James Day

Quasiparticle mass enhancement approaching optimal doping in a high-Tc superconductor

Massive electrons signify correlations Thirty years on, and the mechanism of superconductivity in copper-oxide superconductors remains a mystery. Knowledge of their normal nonsuperconducting state is also incomplete; however, we do know that the more robust the superconductivity, the higher the magnetic fields required to suppress it. Ramshaw et al. studied samples of three different compositions of the copper-oxide YBa2Cu3O6+δ in magnetic fields exceeding 90 T. They found that as the oxygen content increased toward the point of the maximum transition temperature, the conducting electrons became heavier and heavier. This mass enhancement reflected an increase in electronic correlations, which in turn may be a signature of a quantum critical point. Science, this issue p. 317 Quantum oscillation measurements track the doping dependence of the effective electron mass in the cuprate YBa2Cu3O6+δ. In the quest for superconductors with higher transition temperatures (Tc), one emerging motif is that electronic interactions favorable for superconductivity can be enhanced by fluctuations of a broken-symmetry phase. Recent experiments have suggested the existence of the requisite broken-symmetry phase in the high-Tc cuprates, but the impact of such a phase on the ground-state electronic interactions has remained unclear. We used magnetic fields exceeding 90 tesla to access the underlying metallic state of the cuprate YBa2Cu3O6+δ over a wide range of doping, and observed magnetic quantum oscillations that reveal a strong enhancement of the quasiparticle effective mass toward optimal doping. This mass enhancement results from increasing electronic interactions approaching optimal doping, and suggests a quantum critical point at a hole doping of pcrit ≈ 0.18.

Angle dependence of quantum oscillations in YBa2Cu3O6.59 shows free-spin behaviour of quasiparticles

A genetic-algorithm approach to analysing quantum oscillations in a high-temperature superconductor reveals that quasiparticles behave as nearly free spins—split into spin-up and spin-down populations, known as the Zeeman effect.

Two types of nematicity in the phase diagram of the cuprate superconductor YBa 2 Cu 3 O y

Nematicity has emerged as a key feature of cuprate superconductors, but its link to other fundamental properties such as superconductivity, charge order and the pseudogap remains unclear. Here we use measurements of transport anisotropy in YBa

Precision microwave electrodynamic measurements of K- and Co-dopedBaFe2As2

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Vortex lattice melting and H c 2 in underdoped YBa 2 Cu 3 O y

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Direct measurement of shear modulus at low frequencies and small strains

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Evaluating metacognitive scaffolding in Guided Invention Activities

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Making the failure more productive: scaffolding the invention process to improve inquiry behaviors and outcomes in invention activities

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Gender gaps and gendered action in a first-year physics laboratory

to distinguish two types of nematicity. The first is associated with short-range charge-density-wave modulations in a doping region near

Acoustic Resonances and Non-linearity in Solid 4He

p = 0.12