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The interplay between superconductivity and any other competing order is an essential part of the long-standing debate on the origin of high temperature superconductivity in cuprates. Akin to the situation of heavy fermions, organic superconductors and pnictides, it has been proposed that the pairing mechanism in cuprates comes from fluctuations of a nearby quantum phase transition. Recent evidence of charge modulation and the associated fluctuations in the pseudogap phase of YBa_2Cu_3O_y make charge order a likely candidate for a competing order. However, a thermodynamic signature of the charge ordering phase transition is still lacking. Moreover, whether such charge order is one- or two-dimensional is still controversial but pivotal for the understanding the topology of the reconstructed Fermi surface. Here we address both issues by measuring sound velocities in YBCO_6.55 in high magnetic fields, a powerful thermodynamic probe to detect phase transitions. We provide the first thermodynamic signature of the field-induced charge ordering phase transition in YBCO allowing construction of a field-temperature phase diagram, which reveals the competing nature of this charge order. The comparison of different acoustic modes indicates that the charge modulation has a two-dimensional character, thus imposing strong constraints on Fermi surface reconstruction scenarios.
The electrical resistivity rho_c of the underdoped cuprate superconductor YBCO was measured perpendicular to the CuO_2 planes on ultra-high quality single crystals in magnetic fields large enough to suppress superconductivity. The incoherent insulati
The recently demonstrated x-ray scattering approach using a free electron laser with a high field pulsed magnet has opened new opportunities to explore the charge density wave (CDW) order in cuprate high temperature superconductors. Using this approa
Charge density wave (CDW) correlations feature prominently in the phase diagram of the cuprates, motivating competing theories of whether fluctuating CDW correlations aid superconductivity or whether static CDW order coexists with superconductivity i
In a multiorbital model of the cuprate high-temperature superconductors soft antiferromagnetic (AF) modes are assumed to reconstruct the Fermi surface to form nodal pockets. The subsequent charge ordering transition leads to a phase with a spatially
The normal state of cuprates is dominated by the strange metal phase that, near optimal doping, shows a linear temperature dependence of the resistivity persisting down to the lowest $T$, when superconductivity is suppressed. For underdoped cuprates