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Coupling of Spin-orbit Interaction with Phonon Anharmonicity Leads to Significant Impact on Thermoelectricity in SnSe

Apr 11, 2019

Understanding the affections of various intrinsic couplings and interactions on the thermal properties within condensed-matter structures provides opportunities to suppress the phonon transport for developing the high-performance clear thermoelectric energy conversions materials.

One long-standing puzzle is that the spin-orbital interactions, indispensable for electronic structure description and seriously taken into account in electrical transport properties, have been ignored in phonon transport without hesitation and thus lead these interactions in the role of thermal transport still to be uncertain. 

In a study published in Nano Energy, a research group led by Prof. ZHUANG Wei from Fujian Institute of Research on the Structure of Matter (FJIRSM) of Chinese Academy of Sciences revealed that the spin-orbit interactions dramatically enhance the lattice thermal conductivity of the main-group compound Tin selenide (SnSe) via first-principle and model calculations, and SnSe achieved the current record-high thermoelectric energy conversion efficiency due to the ultralow thermal conductivity induced by giant phonon scattering.

Theoretical study shows that Spin-Orbit coupling (SOC) has a significant enhancing effect (up to ~60%) on the lattice thermal conductivity of SnSe, while its influences on the crystal structure and the harmonic properties such as the Young's modulus, the phonon dispersions as well as the propagation velocities are almost negligible.

Further analysis indicates that this dramatic structure-activity relationship originates from the significant effect of SOC on the phonon anharmonicity. SOC transfers the charge density of Se p-orbitals from an in-plane bond (d1) to a cross-plane one (d4), which suppresses the delocalization of the resonant bonding network formed by Se p-orbitals.

As a consequence, the anharmonic force constants along the inter-layer direction are reduced, and the lattice thermal conductivity significantly enhanced.

This discovery will encourage the design of tunable spin-orbit systems for better manipulation of thermoelectricity as well as other phonon transport related material functions.

Contact

ZHUANG Wei

Fujian Institute of Research on the Structure of Matter

E-mail:

Coupling of spin-orbit interaction with phonon anharmonicity leads to significant impact on thermoelectricity in SnSe

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