ChemInform Abstract: Evidence for Hydrodynamic Electron Flow in PdCoO₂.

Abstract

2. -A long-standing question in the physics of solids has been whether the viscosity of the electron fluid plays an observable role in determining the resistance. Experimental evidence is given in this paper that the resistance of restricted channels of ultrapure two-dimensional PdCoO 2 has a large viscous contribution. The electronic viscosity is estimated to be in the range from 6 x 10 -3 to 3 x 10 -4 kg/(m s). -(MOLL, P. J. W.; KUSHWAHA, P.; NANDI, N.; SCHMIDT, B.; MACKENZIE*, A. P.; Science (Washington, DC, U. S.) 351 (2016) 6277, 1061-1064, http://dx.doi.org/10.1126/science.aac8385 ; MPI Chem. Phys. fester Stoffe,

Observation of second sound in graphite over 200 K

“…The hydrodynamic regime takes place when momentum-conserving normal scattering (N-scattering) is stronger than momentum-destroying resistive scattering (Rscattering), leading to a collective drift motion of phonons under a temperature gradient. This strongly correlated collective motion of phonons leads to peculiar thermal transport phenomena such as second sound [5][6][7][8][9][10][11] , phonon Poiseuille flow 6,12,13 and Knudsen minimum 12,14 , parallel to the hydrodynamic regime of strongly correlated electrons [15][16][17][18] . For over half a century, phonon hydrodynamic transport was deemed exotic and mattered only at extremely low temperatures.…”

Layer-resolved many-electron interactions in delafossite PdCoO2 from standing-wave photoemission spectroscopy

“…As a consequence of the two-dimensional confinement, electron conduction in PdCoO2 or PtCoO2 is highly anisotropic with in-plane conductivities in the metallic sheets being ~10 3 times higher than out-of-plane conductivities 5,6 Remarkably, the in-plane conductivity of these materials is the highest reported among all known oxides 7 . In addition, these materials exhibit numerous exotic phenomena, including extremely large magnetoresistance 8 , quantum oscillations 7,9 and hydrodynamic electron flow 10 . Some studies also explored the possibility of using PdCoO2 as a electrocatalyst for the oxygen evolution reaction (OER) 11 and hydrogen evolution reaction (HER) 12,13 .…”

The planar triangular $S=3/2$ magnet AgCrSe$_2$: magnetic frustration, short range correlations, and field tuned anisotropic cycloidal magnetic order

“…Other examples for inorganic 2D materials are hexagonal boron nitrides and transitionmetal chalcogenides [2]. The triangular lattice delafossite PdCoO 2 belongs to the latter material class, which is characterized by an unusually high in-plane chargecarrier mobility [3,4]. Some organic BETS-and ET-salts also exhibit a layered triangular structure.…”

“…Delafossite-type structures form as A 1+ R 3+ X 2− 2 , where A is an alkaline-metal (Li, Na, K, Rb, Cs) or a monovalent transition-metal ion (Pd, Pt, or Cu, Ag), R is a trivalent transition metal or rare-earth ion which might be magnetic (Ti, V, Cr, Fe, Ce, or Yb) or nonmagnetic (Al, Ga, In, Tl, or Co, Rh), and X stands for a chalcogen [17]. So far, most of the research carried out was on oxygen-based delafossites, featuring a wide variety of topical phenomena, including superconductivity (Na x CoO 2 ) [25], large thermoelectricity (Cu[Rh,Mg]O 2 ) [26], multiferroicity (CuFeO 2 ) [27], hydrodynamic 2D conductivity (PdCoO 2 ) [3], and spin-orbit driven frustration on a perfect triangular lattice (NaYbO 2 ) [28].…”