The magnetic phase diagram of underdoped YBa2Cu3Oy inferred from torque magnetization and thermal conductivity

Strong evidence for charge-density correlation in the underdoped phase of the cuprate YBa2Cu3Oy was obtained by nuclear magnetic resonance (NMR) and resonant x-ray scatter- ing. The fluctuations were found to be enhanced in strong magnetic fields. Recently, 3D (three dimensional) charge-density wave (CDW) formation with long-range order (LRO) was observed by x-ray diffraction in H >15 T. To elucidate how the CDW transition impacts the pair condensate, we have used torque magnetization to 45 T and thermal conductivity $\kappa_{xx}$ to construct the magnetic phase diagram in untwinned crystals with hole density p = 0.11. We show that the 3D CDW transitions appear as sharp features in the susceptibility and $\kappa_{xx}$ at the fields HK and Hp, which define phase boundaries in agreement with spectroscopic techniques. From measurements of the melting field Hm(T) of the vortex solid, we obtain evidence for two vortex solid states below 8 K. At 0.5 K, the pair condensate appears to adjust to the 3D CDW by a sharp transition at 24 T between two vortex solids with very different shear moduli. At even higher H (42 T) the second vortex solid melts to a vortex liquid which survives to fields well above 45 T. de Haas-van Alphen oscillations appear at fields 24-28 T, below the lower bound for the upper critical field Hc2.Comment: 7 pages, 8 figures; New version of previous posting, reporting torque measurements to 45 Tesla and final magnetic phase diagra

Influence of the Fermi Surface Morphology on the Magnetic Field-Driven Vortex Lattice Structure Transitions in YBa2_{2}Cu3_{3}O7−δ:δ=_{7-\delta}:\delta=0, 0.15

We report small-angle neutron scattering measurements of the vortex lattice (VL) structure in single crystals of the lightly underdoped cuprate superconductor YBa2Cu3O6.85. At 2 K, and for fields of up to 16 T applied parallel to the crystal c-axis, we observe a sequence of field-driven and first-order transitions between different VL structures. By rotating the field away from the c-axis, we observe each structure transition to shift to either higher or lower field dependent on whether the field is rotated towards the [100] or [010] direction. We use this latter observation to argue that the Fermi surface morphology must play a key role in the mechanisms that drive the VL structure transitions. Furthermore, we show this interpretation is compatible with analogous results obtained previously on lightly overdoped YBa2Cu3O7. In that material, it has long-been suggested that the high field VL structure transition is driven by the nodal gap anisotropy. In contrast, the results and discussion presented here bring into question the role, if any, of a nodal gap anisotropy on the VL structure transitions in both YBa2Cu3O6.85 and YBa2Cu3O7

Dependence of Tc_{c} of YBa2_{2} Cu3_{3} O6.67_{6.67} on in-plane uniaxial stress

We probe the effect on $T_c$ of in-plane uniaxial stress applied to the high-temperature superconductor $YBa_2Cu_3O_{6.67}$. We find a highly anisotropic response. Under compression along the $b$ axis, which reduces the orthorhombicity of the $CuO_2$ planes, $T_c$ is broadly flat for stresses up to at least 1.7 GPa. Under compression along the $a$ axis, $T_c$ decreases steeply. For stresses beyond $≈1$ GPa the decrease is quasilinear. We hypothesize that superconductivity is suppressed by competition with uniaxial charge density wave order, which has been found to onset at $≈1$ GPa

High field charge order across the phase diagram of YBa₂Cu₃Oy

In hole-doped cuprates there is now compelling evidence that inside the pseudogap phase, charge order breaks translational symmetry. In YBa2Cu3O y charge order emerges in two steps: a 2D order found at zero field and at high temperature inside the pseudogap phase, and a 3D order that is superimposed below the superconducting transition Tc when superconductivity is weakened by a magnetic field. Several issues still need to be addressed such as the effect of disorder, the relationship between those charge orders and their respective impact on the Fermi surface. Here, we report high magnetic field sound velocity measurements of the 3D charge order in underdoped YBa2Cu3O y in a large doping range. We found that the 3D charge order exists over the same doping range as its 2D counterpart, indicating an intimate connection between the two distinct orders. Moreover, our data suggest that 3D charge order has only a limited impact on low-lying electronic states of YBa2Cu3O y

Unconventional quantum vortex matter state hosts quantum oscillations in the underdoped high-temperature cuprate superconductors.

A central question in the underdoped cuprates pertains to the nature of the pseudogap ground state. A conventional metallic ground state of the pseudogap region has been argued to host quantum oscillations upon destruction of the superconducting order parameter by modest magnetic fields. Here, we use low applied measurement currents and millikelvin temperatures on ultrapure single crystals of underdoped [Formula: see text] to unearth an unconventional quantum vortex matter ground state characterized by vanishing electrical resistivity, magnetic hysteresis, and nonohmic electrical transport characteristics beyond the highest laboratory-accessible static fields. A model of the pseudogap ground state is now required to explain quantum oscillations that are hosted by the bulk quantum vortex matter state without experiencing sizable additional damping in the presence of a large maximum superconducting gap; possibilities include a pair density wave.Royal Society Winton Programme for the Physics of Sustainability Engineering and Physical Sciences Research Council (EPSRC; studentship and grant numbers EP/R513180/1, EP/M506485/1 and EP/P024947/1) European Research Council under the European Unions Seventh Framework Programme (Grant Agreement numbers 337425 and 772891). EPSRC Strategic Equipment Grant EP/M000524/1 Leverhulme Trust by way of the award of a Philip Leverhulme Prize. National Key Research and Development Program of China (grant no. 2016YFA0401704). Work performed at the National High Magnetic Field Laboratory (NHMFL) supported by NSF Cooperative Agreement DMR-1157490, the State of Florida, and the Department of Energy (DOE) DOE Basic Energy Sciences project: ‘Science of 100 tesla’

Universality of q = 1 2 orbital magnetism in the pseudogap phase of the high- T c superconductor YBa 2 Cu 3 O 6 + x

International audienc

Hidden magnetic texture in the pseudogap phase of high-Tc YBa2Cu3O6.6

International audienceAbstract Despite decades of intense research, the enigmatic pseudo-gap (PG) phase of superconducting cuprates remains unsolved. In the last 15 years, various symmetry breaking states were discovered in the PG phase, including an intra-unit cell (IUC) magnetism, which preserves the lattice translational (LT) symmetry but breaks the time-reversal and parity symmetries, and an additional incipient charge density wave breaking the LT symmetry. However, none of these states can (alone) account for the partial gapping of the Fermi surface. Here we report a hidden LT-breaking magnetism using polarized neutron diffraction. Our measurements reveal magnetic correlations, in two different underdoped YBa 2 Cu 3 O 6.6 single crystals that set in at the PG onset temperature with (i) a planar propagation wave vector ( π , 0) ≡ (0, π ), yielding a doubling or quadrupling of the magnetic unit cell and (ii) magnetic moments mainly pointing perpendicular to the CuO 2 layers. The LT-breaking magnetism is at short-range suggesting the formation of clusters of 5–6 unit cells. Together with the previously reported IUC magnetism, it yields a hidden magnetic texture of the CuO 2 unit cells hosting loop currents, forming large supercells that may be helpful for elucidating the PG puzzle

Hidden magnetic texture in the pseudogap phase of high-Tc YBa2Cu3O6.6

International audienceAbstract Despite decades of intense research, the enigmatic pseudo-gap (PG) phase of superconducting cuprates remains unsolved. In the last 15 years, various symmetry breaking states were discovered in the PG phase, including an intra-unit cell (IUC) magnetism, which preserves the lattice translational (LT) symmetry but breaks the time-reversal and parity symmetries, and an additional incipient charge density wave breaking the LT symmetry. However, none of these states can (alone) account for the partial gapping of the Fermi surface. Here we report a hidden LT-breaking magnetism using polarized neutron diffraction. Our measurements reveal magnetic correlations, in two different underdoped YBa 2 Cu 3 O 6.6 single crystals that set in at the PG onset temperature with (i) a planar propagation wave vector ( π , 0) ≡ (0, π ), yielding a doubling or quadrupling of the magnetic unit cell and (ii) magnetic moments mainly pointing perpendicular to the CuO 2 layers. The LT-breaking magnetism is at short-range suggesting the formation of clusters of 5–6 unit cells. Together with the previously reported IUC magnetism, it yields a hidden magnetic texture of the CuO 2 unit cells hosting loop currents, forming large supercells that may be helpful for elucidating the PG puzzle