We investigate the transport properties of LixCoO2 thin films whose resistivities are nearly an order of magnitude lower than those of the bulk polycrystals. A metal-nonmetal transition occurs at ~0.8 in a biphasic domain, and the Seebeck coefficient (S) is drastically increased at ~140 K (= T*) with increasing the Li concentration to show a peak of magnitude ~120 \muV/K in the S-T curve of x = 0.87. We show that T* corresponds to a crossover temperature in the conduction, most likely reflecting the correlation-induced temperature dependence in the low-energy excitations.
Cd$_3$As$_2$ is one of the prototypical topological Dirac semimetals. Here, we manipulate the band inversion responsible for the emergence of Dirac nodes by alloying Cd$_3$As$_2$ with topologically trivial Zn$_3$As$_2$. We observe the expected topological phase transition around a Zn concentration of $x\sim 1$ while the carrier density monotonically decreases as $x$ is increased. For larger $x$, the thermoelectric figure of merit exhibits comparably large values exceeding 0.3 at room temperature, due to the combined effects of a strong enhancement of the thermopower, an only moderate increase …
Understanding and manipulating properties emerging at a surface or an interface require a thorough knowledge of structure-property relationships. We report a study of a prototype oxide system, La2/3Sr1/3MnO3 grown on SrTiO3(001), by combining in-situ angle-resolved x-ray photoelectron spectroscopy, ex-situ x-ray diffraction, and scanning transmission electron microscopy/spectroscopy with electric transport measurements. We find that La2/3Sr1/3MnO3 films thicker than 20 unit cells (u.c.) exhibit a universal behavior with no more than one u.c. intermixing at the interface but at least 3 u.c. of …
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。
We report a thermal transport study of IrSbSe, which crystallizes in a noncentrosymmetric cubic structure with the $P2_13$ space group and shows a narrow-gap semiconducting behavior. The large discrepancy between the activation energy for conductivity [$E_ρ$ = 128(2) meV] and for thermopower [$E_S$ = 17.7(9) meV] from 200 to 300 K indicates the polaronic transport mechanism. Electrical resistivity varies as $exp(T_0/T)^{1/4}$ and thermopower varies as $T^{1/2}$ at low temperatures, indicating that it evolves into the Mott's variable-range hopping dominant conduction with decreasing temperature…
Analysis on very detailed measurements of resistivity ($ ρ$) and thermoelectric power (S) of magnetic impurity (Co) substituted iron silicide (FeSi) has been presented in this report. The impurity valence electrons of Co dominate the whole physical properties at low temperatures below 35 K, below the critical concentration x$_{c}$. The negative thermopower and the positive slope in the resistivity at low temperatures are exotic and show that the system is not entirely insulator below the critical concentration of MIT (x$_{c}$). So, due to the external impurity electrons, the system's magnetic …
We have investigated the effect of Cu substitution in Eu2(Ir1-xCux)2O7 with the help of magnetic and transport property measurements. XPS measurement reveals that each Cu2+ converts Ir4+ to double amount of Ir5+ ions. The metal-insulator transition temperature (T_MI) is obtained around 120 K. In the insulating phase, at lower temperature below 50 K, the temperature dependent resistivity follows a power law dependence and the magnitude of the exponent increases with Cu concentrations. The temperature dependent thermopower is observed to follow the electrical resistivity down to 50 K, except for…
The transition metal dichalcogenide TiSe$_2$ has received significant research attention over the past four decades. Different studies have presented ways to suppress the 200~K charge density wave transition, vary low temperature resistivity by several orders of magnitude, and stabilize magnetism or superconductivity. Here we give the results of a new synthesis technique whereby samples were grown in a high pressure environment with up to 180~bar of argon gas. Above 100~K, properties are nearly unchanged from previous reports, but a hysteretic resistance region that begins around 80~K, accompa…
Dependence of transport coefficients of the Yb(Rh$_{1-x}$Co$_x$)$_2$Si$_2$ series of alloys on temperature and cobalt concentration is explained by an asymmetric Anderson model which takes into account the exchange scattering of conduction electrons on ytterbium ions and the splitting of 4$f$-states by the crystalline electric field (CEF). The substitution of rhodium by cobalt is described as an increase of chemical pressure which reduces the exchange coupling and the CEF splitting. The scaling analysis and numerical NCA solution of the model show that the effective degeneracy of the 4$f$-stat…
Kondo-hole substitution in heavy fermions: dynamics and transport
近藤空穴替代是研究重费米子材料中相互作用、f-电子稀释和无序相互作用的独特探针。在稀释的周期性安德森模型中，我们研究了单粒子动力学的变化以及响应函数，作为近藤空穴浓度（$x$）和温度的函数。我们发现，由于近藤空穴替代的光谱权重转移具有不同于温度引起的特性;直流电阻率从具有$x\rightarrow 0$极限中的相干峰的高度非单调形式跨越到在低温下饱和的单调单杂质形式。的热功率表现出的特征最大值作为温度的函数，其值的变化与增加$x$的符号，其位置示出对应于系统的低能量尺度。在零温度下，霍尔系数也随着$x$的增加而改变符号，并且对于所有$x$都是高度温度依赖性的。当$x$增大到一定的$x_c$以上时，电导率中的Drude峰和中红外峰几乎完全消失，光散射率中的A峰熔化并最终消失。我们讨论了上述变化的性质的交叉，从相干的，近藤晶格行为的单一杂质一样，不相干的行为与增加$x$。Ce $_{1-x}$ La $_x$ B $_6$的直流电阻率和热电势的理论与实验的比较产生良好的一致性。
