For the thermoelectric properties of NaxCoO2, we analyze the effect of local Coulomb interaction and (disordered) potential differences for Co-sites with adjacent Na-ion or vacancy. The disorder potential alone increases the resistivity and reduces the thermopower, while the Coulomb interaction alone leads only to minor changes compared to the one-particle picture of the local density approximation. Only combined, these two terms give rise to a substantial increase of the thermopower: the number of (quasi-)electrons around the Fermi level is much more suppressed than that of the (quasi-)holes. Hence, there is a particle-hole imbalance acting in the same direction as a similar imbalance for the group velocities. Together, this interplay results in a large positive thermopower. Introducing a thermoelectric spectral density, we located the energies and momenta regions most relevant for the thermopower and changes thereof.
Iron antimonide (FeSb$_2$) is a mysterious material with peculiar colossal thermopower of about $-45$ mV/K at 10 K. However, a unified microscopic description of this phenomenon is far from being achieved. The understanding of the electronic structure in details is crucial in identifying the microscopic mechanism of FeSb$_2$ thermopower. Combining angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations we find that the spectrum of FeSb$_2$ consists of two bands near the Fermi energy: the nondispersive strongly renormalized $α$-band, and the hole-like $β$-band that i…
Thermopower as sensitive probe of electronic nematicity in iron pnictides
本文研究了EuFePDMATHABMM（As $_{1-x}$ P $_{x}$）$_2$退孪晶单晶的热电势和电阻率的面内各向异性。与电阻率各向异性相比，热电势各向异性在远高于结构和磁性相变的温度下更明显并且已经清晰可见。最显著的是，热电势各向异性在结构转变下方改变符号。这是与两个贡献的相互作用，由于各向异性散射和轨道极化，这在高温和低温下分别占主导地位。
We report giant thermopower S = 2.5 mV/K in CoSbS single crystals, a material that shows strong high-temperature thermoelectric performance when doped with Ni or Se. Changes of low temperature thermopower induced by magnetic field point to mechanism of electronic diffusion of carriers in the heavy valence band. Intrinsic magnetic susceptibility is consistent with the Kondo- Insulator-like accumulation of electronic states around the gap edges. This suggests that giant thermopower stems from temperature-dependent renormalization of the non-interacting bands and buildup of the electronic correla…
Paramagnon Heat Capacity and Anomalous Thermopower in Anisotropic Magnetic Systems: Understanding Inter-Layer Spin Correlations in a Magnetically Disordered Phase
Magic-angle twisted bilayer graphene (MtBLG) has proven to be an extremely promising new platform to realize and study a host of emergent quantum phases arising from the strong correlations in its narrow bandwidth flat band. In this regard, thermal transport phenomena like thermopower, in addition to being coveted technologically, is also sensitive to the particle-hole (PH) asymmetry, making it a crucial tool to probe the underlying electronic structure of this material. We have carried out thermopower measurements of MtBLG as a function of carrier density, temperature and magnetic field, and …
Scaling behavior in thermoelectric misfit cobalt oxides
我们研究了失配钴氧化物[Bi $_{1.7}$ Co $_{0.3}$ Ca $_{2}$ O $_{4}$ ] $^{RS}_{0.6}$ CoO $_{2}$的热电和热力学性质。发现一个大的负磁热电势的规模与磁场和温度揭示了显着的自旋熵贡献的热电性能产生一个常数S $_0\approx$ 60 $μ$ V K $^{-1}$等于高温渐近值的自旋1/2熵。低温比热测量使我们能够确定增强的电子部分与$γ\approx$ 50 mJ（摩尔K $^{2}$）$^{-1}$证明强相关性。因此，[Bi $_{1.7}$ Co $_{0.3}$ Ca $_{2}$ O $_{4}$ ] $^{RS}_{0.6}$ CoO $_{2}$、其他钴矿以及其他材料之间的关键比较揭示了作为$γ$的函数的热电低温斜率的普遍行为，从而证明了纯电子起源。这种潜在的通用标度行为表明，在失配钴氧化物的热电势的高室温值的结果从增加的自旋熵的贡献，以扩大电子之一。
International Institute of Physics, Universidade Federal do Rio Grande do Norte（北里奥格兰德联邦大学国际物理研究所）；Departamento de Física, Universidade Federal da Paraíba（帕拉伊巴联邦大学物理系）；Instituto de Física, Universidade Federal do Rio de Janeiro（里约热内卢联邦大学物理研究所）
Confined electrons in low dimensions host desirable material functions for downscaled electronics as well as advanced energy technologies. Thermoelectricity is a most fascinating example, since the dimensionality modifies the electron density of states dramatically, leading to enhanced thermopower as experimentally examined in artificial two-dimensional (2D) structures. However, it is still an open question whether such an enhanced thermopower in low dimensions is realized in layered materials with strong 2D characters such as cuprates. Here, we report unusual enhancement of the thermopower in…
Dirac/Weyl semimetals hosting linearly-dispersing bands have received recent attention for potential thermoelectric applications, since their ultrahigh-mobility carriers could generate large thermoelectric and Nernst power factors. To optimize these efficiencies, the Fermi energy needs to be chemically controlled in a wide range, which is generally difficult in bulk materials because of disorder effects from the substituted ions. Here it is shown that the Fermi energy is tunable across the Dirac point for layered magnet EuMnBi$_2$ by partially substituting Gd$^{3+}$ for Eu$^{2+}$ in the insula…
Exact multi-electronic electron-concentration dependent ground-states for disordered two-dimensional two-band systems in presence of disordered hoppings and finite on-site random interactions
We introduce a computational scheme for calculating the electronic structure of random alloys that includes electronic correlations within the framework of the combined density functional and dynamical mean-field theory. By making use of the particularly simple parameterization of the electron Green's function within the linearized muffin-tin orbitals method, we show that it is possible to greatly simplify the embedding of the self-energy. This in turn facilitates the implementation of the coherent potential approximation, which is used to model the substitutional disorder. The computational t…
We present and discuss an original method to synthesize disordered Nanostructured (NS) VO$_x$ films with controlled stoichiometry and tunable electronic structures. In these NS films, the original lattice symmetry of the bulk vanadium oxides is broken and atoms are arranged in a highly disordered structure . The stoichiometry-dependent disorder as a function of the oxygen concentration has been characterized by in-situ X-ray Absorption Near-Edge Structure (XANES) spectroscopy identifying the spectroscopic fingerprints. Results show structural rearrangements that deviate from the octahedral sym…
