Electron spectrum, thermodynamics, and transport in antiferromagnetic metals at low temperatures (original) (raw)
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Effective number of conduction electrons in antiferromagnetic metals near TN
The temperature derivative of the electronic transport coefficients of magnetic metals diverges at the spin ordering transition temperature. The temperature behaviour of the transport relaxation time seems to be well understood. Previous work is briefly summarized to present the theoretical ground on which another factor has to be studied. i.e. the number of conduction electrons. Important objections (have been and) are (now) raised on the theoretical handling of such a quantity in the vicinity of the Nee1 temperature. The number of conduction electrons is written in terms of a n appropriate self energy. This improves upon a too crude mean field treatment. The critical exponent of dn;dT is found to be r + y -I . The implication for the temperature behaviour of the electrical resistivity in the vicinity of the Nee1 temperature is outlined. Remarks on further improvements are also made.
Finite-temperature properties of doped antiferromagnets
Advances in Physics, 2000
We review recent results for the properties of doped antiferromagnets, obtained by the numerical analysis of the planar t-J model using the novel finite-temperature Lanczos method for small correlated systems. First we shortly summarize our present understanding of anomalous normal-state properties of cuprates, and present the electronic phase diagram, phenomenological scenarios and models proposed in this connection. The numerical method is then described in more detail. Following sections are devoted to various static and dynamical properties of the t-J model. Among thermodynamic properties the chemical potential, entropy and the specific heat are evaluated. Discussing electrical properties the emphasis is on the optical conductivity and the d.c. resistivity. Magnetic properties involve the static and dynamical spin structure factor, as measured via the susceptibility measurements, the NMR relaxation and the neutron scattering, as well as the orbital current contribution. Follows the analysis of electron spectral functions, being studied in photoemission experiments. Finally we discuss density fluctuations, the electronic Raman scattering and the thermoelectric power. Whenever feasible a comparison with experimental data is performed. A general conclusion is that the t-J model captures well the main features of anomalous normal-state properties of cuprates, for a number of quantities the agreement is even a quantitative one. It is shown that several dynamical quantities exhibit at intermediate doping a novel universal behaviour consistent with a marginal Fermi-liquid concept, which seems to emerge from a large degeneracy of states and a frustration induced by doping the antiferromagnet.
Magnetoresistance in quasi-one-dimensional metals due to Fermi surface cold spots
Physical Review B, 2000
In a number of quasi-one-dimensional organic metals the dependence of the magnetoresistance on the direction of the magnetic field is quite different from the predictions of Boltzmann transport theory for a Fermi liquid with a scattering rate that is independent of momentum. We consider a model in which there are large variations in the scattering rate over the Fermi surface. The model is the quasi-one-dimensional version of the "cold spots" model introduced by Ioffe and Millis to explain anomalous transport properties of the metallic phase of the cuprate superconductors. The dependence of the resistance, in the most and least conducting directions, on the direction and magnitude of the magnetic field are calculated. The calculated magnetoresistance has a number of properties that are quite distinct from conventional transport theory such as magic angle effects and a significant magnetoresistance when the field and current are both in the least conducting direction. However, the model cannot give a complete description of the unusual properties of (TMTSF)2PF6 at pressures of 8-11 kbar.
Quantum corrections to the conductivity of itinerant antiferromagnets
Physical Review B, 2015
We present a systematic calculation of the effects of scattering of electrons off spin waves on electron transport properties in itinerant antiferromagnetic thin films in two and three dimensions. We study various regimes set by the parameters related to the spin-wave gap, exchange energy, as well as the exchange splitting, in addition to the scales set by temperature and disorder. We find an interaction-induced quantum correction to the conductivity linear in temperature, similar to that obtained recently for ferromagnetic systems within a certain regime of disorder, although the disorder dependence is different. In addition, we explore the phase relaxation rates and the associated weak-localization corrections for both small and large spin-wave gaps. We obtain a wide variety of temperature and disorder dependence for various parameter regimes. These results should provide an alternative way to study magnetic properties of thin antiferromagnetic films, for which neutron scattering measurements could be difficult, by direct transport measurements.
Physical Review B, 1999
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 quasitwo-dimensional organic metals. We find that the dependence of the magnetoresistance on the direction of the magnetic field is identical for both models except when the field is almost parallel to the layers. An important implication of this result is that a three-dimensional Fermi surface is not necessary for the observation of the Yamaji and Danner oscillations seen in quasi-two-and quasi-one-dimensional metals, respectively. A universal expression is given for the dependence of the resistance at AMRO maxima and minima on the magnetic field and scattering time (and thus the temperature). We point out three distinctive features of coherent interlayer transport: (i) a beat frequency in the magnetic oscillations of quasi-two-dimensional systems, (ii) a peak in the angulardependent magnetoresistance when the field is sufficiently large and parallel to the layers, and (iii) a crossover from a linear to a quadratic field dependence for the magnetoresistance when the field is parallel to the layers. Properties (i) and (ii) are compared with published experimental data for a range of quasi-two-dimensional organic metals.
We calculate the interaction kernel K for two-dimensional diffusive electrons. The screening of the Coulomb interaction together with the Fermi statistics induces a spin selection rule for electronelectron scattering so that in leading order in the inverse conductance only pairs of electrons with antiparallel spins do scatter. At low temperature, this results in a larger coherence length for fully polarized electrons and thus in a positive in-plane magnetoresistance. An applied in-plane magnetic field also induces a nonmonotonous behavior of K at finite temperature. Alternatively, the vanishing of the scattering in the triplet channel strongly reduces ferromagnetism deep in the metallic regime. These effects weaken as the density of charge carriers is reduced.
Theory of itinerant antiferromagnetism: Zero-temperature properties
Physical Review B, 1976
The method of Gutzwiller is extended to include antiferromagnetism in a s-band Hubbard model. A firstorder paramagnetic (PM) to antiferromagnetic (AFM) transition is obtained with increasing U/ W ratio. The AFM ground state in the phase diagram is restricted between the electron density n«1 and n, = 2n,. It is also bounded from below by a critical value of U/ W. The complete AFM ordering appears only for n = 1. As n approaches n, or n, along the phase boundary, the AFM ordering gradually disappears. The AFM ordering is essentially due to virtual electron hopping, and the values of n"n"and critical U/ W depend on the bare density of states and the coordination number. The probability of having antiparallel-spin nearest-neighbor pair is computed. The result is consistent with the phase diagram. We also found a region in the phase diagram where the PM and the AFM states coexist. The AFM ground state at n = 1 is insulating. Depending on the value of U/W, the present theory predicts either an AFM insulating~PM metallic or an AFM insulating~PM insulating CPM metallic transition as the temperature is raised. Therefore, the V,O,-type phase diagram follows from the present theory.
Physical Review B
An approach previously developed for the calculation of transport coefficients via the Mott relations is applied to the calculation of finite temperature transport properties of disordered alloys-electrical resistivity and the electronic part of thermal conductivity. The coherent potential approximation (CPA) is used to treat chemical disorder as well as other sources of electron scattering, i.e. temperature induced magnetic moment fluctuations and lattice vibrations via the alloy analogy model. This approach, which treats all forms of disorder on an equal first principles footing, is applied to the calculation of transport properties of a series of face-centered crystal cubic (fcc) concentrated solid solutions of the 3d-transition metals Ni, Fe, Co and Cr. For the nonmagnetic alloys, Ni 0.8 Cr 0.2 , and Ni 0.33 Co 0.33 Cr 0.3 the combined effects of chemical disorder and electron-lattice vibrations scattering result in a monotonic increase in the resistivity as a function of temperature from an already large, T=0, residual resistivity. For magnetic Ni 0.5 Co 0.5 , Ni 0.5 Fe 0.5 , Ni 0.33 Fe 0.33 Co 0.33 , whose residual resistivity is small, additional electron scattering from temperature induced magnetic moment fluctuations results in a further rapid increase of the resistivity as a function of temperature. The electronic part of the thermal conductivity in nonmagnetic, Ni 0.8 Cr 0.2 , and Ni 0.33 Co 0.33 Cr 0.33 , monotonically increases with temperature. This behavior is a result of the competition between a reduction in the conductivity due to electron-lattice vibrations scattering and temperature induced increase in the number of carriers. In the magnetic alloys, electron scattering from magnetic fluctuations leads to an initial rapid decrease in thermal conductivity until this is overcome by an increasing number of carriers at temperatures slightly below the Curie temperature. Similar to the resistivity above T C , the electronic part of the thermal conductivities are close to each other in all alloys studied.
Fermi- to non-Fermi-liquid crossover and Kondo behavior in two-dimensional (Cu2/3V1/3)V2S4
Journal of Physics: Condensed Matter, 2019
By means of a specific heat (C) and electrical resistivity () study, we give evidence of a pronounced Fermi liquid (FL) behavior with sizable mass renormalization, m * /m = 30, up to unusually high temperatures ∼70 K in the layered system (Cu 2/3 V 1/3)V2S4. At low temperature, a marked upturn of both C and is suppressed by magnetic field, which suggests a picture of Kondo coupling between conduction electrons in the VS2 layers and impurity spins of the V 3+ ions located between layers. This picture opens the possibility of controlling electronic correlations and the FL to non-FL crossover in simple layered materials. For instance, we envisage that the coupling between layers provided by the impurity spins may realize a two-channel Kondo state.
Electronic thermal conductivity of disordered metals
Physical Review B, 2004
We calculate the thermal conductivity of interacting electrons in disordered metals. In our analysis we point out that the interaction affects thermal transport through two distinct mechanims, associated with quantum interference corrections and energy exchange of the quasi particles with the electromagnetic environment, respectively. The latter is seen to lead to a violation of the Wiedemann-Franz law. Our theory predicts a strong enhancement of the Lorenz ratio κ/σT over the value which is predicted by the Wiedemann-Franz law, when the electrons encounter a large environmental impedance.