Large anisotropic thermal conductivity of the intrinsically two-dimensional metallic oxidePdCoO2

Abstract

The highly conductive layered metallic oxide PdCoO 2 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 10 15 cm −2 . 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 10-300 K 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 50 K. 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.

Unconventional aspects of electronic transport in delafossite oxides

“…b) Thermoelectric power of metallic delafossites in zero magnetic field. The thermoelectric power of PdCoO 2 single crystals [50] shows a phonon drag peak at low temperature and a linear dependence with temperatures at high temperatures, as expected from calculations [59]. Older polycrystalline samples [25] may have been further from stoichiometry.…”

“…There are also discrepancies between results on PdCrO 2 single crystals [58,61]. so far not been possible to measure the out-of-plane Seebeck coefficient, however the measured in-plane values are in good agreement with the calculations [50]. The strong predicted anisotropy and sign change of the Seebeck coefficient with respect to crystalline direction are another unique aspect of these materials.…”

Impact of strain-induced electronic topological transition on the thermoelectric properties ofPtCoO2andPdCoO2

“…The estimate for S xx of unstrained PdCoO 2 from Boltzmann theory at room temperature is approximately 1.6 times larger than the experimental value published in Ref. 61 We now turn to the effect of strain, which is varied from -5% compressive to +5% tensile strain. The in-plane thermopower S xx and its variation under strain remains moderate in absolute numbers.…”

“…This is also the case for ZT | for T = 600 K, which can be estimated from the fit to the Debye-Callaway model provided in Ref. 61. In addition, we use an average τ zz = 10 fs for T = 300 K, while for T = 600 K, we take τ zz = 4 fs, as discussed in Sec.…”

Magnetoelectric properties of multiferroic CuCrO2 studied by means of ab initio calculations and Monte Carlo simulations

“…For instance, for A in a d 9 configuration, e.g., A = Pd or Pt, highly metallic compounds with anomalous temperature dependence of the resistivity have been reported [4][5][6][7]. The transport in these compounds has been found to be strongly anisotropic, with a degree of anisotropy that may reach 1000 [4,5,8]. For A in a d 10 configuration, the semi-conducting materials CuBO 2 , with B = Cr, Fe, Rh, may be turned into promising thermoelectric ones through hole doping [9][10][11] -in particular, an especially high power factor has been found in the case of CuRh 1−x Mg x O 2 [12], which transport coefficients served as a basis for the Apparent Fermi Liquid scenario [13].…”