Doped-mott Insulator Realizes Vertical/Lateral Polytype Heterostructures, Demonstrating Transparent Effects in 1H/1T Structures

Transition metal dichalcogenides offer exciting potential for creating new materials with tailored properties, but controlling their complex structural transformations remains a significant challenge, limiting the creation of diverse layered structures within a single crystal. Yanyan Geng, Manyu Wang, Shumin Meng, and colleagues now demonstrate a method for realising vertical and lateral polytype heterostructures within a hole-doped Mott insulator by carefully inducing structural transitions through thermal control. Their work confirms the coexistence of these unique structures using a combination of advanced microscopy techniques, and reveals a surprising ‘transparent effect’ at the interface between different layers, where the electronic properties of one layer influence those of the other. This discovery clarifies how distinct electronic phases interact at interfaces, and establishes a pathway for constructing two-dimensional materials with precisely tunable electronic characteristics.

Correlated Electrons and Charge Density Waves

Scientists are actively investigating correlated electron phenomena in 1T-TaS2, a layered transition metal dichalcogenide. Introducing structural imperfections creates Hb-TaS2, a quasi-one-dimensional arrangement of electrons, and researchers explore alloys to fine-tune material properties. This research focuses on understanding and controlling charge density waves and Mott insulator behavior, with the ultimate goal of realizing superconductivity and harnessing the properties of flat bands that enhance electron interactions. The material’s polymorphism, its ability to exist in different structural forms, is also a central focus.

The research involves fabricating van der Waals heterostructures, layering two-dimensional materials to create structures with tailored properties, and carefully controlling composition through doping and alloying. Surface chemistry is modified through oxidation to influence electronic behavior. Researchers employ Kelvin Probe Force Microscopy, Scanning Tunneling Microscopy and Spectroscopy, transport measurements, and optical and X-ray diffraction to probe the material’s properties. This work demonstrates the ability to manipulate charge density wave states through doping and structural modifications, successfully creating flat bands that enhance electron-electron interactions.

Evidence suggests the possibility of superconductivity, including chiral superconductivity, and the ability to control the material’s polymorph represents a significant achievement. Researchers have observed particle-like correlated electrons that can be manipulated, and hysteresis observed in electronic phase transitions suggests first-order phase transitions. Fabricating van der Waals heterostructures allows for the creation of materials with tailored properties, and the research highlights the importance of surface chemistry and oxidation. This work paves the way for developing novel electronic devices, including high-temperature superconductors, quantum computing devices, low-power electronics, and advanced sensors.

Thermally Induced Polytype Heterostructure Engineering in 1T-TaS2

Scientists have successfully engineered diverse polytype heterostructures within hole-doped 1T-TaS2 by carefully controlling thermally induced structural phase transitions. This innovative approach creates both vertical and lateral arrangements of different material phases within a single crystal. Researchers confirmed the formation of these structures using Raman spectroscopy, atomic force microscopy, and scanning Kelvin probe force microscopy. High-resolution scanning tunneling microscopy and spectroscopy revealed a unique electronic transparency effect at the interfaces between 1H and 1T layers under positive bias, allowing observation of charge density wave modulation through the top layer.

Comparative investigations of 1T/1H and 1T/1T heterostructures revealed that the metallic 1H layer exerts a Coulomb screening effect on the 1T layer, effectively reducing electron interactions and suppressing the formation of phase domain walls. The research involved systematically increasing hole doping, inducing a progression from pristine material to phases exhibiting chiral and mixed domains. Researchers meticulously mapped the energy landscape and lattice structures during the phase transitions, identifying an energy barrier between the 1T and 1H phases, and illustrating the transition from the 1T phase to the 4Hb phase. This detailed analysis provides a fundamental understanding of the mechanisms governing the structural phase transitions and the formation of the polytype heterostructures, establishing a new platform for investigating proximity effects between Mott insulating, metallic, and superconducting phases in two-dimensional materials.

Thermally Induced Polytype Heterostructures in TaS2

This work demonstrates the successful creation of diverse polytype heterostructures within a single crystal of hole-doped 1T-TaS2, achieved through thermally induced structural phase transitions. Researchers confirmed the formation of both vertical and lateral transition metal dichalcogenide heterostructures using Raman spectroscopy, atomic force microscopy, and scanning Kelvin probe force microscopy. High-resolution scanning tunneling microscopy imaging revealed a unique electronic transparency effect at the interface between 1H and 1T layers under positive bias, allowing detection of charge density wave modulation through the metallic 1H layer. The metallic 1H layer exerts a Coulomb screening effect on the 1T layer, effectively reducing electron interactions and suppressing the formation of phase domain walls, leading to more ordered electronic states.

Increasing hole doping concentration progressively induces the appearance of phase domains, chiral domains, and mixed domains within the 1T-TaS2 crystal structure. The 1T phase exhibits a unique correlated electron ground state characterized by a commensurate superlattice of Star of David clusters. Measurements confirm that the energy barrier between the 1T and 1H phases can be overcome through thermal excitation, enabling the in-situ construction of these polytype heterostructures. This work establishes a new platform for investigating proximity effects between Mott insulating, metallic, and superconducting phases in two-dimensional materials and provides a pathway for engineering novel correlated quantum states.

Transparent Interfaces Enable Phase Modulation Transfer

Scientists have successfully created both vertical and lateral polytype heterostructures within a single crystal of a low-hole-doped material through thermally induced structural transitions. The team achieved coexistence of distinct phases, confirmed using Raman spectroscopy, scanning Kelvin probe microscopy, and scanning tunneling microscopy/spectroscopy. These measurements reveal detailed electronic characteristics at the atomic scale, demonstrating a pronounced electronic transparency effect at the interface between the two phases. Specifically, charge density wave modulation present in one phase is visible through the other, indicating strong interfacial coupling. Comparing different stacking configurations, the researchers found that the metallic phase exerts a Coulomb screening effect on its neighboring phase, suppressing electronic correlations and eliminating the formation of domain walls. These findings establish a reliable method for fabricating high-quality polytype heterostructures within a single crystal, providing a.