Breaking the Wiedemann-Franz limit in thermoelectrics via separated flat bands
Abstract
Controlling the charge and spin degrees of freedom of electrons in solids has been at the heart of condensed-matter science for centuries. One hallmark of metallic conduction is the Wiedemann-Franz law which implies that a moving charge carries entropy. Despite centuries of dedicated research, disentangling charge and heat transport has remained an unsolved issue so far. Here we present a direct route to reduce thermal conductivity of conduction electrons with respect to their electrical conductivity via energy-dependent scattering. By constraining electronic transport to a boxcar-type distribution asymmetrically around the Fermi energy, a large Seebeck coefficient and electrical conductivity can be realized simultaneously while electronic heat conduction is suppressed. Based on the case of monolayer Ni3In, which comprises two flat bands around the Fermi energy, we propose flat-band systems as a promising, tunable platform for scattering phase space engineering. Besides this novel approach, our large-scale assessment of ≈ 5× 104 data sets in a 'Wiedemann-Franz plot' of zT vs. S2 provides an effective tool to identify reports of L≪ L0 from literature - pointing towards either new and interesting physical mechanisms - or overlooked measurement artifacts.
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BibTeX
@misc{serhiienko2026breaking,
title = {{Breaking the Wiedemann-Franz limit in thermoelectrics via separated flat bands}},
author = {Illia Serhiienko and Fabian Garmroudi and Stefan Enzner and Izem Dural and Giorgio Sangiovanni and Andrej Pustogow},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.16261},
eprint = {2609.16261},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.16261},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Breaking the Wiedemann-Franz limit in thermoelectrics via separated flat bands
AU - Illia Serhiienko
AU - Fabian Garmroudi
AU - Stefan Enzner
AU - Izem Dural
AU - Giorgio Sangiovanni
AU - Andrej Pustogow
PY - 2026
DA - 2026/09/14
PB - arXiv
DO - 10.48550/arxiv.2609.16261
UR - https://arxiv.org/abs/2609.16261
AB - Controlling the charge and spin degrees of freedom of electrons in solids has been at the heart of condensed-matter science for centuries. One hallmark of metallic conduction is the Wiedemann-Franz law which implies that a moving charge carries entropy. Despite centuries of dedicated research, disentangling charge and heat transport has remained an unsolved issue so far. Here we present a direct route to reduce thermal conductivity of conduction electrons with respect to their electrical conductivity via energy-dependent scattering. By constraining electronic transport to a boxcar-type distribution asymmetrically around the Fermi energy, a large Seebeck coefficient and electrical conductivity can be realized simultaneously while electronic heat conduction is suppressed. Based on the case of monolayer Ni_3In, which comprises two flat bands around the Fermi energy, we propose flat-band systems as a promising, tunable platform for scattering phase space engineering. Besides this novel approach, our large-scale assessment of ≈ 5× 10^4 data sets in a 'Wiedemann-Franz plot' of zT vs. S^2 provides an effective tool to identify reports of L≪ L_0 from literature - pointing towards either new and interesting physical mechanisms - or overlooked measurement artifacts.
ER -