Two-Component Behavior of Cuprate Superconductors from NMR Shifts

Abstract

NMR spin shift data of La1:85Sr0:15CuO4, HgBa2CuO4+ at ambient pressure, andof YBa2Cu4O8 at pressure up to 63 kbar are discussed that fail the traditional single-electronicuid picture used for the discussion of NMR data. Instead the results point to a commonexplanation for all three systems in terms of two electronic components. One of them hasa temperature-dependent magnetic susceptibility while the second component, as well as itscoupling to the rst component, are constant above the superconducting transition temperatureTc. All susceptibilities vanish below Tc.

$^{63}$Cu and $^{199}$Hg NMR study of HgBa$_{2}$CuO$_{4+δ}$ single crystals

“…Here, we present a comprehensive set of Cu and Hg NMR shifts and linewidths data for an underdoped (T c =74 K) and an optimally doped (T c =97 K) sample of HgBa 2 CuO 4+δ . In separate accounts 22,23 we found that the spin shifts cannot be explained with a single Tdependent spin component, but with a two-component scenario where the spin susceptibility is written as the sum of two terms, χ (T, x) = χ 1 (T, x) + χ 2 (T, x), where the first term (χ 1 ) carries the pseudogap feature discovered by NMR shifts measurements, i.e., it is Tdependent far above T c . 24 The second susceptibility (χ 2 ) is T independent above T c , but it quickly disappears below T c , similar to what was concluded previously for La 1.85 Sr 0.15 CuO 4 , and that reminds one of Fermi-liquidlike behavior.…”