Controlled Introduction of Defects to Delafossite Metals by Electron Irradiation

Abstract

The delafossite metals PdCoO2, PtCoO2 and PdCrO2 are among the highest conductivity materials known, with low temperature mean free paths of tens of microns in the best as-grown single crystals. A key question is whether these very low resistive scattering rates result from strongly suppressed backscattering due to special features of the electronic structure, or are a consequence of highly unusual levels of crystalline perfection. We report the results of experiments in which high energy electron irradiation was used to introduce point disorder to the Pd and Pt layers in which the conduction occurs. We obtain the cross-section for formation of Frenkel pairs in absolute units, and cross-check our analysis with first principles calculations of the relevant atomic displacement energies. We observe an increase of resistivity that is linear in defect density with a slope consistent with scattering in the unitary limit. Our results enable us to deduce that the as-grown crystals contain extremely low levels of in-plane defects of approximately 0.001%. This confirms that crystalline perfection is the most important factor in realizing the long mean free paths, and highlights how unusual these delafossite metals are in comparison with the vast majority of other multi-component oxides and alloys. We discuss the implications of our findings for future materials research.

Quasiparticle interference and quantum confinement in a correlated Rashba spin-split 2D electron liquid

“…These materials offer an exceptional experimental platform for studying Rashba physics in a new limit where the ISB becomes the dominant energy scale. The delafossite metals ( 7 – 9 ) grow with astonishing crystalline purity ( 10 ) and show extremely long mean free paths as evidenced by bulk transport ( 11 ), transverse electron focusing ( 12 ), and even coherent Aharonov-Bohm–like oscillations ( 13 ). They have been shown to have surface states with very large Rashba splitting (∼70 meV and ∼150 meV in PdCoO 2 and PdRhO 2 , respectively).…”

Low-symmetry nonlocal transport in microstructured squares of delafossite metals

“…In recent years, however, it has become clear that the delafossite metals PdCoO 2 and PtCoO 2 ( 18 – 20 ) have the potential to be ideal hosts for the study of nonlocal transport effects. Almost uniquely among oxide metals, they have an extremely high purity as grown, with defect levels as low as 1 in 10 5 in the conducting Pd/Pt layers ( 21 ). They also bring the benefit of simplicity, because only one highly dispersive band crosses the Fermi level, giving a single, quasi–two-dimensional Fermi surface as established experimentally by angle-resolved photoemission and measurements of the de Haas–van Alphen effect ( 22 – 25 ).…”

Charge density wave and superconductivity competition in Lu5Ir4Si10 : A proton irradiation study

“…After irradiation, we find that the residual resistivity increases linearly at a rate of 1.57 μ cm/10 16 p/cm 2 without saturation up to 12 × 10 16 p/cm 2 . Such a linear increase is what is typically expected in metals following the "unitary limit" [55], but this was not a priori obvious in Lu 5 Ir 4 Si 10 because of the CDW. Indeed, on one hand, irradiation suppresses the CDW, which increases the density of states at the Fermi level and should reduce the residual resistivity.…”

“…So usually, in the dirty limit H c,2 (0) ∝ T c , however here H c,2 (0) ∝ T 2 c . This unusual scaling can be easily explained by the fact that 1/τ 0 varies linearly with T c due to the competition with the CDW, namely: The prefactor φ 0 1.76 k B 2hv 2 F is independent of irradiation dose, whereas 1/τ 0 is usually proportional to the irradiation dose for uniform nonoverlapping defects in metals [55], and in this compound, empirically, T c increases linearly with the irradiation dose (see Fig. 2).…”