Connection between charge-density-wave order and charge transport in the cuprate superconductors

Abstract: Charge-density-wave (CDW) correlations within the quintessential CuO$2$ planes have been argued to either cause [1] or compete with [2] the superconductivity in the cuprates, and they might furthermore drive the Fermi-surface reconstruction in high magnetic fields implied by quantum oscillation (QO) experiments for YBa$_2$Cu$_3$O${6+{\delta}}$ (YBCO) [3] and HgBa$2$CuO${4+{\delta}}$ (Hg1201) [4]. Consequently, the observation of bulk CDW order in YBCO was a significant development [5,6,7]. Hg1201 features particularly high structural symmetry and recently has been demonstrated to exhibit Fermi-liquid charge transport in the relevant temperature-doping range of the phase diagram, whereas for YBCO and other cuprates this underlying property of the CuO$_2$ planes is partially or fully masked [8-10]. It therefore is imperative to establish if the pristine transport behavior of Hg1201 is compatible with CDW order. Here we investigate Hg1201 ($T_c$ = 72 K) via bulk Cu L-edge resonant X-ray scattering. We indeed observe CDW correlations in the absence of a magnetic field, although the correlations and competition with superconductivity are weaker than in YBCO. Interestingly, at the measured hole-doping level, both the short-range CDW and Fermi-liquid transport appear below the same temperature of about 200 K. Our result points to a unifying picture in which the CDW formation is preceded at the higher pseudogap temperature by $q$ = 0 magnetic order [11,12] and the build-up of significant dynamic antiferromagnetic correlations [13]. Furthermore, the smaller CDW modulation wave vector observed for Hg1201 is consistent with the larger electron pocket implied by both QO [4] and Hall-effect [14] measurements, which suggests that CDW correlations are indeed responsible for the low-temperature QO phenomenon.

• The paper identifies CDW correlations in Hg1201 using resonant X-ray diffraction and inelastic scattering, uncovering their role in Fermi surface reconstruction.
• It compares Hg1201 and YBCO, demonstrating that weaker CDW in Hg1201 aligns with conventional Fermi-liquid behavior without needing a magnetic field.
• The study implicates antiferromagnetic correlations in driving sequential phase transitions, providing insights for tuning superconducting properties.

Overview of Charge-Density-Wave Correlations and Charge Transport in Cuprate Superconductors

The research paper investigates the relationship between charge-density-wave (CDW) order and charge transport within the context of cuprate superconductors, with a focus on HgBa$_2$CuO$_{4+\delta}$ (Hg1201) and YBa$_2$Cu$_3$O$_{6+\delta}$ (YBCO). This study employs resonant X-ray scattering techniques to explore the CDW correlations in these superconductors and evaluate their implications concerning superconductivity and Fermi-liquid charge transport.

Key Findings

1. Observation of CDW in Hg1201:
   • The study identifies CDW correlations in Hg1201 using resonant X-ray diffraction (RXD) and resonant inelastic X-ray scattering (RIXS). The CDW correlations are detected at a hole-doping level of $p \approx 0.09$ and at temperatures below $T_{\text{CDW}} = 200(15) \text{K}$.
2. Comparison to YBCO:
   • In contrast to YBCO, where CDW correlations appear more entangled with superconductivity, Hg1201 demonstrates weaker CDW correlations without the need for a magnetic field and shows conventional Fermi-liquid behavior over a range of temperatures.
3. Phase Diagram Insights:
   • Both Hg1201 and YBCO exhibit a pseudogap region, and CDW order in Hg1201 appears at lower temperatures than the onset of antiferromagnetic (AF) correlations signified by $q = 0$ magnetic order.
   • The investigation provides evidence that the sequence of transitions (q=0 magnetic order, CDW order, and superconductivity) in these materials might be driven fundamentally by AF correlations.
4. Fermi Surface Reconstruction:
   • The study highlights that CDW correlations are likely drivers for the Fermi surface reconstruction inferred from quantum oscillation (QO) experiments. The connection between CDW order and electrons’ topological features such as Fermi pockets is supported by empirical data presenting an association between CDW wave-vector $\mathbf{H}_{\text{CDW}}$ and QO frequencies.

Implications

From a theoretical standpoint, the paper advances the comprehension of how charge order affects superconductivity and electronic transport properties in high-temperature superconductors. It suggests a potential universal role of CDW correlations across different cuprate families in Fermi surface reconstruction and underscores the influence of AF correlations in orchestrating multiple phases.

Practically, this understanding could be crucial in guiding the synthesis of new materials that optimize superconducting properties by potentially tuning the CDW interactions or stabilizing desired electronic phases via careful control of doping levels and structural environments.

Future Directions

Future investigations might focus on refining the understanding of the interplay between CDW, superconductivity, and pseudogap phenomena across a broader spectrum of cuprate families. Enhanced theoretical models that incorporate experimentally observed nuances in CDW behavior could provide deeper insights into the fundamental physics of high-temperature superconductivity. Additionally, exploring advanced techniques for direct visualization of Fermi surface changes in the presence of CDW correlations could yield valuable data to affirm the proposed connections between structural and electronic orders. Thus, ongoing research may continually test and refine these findings to guide the development of novel, high-performing superconducting materials.