The phase diagram of underdoped cuprates in a magnetic field ( H ) is key to understanding the anomalous normal state of these high-temperature superconductors. However, the upper critical field ( H c2 ), the extent of superconducting (SC) phase with vortices, and the role of charge orders at high H remain controversial. Here we study stripe-ordered La-214, i.e., cuprates in which charge orders are most pronounced and zero-field SC transition temperatures T c 0 are lowest. This enables us to explore the vortex phases in a previously inaccessible energy scale window. 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 quantum fluctuations and disorder play a key role as T → 0 , while the high-field ground state is likely a metal, not an insulator, due to the presence of stripes.
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Artificial Pinning Centers in (Y,RE)-Ba-Cu-O Superconductors: Recent Progress and Future Perspective
A microscopic understanding of vortex pinning in type II superconductors began
with the theoretical discovery of magnetic vortices by Abrikosov, which received
the 2003 Nobel Prize in Physics [1, 2]. When type II superconductors are exposed
to magnetic fields (H), the magnetic field enters as quantized vortices, each with a
fundamental flux j0 = 2.07 × 10−11 T cm−2
, or 2.07 × 10−15 Wb. The vortex
core size on the order of the superconducting coherence length can be very small,
e.g. ∼1–2 nm for the cuprate family of high-temperature superconductors (HTSs).
The vortices electrically interact with each other by repelling, and act collectively
together as a flux lattice that is affected by the intrinsic crystal lattice properties
and microstructure defects. For superconducting power applications where applied
magnetic fields are in the range of 0.1 T to >30 T, the areal number density of the
vortices can reach incredibly high values. For example, for an applied magnetic
field of 5 T, the vortex areal density is around 2.5 × 1011 cm−2
, which translates
to inter-vortex spacing of about 20 nm (assuming a square lattice for vortices).
Somewhat surprisingly, if the crystal lattice for type II superconductors, such
as HTS cuprates [3] is nearly perfect without any defects to pin vortices, the
vortices can move collectively and almost freely in an applied magnetic field due
to Lorentz forces, which results in electrical resistance at a fairly low critical
current density Jc(H, T) at an applied magnetic field (H) and temperature (T). In
order to realize useful critical current densities in type II superconductors,
imperfections and defects must be added to the crystal lattice to effectively pin
vortices. The simplest example of this was achieved in the (Y, RE)Ba2Cu3O7
(where RE is rare earth elements) family by depositing thin films, in which
high densities of dislocations and other growth defects are added into the film
microstructure and dramatically increase the critical current density Jc(77 K,
H//c-axis) > 106 A cm−2 compared to Jc (77 K) < 103 A cm−2 for single crystals
[4–6]
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- Award ID(s):
- 1508494
- NSF-PAR ID:
- 10149355
- Date Published:
- Journal Name:
- Superconductor science technology
- Volume:
- 33
- ISSN:
- 1361-6668
- Page Range / eLocation ID:
- 040301
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Iron-based 1111-type superconductors display high critical temperatures and relatively high critical current densities
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null (Ed.)Two new alkali vanadate carbonates with divalent transition metals have been synthesized as large single crystals via a high-temperature (600 °C) hydrothermal technique. Compound I , Rb 2 Mn 3 (VO 4 ) 2 CO 3 , crystallizes in the trigonal crystal system in the space group P 3̄1 c , and compound II , K 2 Co 3 (VO 4 ) 2 CO 3 , crystallizes in the hexagonal space group P 6 3 / m . Both structures contain honeycomb layers and triangular lattices made from edge-sharing MO 6 octahedra and MO 5 trigonal bipyramids, respectively. The honeycomb and triangular layers are connected along the c -axis through tetrahedral [VO 4 ] groups. The MO 5 units are connected with each other by carbonate groups in the ab -plane by forming a triangular magnetic lattice. The difference in space groups between I and II was also investigated with Density Functional Theory (DFT) calculations. Single crystal magnetic characterization of I indicates three magnetic transitions at 77 K, 2.3 K, and 1.5 K. The corresponding magnetic structures for each magnetic transition of I were determined using single crystal neutron diffraction. At 77 K the compound orders in the MnO 6 -honeycomb layer in a Néel-type antiferromagnetic orientation while the MnO 5 triangular lattice ordered below 2.3 K in a colinear ‘up–up–down’ fashion, followed by a planar ‘Y’ type magnetic structure. K 2 Co 3 (VO 4 ) 2 CO 3 ( II ) exhibits a canted antiferromagnetic ordering below T N = 8 K. The Curie–Weiss fit (200–350 K) gives a Curie–Weiss temperature of −42 K suggesting a dominant antiferromagnetic coupling in the Co 2+ magnetic sublattices.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/1088/1361-6668/ab4ccd
