What is it about?

Phase transitions such as the transition from liquid water to ice have an anomalous behaviour precisely at the transition temperature where the specific heat and the expansion coefficients abruptly change. This work uses nanoscale vibrations of 2D materials to track a different type of a transition going from a normal state to a state called charge-density-wave state where the electron densities order themselves into a new lattice. Using this technique, we study a mechanism in which the charge-density-wave state can be enhanced.

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Why is it important?

Conventional methods which probe the anomaly in the specific heat of materials that undergo phase transitions are not adequate for individual flakes of 2D materials which are often only a few microns wide and few atomic layers thick. We use temperature dependent nanomechanics to extract the specific heat in small and thin flakes of 2D materials which are difficult to measure with conventional techniques. Additionally, we demonstrate that degradation in air can surprisingly enhance the charge-density-wave transition in tantalum disulfide.


I am greatly pleased to be a part of this special issue of Applied Physics Letters and to publish an invited paper on the topic of charge density waves. The charge density wave is closely related to superconductivity due to the similarities in their mechanisms and the well known phenomena of the competition of the two states. Therefore, understanding the charge density wave will help solve the mystery of superconductivity, which does not have a universal theory yet. I believe that degradation, which is one of the phenomenon we studied in this work, is a powerful control parameter because it affects both superconductivity and charge density waves.

martin lee
Technische Universiteit Delft

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This page is a summary of: Study of charge density waves in suspended 2H-TaS2 and 2H-TaSe2 by nanomechanical resonance, Applied Physics Letters, May 2021, American Institute of Physics, DOI: 10.1063/5.0051112.
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