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Discovered more than 200 years ago in 1821, thermoelectricity is nowadays of global interest as it enables direct interconversion of thermal and electrical energy via the Seebeck/Peltier effect. In their seminal work, Mahan and Sofo mathematically derived the conditions for ’the best thermoelectric’—a delta-distribution-shaped electronic transport function, where charge carriers contribute to transport only in an infinitely narrow energy interval. So far, however, only approximations to this concept were expected to exist in nature. Here, we propose the Anderson transition in a narrow impurity band as a physical realisation of this seemingly unrealisable scenario. An innovative approach of continuous disorder tuning allows us to drive the Anderson transition within a single sample: variable amounts of antisite defects are introduced in a controlled fashion by thermal quenching from high temperatures. Consequently, we obtain a significant enhancement and dramatic change of the thermoelectric properties from p -type to n -type in stoichiometric Fe 2 VAl, which we assign to a narrow region of delocalised electrons in the energy spectrum near the Fermi energy. Based on our electronic transport and magnetisation experiments, supported by Monte-Carlo and density functional theory calculations, we present a novel strategy to enhance the performance of thermoelectric materials. The mathematical conditions for the best thermoelectric is well known but never realised in real materials. Here, the authors propose the Anderson transition in a narrow impurity band as a physical realisation of this seemingly unrealisable scenario.

Heusler compounds have emerged as important thermoelectric materials due to their combination of promising electronic transport properties, mechanical robustness and chemical stability – key aspects for practical device integration. While a wide range of XYZ-type half-Heusler compounds have been studied for high-temperature applications, X 2 YZ-type full-Heuslers, often characterized by narrower band gaps, may offer potential advantages at different temperature regimes but remain less explored. In this work, the discovery of p -type Ru 2 Ti 1−x Hf x Si full-Heusler thermoelectrics, exhibiting a high figure of merit zT = 0.7 over a broad range of temperatures 700–1000 K, is reported. These results not only represent the largest values known to date among full-Heusler materials but confirm earlier theoretical predictions that p -type Ru 2 TiSi systems would be superior to their n -type counterparts. Moreover, using a two-band model, electronic structure changes induced by the Hf substitution at the Ti site are unveiled and strategies to further improve zT up to zT > 1 are outlined. These findings highlight the untapped potential of new semiconducting full-Heusler phases and the crucial need for continued exploration of this rich materials class for thermoelectric applications. Authors discover a class of p-type thermoelectric full-Heusler compounds and show that by orbital-selective substitution, lattice vibrations can be scattered but charge carriers remain unscathed, yielding a high zT among full-Heusler materials.

IMPACT STATEMENT The performance of p-type Fe2VAL has traditionally lagged far behind the n-type. In this work, exceptionally high thermoelectric performance in p-type Mn-doped Fe2VAl Heusler alloy thin films were achieved.

Decoupling charge and heat transport is essential for optimizing thermoelectric materials. Strategies to inhibit lattice-driven heat transport, however, also compromise carrier mobility, limiting the performance of most thermoelectrics, including Fe 2 VAl Heusler compounds. Here, we demonstrate an innovative approach, which bypasses this tradeoff: via liquid-phase sintering, we incorporate the archetypal topological insulator Bi 1− x Sb x between Fe 2 V 0.95 Ta 0.1 Al 0.95 grains. Structural investigations alongside extensive thermoelectric and magneto-transport measurements reveal distinct modifications in the microstructure, a reduced lattice thermal conductivity and a simultaneously enhanced carrier mobility arising from topologically protected charge transport along the grain boundaries. This yields a huge performance boost, resulting in one of the highest figure of merits among both half- and full-Heusler compounds, z  ≈ 1.6 × 10 −3 K −1 ( z T  ≈ 0.5) at 295 K. Our findings highlight the potential of topological-insulating secondary phases to decouple charge and heat transport and call for more advanced theoretical studies of multiphase composites. Reducing thermal conductivity of thermoelectric materials usually results in a tradeoff of electrical conductivity. Here, the authors demonstrate a strategy, which allows for a decoupling of charge and heat transport by incorporating topological-insulating Bi-Sb alloys at the grain boundaries of Fe 2 VAl-based Heusler compounds.

High-performance thermoelectric (TE) materials near room temperature are crucial for cooling and energy harvesting applications. This study reports the outstanding thermoelectric performance of -type Mn-doped Fe VAl Heusler alloy thin films, specifically Fe V Mn Al, prepared using magnetron sputtering. These films were deposited on insulating oxide substrates to eliminate any spurious contributions from the substrate. Large -type Seebeck coefficients (S) have been observed for all films, revealing a maximum power factor of 4.26 mWK m at 300 K. This study revealed thickness-dependent thermoelectric properties, with the highest power factor achieved in the 500 nm film. Films with d = 300 nm and 500 nm exhibit weak ferromagnetism. Hall resistivity measurements evidence an anomalous Hall effect (AHE) for the 300 nm and 500 nm samples. The AHE is strongest for the 500 nm film, consistent with a magnetic enhancement of the Seebeck coefficient and power factor. Additionally, we synthesized Al-rich p-type Fe V Mn Al thin films at room temperature, 200°C, 400°C, and 600°C. The film deposited at 600°C exhibits an exceptional figure of merit ~0.8 and a power factor of 6.7 mW·K ·m at room temperature, which are respectively, 4 times and 1.5 times larger than the best values ever reported for any bulk or thin film -type Fe VAl-based material.

Non-Centrosymmetric Superconductors presents an overview of this exciting branch of novel superconductors. Its self-contained and tutorial style makes it particularly suitable for self-study, and as source of teaching material for special seminars and courses.

Oxides are of interest for thermoelectrics due to their high thermal stability, chemical inertness, low cost, and eco‐friendly constituting elements. Here, adopting a unique synthesis route via chemical co‐precipitation at strongly alkaline conditions, one of the highest thermoelectric performances for ZnO ceramics (PFmax= $PF_{\\text{max}} =$  21.5 µW cm−1 K−2 and zTmax= $zT_{\\text{max}} =$  0.5 at 1100 K in Zn0.96Al0.04O ${\\rm Zn}_{0.96} {\\rm Al}_{0.04}{\\rm O}$ ) is achieved. These results are linked to a distinct modification of the electronic structure: charge carriers become trapped at the edge of the conduction band due to Anderson localization, evidenced by an anomalously low carrier mobility, and characteristic temperature and doping dependencies of charge transport. The bi‐dimensional optimization of doping and carrier localization enable a simultaneous improvement of the Seebeck coefficient and electrical conductivity, opening a novel pathway to advance ZnO thermoelectrics. This study reports on the thermoelectric properties of Al‐doped ZnO ceramics, synthesized via chemical co‐precipitation at strongly alkaline conditions. A large enhancement of the thermoelectric performance (zT = 0.5) is obtained and attributed to disorder‐induced modifications of the electronic structure, namely Anderson localization of band edge states, as evidenced by anomalous temperature and doping dependencies of electronic transport.

SeeBand is an interactive tool for extracting microscopic material parameters by fitting temperature-dependent thermoelectric transport properties using Boltzmann transport theory. With real-time comparison between electronic band structures and transport data, it analyzes the Seebeck coefficient, resistivity, and Hall coefficient. Neural-network-assisted guesses and efficient fitting routines enable high-throughput processing of large datasets. SeeBand accelerates material design by allowing electronic band structure models to be derived directly from a single sample’s transport measurements.

A hydride of Yb2Pd2Sn could be synthesized with approximately 2 H atoms per f.u. The hydrogenation leads to a volume expansion while preserving the tetragonal symmetry (P4/mbm). The lattice reaction is strongly anisotropic, and the 5% expansion in c is partly compensated by the 0.5% compression in a. The hydride is paramagnetic at least down to 0.5 K. Yb remains at or very close to the 3+ (4f13) state, as in Yb2Pd2Sn. Specific heat C/T vs. T shows an upturn existing already in Yb2Pd2Sn, but it is much more pronounced in the hydride (1.8 J/mol f.u. K2 for T → 0, i.e., more than twice higher than in its precursor). This is interpreted as lowering the Kondo temperature due to H bonding.

A pressure-induced anomalous valence crossover without structural phase transition is observed in archetypal cubic YbCu 5 based heavy Fermion systems. The Yb valence is found to decrease with increasing pressure, indicating a pressure-induced crossover from a localized 4 f 13 state to the valence fluctuation regime, which is not expected for Yb systems with conventional c – f hybridization. This result further highlights the remarkable singularity of the valence behavior in compressed YbCu 5 -based compounds. The intermetallics Yb 2 Pd 2 Sn, which shows two quantum critical points (QCP) under pressure and has been proposed as a potential candidate for a reentrant Yb 2+ state at high pressure, was also studied for comparison. In this compound, the Yb valence monotonically increases with pressure, disproving a scenario of a reentrant non-magnetic Yb 2+ state at the second QCP.