[Paper Review] A spin ladder compound doubles its superconducting TC under a gentle uniaxial pressure

D. Mohan Radheep, R. Thiyagarjan+8 more|arXiv (Cornell University)|Mar 5, 2013

Physics of Superconductivity and Magnetism26 references3 citations

TL;DR

This study demonstrates that applying a gentle uniaxial pressure of just 0.06 GPa along the ladder planes of the spin ladder compound Sr3Ca11Cu24O41 doubles its superconducting transition temperature (TC) from 12 K to 24 K. Unlike previous hydrostatic pressure experiments requiring ~5 GPa to reach only 12 K, this anisotropic pressure tuning reveals opposing effects: in-plane pressure enhances TC while out-of-plane pressure suppresses it, offering a new pathway to engineer higher TC in cuprates.

ABSTRACT

Discovery of new high TC superconductors, with TC > 23 K, continues to be challenging. We have doubled the existing TC of single crystal Sr3Ca11Cu24O41, a spin ladder cuprate, from 12K to 24K, using a gentle uniaxial pressure ~ 0.06 GPa. In contrast, earlier works used a nearly 100 times larger hydrostatic pressure 5 GPa, only to reach a maximum TC ~ 12K. Our work exposes large and nearly equal, but opposing contributions to changes in TC, arising from compressions along and perpendicular to ladder planes, in hydrostatic pressure experiments. In our resistivity measurements, uniaxial pressure applied along ladder planes increase TC, while that perpendicular to ladder planes decrease TC. Our findings i) offers a new hope for further increase in TC in spin ladder compounds and ii) calls for a large shift in phase boundaries of the currently accepted pressure-temperature phase diagram.

Motivation & Objective

• To explore the effect of anisotropic pressure on the superconducting transition temperature (TC) in the spin ladder compound Sr3Ca11Cu24O41.
• To overcome the limitations of hydrostatic pressure, which previously failed to exceed 12 K TC despite high pressures (~5 GPa).
• To investigate whether uniaxial pressure can induce a larger TC enhancement than hydrostatic pressure in this complex cuprate.
• To clarify the role of lattice distortions along different crystallographic directions in modulating superconductivity.

Proposed method

• Application of uniaxial pressure along the ladder planes (c-axis) of single-crystal Sr3Ca11Cu24O41 using a specially designed anvil cell.
• Measurement of resistivity as a function of temperature under uniaxial pressure to determine the superconducting transition temperature (TC).
• Comparison of results with prior hydrostatic pressure experiments to isolate the directional dependence of pressure effects.
• Use of precise pressure calibration and control to apply low uniaxial pressures (~0.06 GPa), significantly lower than the 5 GPa used in earlier hydrostatic studies.
• Analysis of the pressure-induced changes in TC to disentangle contributions from in-plane and out-of-plane lattice compression.
• Systematic variation of pressure direction to isolate the anisotropic response of the superconducting state.

Experimental results

Research questions

• RQ1 Can uniaxial pressure induce a larger enhancement in TC than hydrostatic pressure in the spin ladder compound Sr3Ca11Cu24O41?
• RQ2 What is the directional dependence of pressure on TC, particularly along versus perpendicular to the ladder planes?
• RQ3 Why does hydrostatic pressure fail to increase TC beyond 12 K despite high pressures, while uniaxial pressure achieves 24 K?
• RQ4 How do compressive strains along different crystallographic axes differentially affect the superconducting pairing mechanism in this material?
• RQ5 What implications does this anisotropic pressure response have for the current understanding of the pressure-temperature phase diagram of this cuprate?

Key findings

• Applying uniaxial pressure along the ladder planes increased the superconducting transition temperature (TC) from 12 K to 24 K, effectively doubling it.
• The enhancement was achieved with only 0.06 GPa of uniaxial pressure, a factor of ~100 lower than the 5 GPa required in hydrostatic pressure experiments.
• In-plane uniaxial pressure enhanced TC, while out-of-plane pressure suppressed it, revealing large and opposing contributions from different lattice directions.
• The results indicate that hydrostatic pressure experiments mask a strong anisotropy in pressure response, which is critical for TC tuning.
• The findings challenge the current pressure-temperature phase diagram, suggesting a significant need for revision to account for directional pressure effects.
• This work opens a new route to engineer higher TC in spin ladder compounds through targeted anisotropic strain engineering.