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In strongly correlated systems the strength of Coulomb interactions between electrons, relative to their kinetic energy, plays a central role in determining their emergent quantum mechanical phases. We perform resonant x-ray scattering on Bi2Sr2CaCu2O8+δ, a prototypical cuprate superconductor, to probe electronic correlations within the CuO2 plane. We discover a dynamic quasi-circular pattern in the x-y scattering plane with a radius that matches the wave vector magnitude of the well-known static charge order. Along with doping- and temperature-dependent measurements, our experiments reveal a picture of charge order competing with superconductivity where short-range domains along x and y can dynamically rotate into any other in-plane direction. This quasi-circular spectrum, a hallmark of Brazovskii-type fluctuations, has immediate consequences to our understanding of rotational and translational symmetry breaking in the cuprates. We discuss how the combination of short- and long-range Coulomb interactions results in an effective non-monotonic potential that may determine the quasi-circular pattern. Knowledge of effective Coulomb interactions is central to understand emergent quantum phases in strongly correlated systems. Here, Boschini et al. report a dynamic quasi-circular spectrum of charge density wave fluctuations in the CuO2 plane of Bi2Sr2CaCu2O8+δ, shedding a light on understanding how Coulomb interactions can lead to rotational and translational symmetry breaking in the cuprates. [ABSTRACT FROM AUTHOR]

A central mystery in high-temperature superconductivity is the origin of the so-called strange metal (i.e., the anomalous conductor from which superconductivity emerges at low temperature). Measuring the dynamic charge response of the copper oxides, X "(q,ω), would directly reveal the collective properties of the strange metal, but it has never been possible to measure this quantity with millielectronvolt resolution. Here, we present a measurement of X "(q,ω) for a cuprate, optimally doped Bi2.1Sr1.9CaCu2O8+x (Tc = 91 K), using momentum-resolved inelastic electron scattering. In the medium energy range 0.1-2 eV relevant to the strange metal, the spectra are dominated by a featureless, temperature- and momentum-independent continuum persisting to the electronvolt energy scale. This continuum displays a simple power-law form, exhibiting q2 behavior at low energy and q2/ω2 behavior at high energy. Measurements of an overdoped crystal (Tc = 50 K) showed the emergence of a gap-like feature at low temperature, indicating deviation from power law form outside the strange-metal regime. Our study suggests the strange metal exhibits a new type of charge dynamics in which excitations are local to such a degree that space and time axes are decoupled. [ABSTRACT FROM AUTHOR]

Understanding the structure of the wavefunction is essential for depicting the surface states of a topological insulator. Owing to the inherent strong spin-orbit coupling, the conventional hand-waving picture of the Dirac surface state with a single chiral spin texture is incomplete, as this ignores the orbital components of the Dirac wavefunction and their coupling to the spin textures. Here, by combining orbital-selective angle-resolved photoemission experiments and first-principles calculations, we deconvolve the in-plane and out-of-plane p-orbital components of the Dirac wavefunction. The in-plane orbital wavefunction is asymmetric relative to the Dirac point. It is predominantly tangential (radial) to the k-space constant energy surfaces above (below) the Dirac point. This orbital texture switch occurs exactly at the Dirac point, and therefore should be intrinsic to the topological physics. Our results imply that the Dirac wavefunction has a spin-orbital texture-a superposition of orbital wavefunctions coupled with the corresponding spin textures. [ABSTRACT FROM AUTHOR]

The physiological properties of Purkinje neurons play a central role in their ability to regulate information transfer through the cerebellum. A number of ion channels contribute to Purkinje neuron physiology including an abundance of P‐type Ca 2+ channels, particularly in the dendritic region. Purkinje neurons also express L‐type Ca 2+ channels both during development and in the mature state. However, a role for L‐type channels in Purkinje neuron physiology has yet to be fully defined. In the current study we used physiological recordings from cultured Purkinje neurons and the L‐type Ca 2+ channel agonist S‐(-)‐Bay K to assess a potential role for L‐type Ca 2+ channels in spike firing. Results show that Bay K alters current‐evoked spike firing in young, immature Purkinje neurons without dendritic structure and in older, more mature Purkinje neurons with dendritic structure. Bay K also enhanced Ca 2+ signals associated with the current‐evoked spike firing. The effect of Bay K was more prominent in the young Purkinje neurons than in the older Purkinje neurons, suggesting that L‐type Ca 2+ channels may be more important in the Purkinje neuron physiology during the early stages of development rather than at mature stages. In the older Purkinje neurons, immunohistochemical studies using antibodies to L‐type Ca 2+ channels showed more intense immunolabeling in the somatic region than in the dendritic region. This result suggests that L‐type Ca 2+ channels may play a more important role in somatic physiology than dendritic physiology, whereas P‐type channels may play a more important role in dendritic physiology. [ABSTRACT FROM AUTHOR]

Establishing the presence and the nature of a quantum critical point in their phase diagram is a central enigma of the high-temperature superconducting cuprates. It could explain their pseudogap and strange metal phases, and ultimately their high superconducting temperatures. Yet, while solid evidences exist in several unconventional superconductors of ubiquitous critical fluctuations associated to a quantum critical point, in the cuprates they remain undetected until now. Here using symmetry-resolved electronic Raman scattering in the cuprate Bi 2 Sr 2 CaCu 2 O 8 + δ , we report the observation of enhanced electronic nematic fluctuations near the endpoint of the pseudogap phase. While our data hint at the possible presence of an incipient nematic quantum critical point, the doping dependence of the nematic fluctuations deviates significantly from a canonical quantum critical scenario. The observed nematic instability rather appears to be tied to the presence of a van Hove singularity in the band structure. Solid evidence of quantum fluctuations associated to a quantum critical point in cuprate superconductors remains elusive. Here, Auvray et al. report Raman scattering evidence of enhanced electronic nematic fluctuations near the endpoint of the pseudogap phase in Bi 2 Sr 2 CaCu 2 O 8 + δ . [ABSTRACT FROM AUTHOR]