candidate state 23 . The 1T polytype is metallic above K. In the range K it displays an incommensurate (IC) charge density wave (CDW), which undergoes a transition to a nearly-commensurate (NC) phase below K. Below K, the material becomes insulating and fully commensurate (C), discussed either in terms of a CCDW, a polaronic Wigner crystal [24][25][26] or a Mott state 22 .…”