We investigate the low temperature magnetic field dependences of both the resistivity and the magnetization in the misfit cobaltate Ca3Co4O9 from 60 K down to 2 K. The measured negative magnetoresistance reveals a scaling behavior with the magnetization which demonstrates a spin dependent diffusion mechanism. This scaling is also found to be consistent with a shadowed metalliclike conduction over the whole temperature range. By explaining the observed transport crossover, this result shed a new light on the nature of the elementary excitations relevant to the transport.
The structure of the low-energy electronic states in layered cobaltates is considered starting from the Mott insulating limit. We argue that the coherent part of the wave-functions and the Fermi-surface topology at low doping are strongly influenced by spin-orbit coupling of the correlated electrons on the $t_{2g}$ level. An effective t-J model based on mixed spin-orbital states is radically different from that for the cuprates, and supports unconventional, pseudospin-triplet pairing.
A natural explanation for the carrier concentration-dependent electronic behavior in the layered cobaltates emerges within correlated-electron Hamiltonians with finite on-site and significant nearest neighbor hole-hole Coulomb repulsions. The nearest neighbor repulsion decreases hole double-occupancy below hole density 1/3, but increases the same at higher hole densities. Our conclusion is valid for both single-band and three-band extended Hubbard Hamiltonians, and sheds light on concentration-dependent $e_g^\prime$ hole occupancy within the latter.
Recently, strong reduction of the quasiparticle peaks and pronounced incoherent structures have been observed in the photoemission spectra of layered cobaltates. Surprisingly, these many-body effects are found to increase near the band insulator regime. We explain these unexpected observations in terms of a novel spin-polaron model for CoO_2 planes which is based on a fact of the spin-state quasidegeneracy of Co^{3+} ions in oxides. Scattering of the photoholes on spin-state fluctuations suppresses their coherent motion. The observed ``peak-dip-hump'' type lineshapes are well reproduced by the…
The apparently counterintuitive carrier concentration-dependent electronic properties of layered cobaltates have attracted wide interest. Here we point out that very similar carrier-concentration dependence has previously been noted in strongly correlated quasi-one dimensional (quasi-1D) organic charge-transfer solids. The normal states of both families can be understood, over the entire range of carrier concentration of interest, within the extended Hubbard Hamiltonian with significant intersite Coulomb interaction. As with the charge-transfer solids, superconductivity in the cobaltates appea…
Measurements of polarization and temperature dependent soft x-ray absorption have been performed on Na_xCoO_2 single crystals with x=0.4 and x=0.6. They show a deviation of the local trigonal symmetry of the CoO_6 octahedra, which is temperature independent in a temperature range between 25 K and 372 K. This deviation was found to be different for Co^{3+} and Co^{4+} sites. With the help of a cluster calculation we are able to interpret the Co L_{23}-edge absorption spectrum and find a doping dependent energy splitting between the t_{2g} and the e_g levels (10Dq) in Na_xCoO_2.
We report here a discovery of electrically driven insulator to metal transition (IMT) and concomitant isostructural volume expansion in the layered cobaltates which otherwise do not exhibit temperature dependent IMT. These findings are demonstrated at macroscopic, microscopic and atomic scales. With application of voltage growth of metallic regions have been observed in the 2D layered La2-xSrxCoO4. Growth of metallic regions is associated with volume increase (strain as high as 0.3%). Non thermal IMT and electro-strain are proposed to be caused by electro-proliferation of the Co3+ high spin st…
Effects of Fe-substitution on the crystal structure and magnetic correlations of the geometrically frustrated antiferromagnets YBaCo4-xFexO7+δ (x = 0, 0.2, 0.4, 0.5, 0.6, and 0.8) have been studied by neutron diffraction, Mössbauer spectroscopy, and ac susceptibility. The compounds YBaCo4-xFexO7+δ have a special layered-type crystal structure with an alternating Kagomé (6c site) and triangular (2a site) layers along the c axis. Fe3+ ions are found to be substituted at both the crystallographic 2a and 6c sites of Co ions. Mössbauer results show a high spin state of Fe3+ ions in a tetrahedral co…
ARPES is a priori a technique of choice to measure the Fermi velocities vF in metals. In correlated systems, it is interesting to compare this experimental value to that obtained in band structure calculations, as deviations are usually taken as a good indicator of the presence of strong electronic correlations. Nevertheless, it is not always straightforward to extract vF from ARPES spectra. We study here the case of layered cobaltates, an interesting family of correlated metals. We compare the results obtained by standard methods, namely the fit of spectra at constant momentum k (energy distr…
Neutron scattering experiments were performed on single crystals of layered cobalt-oxides La2-xCaxCoO4 (LCCO) to characterize the charge and spin orders in a wide hole-doping range of 0.3<x<0.8. For a commensurate value of x=0.5 in (H,0,L) plane, two types of superlattice reflections concomitantly appear at low temperature; one corresponds to a checkerboard charge ordered pattern of Co2+/Co3+ ions and the other is magnetic in origin. Further, the latter magnetic-superlattice peaks show two types of symmetry in the reflections, suggesting antiferromagnetic-stacking (AF-S) and ferromagnetic-stac…
We have performed non-resonant x-ray diffraction, resonant soft and hard x-ray magnetic diffraction, soft x-ray absorption and x-ray magnetic circular dichroism measurements to clarify the electronic and magnetic states of the Co3+ ions in GdBaCo2O5.5. Our data are consistent with a 3+ Py Co HS state at the pyramidal sites and a 3+ Oc Co LS state at the octahedral sites. The structural distortion, with a doubling of the a axis (2ap x 2ap x 2ap cell), shows alternating elongations and contractions of the pyramids and indicates that the metal-insulator transition is associated with orbital order…
We present a numerical treatment of a spin-orbital polaron model for Na_xCoO_2 at small hole concentration (0.7 < x < 1). We demonstrate how the polarons account for the peculiar magnetic properties of this layered compound: They explain the large susceptibility; their internal degrees of freedom lead both to a negative Curie-Weiss temperature and yet to a ferromagnetic intra-layer interaction, thereby resolving a puzzling contradiction between these observations. We make specific predictions on the momentum and energy location of excitations resulting from the internal degrees of freedom of t…
We observe quasi-static incommensurate magnetic peaks in neutron scattering experiments on layered cobalt oxides La2-xSrxCoO4 with high Co oxidation states that have been reported to be paramagnetic. This enables us to measure the magnetic excitations in this highly hole-doped incommensurate regime and compare our results with those found in the low-doped incommensurate regime that exhibit hourglass magnetic spectra. The hourglass shape of magnetic excitations completely disappears given a high Sr doping. Moreover, broad low-energy excitations are found, which are not centered at the incommens…
Studies of interlayer transport in layered metals have generally made use of zero temperature conductivity expressions to analyze angle-dependent magnetoresistance oscillations (AMRO). However, recent high temperature AMRO experiments have been performed in a regime where the inclusion of finite temperature effects may be required for a quantitative description of the resistivity. We calculate the interlayer conductivity in a layered metal with anisotropic Fermi surface properties allowing for finite temperature effects. We find that resistance maxima are modified by thermal effects much more …
Herein, we report the magneto-transport and exchange bias effect in a "314 - type" oxygen - vacancy ordered material with composition SrCo$_{0.85}$Fe$_{0.15}$O$_{2.62}$. This material exhibits a ferrimagnetic transition above room temperature, at 315 K. The negative magnetoresistance starts to appear from room temperature (-1.3 $\%$ at 295 K in 70 kOe) and reaches a sizable value of 58 $\%$ at 4 K in 70 kOe. Large exchange bias effect is observed below 315 K when the sample is cooled in the presence of a magnetic field. The coexistence of nearly compensated and ferrimagnetic regions in the lay…
Two-dimensional magnetic materials have recently attracted great interest due to their unique functions as the electric field control of a magnetic phase and the anomalous spin Hall effect. For such remarkable functions, a spin-orbit coupling (SOC) serves as an essential ingredient. Here we report a giant positive magnetoresistance in a layered magnetic semiconductor AgCrSe2, which is a manifestation of the subtle combination of the SOC and Zeeman-type spin splitting. When the carrier concentration approaches the critical value of 2.5\times10^18 cm^-3, a sizable positive magnetoresistance of ~…
The effect of incoherent interlayer transport on the interlayer resistance of a layered metal is considered. We find that for both quasi-one-dimensional and quasi-two-dimensional Fermi liquids the angular dependence of the magnetoresistance is essentially the same for coherent and incoherent transport. Consequently, the existence of a three-dimensional Fermi surface is not necessary to explain the oscillations in the magnetoresistance that are seen in many organic conductors as the field direction is varied.
Many of the most interesting and technologically important electronic materials discovered in the past two decades have two common features: a layered crystal structure and strong interactions between electrons. Two of the most fundamental questions about such layered metals concern the origin of intralayer anisotropies and the coherence of interlayer charge transport. We show that angle dependent magnetoresistance oscillations (AMRO) are sensitive to anisotropies around an intralayer Fermi surface. Hence, AMRO can be a probe of intralayer anisotropies that is complementary to angle-resolved p…
The angle-dependences of the magnetoresistance of two different isotopic substitutions (deuterated and undeuterated) of the layered organic superconductor κ-(ET)2Cu(NCS)2 are presented. The angle dependent magnetoresistance oscillations (AMRO) arising from the quasi-one-dimensional (Q1D) and quasi-two-dimensional (Q2D) Fermi surfaces in this material are often confused. By using the Boltzman transport equation extensive simulations of the AMRO are made that reveal the subtle differences between the different species of oscillation. No significant differences are observed in the electronic para…
Studies of angle-dependent magnetoresistance oscillations (AMRO) in the interlayer conductivity of layered metals have generally considered semi-classical electron transport. We consider a quantum correction to the semi-classical conductivity that arises from what can be described as an interlayer Cooperon. This depends on both the disorder potential within a layer and the correlations of the disorder potential between layers. We compare our results with existing experimental data on organic charge transfer salts that are not explained within the standard semi-classical transport picture. In p…
Angle-resolved photoemission spectroscopy data for the bilayer manganite La1.2Sr1.8Mn2O7 show that, upon lowering the temperature below the Curie point, a coherent polaronic metallic groundstate emerges very rapidly with well defined quasiparticles which track remarkably well the electrical conductivity, consistent with macroscopic transport properties. Our data suggest that the mechanism leading to the insulator-to-metal transition in La1.2Sr1.8Mn2O7 can be regarded as a polaron coherence condensation process acting in concert with the Double Exchange interaction.
Magnetic frustration in metallic rare earth lanthanides ($Ln$) with $4f$-electrons is crucial for producing interesting magnetic phases with high magnetic anisotropy where intertwined charge and spin degrees of freedom lead to novel phenomena. Here we report on the magnetic, thermodynamic, and electrical transport properties of TbAuAl$_4$Ge$_2$. Tb ions form 2-dimensional triangular lattice layers which stack along the crystalline $c$-axis. The magnetic phase diagram reveals multiple nearly degenerate ordered states upon applying field along the magnetically easy $ab$-plane before saturation. …
Materials with strong magnetoresistive responses are the backbone of spintronic technology, magnetic sensors, and hard drives. Among them, manganese oxides with a mixed valence and a cubic perovskite structure stand out due to their colossal magnetoresistance (CMR). A double exchange interaction underlies the CMR in manganates, whereby charge transport is enhanced when the spins on neighboring Mn3+ and Mn4+ ions are parallel. Prior efforts to find different materials or mechanisms for CMR resulted in a much smaller effect. Here we show an enormous CMR at low temperatures in EuCd2P2 without man…
The interlayer magnetoresistance of layered metals in a tilted magnetic field is calculated for two distinct models for the interlayer transport. The first model involves coherent interlayer transport and makes use of results of semi-classical or Bloch-Boltzmann transport theory. The second model involves weakly incoherent interlayer transport where the electron is scattered many times within a layer before tunneling into the next layer. The results are relevant to the interpretation of experiments on angular-dependent magnetoresistance oscillations (AMRO) in quasi-one- and quasi-two-dimension…
The layered compound La2-2xSr1+2xMn2O7 (x=0.3) consists of bilayers of metallic MnO2 sheets separated by insulating material. The compound exhibits markedly anisotropic magnetoresistance at temperatures well below the three-dimensional magnetic ordering temperature TC=90 K in addition to colossal magnetoresistance around TC. We present neutron diffraction data which show that the magnetic structure of this material switches from antiferromagnetic stacking of the (ferromagnetically ordered) sheets in zero field to ferromagnetic stacking in a field of 1.5 Tesla. The data are the first to be coll…
The large magnetic anisotropy in the layered ferromagnet Fe_{1/4}TaS_2 leads to very sharp reversals of the magnetization $\bf M$ at the coercive field. We have exploited this feature to measure the anomalous Hall effect (AHE), focussing on the AHE conductivity $σ^A_{xy}$ in the inelastic regime. At low temperature T (5-50 K), $σ^A_{xy}$ is T-independent, consistent with the Berry-phase/Karplus-Luttinger theory. Above 50 K, we extract an inelastic AHE conductivity $σ^{in}_{xy}$ that scales as the square of $Δρ$ (the T dependent part of the resistivity $ρ$). The term $σ^{in}_{xy}$ clarifies the…
The magnetic-field, temperature, and angular dependence of the interlayer magnetoresistance of two different quasi-two-dimensional (2D) organic superconductors is reported. For $κ$-(BEDT-TTF)$_2$I$_3$ we find a well-resolved peak in the angle-dependent magnetoresistance at $Θ= 90^\circ$ (field parallel to the layers). This clear-cut proof for the coherent nature of the interlayer transport is absent for $β$''-(BEDT-TTF)$_2$SF$_5$CH$_2$CF$_2$SO$_3$. This and the non-metallic behavior of the magnetoresistance suggest an incoherent quasiparticle motion for the latter 2D metal.
A two-staged, uniaxial magnetoresistive effect has been discovered in SrCo6O11 having a layered hexagonal structure. Conduction electrons and localized Ising spins are in different sublattices but their interpenetration makes the conduction electrons sensitively pick up the stepwise field-dependence of magnetization. The stepwise field-dependence suggests two competitive interlayer interactions between ferromagnetic Ising-spin layers, i.e., a ferromagnetic nearest-layer interaction and an antiferromagnetic next-nearest-layer interaction. This oxide offers a unique opportunity to study nontrivi…
Pressure-Tuned Competing Electronic States in Layered Tellurides
University of Sharjah（沙迦大学）；University of Doha for Science and Technology（多哈科学与技术大学）；Korzhinskii Institute of Experimental Mineralogy RAS（俄罗斯科学院科尔任斯基实验矿物学研究所）；Ural Federal University（乌拉尔联邦大学）；Qatar Environment and Energy Research Institute (QEERI), Hamad Bin Khalifa University（卡塔尔环境能源研究所（QEERI），哈利法大学）；Izmir Institute of Technology（伊兹密尔理工大学）；American University of Sharjah（沙迦美国大学）
The evolution of the low temperature electronic structure of the cuprate metals from the overdoped to the underdoped side has recently been addressed through Angle-Dependant Magneto-Resistance (ADMR) experiments in La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$. The results show a striking difference between hole dopings $p = 0.24$ and $p = 0.21$ which lie on either side of a putative quantum critical point at intermediate $p$. Motivated by this, we here study the theory of ADMR in correlated layered materials, paying special attention to the role of angle dependent quasiparticle weights $Z_{\mathbf{k}}$…
We present the quantum-mechanical calculations of the angular dependence of interlayer conductivity $σ_{zz}(θ)$ in a tilted magnetic field in quasi-2D layered metals. Our calculation shows that the LL shape is important for this angular dependence. In particular, the amplitude of angular magnetoresistance oscillations (AMRO) is much stronger for the Gaussian LL shape than for the Lorentzian. The ratio $σ_{zz}(θ=0)/ σ_{zz}(θ->\pm 90^{\circ})$ is also several times larger for the Gaussian LL shape. AMRO and Zeeman energy splitting lead to a spin current. For typical organic metals and for a medi…
We analyzed the in-plane and out-of-plane magnetoresistance (MR) for overdoped Bi$_{1.6}$Pb$_{0.4}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ (Bi-2212) single crystals using superconductive fluctuation theory, which considers the density-of-states (DOS) contribution in layered superconductors with the conventional s-wave pairing state. The out-of-plane results are well reproduced by the theory, implying that the large, negative out-of-plane MR as well as the sharp increase in the zero-field out-of-plane resistivity $ρ_{c}$ near the superconducting transition temperature $T_c$ originate from the superconducti…
Resonant elastic X-ray scattering (REXS) at the Eu $M_5$ edge reveals an antiferromagnetic structure in layered EuCd$_2$Sb$_2$ at temperatures below $T_\textrm{N}$ = 7.4 K with a magnetic propagation vector of $(0,0,1/2)$ and spins in the basal plane. Magneto-transport and REXS measurements with an in-plane magnetic field show that features in the magnetoresistance are correlated with changes in the magnetic structure induced by the field. Ab initio electronic structure calculations predict that the observed spin structure gives rise to a gapped Dirac point close to the Fermi level with a gap …
$^{59}$Co NMR experiments have been performed on single crystals of the layered cobaltate Na$_{x}$CoO$_{2}$ with x=0.77 which is an antiferromagnet with Néel temperature $T_{N}=22$~K. In this metallic phase six Co sites are resolved in the NMR spectra, with distinct quadrupole frequencies $ν_{Q}$, magnetic shifts $K_{ZZ}$ and nuclear spin lattice relaxation rates $% 1/T_{1}$. Contrary to the $x=1/2$ or $x=2/3$ phases the 3D stacking of the Na planes is not perfect for $x=0.77$ but this does not influence markedly the electronic properties. We evidence that the magnetic and charge properties of…
The electronic structure basis of the extremely large magnetoresistance in layered non-magnetic tungsten ditelluride has been investigated by angle-resolved photoelectron spectroscopy. Hole and electron pockets of approximately the same size were found at the Fermi level, suggesting that carrier compensation should be considered the primary source of the effect. The material exhibits a highly anisotropic, quasi one-dimensional Fermi surface from which the pronounced anisotropy of the magnetoresistance follows. A change in the Fermi surface with temperature was found and a high-density-of-state…
Here, we report an investigation of structural, magnetic and electronic properties in Y-doped layered iridate (Sr$_{1-x}$Y$_x$)$_2$IrO$_4$ ($x$ $\leq$ 0.1). The parent Sr$_2$IrO$_4$ is a well-studied spin-orbit coupling (SOC) induced insulator with an antiferromagnetic ground state. The Y-doping here equivalently acts for electron doping without altering the vital parameters such as, SOC and electron correlation. Experimental results show a minute change in structural parameters and an equivalent charge conversion from Ir$^{4+}$ to Ir$^{3+}$. Unlike similarly other electron-doped system, the l…
We present magnetoresistance studies of the quasi-two-dimensional organic conductor $κ$-(BETS)$_2$Mn[N(CN)$_2$]$_3$, where BETS stands for bis\-(ethylene\-dithio)\-tetra\-selena\-fulvalene. Under a moderate pressure of 1.4\,kbar, required for stabilizing the metallic ground state, Shubnikov - de Haas oscillations, associated with a classical and a magnetic-breakdown cyclotron orbits on the cylindrical Fermi surface, have been found at fields above 10\,T. The effective cyclotron masses evaluated from the temperature dependence of the oscillation amplitudes reveal strong renormalization due to m…
Hall, resistivity, magnetization, and thermoelectric power measurements were performed on single crystals of the highly anisotropic layered metal LaSb2. A 100-fold linear magnetoresistance (MR) was observed in fields up to 45 T, with no indication of saturation. We show that the MR is associated with a magnetic-field-dependent holelike carrier density, n(H) \propto 1/H. The effect is orbital, depending upon the component of the magnetic field normal to the layers. At low temperature, a field of 9 T reduces the carrier density by more than an order of magnitude.
For many layered metals the temperature dependence of the interlayer resistance has a different behavior than the intralayer resistance. In order to better understand interlayer transport we consider a concrete model which exhibits this behavior. A small polaron model is used to illustrate how the interlayer transport is related to the coherence of quasi-particles within the layers. Explicit results are given for the electron spectral function, interlayer optical conductivity and the interlayer magnetoresistance. All these quantities have two contributions: one coherent (dominant at low temper…
Extremely large magnetoresistance is realized in the nonmagnetic layered metal PdCoO2. In spite of a highly conducting metallic behavior with a simple quasi-two-dimensional hexagonal Fermi surface, the interlayer resistance reaches up to 35000% for the field along the [1-10] direction. Furthermore, the temperature dependence of the resistance becomes nonmetallic for this field direction, while it remains metallic for fields along the [110] direction. Such severe and anisotropic destruction of the interlayer coherence by a magnetic field on a simple Fermi surface is ascribable to orbital motion…
The interlayer magnetoresistance of a quasi-two-dimensional layered metal with a d-wave pseudogap is calculated semiclassically. An expression for the interlayer resistivity as a function of the strength and direction of the magnetic field, the magnitude of the pseudogap, temperature, and scattering rate is obtained. We find that the pseudogap, by introducing low-energy nodal quasiparticle contours, smooths the dependence on field direction in a manner characteristic of its anisotropy. We thus propose that interlayer resistance measurements under a strong field of variable orientation can be u…
Magnetization (M) and magnetoresistance (MR) measurements on polycrystalline R2Mn3Si5 (R = Tb, Dy and Ho) compounds (tetragonal, space group P4/mnc) have been carried out in the temperature range of 2 K-300 K, in various applied fields. Both, the rare earth and the Mn, are found to carry magnetic moments in these compounds. Mn has two sub-lattices (Mn1 and Mn2) that order magnetically at two different temperatures. Rare earth and Mn1 moments order ferromagnetically at TC1 whereas Mn2 is found to magnetically order at TC2 (TC1 = 89 K, 86 K, 78 K and TC2 = 18 K, 34 K, 16 K for R = Tb, Dy and Ho …
We report two-dimensional quantum transport and Dirac fermions in BaMnBi2 single crystals. BaMnBi2 is a layered bad metal with highly anisotropic conductivity and magnetic order below 290 K. Magnetotransport properties, nonzero Berry phase, small cyclotronmass, and the first-principles band structure calculations indicate the presence of Dirac fermions in Bi square nets. Quantum oscillations in the Hall channel suggest the presence of both electron and hole pockets, whereas Dirac and parabolic states coexist at the Fermi level.
Elastoresistivity Signatures of Nematic Fluctuations in Layered Antiferromagnet CoTa3S6
Division of Physics, Mathematics and Astronomy, California Institute of Technology（加州理工学院物理、数学与天文学部）；Institute of Quantum Information and Matter, California Institute of Technology（加州理工学院量子信息与物质研究所）；Department of Physics and Astronomy, University of Utah（犹他大学物理与天文学系）
We present detailed studies of the high-field magnetoresistance of the layered organic metal $κ$-(BETS)$_2$\-Mn\-[N(CN)$_2$]$_3$ under a pressure slightly above the insulator-metal transition. The experimental data are analysed in terms of the Fermi surface properties and compared with the results of first-principles band structure calculations. The calculated size and shape of the inplane Fermi surface are in very good agreement with those derived from Shubnikov-de Haas oscillations as well as the classical angle-dependent magnetoresistance oscillations. A comparison of the experimentally obt…
We report quasi-two-dimensional Dirac fermions and quantum magnetoresistance in LaAgBi$_2$. The band structure shows several narrow bands with nearly linear energy dispersion and Dirac-cone-like points at the Fermi level. The quantum oscillation experiments revealed one quasi-two-dimensional Fermi pocket and another complex pocket with small cyclotron resonant mass. The in-plane transverse magnetoresistance exhibits a crossover at a critical field $B^*$ from semiclassical weak-field $B^2$ dependence to the high-field unsaturated linear magnetoresistance which is attributed to the quantum limit…
The longitudinal interlayer magnetoresistance $R_{zz}(B_{z})$ is calculated in strongly anisotropic layered metals, when the interlayer band width $4t_{z}$ is less than the Landau level separation $\hbar ω_{c}$. The impurity scattering has much stronger effect in this regime than in 3D metals and leads to a linear longitudinal interlayer magnetoresistance $R_{zz}\propto B_{z}$ in the interval $\hbar ω_{c}>4t_{z}>>\sqrt{Γ_{0}\hbar ω_{c}}$ changing to a square-root dependence $R_{zz}\propto B_{z}^{1/2}$ at higher field or smaller $t_{z}$. The crossover field allows to estimate the interlayer tra…
In order to gain insights into the origin of colossal magneto-resistance (CMR) in manganese oxides, we performed a ^{139}La NMR study in the double-layered compound La_{1.2}Sr_{1.8}Mn_2O_7. We find that above the Curie temperature T_C=126 K, applying a magnetic field induces a long-range ferromagnetic order that persists up to T=330 K. The critical field at which the induced magnetic moment is saturated coincides with the field at which the CMR effect reaches to a maximum. Our results therefore indicate that the CMR observed above T_C in this compound is due to the field-induced ferromagnetism…
We consider the quasiparticle c-axis conductivity in highly anisotropic layered compounds in the presence of the magnetic field parallel to the layers. We show that at low temperatures the quasiparticle interlayer conductivity depends strongly on the orientation of the in-plane magnetic field if the excitation gap has nodes on the Fermi surface. Thus measurements of the angle-dependent c-axis (out-of-plane) magnetoresistance, as a function of the orientation of the magnetic field in the layers, provide information on the momentum dependence of the superconducting gap (or pseudogap) on the Ferm…
