Bulk and surface nanoscale hole density inhomogeneity in HgBa2CuO4+δand Bi

Wei Chen

¹

,

Giniyat Khaliullin

²

,

O. P. Sushkov

³

Abstract

It is well established that the hole density in the prototypical superconductor La 2−x Sr x CuO 4 is very inhomogeneous due to Sr-dopant induced disorder. On the other hand, the hole distribution in HgBa 2 CuO 4+δ and Bi 2 Sr 2 CaCu 2 O 8+δ doped by interstitial oxygen is believed to be much more uniform. Recent nuclear magnetic resonance measurements indicate, however, that the charge inhomogeneity in HgBa 2 CuO 4+δ is close to that in La 2−x Sr x CuO 4 . Calculations performed in the present paper confirm this observation. We also show that the charge inhomogeneity is most pronounced at the surface layer that can be probed by scanning tunneling microscope. Our simulations demonstrate that, despite having similar amplitudes of charge inhomogeneity, the hole mean free path in HgBa 2 CuO 4+δ is substantially longer than that in La 2−x Sr x CuO 4 . The screening of the Coulomb repulsion in HgBa 2 CuO 4+δ is also stronger. These two reasons might explain the difference in the superconducting critical temperatures between these two compounds.

Synchrotron x-ray scattering study of charge-density-wave order in HgBa2CuO4+δ

“…mean-free path and the screening of the Coulomb repulsion have been estimated to be rather large, which may contribute to the high T c of Hg1201 [30]. This is supported by the observation of a tiny residual resistivity [12] of Shubnikov-de-Haas oscillations [20,21], and of Kohler scaling of the magnetoresistance in the PG state [14].…”

Doping dependence of gap inhomogeneities at Bi2Sr2CaCu2O8+δsurfaces

“…In the disorder case, λ i serves as a local correction to the chemical potential in order to satisfy the nondouble occupancy constraint. To make a comparison with the density inhomogeneity in [25], we assume that oxygens are located on top of four adjacent Cu sites, although this is slightly different from the most energetically favorable position [19]. We assume that the positions of oxygen dopants are truly random, unlike the nonadjacent condition used in [25].…”

“…To make a comparison with the density inhomogeneity in [25], we assume that oxygens are located on top of four adjacent Cu sites, although this is slightly different from the most energetically favorable position [19]. We assume that the positions of oxygen dopants are truly random, unlike the nonadjacent condition used in [25]. This is because if the oxygens are assumed to be nonadjacent to each other, then in a 2D square lattice their concentration can be at most 25%, whereas a higher oxygen concentration is necessary to achieve higher doping level in this work.…”

Strain derivatives ofTcin HgBa2CuO4+δ: The CuOWang1, Zhang2, Yan3 et al. 2014Phys. Rev. B

“…However, the effect of the Hg-O layers seems to be more than merely separating the CuO 6 octahedra, as they exhibit a high degree of polarizability and hence serve to screen long-range Coulomb interactions in the quintessential CuO 2 sheets [39,40]. We note that the above considerations have focused on average bond distances and bond angles.…”

“…There exists ample evidence from local bulk probes that the cuprates exhibit significant compound-specific local deviations from the average crystal structure [41,42], and that the charge distributions in both LSCO [43] and Hg1201 [44] vary on the nanoscale. Based on modeling the disorder in the interstitial layers, it was concluded that the hole mean free path and the screening of the Coulomb repulsion in Hg1201 are substantially larger than in LSCO, hence contributing to the higher T c [39]. In order to fully account for the differences between the two compounds, further consideration of the screening of electronic inhomogeneity inherent to the CuO 2 planes may be necessary.…”