The rare-earth tritellurides (RTe 3 ) are a distinct class of 2D layered materials that recently gained significant attention due to hosting such quantum collective phenomena as superconductivity or charge density waves (CDWs). Many members of this van der Waals (vdW) family crystals exhibit CDW behavior at room temperature, i.e. , RTe 3 compound where R = La, Ce, Pr, Nd, Sm, Gd, and Tb. Here, our systematic studies establish the CDW properties of RTe 3 when the vdW spacing/interaction strength between adjacent RTe 3 layers is engineered under extreme hydrostatic pressures. Using a non-destructive spectroscopy technique, pressure-dependent Raman studies first establish the pressure coefficients of phonon and CDW amplitude modes for a variety of RTe 3 materials, including LaTe 3 , CeTe 3 , PrTe 3 , NdTe 3 , SmTe 3 , GdTe 3 , and TbTe 3 . Results further show that the CDW phase is eventually suppressed at high pressures when the interlayer spacing is reduced and interaction strength is increased. Comparison between different RTe 3 materials shows that LaTe 3 with the largest thermodynamic equilibrium interlayer spacing (smallest chemical pressure) exhibits the most stable CDW phases at high pressures. In contrast, CDW phases in late RTe 3 systems with the largest internal chemical pressures are suppressed easily with applied pressure. Overall results provide comprehensive insights into the CDW response of the entire RTe 3 series under extreme pressures, offering an understanding of CDW formation/engineering in a unique class of vdW RTe 3 material systems.
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Two-dimensional charge order stabilized in clean polytype heterostructures
Abstract Compelling evidence suggests distinct correlated electron behavior may exist only in clean 2D materials such as 1T-TaS 2 . Unfortunately, experiment and theory suggest that extrinsic disorder in free standing 2D layers disrupts correlation-driven quantum behavior. Here we demonstrate a route to realizing fragile 2D quantum states through endotaxial polytype engineering of van der Waals materials. The true isolation of 2D charge density waves (CDWs) between metallic layers stabilizes commensurate long-range order and lifts the coupling between neighboring CDW layers to restore mirror symmetries via interlayer CDW twinning. The twinned-commensurate charge density wave (tC-CDW) reported herein has a single metal–insulator phase transition at ~350 K as measured structurally and electronically. Fast in-situ transmission electron microscopy and scanned nanobeam diffraction map the formation of tC-CDWs. This work introduces endotaxial polytype engineering of van der Waals materials to access latent 2D ground states distinct from conventional 2D fabrication.
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- NSF-PAR ID:
- 10324028
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 13
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract TiSe2is an exciting material because it can be tuned between superconducting and charge density wave (CDW) transitions. In the monolayer limit, TiSe2exhibits a sizable energy gap in the CDW phase that makes it a promising quantum material. It is shown that interfacing a single layer of TiSe2with dissimilar van der Waals materials enables control of its properties. Using angle‐resolved photoemission spectroscopy, the energy gap opening is analyzed as a function of temperature for TiSe2monolayers supported on different van der Waals substrates. A substantial increase in the CDW transition temperature of ≈45 K is observed on MoS2compared to graphite (highly oriented pyrolytic graphite) substrates. This control of the CDW in monolayer TiSe2is suggested to arise from varying charge screening of the unconventional CDW of TiSe2by the substrate. In addition, the suppression of CDW order and a complete closing of the energy gap by electron doping of monolayer TiSe2is demonstrated. Regulating the many‐body physics phenomena in monolayer TiSe2lays the foundation of modifying TiSe2in, for example, artificial van der Waals heterostructures and thus creates a new approach for utilizing the quantum states of TiSe2in device applications.
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Van der Waals heterojunctions of two-dimensional transition-metal dichalcogenides are intensely investigated for multiple optoelectronics applications. Strong and adjustable interactions between layers can influence the charge and energy flow that govern material performance. We report ab initio quantum molecular dynamics investigation of the influence of the bilayer twist angle on charge transfer and recombination in MoS 2 /WS 2 heterojunctions, including high-symmetry 0° and 60° configurations, and low symmetry 9.43° and 50.57° structures with Moiré patterns. The twist angle modulates interlayer coupling, as evidenced by changes in the interlayer distance, electron-vibrational interactions, and spectral shifts in the out-of-plane vibrational frequencies. Occurring on a femtosecond timescale, the hole transfer depends weakly on the twist angle and is ultrafast due to high density of acceptor states and large nonadiabatic coupling. In contrast, the electron–hole recombination takes nanoseconds and varies by an order of magnitude depending on the twist angle. The recombination is slow because it occurs across a large energy gap. It depends on the twist angle because the nonadiabatic coupling is sensitive to the interlayer distance and overlap of electron and hole wavefunctions. The Moiré pattern systems exhibit weaker interlayer interaction, generating longer-lived charges. Both charge separation and recombination are driven by out-of-plane vibrational motions. The simulations rationalize the experimental results on the influence of the bilayer twist angle on the charge separation and recombination. The atomistic insights provide theoretical guidance for design of high-performance optoelectronic devices based on 2D van der Waals heterostructures.more » « less
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Recently a new research field of quasi-one-dimensional (1D) van der Waals quantummaterials has emerged from earlier work on low-dimensional systems [1-2]. The quasi-1D van der Waalsmaterials have 1D motifs in their crystal structure [1]. Many of these materials reveal strongly correlatedphenomena such as charge density waves (CDW) [1-2]. The CDW phase is a periodic modulation of theelectronic charge density, accompanied by distortions in the underlying crystal lattice. Potential uses for CDWmaterials include memory storage and oscillators [3]. Raman spectroscopy can identify the CDW transitions todifferent phases via the appearance of phonon peaks due to emerging superstructure or the disappearance ofcertain peaks due to the loss of translation symmetry in the crystal lattice [3]. In this presentation, we report theresults of the angle and temperature-dependent Raman scattering spectroscopy investigation of themechanically exfoliated nanowires of the quasi-1D Nb van der Waals material. It is known that Nb forms in atetragonal crystal structure with space group 124 (P4/mcc). Recently, this material attracted attention as aCDW material with multiple phase transitions, some of them, possibly, near room temperature. Littleinformation is known on the Raman characteristics of this material. Our Raman data for different polarizationangles show strong anisotropy in the response depending on the crystal direction. The most pronouncedRaman peaks reveal strong temperature dependence. The results of the measurements will be compared withthe theoretical predictions. Our data is important for further investigation of this quasi-1D CDW material forpossible applications in phase-change memory and reconfigurable devices. A.A.B. acknowledges the support of the Vannevar Bush Faculty Fellowship (VBFF) from the Office of NavalResearch (ONR) contract N00014-21-1-2947 “One-Dimensional Quantum Materials” and the National ScienceFoundation (NSF) program Designing Materials to Revolutionize and Engineer our Future (DMREF) via aproject DMR-1921958 “Data-Driven Discovery of Synthesis Pathways and Distinguishing ElectronicPhenomena of 1D van der Waals Bonded Solids”. A. D. and S. K. acknowledge support through the MaterialGenome Initiative funding allocated to the National Institute of Standards and Technology. [1] A. A. Balandin, F. Kargar, T. T. Salguero, and R. Lake, “One-dimensional van der Waals quantummaterials", Mater. Today, 55, 74 (2022). [2] A. A. Balandin, R. K. Lake, and T. T. Salguero, "One-dimensional van der Waals materials - Advent of a newresearch field" Appl. Phys. Lett., 121, 040401 (2022). [3] A. A. Balandin, S. V. Zaitzev-Zotov, and G. Grüner, "Charge-density-wave quantum materials and devices—New developments and future prospects", Appl. Phys. Lett., 119, 170401 (2021). [4] R. Samnakay, et al., “Zone-folded phonons and the charge-density-wave transition in 1T-TaSe2 thin films, Nano Lett., 15, 2965 (2015).more » « less
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Abstract Body: Recently a new research field of quasi-one-dimensional (1D) van der Waals quantummaterials has emerged from earlier work on low-dimensional systems [1-2]. The quasi-1D van der Waalsmaterials have 1D motifs in their crystal structure [1]. Many of these materials reveal strongly correlatedphenomena such as charge density waves (CDW) [1-2]. The CDW phase is a periodic modulation of theelectronic charge density, accompanied by distortions in the underlying crystal lattice. Potential uses for CDWmaterials include memory storage and oscillators [3]. Raman spectroscopy can identify the CDW transitions todifferent phases via the appearance of phonon peaks due to emerging superstructure or the disappearance ofcertain peaks due to the loss of translation symmetry in the crystal lattice [3]. In this presentation, we report theresults of the angle and temperature-dependent Raman scattering spectroscopy investigation of themechanically exfoliated nanowires of the quasi-1D Nb van der Waals material. It is known that Nb forms in atetragonal crystal structure with space group 124 (P4/mcc). Recently, this material attracted attention as aCDW material with multiple phase transitions, some of them, possibly, near room temperature. Littleinformation is known on the Raman characteristics of this material. Our Raman data for different polarizationangles show strong anisotropy in the response depending on the crystal direction. The most pronouncedRaman peaks reveal strong temperature dependence. The results of the measurements will be compared withthe theoretical predictions. Our data is important for further investigation of this quasi-1D CDW material forpossible applications in phase-change memory and reconfigurable devices. A.A.B. acknowledges the support of the Vannevar Bush Faculty Fellowship (VBFF) from the Office of NavalResearch (ONR) contract N00014-21-1-2947 “One-Dimensional Quantum Materials” and the National ScienceFoundation (NSF) program Designing Materials to Revolutionize and Engineer our Future (DMREF) via aproject DMR-1921958 “Data-Driven Discovery of Synthesis Pathways and Distinguishing ElectronicPhenomena of 1D van der Waals Bonded Solids”. A. D. and S. K. acknowledge support through the MaterialGenome Initiative funding allocated to the National Institute of Standards and Technology. [1] A. A. Balandin, F. Kargar, T. T. Salguero, and R. Lake, “One-dimensional van der Waals quantummaterials", Mater. Today, 55, 74 (2022). [2] A. A. Balandin, R. K. Lake, and T. T. Salguero, "One-dimensional van der Waals materials - Advent of a newresearch field" Appl. Phys. Lett., 121, 040401 (2022). [3] A. A. Balandin, S. V. Zaitzev-Zotov, and G. Grüner, "Charge-density-wave quantum materials and devices—New developments and future prospects", Appl. Phys. Lett., 119, 170401 (2021). [4] R. Samnakay, et al., “Zone-folded phonons and the charge-density-wave transition in 1T-TaSe2 thin films,” Nano Lett., 15, 2965 (2015).more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41467-021-27947-5
