Friction anomalies at first-order transition spinodals: 1T-TaS<sub>2</sub>

Panizon, Emanuele; Marx, Torben; Dietzel, Dirk; Pellegrini, Franco; Santoro, Giuseppe E.; Schirmeisen, André; Tosatti, Erio

doi:10.1088/1367-2630/aaac00

Cited by 4 publications

(10 citation statements)

References 31 publications

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“…The absence of strongly correlated electrons for the Mott insulating gap also explains the absence of ΔV fluctuation in the nearly commensurate CDW phase, where effective electronic screening can occur due to the abundant electrons at the Fermi level of the 1T-TaS 2 . We note that local fluctuations in electronic structures have not been observed in previous studies based on 1T-TaS 2 using STM 37 – 39 .…”

Section: Resultscontrasting

confidence: 48%

Atomic-scale thermopower in charge density wave states

et al. 2022

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The microscopic origins of thermopower have been investigated to design efficient thermoelectric devices, but strongly correlated quantum states such as charge density waves and Mott insulating phase remain to be explored for atomic-scale thermopower engineering. Here, we report on thermopower and phonon puddles in the charge density wave states in 1T-TaS2, probed by scanning thermoelectric microscopy. The Star-of-David clusters of atoms in 1T-TaS2 exhibit counterintuitive variations in thermopower with broken three-fold symmetry at the atomic scale, originating from the localized nature of valence electrons and their interlayer coupling in the Mott insulating charge density waves phase of 1T-TaS2. Additionally, phonon puddles are observed with a spatial range shorter than the conventional mean free path of phonons, revealing the phonon propagation and scattering in the subsurface structures of 1T-TaS2.

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Section: Resultscontrasting

confidence: 48%

Atomic-scale thermopower in charge density wave states

et al. 2022

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“…Nonetheless, this result of a decreasing friction peak further corroborates the concept of Panizon et al about triggering local nucleation by overcoming an energy barrier that decreases toward the spinodal point . But while the experimental results about the NC → C transition can be well described, the absence of equivalent friction peaks for the C → T or T → NC transitions during the heating process remains puzzling.…”

Section: Resultssupporting

confidence: 85%

“…More recently, the concept of measuring nanoscale friction over structural phase transitions was also demonstrated by experiments on the charge density wave material 1T-TaS 2 that was analyzed during continuous variation of the sample temperature across two first-order phase transitions when heating and cooling. These experiments revealed distinct and narrow friction peaks, that were attributed to triggering local transformation by perturbation through the AFM tip close to the spinodal points of the first-order phase transitions …”

Section: Introductionmentioning

confidence: 94%

Nanoscale Friction across the First-Order Charge Density Wave Phase Transition of 1T-TaS₂

Wang

Dietzel

Liu

et al. 2023

ACS Appl. Mater. Interfaces

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Nanotribology using atomic force microscopy (AFM) can be considered as a unique approach to analyze phase transition materials by localized mechanical interaction. In this work, we investigate friction on the lamellar transition metal dichalcogenide 1T-TaS2, which can undergo first-order charge density wave (CDW) phase transitions. Based on temperature-dependent atomic force microscopy under ultrahigh vacuum conditions (UHV), we can characterize the general friction levels across the first-order phase transitions and for the different phases. While structural and electronic properties for different phases appear to be of minor influence on friction, a distinct peak in friction is observed during the phase transition when cooling the sample from the nearly commensurate CDW (NC-CDW) phase to the commensurate CDW (C-CDW) phase. By performing systematic measurements as a function of load, scan velocity, and scan time, a recently proposed friction mechanism can be corroborated, where the AFM tip gradually induces local transformations of the material close to the spinodal point in a thermally activated and shear-assisted process until the surface is fully “harvested”. Our results demonstrate that repeated nanomechanical stress can trigger local first-order phase transitions constituting a so far little explored mechanical energy dissipation channel.

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“…The basic protocol of our measurements is already outlined in ref. 6 . In principle, the sample is continually scanned while the temperature is simultaneously varied and the z -position of the tip is recorded together with the sample temperature.…”

Section: Resultsmentioning

confidence: 99%

“…During the past decades, it was found, that first order phase transitions in quasi-two-dimensional (2D) materials can lead to a variety of interesting phenomena, such as superconductivity, occurrence of charge density waves, or friction anomalies 1–6 . Fundamentally, these first order phase transitions are often characterized by a close correlation between the structural and electronic properties driven by interactions based on electron-electron and electron-phonon coupling, which result in periodic distortions of the lattice and modified spatial distribution of the charge density 7 .…”

Section: Introductionmentioning

confidence: 99%

Lattice Discontinuities of 1T-TaS2 across First Order Charge Density Wave Phase Transitions

Wang

Dietzel

Schirmeisen

2019

Sci Rep

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Transition metal dichalcogenides are lamellar materials which can exhibit unique and remarkable electronic behavior due to effects of electron-electron and electron-phonon coupling. Among these materials, 1T-tantalum disulfide (1T-TaS 2 ) has spurred considerable interest, due to its multiple first order phase transitions between different charge density wave (CDW) states. In general, the basic effects of charge density wave formation in 1T-TaS 2 can be attributed to in plane re-orientation of Ta-atoms during the phase transitions. Only in recent years, an increasing number of studies has also emphasized the role of interlayer interaction and stacking order as a crucial aspect to understand the specific electronic behavior of 1T-TaS 2 , especially for technological systems with a finite number of layers. Obviously, continuously monitoring the out of plane expansion of the sample can provide direct inside into the rearrangement of the layer structure during the phase transition. In this letter, we therefore investigate the c -axis lattice discontinuities of 1T-TaS 2 by atomic force microscopy (AFM) method under ultra-high vacuum conditions. We find that the c -axis lattice experiences a sudden contraction across the nearly-commensurate CDW (NC-CDW) phase to commensurate CDW (C-CDW) phase transition during cooling, while an expansion is found during the transition from the C-CDW phase to a triclinic CDW phase during heating. Thereby our measurements reveal, how higher order C-CDW phase can favor a more dense stacking. Additionally, our measurements also show subtler effects like e.g. two expansion peaks at the start of the transitions, which can provide further insight into the mechanisms at the onset of CDW phase transitions.

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Friction anomalies at first-order transition spinodals: 1T-TaS₂

Cited by 4 publications

References 31 publications

Atomic-scale thermopower in charge density wave states

Atomic-scale thermopower in charge density wave states

Nanoscale Friction across the First-Order Charge Density Wave Phase Transition of 1T-TaS₂

Lattice Discontinuities of 1T-TaS2 across First Order Charge Density Wave Phase Transitions

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Friction anomalies at first-order transition spinodals: 1T-TaS2

Cited by 4 publications

References 31 publications

Atomic-scale thermopower in charge density wave states

Atomic-scale thermopower in charge density wave states

Nanoscale Friction across the First-Order Charge Density Wave Phase Transition of 1T-TaS2

Lattice Discontinuities of 1T-TaS2 across First Order Charge Density Wave Phase Transitions

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Product

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Friction anomalies at first-order transition spinodals: 1T-TaS₂

Nanoscale Friction across the First-Order Charge Density Wave Phase Transition of 1T-TaS₂