Vortex phase diagram and the normal state of cuprates with charge and spin orders

Abstract

The phase diagram of underdoped cuprates in a magnetic field (H) is the key ingredient in understanding the anomalous normal state of these high-temperature superconductors. However, the upper critical field (H c2 ) or the extent of superconducting phase with vortices, a type of topological excitations, and the role of charge orders that are present at high H, remain under debate. We address these questions by studying stripe-ordered La-214, i.e. cuprates in which charge orders are most pronounced and zero-field transition temperatures T 0 c are lowest; the latter opens a much larger energy scale 1 arXiv:1907.11706v1 [cond-mat.supr-con] 25 Jul 2019 window to explore the vortex phases compared to previous studies.By combining linear and nonlinear transport techniques sensitive to vortex matter, we determine the T -H phase diagram, directly detect H c2 , and reveal novel properties of the high-field ground state.Our results demonstrate that, while the vortex phase diagram of underdoped cuprates is not very sensitive to the details of the charge orders, quantum fluctuations and disorder play a key role as T → 0.The presence of stripes, on the other hand, seems to alter the nature of the anomalous normal state, such that the high-field ground state is a metal, as opposed to an insulator.

Pair density wave at high magnetic fields in cuprates with charge and spin orders

“…At T = 0.017 K, for example, the anisotropy increases with H ⊥ by over an order of magnitude before reaching a peak (ρ c /ρ ab > 10 5 ) at H ⊥ = H p , signifying decoupling of or the loss of phase coherence between the planes. However, strong SC correlations persist in the planes for H ⊥ > H p : here ρ c /ρ ab decreases with H ⊥ to H ⊥ -independent values, comparable to those at high T, for the highest H ⊥ > 20 T. This is in agreement with previous evidence 23 that the H ⊥ > 20 T region corresponds to the normal state. A smooth, rapid decrease of the anisotropy for H ⊥ > H p is interrupted by a bump or an enhancement in ρ c /ρ ab , centered at H b .…”

“…Supplementary Fig. 2a), which corresponds 23 to the upper critical field H c2 in these materials (see also Supplementary Note 1). Indeed, at a fixed T, ρ c /ρ ab starts to increase as H ⊥ is reduced below H peak .…”

“…SC-like) or insulating-like, when the normal state sheet resistance R □/layer ≈ R Q , where R Q = h/(2e) 2 is the quantum resistance for Cooper pairs, further supports this conclusion: it agrees with the expectations for a 2D superconductor-insulator transition (SIT) driven by quantum fluctuations of the SC phase 24 . In addition, as previously noted 23 , the two-step ρ ab (T) is reminiscent of that in granular films of conventional superconductors and systems with nanoscale phase separation, including engineered 17 16 15 Josephson junction arrays, where they are generally attributed to the onset of local (e.g. in islands or puddles) and global, 2D superconductivity.…”

“…The ρ ab (T) data were extracted from the in-plane magnetoresistance (MR) measurements (ref. 23 , Supplementary Fig. 2a; unless stated otherwise, the results are shown for La 1.7 Eu 0.2 Sr 0.1 CuO 4 sample B, see "Methods" section); the raw ρ c (H) data are shown in Supplementary Fig.…”

“…The striking splitting of the ρ ab (T) curves in both materials (ref. 23 , Fig. 2c, d), into either metallic-like (i.e.…”