Electronic inhomogeneity appears to be an inherent characteristic of the enigmatic cuprate superconductors. Here we report the observation of charge-density-wave correlations in the model cuprate superconductor HgBa2CuO(4+δ) (T(c)=72 K) via bulk Cu L3-edge-resonant X-ray scattering. At the measured hole-doping level, both the short-range charge modulations and Fermi-liquid transport appear below the same temperature of about 200 K. Our result points to a unifying picture in which these two phenomena are preceded at the higher pseudogap temperature by q=0 magnetic order and the build-up of significant dynamic antiferromagnetic correlations. The magnitude of the charge modulation wave vector is consistent with the size of the electron pocket implied by quantum oscillation and Hall effect measurements for HgBa2CuO(4+δ) and with corresponding results for YBa2Cu3O(6+δ), which indicates that charge-density-wave correlations are universally responsible for the low-temperature quantum oscillation phenomenon.

Carrier relaxation and recombination in self-organized InAs/GaAs quantum dots ͑QD's͒ is investigated by photoluminescence ͑PL͒, PL excitation ͑PLE͒, and time-resolved PL spectroscopy. We demonstrate inelastic phonon scattering to be the dominant intradot carrier-relaxation mechanism. Multiphonon processes involving up to four LO phonons from either the InAs QD's, the InAs wetting layer, or the GaAs barrier are resolved. The observation of multiphonon resonances in the PLE spectra of the QD's is discussed in analogy to hot exciton relaxation in higher-dimensional semiconductor systems and proposed to be intricately bound to the inhomogeneity of the QD ensemble in conjunction with a competing nonradiative recombination channel observed for the excited hole states. Carrier capture is found to be a cascade process with the initial capture into excited states taking less than a few picoseconds and the multiphonon ͑involving three LO phonons͒ relaxation time of the first excited hole state being 40 ps. The ͉001͘ hole state presents a relaxation bottleneck that determines the ground-state population time after nonresonant excitation. For the small self-organized InAs/GaAs QD's the intradot carrier relaxation is shown to be faster than radiative ͑Ͼ1 ns͒ and nonradiative ͑Ϸ100 ps͒ recombination explaining the absence of a ''phonon bottleneck'' effect in the PL spectra. ͓S0163-1829͑97͒09340-5͔

We report in-plane resistivity (ρ) and transverse magnetoresistance (MR) measurements in underdoped HgBa2CuO 4+δ (Hg1201). Contrary to the longstanding view that Kohler's rule is strongly violated in underdoped cuprates, we find that it is in fact satisfied in the pseudogap phase of Hg1201. The transverse MR shows a quadratic field dependence, δρ/ρo = aH 2 , with a(T ) ∝ T −4 . In combination with the observed ρ ∝ T 2 dependence, this is consistent with a single Fermi-liquid quasiparticle scattering rate. We show that this behavior is universal, yet typically masked in cuprates with lower structural symmetry or strong disorder effects.The unusual metallic 'normal state' of the cuprates, from which superconductivity evolves upon cooling, has remained an enigma. A number of atypical observations seemingly at odds with the conventional Fermi-liquid theory of metals have been made particularly in the strangemetal regime above the pseudogap (PG) temperature T * (inset of Fig. 1(b)) [1]. In this regime, the in-plane resistivity exhibits an anomalous extended linear temperature dependence, ρ ∝ T [2], and the Hall effect is often described as R H ∝ 1/T [3,4]. In order to account for this anomolous behavior without abandoning a Fermi-liquid formalism, some descriptions have been formulated based on a scattering rate whose magnitude varies around the in-plane Fermi surface, for example due to anisotropic Umklapp scattering or coupling to a bosonic mode [1] (e.g., spin [5] or charge [6] fluctuations). Prominent nonFermi-liquid prescriptions with far-ranging implications for the cuprate phase-diagram, such as the two-lifetime picture [7] and the marginal-Fermi-liquid [8] have also been put forth. The former implies charge-spin separation while the latter is a signature of a proximate quantum critical point.The transport behavior in the PG state (T < T * ) seems to be even less clear. Interpretation of this regime has been complicated not only because of the opening of the PG along portions of the Fermi surface, but also due to possible superconducting [9], antiferromagnetic [5,10], and charge-spin stripe fluctuations [11], which might influence transport properties. Electrical transport for temperatures below T * therefore has been generally described as a deviation from the better-behaved hightemperature behavior [1].Recent developments, however, suggests that T * marks a phase transition [12] into a state with broken timereversal symmetry [13,14]. Additionally, the measurable extent of superconducting fluctuations is likely limited to only a rather small temperature range (≈ 30 K) above T c [15,16]. These strong indications that the PG regime is indeed a distinct phase calls for a clear description of its intrinsic properties. In fact, a simple ρ = A 2 T 2 dependence was recently reported for underdoped HgBa 2 CuO 4+δ (Hg1201) [17]. It was also found that this Fermi-liquid-like behavior universally appears below a characteristic temperature T

Antiferromagnetic correlations have been argued to be the cause of the d-wave superconductivity and the pseudogap phenomena exhibited by the cuprates. Although the antiferromagnetic response in the pseudogap state has been reported for a number of compounds, there exists no information for structurally simple HgBa2CuO4+δ. Here we report neutron-scattering results for HgBa2CuO4+δ (superconducting transition temperature Tc≈71 K, pseudogap temperature T*≈305 K) that demonstrate the absence of the two most prominent features of the magnetic excitation spectrum of the cuprates: the X-shaped ‘hourglass' response and the resonance mode in the superconducting state. Instead, the response is Y-shaped, gapped and significantly enhanced below T*, and hence a prominent signature of the pseudogap state.