The Lorenz number (L) of a conductor is the ratio between its electronic thermal conductivity and electrical conductivity. It takes the Sommerfeld value of L0=π2/3kB/e2 in simple, metallically electronic systems where charge and heat are both carried by the same group of quasi-particles that experience elastic scattering. Higher values of L than L0 are possible in semiconductors where both electrons and holes co-exist at high densities, that is, in bipolar conduction. As a narrow-bandgap semiconductor, Bi2Te3 exhibits L > L0 which has been generally attributed to such bipolar conduction mechanisms. However, in this work, we report that L > L0 is still observed in individual, single-crystal Bi2Te3 nanoribbons even at low temperatures and when degenerately doped, that is, far from the bipolar conduction condition. This discovery calls for different mechanisms to explain the unconventional electronic thermal transport behavior in Bi2Te3.
Bibliographical noteFunding Information:
This work was supported by the U.S. NSF Grant No. DMR-1608899. J.W. acknowledges support from the Tsinghua-Berkeley Shenzhen Institute (TBSI). The materials preparation was supported by Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (2018M3D1A1058536). H.Z. thanks the support of the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-05CH11231 within the KC22ZH program. The helium ion irradiation experiments were performed at the Biomolecular Nanotechnology Center of the California Institute for Quantitative Biosciences, UC Berkeley. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy (miscellaneous)