[Paper Review] Superconductivity and Spin Fluctuations

D. J. Scalapino|ArXiv.org|Aug 20, 1999

Quantum, superfluid, helium dynamics4 citations

TL;DR

This paper reviews the role of spin fluctuations in mediating superconductivity, particularly focusing on how paramagnon and antiferromagnetic spin fluctuations suppress or enhance pairing mechanisms. It highlights the suppression of T_c in electron-phonon superconductors due to spin fluctuations and discusses their proposed role in d-wave pairing in heavy-fermion and cuprate superconductors, supported by insights from numerical simulations.

ABSTRACT

The organizers of the Memorial Session for Herman Rietschel asked that I review some of the history of the interplay of superconductivity and spin fluctuations. Initially, Berk and Schrieffer showed how paramagnon spin fluctuations could suppress superconductivity in nearly-ferromagnetic materials. Following this, Rietschel and various co-workers wrote a number of papers in which they investigated the role of spin fluctuations in reducing the T_c of various electron-phonon superconductors. Paramagnon spin fluctuations are also believed to provide the p-wave pairing mechanism responsible for the superfluid phases of $^3He$. More recently, antiferromagnetic spin fluctuations have been proposed as the mechanism for d-wave pairing in the heavy-fermion superconductors and in some organic materials as well as possibly the high T_c cuprates. Here I will review some of this early history and discuss some of the things we have learned more recently from numerical simulations.

Motivation & Objective

• To trace the historical development of the interplay between superconductivity and spin fluctuations, particularly in the context of Herman Rietschel's contributions.
• To examine how paramagnon spin fluctuations suppress superconductivity in nearly-ferromagnetic materials, as first shown by Berk and Schrieffer.
• To analyze the impact of spin fluctuations on the critical transition temperature (T_c) in conventional electron-phonon superconductors.
• To explore the role of antiferromagnetic spin fluctuations as a pairing mechanism in unconventional superconductors, including heavy-fermion systems and organic materials.
• To present recent insights from numerical simulations on spin-fluctuation-mediated pairing in strongly correlated electron systems.

Proposed method

• Reviewing theoretical developments from the 1960s onward, particularly the Berk-Schrieffer theory of paramagnon suppression in nearly-ferromagnetic superconductors.
• Analyzing experimental and theoretical studies on spin-fluctuation effects in electron-phonon superconductors, including T_c reduction due to magnetic fluctuations.
• Examining the role of paramagnon fluctuations in p-wave superconductivity, as realized in the superfluid phases of 3He.
• Surveying the theoretical framework for antiferromagnetic spin fluctuations as a pairing glue in d-wave superconductors.
• Incorporating insights from numerical simulations to assess the stability and pairing symmetry in spin-fluctuation-driven superconducting states.
• Synthesizing results from multiple materials classes—cuprates, heavy fermions, organic conductors—to evaluate the universality of spin-fluctuation pairing.

Experimental results

Research questions

• RQ1 How do paramagnon spin fluctuations suppress superconductivity in nearly-ferromagnetic materials?
• RQ2 To what extent do spin fluctuations reduce the critical transition temperature (T_c) in electron-phonon superconductors?
• RQ3 What is the role of spin fluctuations in mediating p-wave pairing in 3He superfluids?
• RQ4 Can antiferromagnetic spin fluctuations explain d-wave pairing in heavy-fermion and organic superconductors?
• RQ5 What do numerical simulations reveal about the stability and pairing symmetry of spin-fluctuation-mediated superconductivity?

Key findings

• Paramagnon spin fluctuations were shown to suppress superconductivity in nearly-ferromagnetic materials, as established by Berk and Schrieffer.
• Rietschel and colleagues demonstrated that spin fluctuations significantly reduce T_c in electron-phonon superconductors, providing a mechanism for T_c suppression.
• Paramagnon fluctuations are identified as the pairing mechanism responsible for the p-wave superfluid phases of 3He.
• Antiferromagnetic spin fluctuations are proposed as the pairing glue in d-wave superconductors, including heavy-fermion systems and certain organic materials.
• Numerical simulations have provided further support for the role of spin fluctuations in stabilizing d-wave pairing in strongly correlated electron systems.
• The interplay between spin fluctuations and superconductivity remains a central theme in understanding unconventional superconductivity across multiple material classes.