[Paper Review] Unconventional short-range structural fluctuations in cuprate high-$T_c$ superconductors

Damjan Pelc, R. J. Spieker+15 more|arXiv (Cornell University)|Mar 9, 2021

Physics of Superconductivity and Magnetism2 references4 citations

TL;DR

This study reveals universal, unconventional short-range structural fluctuations in cuprate high-Tc superconductors La2-xSrxCuO4 and Tl2Ba2CuO6+δ using neutron and X-ray diffuse scattering. Despite distinct disorder effects and Tc values, the fluctuations exhibit robust, simple scaling across wide doping and temperature ranges, suggesting a common origin in intrinsic nanoscale inhomogeneity that may underlie unconventional superconductivity.

ABSTRACT

The interplay between structural and electronic degrees of freedom in complex materials is the subject of extensive debate in physics and materials science. Particularly interesting questions pertain to the nature and extent of pre-transitional short-range order in diverse systems ranging from shape-memory alloys to unconventional superconductors, and how this microstructure affects macroscopic properties. Here we use neutron and X-ray diffuse scattering to uncover universal structural fluctuations in La$_{2-x}$Sr$_x$CuO$_4$ and Tl$_2$Ba$_2$CuO$_{6+δ}$, two cuprate superconductors with distinct point disorder effects and optimal superconducting transition temperatures. The fluctuations are present in wide doping and temperature ranges, including compositions that maintain high average structural symmetry, and they exhibit unusual, yet simple scaling behavior. The scaling regime is robust and universal, similar to the well-known critical fluctuations close to second-order phase transitions, but with a distinctly different physical origin. We relate this behavior to pre-transitional phenomena in a broad class of systems with structural and magnetic transitions, and propose an explanation based on rare structural fluctuations caused by intrinsic nanoscale inhomogeneity. We also uncover parallels with superconducting fluctuations, which indicates that the underlying inhomogeneity plays an important role in cuprate physics.

Motivation & Objective

• To investigate the nature and universality of short-range structural fluctuations in cuprate high-Tc superconductors with different disorder and Tc values.
• To determine whether these fluctuations persist in compositions with high average structural symmetry and how they scale across doping and temperature.
• To explore the physical origin of these fluctuations and their potential connection to pre-transitional phenomena and superconducting fluctuations.
• To assess the role of intrinsic nanoscale inhomogeneity in shaping macroscopic electronic and structural properties in cuprates.

Proposed method

• Employed neutron and X-ray diffuse scattering to probe short-range structural correlations in La2-xSrxCuO4 and Tl2Ba2CuO6+δ.
• Measured diffuse scattering intensity across wide ranges of doping and temperature to identify scaling behavior.
• Analyzed the scaling regime to distinguish it from conventional critical fluctuations near second-order phase transitions.
• Compared structural fluctuations with known superconducting fluctuations to identify parallels and potential interplay.
• Used symmetry analysis to assess the role of average structural symmetry in sustaining the observed fluctuations.
• Applied data collapse techniques to test the universality and robustness of the scaling behavior.

Experimental results

Research questions

• RQ1 Do short-range structural fluctuations persist in cuprates with high average structural symmetry and distinct disorder effects?
• RQ2 What is the scaling behavior of these fluctuations, and how does it differ from critical fluctuations near second-order transitions?
• RQ3 Can the observed fluctuations be attributed to intrinsic nanoscale inhomogeneity rather than long-range order or disorder?
• RQ4 How are these structural fluctuations related to pre-transitional phenomena and superconducting fluctuations?
• RQ5 Is the scaling behavior universal across different cuprate families with varying optimal Tc and point defect characteristics?

Key findings

• Unconventional short-range structural fluctuations were observed in both La2-xSrxCuO4 and Tl2Ba2CuO6+δ across wide doping and temperature ranges, even in compositions with high average structural symmetry.
• The fluctuations exhibit a robust, simple scaling behavior that is universal across the two cuprate systems despite differences in point disorder and optimal Tc.
• The scaling regime resembles critical fluctuations near second-order transitions but has a distinct physical origin, not tied to long-range order or symmetry breaking.
• The fluctuations are attributed to rare structural fluctuations driven by intrinsic nanoscale inhomogeneity, suggesting a common microscopic origin.
• Strong parallels were found between the structural fluctuations and superconducting fluctuations, indicating a shared underlying inhomogeneity in cuprate physics.
• The findings imply that nanoscale inhomogeneity plays a fundamental role in mediating electronic properties in high-Tc cuprates, potentially influencing superconducting pairing mechanisms.