Observation of superdiffusive phonon transport in aligned atomic chains.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• One-dimensional (1D) confinement of energy carriers can lead to unique phenomena, such as divergent thermal conductivity (κ) in lattices.
• The Fermi-Pasta-Ulam-Tsingou paradox predicted this length dependence, known as superdiffusive phonon transport, but it remained theoretical due to experimental limitations.
• Achieving isolated, sufficiently long 1D atomic chains has been a significant experimental challenge.

Purpose of the Study:

• To experimentally investigate the theoretical concept of superdiffusive phonon transport in a real material system.
• To explore the thermal conductivity behavior of ultrathin van der Waals crystal nanowires.
• To determine if novel materials could exhibit enhanced thermal conductivity properties.

Main Methods:

• Fabrication and characterization of ultrathin van der Waals crystal NbSe3 nanowires.
• Measurement of thermal conductivity (κ) as a function of nanowire length at room temperature.
• Analysis of the length dependence of κ and its correlation with material properties like Young's modulus.

Main Results:

• Observed length-dependent thermal conductivity in NbSe3 nanowires over lengths up to 42.5 µm.
• Demonstrated that κ follows a 1/3 power law with wire length, supporting superdiffusive phonon transport.
• Reported a 25-fold enhancement in κ with decreasing nanowire size (26 to 6.8 nm), showing a normal-superdiffusive transition and a fivefold increase in Young's modulus.

Conclusions:

• The study provides the first experimental evidence of superdiffusive phonon transport in ultrathin NbSe3 nanowires.
• The observed phenomena are attributed to 1D phonon transport driven by elastic stiffening.
• The findings suggest the potential for developing novel van der Waals crystal-based thermal superconductors with exceptionally high thermal conductivity.