Magnetic phase diagram of underdoped YBa ₂ Cu ₃ O _y inferred from torque magnetization and thermal conductivity

Abstract

Strong evidence for charge-density correlation in the underdoped phase of the cuprate YBa 2 Cu 3 O y was obtained by NMR and resonant X-ray scattering. The fluctuations were found to be enhanced in strong magnetic fields. Recently, 3D 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 κ 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 κ xx at the fields H K and H p , which define phase boundaries in agreement with spectroscopic techniques. From measurements of the melting field H m (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 (41 T), the second vortex solid melts to a vortex liquid which survives to fields well above 41 T. de Haas-van Alphen oscillations appear at fields 24-28 T, below the lower bound for the upper critical field H c2 .cuprate superconductivity | high-field phase diagram | vortex liquid | torque magnetometry | thermal conductivity T he existence of static charge order in underdoped YBa 2 Cu 3 O y (YBCO) in an intense magnetic field was reported by Wu et al.(1) using NMR. Subsequently, Ghiringhelli et al. (2) uncovered temperature-dependent charge-density-wave (CDW) correlations in zero magnetic field by resonant X-ray scattering (RXS). The RXS signal onsets near 180 K and peaks at the superconducting critical temperature T c before falling. Several groups (3-5) recently showed that the RXS intensity is enhanced in finite field H. At low temperature T, several experiments have uncovered field-induced transitions. These include a transition at 18 T from ultrasonic measurements (6), features in the high-field thermal conductivity (7), and the onset of line splitting in the NMR spectra starting at the charge-ordering field H ch = 10-15 T and saturating at around 18-20 T (depending on the hole density p) (8). Recent X-ray diffraction experiments (9-11) show that the transition to a 3D CDW with long-range order (LRO) onsets near H = 15 T.The field-induced CDW state raises several intriguing questions regarding its relation to superconductivity. Does CDW formation with LRO suppress the superconducting condensate? Where is the true upper critical field H c2 ? How does it affect the stability of the vortex solid? Although NMR and X-ray diffraction are incisive probes of charge modulation and CDW formation, they do not couple directly to the fundamental excitations of the pair condensate (quasi-particles and vortices), so they are less sensitive to the pairing correlations which reflect superconductivity. By contrast, the diamagnetic magnetization M d (which dominates the observed mag...

Vortex-core order and field-driven supersolidity

“…This suggests an underlying phase transition driven by tuning vortex density. A similar transition into a second vortex lattice phase has been suggested in YBCO from torque magnetometry results [24]. For α > 8, we find phase separation into square and triangular vortex lattices.…”

“…We see that vortices themselves show interesting ordering phenomena with the vortex lattice changing from triangular to square configuration. This resembles the suggestion of two vortex solid states in YBCO from torque magnetometry measurements [24].…”

“…This is an exciting direction for future study. In fact, field-induced coexistence and a charge-ordered vortex-liquid state have been reported in YBCO [24,26,27]. …”

Resonant x-ray scattering study of charge-density wave correlations inYBa2Cu3O6+x

“…While d-wave superconductivity preempts PDW long-range order for H = 0, recent magnetometric experiments suggest that it may be the leading instability in high magnetic fields. [88] In-plane anisotropy and relationship to stripes…”

Andreev-Bragg Reflection from an Amperian Superconductor

“…The pairing mechanism comes from the gauge field formulation of the resonating valence bond theory of high-T c superconductivity [1,[13][14][15][16], where electrons moving in the same direction feel an attractive force analogous to Ampère's force between current-carrying wires [17]. Lee has proposed this Amperian pairing to explain the diversity of anomalous properties that characterize the pseudogap phase in underdoped cuprate superconductors, including the appearance of Fermi arcs in the quasiparticle spectrum [18], charge order with a doping-dependent wave vector [19][20][21][22][23][24][25][26][27][28], and indications of short-range superconducting order [29][30][31][32].Phase-sensitive experimental tests for Amperian pairing are hindered by phase fluctuations and the nucleation of vortex antivortex pairs that are believed to suppress longrange phase coherence [12]. Here we propose to use Andreev reflection as a phase-insensitive probe, which being a local process would not require long-range superconducting order.…”