Certain classes of strongly correlated systems promise high thermopower efficiency, but a full understanding of correlation effects on the Seebeck coefficient is lacking. This is partly due to limitations of Boltzmann-type approaches. One needs a formula for the thermopower that allows separate investigations of the kinetic and potential energy contributions to the evolution with temperature and doping of the thermopower. Here we address this issue by deriving for Hubbard-like interactions a formula for the thermopower that separates the potential from the kinetic energy contribution and facilitates a better understanding of correlation effects on the Seebeck coefficient. As an example, the thermopower of the one-band Hubbard model is calculated from dynamical mean-field. For interactions in both the intermediate and strong correlation limit, the contributions from kinetic and potential energy nearly cancel.
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…
Relationship between the thermopower and entropy of strongly correlated electron systems
最近的一些实验报道了强关联电子系统的低温热电势$α$和比热系数$γ=C_V/T$。用输运方程描述热电偶中的电荷和热输运，并假定电荷电流密度和热电流密度与载流子数密度成正比，得到了一个简单的平均场关系式，即$α$与载流子熵密度$\cal S$之间的关系式.我们讨论这个平均场公式的修正，并使用周期性安德森和Falicov-Kimball模型的结果来解释EuCu $_2$（Ge $_{1-x}$ Si $_x$）$_2$，CePt $_{1-x}$ Ni $_x$和Yb In $_{1-x}$ Ag ${_x}$ Cu $_4$金属间化合物中$α/γT$的浓度（化学压力）和温度依赖性。我们还表明，使用“穷人的映射”，它近似的周期性安德森晶格的单杂质安德森模型，似乎复杂的行为$α(T)$可以解释在简单的条款和温度依赖性的$α(T)$在每个掺杂水平是一致的4{ \it f}离子的磁性。
Signatures of the Kondo effect in the electrical conductance of strongly correlated quantum dots are well understood both experimentally and theoretically, while those in the thermopower have been the subject of recent interest. Here, we extend theoretical work [T. A. Costi, Phys. Rev. B {\bf 100}, 161106(R) (2019)] on the field-dependent thermopower of such systems, and carry out calculations in order to address a recent experiment on the field dependent thermoelectric response of Kondo-correlated quantum dots [A. Svilans {\em et al.,} Phys. Rev. Lett. {\bf 121}, 206801 (2018)]. In addition t…
Recent experiments have measured the signatures of the Kondo effect in the zero-field thermopower of strongly correlated quantum dots [Svilans {\em et al.,} Phys. Rev. Lett. {\bf 121}, 206801 (2018); Dutta {\em et al.,} Nano Lett. {\bf 19}, 506 (2019)]. They confirm the predicted Kondo-induced sign change in the thermopower, upon increasing the temperature through a gate-voltage dependent value $T_{1}\gtrsim T_{\rm K}$, where $T_{\rm K}$ is the Kondo temperature. Here, we use the numerical renormalization group (NRG) method to investigate the effect of a finite magnetic field $B$ on the thermo…
Energy scales of Lu(1-x)Yb(x)Rh2Si2 by means of thermopower investigations
本文给出了Lu（1-x）Yb（x）Rh_2Si_2在3 K < T < 300 K温度范围内的热电势S（T）和电阻率ρ（T）。发现S（T）从稀体系（x < 0.5）的两个极小值变为纯YbRh_2Si_2中的一个大的极小值。对于磁对电阻率rho_mag（T）的贡献也发现了类似的行为。S（T）和rho_mag（T）中低温极值的出现是由于近藤尺度随x减小而降低。推导了近藤效应和晶体电场分裂的特征能量尺度的演化规律。外推法可以估计YbRh_2Si_2的近藤温度为29 K。
We investigated the effect of pressure on the magnetic and thermoelectric properties of Sr$_{3.1}$Y$_{0.9}$Co$_{4}$O$_{10+δ}$. The magnetization is reduced with the application of pressure, reflecting the spin-state modification of the Co$^{3+}$ ions into the nonmagnetic low-spin state. Accordingly, with increasing pressure, the Seebeck coefficient is enhanced, especially at low temperatures, at which the effect of pressure on the spin state becomes significant. These results indicate that the spin-orbital entropy is a key valuable for the thermoelectric properties of the strongly correlated c…
Nernst Effect as a Probe of Local Kondo Scattering in Heavy Fermions
CeCu $_2$ Si $_2$和Ce $_{0.8}$ La $_{0.2}$ Cu $_2$ Si $_2$在$T$ = 2 K和300 K之间观察到大的、强烈温度依赖性的能斯特系数$ν$。增强的$ν(T)$由现场近藤（传导电子$-4f$电子）散射速率的不对称性决定。考虑到测得的霍尔迁移率，$μ_H$，这些系统的高度不寻常的热电势，$S$，可以半定量地描述为$S(T)$ $=$ $-$ $ν(T)/μ_H(T)$，这明确表明，热电势起源于本地近藤散射过程在很宽的温度范围内从远高于低于相干温度（$\approx$ 20 K的CeCu $_2$ Si $_2$）。我们的结果表明，能斯特效应可以作为一个适当的探针的本地电荷载流子散射。这对探索适合于潜在应用的相关材料中的非常规热电势增强具有重要意义。
Upon chemical substitution of oxygen with fluor, LaMnAsO has been electron-doped in experiments, resulting in samples with remarkably high Seebeck coefficients of around -300$μVK^{-1}$ at room temperature and 3% doping. Within the framework of density functional theory plus dynamical mean-field theory we are not only able to reproduce these experimental observations, but can also provide a thorough investigation of the underlying mechanisms. By considering electronic correlations in the half-filled Mn-3d shells, we trace the high Seebeck coefficient back to an asymmetry in the spectral functio…
An important role of temperature dependent scattering time in understanding the high temperature thermoelectric behavior of strongly correlated system: La$_{0.75}$Ba$_{0.25}$CoO$_{3}$
The electronic band structure of correlated Ca3Ru2O7 featuring an antiferromagnetic as well as a structural transition has been determined theoretically at high temperatures, which has led to the understanding of the remarkable properties of Ca3Ru2O7 such as the bulk spin valve effects. However, its band structure and Fermi surface (FS) below the structural transition have not been resolved even though a FS consisting of electron pockets was found experimentally. Here we report magneto electrical transport and thermoelectric measurements with the electric current and temper- ature gradient dir…
We theoretically study the nonequilibrium thermoelectric transport properties of a strongly-correlated molecule (or quantum dot) embedded in a tunnel junction. Assuming that the coupling of the molecule to the contacts is asymmetric, we determine the nonlinear current driven by the voltage and temperature gradients by using the perturbation theory. However, the subsystem consisting of the molecule strongly coupled to one of the contacts is solved by using the numerical renormalization group method, which allows for accurate description of Kondo correlations. We study the temperature gradient a…
We review many-body effects, their microscopic origin, as well as their impact onto thermoelectricity in correlated narrow-gap semiconductors. Members of this class---such as FeSi and FeSb$_2$---display an unusual temperature dependence in various observables: insulating with large thermopowers at low temperatures, they turn bad metals at temperatures much smaller than the size of their gaps. This insulator-to-metal crossover is accompanied by spectral weight-transfers over large energies in the optical conductivity and by a gradual transition from activated to Curie-Weiss-like behaviour in th…
Phase Separation in the Two-Dimensional Systems of Strongly Correlated electrons; the Role of Spin Singlet Pairs on Hole Pairing Contribution to Hole-rich Phase
