Akash V. Maharaj

Ideal charge-density-wave order in the high-field state of superconducting YBCO

Significance Compelling evidence of various forms of nonsuperconducting electronic order in the cuprate high-temperature superconductors has fundamentally altered our understanding of the essential physics of these materials. However, it has been difficult to establish the nature of the quantum (zero-temperature) phases that compete and/or coexist with superconductivity. By studying high-quality crystals of YBCO using an X-ray laser and pulsed magnetic fields, we have established that the field induced charge-density-wave (CDW) order that arises when superconductivity is suppressed at low temperatures is incommensurate, unidirectional, and 3D-ordered. While disorder ultimately precludes true CDW long-range order, there does appear to be a sharply defined crossover field, which we associate with a transition to a nematic state with long-range orientational order. The existence of charge-density-wave (CDW) correlations in cuprate superconductors has now been established. However, the nature of the CDW ground state has remained uncertain because disorder and the presence of superconductivity typically limit the CDW correlation lengths to only a dozen unit cells or less. Here we explore the field-induced 3D CDW correlations in extremely pure detwinned crystals of YBa2Cu3O2 (YBCO) ortho-II and ortho-VIII at magnetic fields in excess of the resistive upper critical field (Hc2) where superconductivity is heavily suppressed. We observe that the 3D CDW is unidirectional and possesses a long in-plane correlation length as well as significant correlations between neighboring CuO2 planes. It is significant that we observe only a single sharply defined transition at a critical field proportional to Hc2, given that the field range used in this investigation overlaps with other high-field experiments including quantum oscillation measurements. The correlation volume is at least two to three orders of magnitude larger than that of the zero-field CDW. This is by far the largest CDW correlation volume observed in any cuprate crystal and so is presumably representative of the high-field ground state of an “ideal” disorder-free cuprate.

Crisscrossed stripe order from interlayer tunneling in hole-doped cuprates

Motivated by recent observations of charge order in the pseudogap regime of hole-doped cuprates, we show that {\it crisscrossed} stripe order can be stabilized by coherent, momentum-dependent interlayer tunneling, which is known to be present in several cuprate materials. We further describe how subtle variations in the couplings between layers can lead to a variety of stripe ordering arrangements, and discuss the implications of our results for recent experiments in underdoped cuprates.

Disruption of quantum oscillations by an incommensurate charge density wave

Because a material with an incommensurate charge density wave (ICDW) is only quasiperiodic, Blochs theorem does not apply and there is no sharply defined Fermi surface. We will show that, as a consequence, there are no quantum oscillations which are truly periodic functions of

Particle-hole condensates of higher angular momentum in hexagonal systems

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Hall number across a van Hove singularity

(where

Symmetry constraints on the elastoresistivity tensor

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Elastoconductivity as a probe of broken mirror symmetries

is the magnitude of an applied magnetic field). For a weak ICDW, there exist broad ranges of

Transverse fields to tune an Ising-nematic quantum phase transition

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Quantum oscillations in a bilayer with broken mirror symmetry: A minimal model for YBa 2 Cu 3 O 6 + δ

in which approximately periodic variations occur, but with frequencies that vary inexorably in an unending cascade with increasing

The almost mobility edge in the almost Mathieu equation

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