63 research outputs found
Unconventional aspects of electronic transport in delafossite oxides
The electronic transport properties of the delafossite oxides ABO are
usually understood in terms of two well separated entities, namely, the
triangular A and (BO) layers. Here we review several cases among
this extensive family of materials where the transport depends on the
interlayer coupling and displays unconventional properties. We review the doped
thermoelectrics based on CuRhO and CuCrO, which show a high-temperature
recovery of Fermi-liquid transport exponents, as well as the highly anisotropic
metals PdCoO, PtCoO and PdCrO where the sheer simplicity of the
Fermi surface leads to unconventional transport. We present some of the
theoretical tools that have been used to investigate these transport properties
and review what can and cannot be learned from the extensive set of electronic
structure calculations that have been performed.Comment: 35 pages, 19 figure
Intrinsic effects of substitution and intercalation on thermal transport in two-dimensional TiS single crystals
The promising thermoelectric material TiS can be easily chemically doped
and intercalated. We present here studies of single crystals that are
intercalated with excess Ti or Co, or substituted with Ta. We demonstrate the
intrinsic impact of these dopants on the thermal transport in the absence of
grain boundary scattering. We show that Ta doping has the greatest impact on
the thermal scattering rate per ion added, leading to a five-fold reduction in
the lattice thermal conductivity as compared to stoichiometric single crystals.Comment: 5 pages, 2 figure
Thermoelectric transport across the metamagnetic transition of CeRu2Si2
We have measured the thermopower across the metamagnetic transition of the
heavy fermion compound CeRu2Si2 at temperatures down to 0.1K and magnetic
fields up to 11.5T. We find a large negative enhancement of the thermopower on
crossing the metamagnetic field, as well as a sudden change in slope. We argue
that this is consistent with the Zeeman-driven deformation of the Fermi surface
through a topological transition. The field dependence of the thermopower
highlights the discrepancy between thermodynamic and transport properties
across the metamagnetic transition.Comment: 5 pages, 4 figure
Large anisotropic thermal conductivity of intrinsically two-dimensional metallic oxide PdCoO
The highly conductive layered metallic oxide \pdcoo{} is a near-perfect
analogue to an alkali metal in two dimensions. It is distinguished from other
two-dimensional electron systems where the Fermi surface does not reach the
Brillouin zone boundary by a high planar electron density exceeding
cm. The simple single-band quasi-2D electronic structure results in
strongly anisotropic transport properties and limits the effectiveness of
electron-phonon scattering. Measurements on single crystals in the temperature
range from 10-300K show that the thermal conductivity is much more weakly
anisotropic than the electrical resistivity, as a result of significant phonon
heat transport. The in-plane thermoelectric power is linear in temperature at
300\,K and displays a purity-dependent peak around 50K. Given the extreme
simplicity of the band-structure, it is possible to identify this peak with
phonon drag driven by normal electron-phonon scattering processes.Comment: 3 figure
Anisotropic Seebeck coefficient of in the incoherent regime
Intuitive entropic interpretations of the thermoelectric effect in metals
predict an isotropic Seebeck coefficient at high temperatures in the incoherent
regime even in anisotropic metals since entropy is not directional.
is an enigmatic material known for a
well characterised anisotropic normal state and unconventional
superconductivity. Recent ab-initio transport calculations of
that include the effect of strong
electronic correlations predicted an enhanced high-temperature anisotropy of
the Seebeck coefficient at temperatures above 300 K, but experimental evidence
is missing. From measurements on clean
single crystals along both crystallographic directions, we find that the
Seebeck coefficient becomes increasingly isotropic upon heating towards room
temperature as generally expected. Above 300 K, however, acquires a new
anisotropy which rises up to the highest temperatures measured (750 K), in
qualitative agreement with calculations. This is a challenge to entropic
interpretations and highlights the lack of an intuitive framework to understand
the anisotropy of thermopower at high temperatures.Comment: 5 pages, 2 figure
Investigation of Planckian behavior in a high-conductivity oxide : PdCrO2
Funding: JFMV and DC are supported by faculty startup grants at Cornell University. ET and EB were supported by the European Research Council (ERC) under grant HQMAT (Grant Agreement No. 817799), the Israel-US Binational Science Foundation (BSF), and the Minerva Foundation.The layered delafossite metal PdCrO2 is a natural heterostructure ofhighly conductive Pd layers Kondo coupled to localized spins in the adjacentMott insulating CrO2 layers. At high temperatures T it has a T-linearresistivity which is not seen in the isostructural but non-magnetic PdCoO2.The strength of the Kondo coupling is known, as-grown crystals are extremelyhigh purity and the Fermi surface is both very simple and experimentally known.It is therefore an ideal material platform in which to investigate 'Planckianmetal' physics. We do this by means of controlled introduction of pointdisorder, measurement of the thermal conductivity and Lorenz ratio and studyingthe sources of its high temperature entropy. The T-linear resistivity is seento be due mainly to elastic scattering and to arise from a sum of severalscattering mechanisms. Remarkably, this sum leads to a scattering rate within10% of the Planckian value of kBT/â.Publisher PDFPeer reviewe
Revealing the Orbital Composition of Heavy Fermion Quasiparticles in CeRu2Si2
We present a resonant angle-resolved photoemission spectroscopy (ARPES) study of the electronic band structure and heavy fermion quasiparticles in CeRu2Si2. Using light polarization analysis, considerations of the crystal field environment and hybridization between conduction and f electronic states, we identify the d-electronic orbital character of conduction bands crossing the Fermi level. Resonant ARPES spectra suggest that the localized Ce f states hybridize with eg and t2g states around the zone center. In this fashion, we reveal the orbital structure of the heavy fermion quasiparticles in CeRu2Si2 and discuss its implications for metamagnetism and superconductivity in the related compound CeCu2Si2
Suppression of superconductivity and resistivity anomaly in Rh17S15 by cobalt substitution
The chalcogenide superconductor Rh17S15 is known for having an upper critical field of nearly twice the Pauli limit and an unusual temperature dependence of the resistivity. When doped with small amounts of cobalt, superconductivity in Rh17-xCoxS15 (0 < x < 3) is systematically suppressed. We explore the evolution of the electrical transport properties from 2-300 K as a function of x. We identify three temperature regimes which are differently affected by doping. The disappearance of an electron-like contribution to the transport at low temperature is correlated with the suppression of superconductivity
Suppression of superconductivity and resistivity anomaly in Rh17S15 by cobalt substitution
International audienceThe chalcogenide superconductor Rh17S15 is known for having an upper critical field of nearly twice the Pauli limit and an unusual temperature dependence of the resistivity. When doped with small amounts of cobalt, superconductivity in Rh17-xCoxS15 (0 < x < 3) is systematically suppressed. We explore the evolution of the electrical transport properties from 2-300 K as a function of x. We identify three temperature regimes which are differently affected by doping. The disappearance of an electron-like contribution to the transport at low temperature is correlated with the suppression of superconductivity
A straightforward 2Ï technique for the measurement of the Thomson effect
International audienceWe present a simplified, rapid, and accurate method for the measurement of the thermoelectric Thomson coefficient by the dynamical heating of a suspended wire by an alternating current. By applying a temperature gradient across the wire, we find that the response at the second harmonic of the excitation frequency is directly proportional to the Thomson coefficient. The absolute thermoelectric coefficient of a single material can therefore be extracted with high precision by using a phase sensitive detector. We test our method on platinum and nickel wires and develop both analytical and numerical models to determine the leading sources of error
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