本文采用霍尔效应测量方法研究了两腿梯形化合物Sr_{14-x} Ca_xCu_24O_41（0 <= x <= 11.5）中参与直流输运的载流子数。空穴在梯形子系统和链状子系统之间的分布是理解这些化合物物理的关键问题之一。我们的霍尔效应和电阻率测量显示了x < 11.5时的典型半导体行为。然而，对于x=11.5，结果完全不同，霍尔系数和电阻率行为定性地类似于高温铜氧化物超导体。我们已经确定了在室温下的有效载流子数，并将其与通过其他实验技术获得的梯子中的孔数进行了比较。我们提出，从x=0到x=11.5，每个分子式单元中添加不到1个孔到阶梯，并且负责Ca掺杂的电阻率的显著变化。
英文摘要：
We present Hall-effect measurements of two-leg ladder compounds Sr_{14-x}Ca_xCu_24O_41 (0 <= x <= 11.5) with the aim to determine the number of carriers participating in dc transport. Distribution of holes between the ladder and chain subsystems is one of the crucial questions important for understanding the physics of these compounds. Our Hall effect and resistivity measurements show typical semiconducting behavior for x < 11.5. However, for x=11.5, the results are completely different, and the Hall coefficient and resistivity behavior is qualitatively similar to that of high temperature copper-oxide superconductors. We have determined the effective number of carriers at room temperature and compared it to the number of holes in the ladders obtained by other experimental techniques. We propose that going from x=0 to x=11.5 less than 1 hole per formula unit is added to the ladders and is responsible for a pronounced change in resistivity with Ca doping.
We present experimental results for the in-plane resistivity of the electron-doped cuprate superconductor $La_{2-x}Ce_xCuO_4$ above its transition temperature $T_c$ as a function of Ce doping x and temperature. For the doping x between 0.11 and 0.17, where $T_c$ varies from 30 K (x=0.11) to 5 K (x=0.17), we find that the resistivity shows an approximate $T^2$ behavior for all values of doping over the measurement range from 100 K to 400 K. The coefficient of the $T^2$ resistivity term decreases with increasing x following the trend in $T_c$. We analyze our data theoretically and posit that n-t…
Cu Nuclear Quadrupole Resonance Study of La_{2-x}Sr_xCu_{1-y}Zn_yO_4 (x=0.10, 0.15 and 0.20): Zn-induced Wipeout Effect near the Magnetic and Electric Instability
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…
Hole superconductivity in the electron-doped superconductor PCCO
我们测量了电子掺杂超导体Pr_{2-x} Ce_xCuO_4的电阻率和霍尔角随掺杂和温度的变化。温度为100 K < T <300 K时的电阻率Rho_xx对电子最为敏感。它的温度行为在很宽的掺杂范围内与掺杂无关，甚至对非超导样品也是如此。另一方面，横向电阻率rho_xy或霍尔角θ_H（其中cot（θ_H）= rho_xx/rho_xy）对空穴和电子都敏感。它的温度依赖性受到掺杂的强烈影响，并且cot（theta_H）可以用于识别最佳掺杂（最大Tc），甚至远高于临界温度。这些结果表明，在电子掺杂的铜氧化物中，空穴是超导电性的主要来源。
We present a study of Cu-substitution effects in 4f-Ce intermetallic compound CeAu1-xCuxGe, with potentially unusual electronic states, in the whole concentration range (x = 0.0 - 1.0). The parent CeAuGe compound, crystallizing in a non-centrosymmetric hexagonal structure, is a ferromagnetic semimetal with Curie temperature 10 K. Cu-doping on Au-site of CeAuGe, CeAu1-xCuxGe, changes the crystal structure from the non-centrosymmetric (P63mc) to centrosymmetric (P63/mmc) space group at the concentration x ~ 0.5, where the c-lattice constant has a maximum value. Magnetic susceptibility and electr…
A unique property of a dynamically generated quantum spin Hall state are Goldstone modes that correspond to the long-wavelength fluctuations of the spin-orbit coupling order parameter whose topological Skyrmion excitations carry charge 2$e$. Within the model considered here, upon varying the chemical potential, we observe two transitions: An s-wave superconducting order parameter develops at a critical chemical potential $μ_{c1}$, corresponding to the excitation gap of pairs of fermions, and at $μ_{c2}$ the SO(3) order parameter of the quantum spin Hall state vanishes. Using negative-sign-free…
We present theoretical analysis of Hall effect in doped Mott-Hubbard insulator, considered as a prototype of cuprate superconductor. We consider the standard Hubbard model within DMFT approximation. As a typical case we consider the partially filled (hole doping) lower Hubbard band. We calculate the doping dependence of both the Hall coefficient and Hall number and determine the value of carrier concentration, where Hall effect changes its sign. We obtain a significant dependence of Hall effect parameters on temperature. Disorder effects are taken into account in a qualitative way.We also perf…
Carrier-doping effect and anomalous transport properties in Ni-doped CeCoIn5 investigated by Hall resistivity measurements
College of Science, Ibaraki University（茨城大学理学部）；Institute for Solid State Physics, The University of Tokyo（东京大学固体物理研究所）；Institute for Materials Research, Tohoku University（东北大学材料科学高等研究所）；Faculty of Education, Shinshu University（信州大学教育学部）
In the framework of dynamical mean field theory (DMFT) we analyze Hall effect in doped Mott insulator as a parent cuprate superconductor. We consider the partial filling (hole doping) of the lower Hubbard band and calculate the dependence of Hall coefficient and Hall number on hole doping, determining the critical concentration for sign change of the Hall coefficient. Significant temperature dependence of Hall effect is noted. A good agreement is demonstrated with concentration dependence of Hall number obtained in experiments in the normal state of YBCO.
Since its experimental discovery, many phenomenological theories successfully reproduced the rapid rise from $p$ to $1+p$ found in the Hall number $n_H$ at the critical doping $p^*$ of the pseudogap in superconducting cuprates. Further comparison with experiments is now needed in order to narrow down candidates. In this paper, we consider three previously successful phenomenological theories in a unified formalism---an antiferromagnetic mean field (AF), a spiral incommensurate antiferromagnetic mean field (sAF), and the Yang-Rice-Zhang (YRZ) theory. We find a rapid rise in the specific heat an…
Thermal Hall conductivity of electron-doped cuprates: Electrons and phonons
Université de Sherbrooke（舍布鲁克大学）；Univ. Grenoble Alpes（格勒诺布尔阿尔卑斯大学）；Univ. Toulouse（图卢兹大学）；INSA-T（图卢兹国立应用科学学院）；École Polytechnique（巴黎综合理工学院）；Institut Polytechnique de Paris（巴黎理工学院）；Stanford University（斯坦福大学）；SLAC National Accelerator Laboratory（斯坦福线性加速器中心）
Doping-Driven Collapse of the SDW Correlation Gap in SmFeAsO$_{1-x}$F$_{x}$
我们报告的霍尔电阻率，$ρ_{xy}$的多晶SmFeAsO $_{1-x}$ F $_{x}$为四个不同的氟浓度从超导性的开始，通过崩溃的结构相变。对于两个更高掺杂的样品，$ρ_{xy}$在高达50 T的磁场中是线性的，仅具有弱的温度依赖性，使人联想到简单的费米液体。对于轻掺杂的$x<0.15$样品，我们发现了一个低温区，其特征在于$ρ_{xy}(H)$在磁场中是非线性的，并且即使霍尔角很小也具有很强的温度依赖性。这种非线性制度的起始温度在结构相（SPT）/自旋密度波（SDW）转变附近。的霍尔电阻率的温度依赖性是一致的热激活的载流子跨越能隙。报道了能隙随掺杂的演化。
Two-dimensional (2D) van der Waals (vdW) magnetic materials have attracted a lot of attention owing to the stabilization of long-range magnetic order down to atomic dimensions, and the prospect of novel spintronic devices with unique functionalities. The clarification of the magnetoresistive properties and its correlation to the underlying magnetic configurations is essential for 2D vdW-based spintronic devices. Here, the effect of Co-doping on the magnetic and magnetotransport properties of Fe3GeTe2 have been investigated. Magnetotransport measurements reveal an unusual Hall effect behavior w…
We point out that there are two different chiral spin liquid states on the triangular lattice and discuss the conducting states that are expected on doping them. These states labeled CS1 and CS2 are associated with two distinct topological orders with different edge states, although they both spontaneously break time reversal symmetry and exhibit the same quantized spin Hall conductance. While CSL1 is related to the Kalmeyer-Laughlin state, CSL2 is the $ν=4$ member of Kitaev's 16 fold way classification. Both states are described within the Abrikosov fermion representation of spins, and the ef…
Evolution of transport properties of BaFe2-xRuxAs2 in a wide range of isovalent Ru substitution
通过测量高质量BaFe_（2-x）Ru_xAs_2单晶的电阻率和霍耳系数，研究了在较宽掺杂范围内（0 < x < 1.4），Ru在Fe位上的等效替代效应。Ru取代削弱了反铁磁（AFM）序，对于0.4 < x < 0.9的相对高的掺杂水平诱导超导性。在AFM相边界附近，输运性质表现为非费米液体性质，电阻率随温度呈线性变化，霍尔系数随温度呈强的温度依赖性，并随温度变化而变化.然而，在更高的掺杂，他们都恢复传统的费米液体行为。强掺杂的霍尔系数的依赖性与一个小的磁阻表明，异常的传输特性可以解释在各向异性载流子散射由于带间AFM波动，而不是一个传统的多带的情况。
The presence of incommensurate spiral spin-density waves (SDW) has been proposed to explain the $p$ (hole doping) to $1+p$ jump measured in the Hall number $n_H$ at a doping $p^*$. Here we explore {\it collinear} incommensurate SDW as another possible explanation of this phenomenon, distinct from the incommensurate {\it spiral} SDW proposal. We examine the effect of different SDW strengths and wavevectors and we find that the $n_H\sim p$ behavior is hardly reproduced at low doping. The calculated $n_H$ and Fermi surfaces give characteristic features that should be observed, thus the lack of th…
We study possible Weyl semimetals of strongly-correlated electrons by investigating magnetotransport properties in pyrochlore R2Ir2O7 (R=rare-earth ions), choosing three types of R ions to design the exchange coupling scheme between R 4f and Ir 5d moments; non-magnetic Eu (4f6), isotropic Gd (4f7), and anisotropic Tb (4f8). In the doping-induced semimetallic state, distinctive features of magnetoresistance and Hall effect are observed in R=Gd and Tb compounds due to the effects of the exchange-enhanced isotropic and anisotropic Zeeman fields, respectively, exemplifying the double Weyl semimeta…
It is widely recognised that the effect of doping into a Mott insulator is complicated and unpredictable, as can be seen by examining the Hall coefficient in high $T_{\rm c}$ cuprates. The doping effect, including the electron-hole doping asymmetry, may be more straightforward in doped organic Mott insulators owing to their simple electronic structures. Here we investigate the doping asymmetry of an organic Mott insulator by carrying out electric-double-layer transistor measurements and using cluster perturbation theory. The calculations predict that strongly anisotropic suppression of the spe…
Magnetic topological materials, in which strong correlations between magnetic and electronic properties of matter, give rise to various exotic phenomena such as anomalous Hall effect (AHE), topological Hall effect (THE), and skyrmion lattice. Here, we report on the electronic, magnetic, and topological properties of Mn$_{3-\it{x}}$Fe$_{\it{x}}$Sn single crystals ($\it{x}$=0, 0.25, and 0.35). Low temperature magnetic properties have been significantly changed with Fe doping. Most importantly, we observe that large uniaxial magnetocrystalline anisotropy that is induced by the Fe doping in combin…
Two-dimensional (2D) van der Waals (vdW) magnetic materials have garnered considerable attention owing to the existence of magnetic order down to atomic dimensions and flexibility towards interface engineering, offering an attractive platform to explore novel spintronic phenomena and functionalities. Understanding of the magnetoresistive properties and their correlation to the underlying magnetic configurations is essential for 2D vdW-based spintronic or quantum information devices. Among the promising candidates, vdW ferromagnet (FM) Fe3GeTe2 shows an unusual magnetotransport behavior, tunabl…
Using first-principles calculation methods, we reveal a series of phase transitions as a function of electron doping in single-layer 1T$'$-MoTe$_2$ and 1T$'$-WTe$_2$ exhibiting quantum spin Hall (QSH) edge states without doping. As increasing doping, we show that a phonon mediated superconducting phase first realizes and is followed by a charge density wave (CDW) phase with a nonsymmorphic lattice symmetry. The newly found CDW phase exhibits Dirac or Weyl energy bands with a spin-orbit coupling in case of a fractional band filling and re-enters into topological insulating phase with fully fill…
