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

Abstract

We present a detailed synchrotron x-ray scattering study of the charge-density-wave (CDW) order in simple tetragonal HgBa 2 CuO 4+δ (Hg1201). Resonant soft x-ray scattering measurements reveal that short-range order appears at a temperature that is distinctly lower than the pseudogap temperature and in excellent agreement with a prior transient reflectivity result. Despite considerable structural differences between Hg1201 and YBa 2 Cu 3 O 6+δ , the CDW correlations exhibit similar doping dependencies, and we demonstrate a universal relationship between the CDW wave vector and the size of the reconstructed Fermi pocket observed in quantum oscillation experiments. The CDW correlations in Hg1201 vanish already below optimal doping, once the correlation length is comparable to the CDW modulation period, and they appear to be limited by the disorder potential from unit cells hosting two interstitial oxygen atoms. A complementary hard x-ray diffraction measurement, performed on an underdoped Hg1201 sample in magnetic fields along the crystallographic c axis of up to 16 T, provides information on the form factor of the CDW order. As expected from the single-CuO 2 -layer structure of Hg1201, the CDW correlations vanish at half-integer values of L and appear to be peaked at integer L. We conclude that the atomic displacements associated with the short-range CDW order are mainly planar, within the CuO 2 layers.

Evidence for a universal Fermi-liquid scattering rate throughout the phase diagram of the copper-oxide superconductors

“…In particular, we find that n H ∝ p, consistent with the result for LSCO (p = x < 0.08) and with the observation that the dc-resistivity scales as 1/p ( [4]). In fact, a systematically larger carrier density of~25% for Hg1201 would shift the center of the T(p) plateau and the doping level of the strongest charge-order effects from p≈0.09 to p=0.11-0.12, consistent with analogous results for other cuprates [8,37].…”

“…At temperatures below T ** , these n H =p/V planar holes per CuO 2 unit give rise to the previously observed unmasked PG/FL behavior [4,22,23]. This characteristic temperature furthermore appears to be an upper bound to the charge-density-wave order exhibited by a range of cuprates, including Hg1201 [37,62]. On the very overdoped side of the phase diagram, the observation of pristine FL behavior in both transport and thermodynamic properties [2,3] indicates that the remnants of the PG are gone.…”

“…We note that quantum oscillation experiments for underdoped YBCO and Hg1201 indicate a small, pocketlike Fermi-surface with an effective mass of m * =2−3 m e (m e is the free-electron mass) that is approximately half as large as that for highly doped Tl2201 [87]. Whereas the small Fermi surface measured in underdoped Hg1201 and YBCO is the result of a Fermi-surface reconstruction [37,62,[87][88][89] that can be expected to modify the effective mass, the experiments on Tl2201 determine the large unreconstructed Fermi surface [3] and hence are directly relevant to the present discussion.…”

“…The weak temperature dependence of R H between T c and T ** might therefore be related to the subtleties of the arc-tip formation. Alternatively, it might be associated with the appearance of SC traces [34][35][36] or with charge-density-wave correlations [37]. Second, with increasing hole concentration, the cuprates undergo a change from Fermi arcs to a closed Fermi surface in a non-universal, compound-specific fashion [25].…”

Dual structure in the charge excitation spectrum of electron-doped cuprates

“…The origin of the charge order (CO), originally observed in underdoped hole-doped cuprates (h-cuprates) [1][2][3][4][5][6][7][8][9][10][11][12][13][14] , is an active topic in condensed matter physics. The recent xray experiments for electron-doped cuprates (e-cuprates) 15,16 push the field even further.…”