Kohler's Rule Research Articles

Unconventional − Log T Dependent Resistivity in SmxLa1−xTa2Al20

We have succeeded in growing SmxLa1-xTa2Al20 single-crystals, and performed electronic transport measurements to investigate the characteristic features of conduction electron scattering relevant to the field-insensitive – logT dependence of the resistivity. We have found that the – logT dependence of the resistivity remains in a Sm-dilute compound with x = 0.01. This finding provides clear evidence for that the – logT dependence is caused by a local single-ion Kondo effect. We have measured magnetoresistance (MR) of SmTa2Al20 up to 14 T and confirmed that the positive MR continues to develop with decreasing temperature even at 0.5K, evidencing a large deviation from Kohler's rule. This fact indicates that strong wave-vector dependence of conduction-electron scattering by 4f electrons still remains at 0.5K in the magnetically ordered state.

Magnetoresistance of Au films

Classical magnetoresistance (MR) in nonmagnetic metals are conventionally understood in terms of the Kohler rule, with violation usually viewed as anomalous electron transport, in particular, as evidence of non-Fermi liquid behavior. Measurement of the MR of Au films as a function of temperature and film thickness reveals a strong dependence on grain size distribution and clear violation of the Kohler rule. Using a model of random resistor network, we show that this result can be explained if the MR arises entirely from inhomogeneity due to grain boundary scattering and thermal activation of grain boundary atoms. Consequently, the Kohler rule should not be used to distinguish normal and anomalous electron transport in solids.

Ultrahigh mobility and giant magnetoresistance in the Dirac semimetalCd3As2.

Dirac and Weyl semimetals are 3D analogues of graphene in which crystalline symmetry protects the nodes against gap formation. Na3Bi and Cd3As2 were predicted to be Dirac semimetals, and recently confirmed to be so by photoemission experiments. Several novel transport properties in a magnetic field have been proposed for Dirac semimetals. Here, we report a property of Cd3As2 that was unpredicted, namely a remarkable protection mechanism that strongly suppresses backscattering in zero magnetic field. In single crystals, the protection results in ultrahigh mobility, 9 × 10(6) cm(2) V(-1) s(-1) at 5 K. Suppression of backscattering results in a transport lifetime 10(4) times longer than the quantum lifetime. The lifting of this protection by the applied magnetic field leads to a very large magnetoresistance. We discuss how this may relate to changes to the Fermi surface induced by the applied magnetic field.

In-Plane Magnetoresistance Obeys Kohler’s Rule in the Pseudogap Phase of Cuprate Superconductors

We report in-plane resistivity (ρ) and transverse magnetoresistance (MR) measurements for underdoped HgBa(2)CuO(4+δ) (Hg1201). Contrary to the long-standing view that Kohler's rule is strongly violated in underdoped cuprates, we find that it is in fact satisfied in the pseudogap phase of Hg1201. The transverse MR shows a quadratic field dependence, δρ/ρ(0)=aH(2), with a(T)∝T(-4). In combination with the observed ρ∝T(2) dependence, this is consistent with a single Fermi-liquid quasiparticle scattering rate. We show that this behavior is typically masked in cuprates with lower structural symmetry or strong disorder effects.

Strong and nonmonotonic temperature dependence of Hall coefficient in superconductingKxFe2−ySe2single crystals

In-plane resistivity, magnetoresistance, and Hall-effect measurements have been conducted on quenched ${\text{K}}_{x}{\text{Fe}}_{2\ensuremath{-}y}{\text{Se}}_{2}$ single crystals in order to analyze the normal-state transport properties. It is found that Kohler's rule is well obeyed below about 80 K, but clearly violated above 80 K. Measurements of the Hall coefficient reveal a strong but nonmonotonic temperature dependence with a maximum at about 80 K, in contrast to any other FeAs-based superconductors. With the two-band model analysis on the Hall coefficient, we conclude that a gap may open below 65 K. The data above 65 K are interpreted as a temperature-induced crossover from a metallic state at a low temperature to an orbital-selective Mott phase at a high temperature. This is consistent with the recent data of angle-resolved photoemission spectroscopy. These results call for a refined theoretical understanding, especially when the hole pockets are absent or become trivial in ${\text{K}}_{x}{\text{Fe}}_{2\ensuremath{-}y}{\text{Se}}_{2}$ superconductors.

Investigations on pseudogap semimetal CoSi

The theoretically proposed pseudogap semimetal CoSi has been investigated by detailed experimental studies of magnetotransport, calorimetric and thermopower measurements. The two parallel resistor model is applied to understand its semimetal nature. The obtained gap is around 13 meV. The conduction process is explained by the single relaxation method by implementing Kohler's rule, , . The excess heat capacity is a consequence of thermally activated behaviour across the gap and the calculated is about . At K, the metallic behaviour without the gap, vanishing of excess heat capacity, reasonable metallic value of and linear diffusion thermopower, signifies the closure of pseudogap. The correlation amongst the T-dependent features of resistivity, excess heat capacity and thermoelectric power reveals the hidden metal-to-insulator transition in CoSi. The high magnetoresistance at low temperatures is reported to arise due to Lorentz force and its applications as a low temperature magnetic field sensor is also discussed.

Geometric factors in the magnetoresistance of n-doped InAs epilayers

We investigate the magnetoresistance (MR) effect in n-doped InAs and InAs/metal hybrid devices with geometries tailored to elucidate the physical mechanism and the role of geometry in the MR. Despite the isotropic Fermi surface in InAs, we observe a strong intrinsic MR in the InAs epilayer due to the existence of a surface conducting layer. Experimental comparison confirms that the extraordinary MR in the InAs/metal hybrids outperforms the orbital MR in the Corbino disk in terms of both the MR ratio and the magnetic field resolution. The results also indicate the advantage of a two-contact configuration in the hybrid devices over a four-contact one with respect to the magnetic field resolution. This is in contrast to previously reported results, where performance was evaluated in terms of the MR ratio and a four-contact configuration was found to be optimal. By applying Kohler's rule, we find that at temperatures above 75 K the extraordinary MR violates Kohler's rule, due to multiple relaxation rates, whereas the orbital MR obeys it. This finding can be used to distinguish the two geometric effects, the extraordinary MR and the orbital MR, from each other.

Longitudinal and transverse Hall resistivities in NaFe1−xCoxAs single crystals with x = 0.022 and 0.0205: weak pinning and anomalous electrical transport properties

The in-plane longitudinal and Hall resistivities, ρxx and ρxy, of superconducting NaFe1−xCoxAs (NFCA) single crystals with x = 0.022 and 0.0205 in the mixed state and the normal state were measured to study the electrical transport properties in nearly optimum-doping iron-based superconductors. The resistivities under magnetic fields show thermally activated behavior and a power law magnetic field dependence of activation energy has been obtained. Due to the weak flux pinning, there is no sign reversal of Hall resistivities observed for NFCA with either x = 0.022 or 0.0205. The correlation between longitudinal and Hall resistivities shows that the scaling behavior of |ρxy| ∝ (ρxx)β with the exponent β ≈ 2.0 is in agreement with theoretical predictions for weak-pinning superconductors. Anisotropic upper critical fields and coherence lengths with an anisotropy ratio of γ ≈ 1.63 have been deduced. Furthermore, the normal-state transport properties show that the anomalies of the linear-T resistivity, the T2-dependent cotangent of the Hall angle, the linear-T-like Hall number, and the magnetoresistance, which can be scaled by the modified Kohler rule, are analogous to those observed on optimally doped high-Tc superconducting cuprates and other pnictides. The longitudinal resistivity can be understood within a widely accepted scenario of the spin density-wave quantum critical point, while the transverse resistivity requires some further explanation. It is suggested that all the transport anomalies should be simultaneously taken into account when developing theory.

The magnetotransport properties of the intermetallic compound GdCu6

We have studied the temperature and magnetic field dependence of the electrical resistivity of GdCu6 and have co-related the results with the temperature dependence of heat capacity and magnetization. The magnetoresistance of GdCu6 is found to be positive both in the paramagnetic and antiferromagnetic regimes. Within the antiferromagnetic regime, the magnetoresistance is very high and increases to still higher values both with increasing field and decreasing temperature. In the paramagnetic regime the magnetoresistance continues to exhibit a finite positive value up to temperatures much higher than that corresponding to the antiferromagnetic to paramagnetic phase transition. We have shown through quantitative analysis that both the temperature dependences of resistivity and heat capacity indicate the presence of spin fluctuations within the paramagnetic regime of GdCu6. The field dependence of electrical resistivity indicates that the positive magnetoresistance in the paramagnetic phase is not related to the orbital motion of the conduction electrons in a magnetic field (the Kohler rule). In contrast, our analysis indicates that these spin fluctuations are responsible for the positive magnetoresistance observed within this paramagnetic regime. The nature of the field dependence of electrical resistivity is found to be qualitatively similar both in the antiferromagnetic and paramagnetic regimes, which probably indicates that spin fluctuations in the paramagnetic regime are of the antiferromagnetic type.

Magnetic field effects on transport properties of PtSn4

The anisotropic physical properties of single crystals of orthorhombic PtSn4 are reported for magnetic fields up to 140 kOe, applied parallel and perpendicular to the crystallographic b-axis. The magnetic susceptibility has an approximately temperature independent behavior and reveals an anisotropy between ac-plane and b-axis. Clear de Haas-van Alphen oscillations in fields as low as 5 kOe and at temperatures as high as 30 K were detected in magnetization isotherms. The thermoelectric power and resistivity of PtSn4 show the strong temperature and magnetic field dependencies. A change of the thermoelectric power at H = 140 kOe is observed as high as ~ 50 mu-V/K. Single crystals of PtSn4 exhibit very large transverse magnetoresistance of ~ 5x10^5% for the ac-plane and of ~ 1.4x10^5% for the b-axis resistivity at 1.8 K and 140 kOe, as well as pronounced Shubnikov-de Haas oscillations. The magnetoresistance of PtSn4 appears to obey Kohler's rule in the temperature and field range measured. The Hall resistivity shows a linear temperature dependence at high temperatures followed by a sign reversal around 25 K which is consistent with thermoelectric power measurements. The observed quantum oscillations and band structure calculations indicate that PtSn4 has three dimensional Fermi surfaces.

Multiband conduction in the type-I clathrate Ba8Ge43□3

Hall effect and magnetoresistance measurements were carried out on a single-phase polycrystalline sample of the type-I clathrate Ba${}_{8}$Ge${}_{43}$\ensuremath{\square}${}_{3}$ in the 2--350 K temperature range. These experiments were complemented by electronic band structure and Fermi surface calculations performed by an all-electron, full potential first-principles method. These calculations have revealed the presence of three pieces of the Fermi surface originating from both holelike and electronlike bands crossing the Fermi level suggesting that both types of carriers play a role in the electrical conduction of this material. These results were experimentally confirmed via a strongly temperature-dependent and dominant holelike signal in the Hall coefficient and a breakdown of Kohler's rule in the magnetoresistance data. We analyze the Hall coefficient and magnetoresistance data within the framework of a two-band model with temperature-dependent carrier concentrations and mobilities and discuss its limits in capturing the essential features governing the magnetotransport. Combined with the temperature dependences of the thermopower and the electrical resistivity, all these results suggest that Ba${}_{8}$Ge${}_{43}$\ensuremath{\square}${}_{3}$ can be classified as a nearly compensated semimetal.

Multiband effect in the noncentrosymmetric superconductorsMg12−δIr19B16revealed by Hall effect and magnetoresistance measurements

We report the longitudinal resistivity and Hall effect measurements on the noncentrosymmetric superconducting ${\text{Mg}}_{12\ensuremath{-}\ensuremath{\delta}}{\text{Ir}}_{19}{\text{B}}_{16}$ samples with different critical transition temperatures. A strong temperature dependence of the Hall coefficient ${R}_{H}$ and nonlinear magnetic field dependence of the Hall resistivity ${\ensuremath{\rho}}_{xy}$ in wide temperature region are observed, suggesting a strong multiband effect in this system. Moreover, a large magnetoresistance up to 20% is found at the field of 9 T. We also observe the violation of the Kohler's rule from our magnetoresistance data, further confirming the presence of multiband effect in our samples. A detailed analysis shows that the data cannot be simply described within the two-band scenario at low temperatures so we argue that there may be more than two bands contributing to the conduction of the samples.

Angular Dependence of the Magnetoresistance of the SrTiO$_{3}$/LaAlO$_{3}$ Interface

We study the magnetoresistance (MR) of the quasi-2-D electron liquid at the interface that forms between SrTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> as a function of the magnitude and orientation of the magnetic field. We find that at T ¿ 60 K, the MR is described by a + b cos <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ¿ + c sin <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ¿ cos <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ¿, where ¿ is the angle between the field and the film normal and ¿ is the angle between the in-plane component of the field and the current. For ¿ = 0° (field perpendicular to the plane), we show that the MR obeys Kohler's rule while for ¿ = 90° (field in the plane) the MR is significantly smaller, and it is almost temperature independent, suggesting it is dominated by interface scattering.

Evolution from non-Fermi- to Fermi-liquid transport via isovalent doping inBaFe2(As1−xPx)2superconductors

The normal-state charge transport is studied systematically in high-quality single crystals of ${\text{BaFe}}_{2}{({\text{As}}_{1\ensuremath{-}x}{\text{P}}_{x})}_{2}$ $(0\ensuremath{\le}x\ensuremath{\le}0.71)$. By substituting isovalent P for As, the spin-density-wave (SDW) state is suppressed and the dome-shaped superconducting phase $({T}_{c}\ensuremath{\lesssim}31\text{ }\text{K})$ appears. Near the SDW end point $(x\ensuremath{\approx}0.3)$, we observe striking linear temperature $(T)$ dependence of resistivity in a wide $T$ range, and remarkable low-$T$ enhancement of Hall-coefficient magnitude from the carrier number estimates. We also find that the magnetoresistance apparently violates the Kohler's rule and is well scaled by the Hall angle ${\ensuremath{\Theta}}_{H}$ as $\ensuremath{\Delta}{\ensuremath{\rho}}_{xx}/{\ensuremath{\rho}}_{xx}\ensuremath{\propto}{\text{tan}}^{2}\text{ }{\ensuremath{\Theta}}_{H}$. These non-Fermi-liquid transport anomalies cannot be attributed to the simple multiband effects. These results capture universal features of correlated electron systems in the presence of strong antiferromagnetic fluctuations.

Magnetic and transport properties in Ba1−xSrxRuO3 single crystals

We have investigated the magnetic and the electrical transport properties in Ba1−xSrxRuO3 single crystals. In BaRuO3, which has a nine-layer rhombohedral (9R) structure, the magnetic susceptibility has two components; a Curie-Weiss component (χcw) and a Pauli paramagnetic-like one (χpp). χpp(T) increases monotonically with increasing temperature up to 400 K, suggesting an exchange enhanced Pauli paramagnetism by the spin fluctuation. The temperature dependence of the resistivity (ρ) shows a minimum around 130 K. In the whole temperature region, the positive magnetoresistance was observed, which cannot be scaled by Kohler rule. The Hall resistivity (ρH) is positive and decreases with increasing temperature. In Ba0.7Sr0.3RuO3, which has a four-layer hexagonal (4H) structure, the increment of χpp(T) above ~100 K and the minimum of ρ(T) were not observed, though χcw(T) is almost the same as that of 9R BaRuO3. The magnetoresistance was negative suggesting the suppression of the spin fluctuation scattering of the conduction electrons. ρH is negative at low temperatures, and changes its sign around 100 K. We infer that the difference of the Fermi surface resulting from the different layered-structure yields the distinct magnetic and transport properties.

Sr3Sc2Fe2As2O5as a possible parent compound for FeAs-based superconductors

A compound with the FeAs-layers, namely, $({\text{Sr}}_{3}{\text{Sc}}_{2}{\text{O}}_{5}){\text{Fe}}_{2}{\text{As}}_{2}$ (abbreviated as FeAs-32522), was successfully fabricated. It has a layered structure with the space group of $I4/mmm$, and with the lattice constants $a=4.069\text{ }\text{\AA{}}$ and $c=26.876\text{ }\text{\AA{}}$. The in-plane Fe ions construct a square lattice which is close to that of other FeAs-based superconductors, such as REFeAsO ($\text{RE}=\text{rare}$ earth elements) and $(\text{Ba},\text{Sr}){\text{Fe}}_{2}{\text{As}}_{2}$. However the inter-FeAs-layer spacing in the compound is greatly enlarged. The temperature dependence of resistivity exhibits a weak upturn in the low-temperature region, but a metallic behavior was observed above about 60 K. The magnetic susceptibility shows also a nonmonotonic behavior. Interestingly, the well-known resistivity anomaly which was discovered in all other parent compounds, such as REFeAsO, $(\text{Ba},\text{Sr}){\text{Fe}}_{2}{\text{As}}_{2}$ and (Sr,Ca,Eu)FeAsF and associated with the spin-density wave/structural transition has not been found in the new system either on the resistivity data or the magnetization data. This could be induced by the large spacing distance between the FeAs-planes, therefore the antiferromagnetic correlation between the moments of Fe ions in neighboring FeAs layers cannot be established. Alternatively it can also be attributed to the self-doping effect between Fe and Sc ions. The Hall coefficient ${R}_{H}$ is negative but strongly temperature dependent in wide temperature region, which indicates the dominance of electrical conduction by electronlike charge carriers and probably a multiband effect or a spin related scattering effect. It is found that the magnetoresistance cannot be described by Kohler's rule, which gives further support to above arguments.

Magnetoresistance and Hall effect of the complex metal alloyMg2Al3

Unusual electronic transport properties have been found in the rhombohedral ${\ensuremath{\beta}}^{\ensuremath{'}}$-phase of the complex metallic alloy ${\text{Mg}}_{2}{\text{Al}}_{3}$. The magnetoresistance (MR) is 2 orders of magnitude larger than in the related cubic $\ensuremath{\beta}\ensuremath{-}{\text{Mg}}_{2}{\text{Al}}_{3}$-phase and Kohler's rule is strongly violated in the ${\ensuremath{\beta}}^{\ensuremath{'}}$-phase at higher temperatures. Above about 100 K the Hall coefficient ${R}_{H}$ of the $\ensuremath{\beta}$- and ${\ensuremath{\beta}}^{\ensuremath{'}}$-phases are similar and free-electron-like, while in the ${\ensuremath{\beta}}^{\ensuremath{'}}$-phase, ${R}_{H}$ changes sign with decreasing temperature at low fields. We have inquired into the sources of these transport anomalies, but have not been able to clearly identify the grounds. Several conventional mechanisms for a large magnetoresistance are discussed, and found not to be applicable. The different properties in the $\ensuremath{\beta}$- and the ${\ensuremath{\beta}}^{\ensuremath{'}}$-phases are puzzling since the magnitudes of the electrical resistivities are similar and ${\ensuremath{\omega}}_{c}\ensuremath{\tau}$ (cyclotron $\text{frequency}\ifmmode\times\else\texttimes\fi{}\text{scattering}$ time) is equally small in both phases. The similar temperature range in which anomalies occur in the ${\ensuremath{\beta}}^{\ensuremath{'}}$-phase in the resistivity, the Hall effect, and the magnetoresistance indicates an electronic transition or a change of the electron structure in this phase below about 100 K.

Non-Fermi liquid behavior in the magnetotransport of quasi two-dimensional heavy Fermion compounds CeMIn 5

We observe several non-Fermi liquid behaviors in the normal-state transport properties of CeMIn 5 (M: Rh and Co) under pressure at low temperatures: (1) The dc-resistivity shows T-linear dependence, ρ xx ∝ T . (2) The magnitude of Hall coefficient | R H | increases rapidly with decreasing temperature, and reaches a value much larger than | 1 / ne | at low temperatures. (3) The magnetoresistance displays T- and H-dependence that strongly violate Kohler's rule, and is well scaled by the tangent of the Hall angle, Δ ρ xx / ρ xx ∝ tan 2 Θ H . These non-Fermi liquid properties in the electron transport are remarkably pronounced when the AF fluctuations are enhanced in the vicinity of the quantum critical point. Since all of these salient features have been also reported for high- T c cuprates, we infer that the non-Fermi liquid transport properties capture universal features of strongly correlated electron systems in the presence of strong antiferromagnetic fluctuations.

Hump Like Resistance Anomaly in Organic Conductor β''-(BEDT-TTF)2CsCd(SCN)4

We investigate the low-temperature electronic phase of a two-dimensional organic conductor, β''-(BEDT-TTF) 2 CsCd(SCN) 4 [where BEDT-TTF denotes bis(ethylenedithio)tetrathiafulvalene], which has a large hump between 32 and around 5 K in the temperature dependence of the interlayer resistance. We present experimental results for the temperature dependence of the resistance under magnetic fields and its Kohler plots, and an x-ray diffraction study. We find that I) Kohler's rule is strongly violated below 32 K, although the rule is valid above 32 K, and II) weak superlattice spots appear at 15.6 K in the x-ray study. On the basis of the experimental results, we suggest that the origin of the resistance hump is the formation of a possible charge density wave transition at about 32 K by the nesting of a pair of large one-dimensional Fermi surfaces obtained in the electronic structure calculation based on the crystal structure at room temperature.

Magnetotransport properties governed by antiferromagnetic fluctuations in the heavy-fermion superconductorCeIrIn5

In quasi-two-dimensional $\text{Ce}(\text{Ir},\text{Rh}){\text{In}}_{5}$ system, it has been suggested that the phase diagram contains two distinct domes with different heavy-fermion superconducting states. Here, we report the systematic pressure dependence of the electron transport properties in the normal state of ${\text{CeRh}}_{0.2}{\text{Ir}}_{0.8}{\text{In}}_{5}$ and ${\text{CeIrIn}}_{5}$, which locates in first and second superconducting domes, respectively. We observed non-Fermi liquid behavior at low temperatures in both compounds, including nonquadratic $T$ dependence of the resistivity, large enhancement of the Hall coefficient, and the violation of the Kohler rule in the magnetoresistance. We show that the cotangent of the Hall angle $\text{cot}\text{ }{\ensuremath{\Theta}}_{H}$ varies as ${T}^{2}$, and the magnetoresistance is quite scaled well by the Hall angle as $\ensuremath{\Delta}{\ensuremath{\rho}}_{xx}/{\ensuremath{\rho}}_{xx}\ensuremath{\propto}{\text{tan}}^{2}\text{ }{\ensuremath{\Theta}}_{H}$. The observed transport anomalies are common features of $\text{Ce}M{\text{In}}_{5}$ ($M=\text{Co}$, Rh, and Ir) and high-${T}_{c}$ cuprates, which suggest that the anomalous transport properties observed in ${\text{CeIrIn}}_{5}$ are mainly governed by the antiferromagnetic spin fluctuations not by the Ce-valence fluctuations, which have been proposed to be the possible origin for the second superconducting dome.