Search

Abstract Transverse thermoelectric effect, the conversion of longitudinal heat current into transverse electric current, or vice versa, offers a promising energy harvesting technology. Materials with axis-dependent conduction polarity, known as p × n-type conductors or goniopolar materials, are potential candidate, because the non-zero transverse elements of thermopower tensor appear under rotational operation, though the availability is highly limited. Here, we report that a ternary metal LaPt2B with unique crystal structure exhibits axis-dependent thermopower polarity, which is driven by mixed-dimensional Fermi surfaces consisting of quasi-one-dimensional hole sheet with out-of-plane velocity and quasi-two-dimensional electron sheets with in-plane velocity. The ideal mixed-dimensional conductor LaPt2B exhibits an extremely large transverse Peltier conductivity up to ∣α y x ∣ = 130 A K−1 m−1, and its transverse thermoelectric performance surpasses those of topological magnets utilizing the anomalous Nernst effect. These results thus manifest the mixed-dimensionality as a key property for efficient transverse thermoelectric conversion.

Lifshitz transitions are being increasingly recognized as significant in a wide variety of strongly correlated and topological materials, and understanding the origin and influence of Lifshitz transitions is leading to deeper understanding of key aspects of magnetic, transport, or quantum critical behavior. In the ferromagnetic superconductor UCoGe, a magnetic field applied along the c axis has been shown to induce a series of anomalies in both transport and thermopower that may be caused by Lifshitz transitions. The need to understand the subtleties of the relationship between magnetism, superconductivity and a heavy-electron Fermi surface in the ferromagnetic superconductors makes it important to explore if and why a series of magnetic-field-induced Lifshitz transitions occurs in UCoGe. Here we report magnetic susceptibility measurements of UCoGe, performed at temperatures down to 45 mK and magnetic fields (μ_{0}H||c) up to 30 T. We observe a series of clearly defined features in the susceptibility, and multiple sets of strongly field-dependent de Haas-van Alphen oscillations, from which we extract detailed field dependence of the quasiparticle properties. We complement our experimental results with density functional theory band structure calculations, and include a simple model of the influence of magnetic field on the calculated Fermi surface. By comparing experimental and calculated results, we determine the likely shape of the Fermi surface and identify candidate Lifshitz transitions that could correspond to two of the features in susceptibility. We connect these results to the development of magnetization in the system.

In a magnetic field, superconductivity can be induced or reinforced near a metamagnetic transition, where ferromagnetic fluctuations are suspected to mediate the pairing strength of the Cooper pairs. Here, the authors investigate the superconductor UTe2 and report on the variation in the superconducting properties as the magnetic field is applied along two particular crystallographic axes and their relation to metamagnetism.

The recently discovered superconductor UTe_{2}, with a superconducting transition temperature T_{c} between 1.5 and 2 K, is attracting much attention due to strong suspicion of spin-triplet and topological superconductivity. Its properties under magnetic field are also remarkable, with field-reinforced (H∥b) and field-induced [H in the (b,c) plane] superconducting phases. Here, we report the first complete thermodynamic determination of the phase diagram for fields applied along the three crystallographic directions. For field along the easy a axis, we uncover a strong negative curvature of the upper critical field very close to T_{c}, revealing a strong suppression of the pairing strength at low magnetic fields. By contrast, measurements performed up to 36 T along the hard magnetization b axis confirm a bulk field-reinforced superconducting phase. Most of all, they also reveal the existence of a phase transition line within the superconducting phase. Drastic differences occur between the low-field and high-field phases pointing to different pairing mechanisms. Detailed analysis suggests a possible transition between a low-field spin-triplet to high-field spin-singlet state, a unique case among superconductors.

The strongly-correlated electron system URu2Si2 possesses a hidden-order phase whose order parameter remains unidentified. Here, the authors demonstrate the development of spin-density-wave phases in URu2Si2under high magnetic fields, providing a potential in-road to understanding this system.

Thermoelectric power (S) and Hall effect (R_{H}) measurements on the paramagnetic superconductor UTe_{2} with the magnetic field applied along the hard magnetization b axis are reported. The first-order nature of the metamagnetic transition at H_{m}=H_{c2}^{b}=35 T leads to drastic consequences on S and R_{H}. In contrast to the field dependence of the specific heat in the normal state through H_{m}, S(H) is not symmetric with respect to H_{m}. This implies a strong interplay between ferromagnetic fluctuations and a Fermi-surface reconstruction at H_{m}. R_{H} is very well described by incoherent skew scattering above the coherence temperature T_{m} corresponding roughly to the temperature of the maximum in the susceptibility T_{χ_{max}} and coherent skew scattering at lower temperatures. The discontinuous field dependence of both S(H) and the ordinary Hall coefficient R_{0}, at H_{m} and at low temperature, provides evidence of a change in the band structure at the Fermi level.