• Open Access

Spin-Fluctuation-Induced Non-Fermi-Liquid Behavior with Suppressed Superconductivity in LiFe1xCoxAs

Y. M. Dai, H. Miao, L. Y. Xing, X. C. Wang, P. S. Wang, H. Xiao, T. Qian, P. Richard, X. G. Qiu, W. Yu, C. Q. Jin, Z. Wang, P. D. Johnson, C. C. Homes, and H. Ding
Phys. Rev. X 5, 031035 – Published 15 September 2015

Abstract

We study a series of LiFe1xCoxAs compounds with different Co concentrations by transport, optical spectroscopy, angle-resolved photoemission spectroscopy, and nuclear magnetic resonance. We observe a Fermi-liquid to non-Fermi-liquid to Fermi-liquid (FL-NFL-FL) crossover alongside a monotonic suppression of the superconductivity with increasing Co content. In parallel to the FL-NFL-FL crossover, we find that both the low-energy spin fluctuations and Fermi surface nesting are enhanced and then diminished, strongly suggesting that the NFL behavior in LiFe1xCoxAs is induced by low-energy spin fluctuations that are very likely tuned by Fermi surface nesting. Our study reveals a unique phase diagram of LiFe1xCoxAs where the region of NFL is moved to the boundary of the superconducting phase, implying that they are probably governed by different mechanisms.

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  • Received 5 February 2015

DOI:https://doi.org/10.1103/PhysRevX.5.031035

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Authors & Affiliations

Y. M. Dai1, H. Miao2, L. Y. Xing2, X. C. Wang2, P. S. Wang3, H. Xiao2, T. Qian2, P. Richard2,4, X. G. Qiu2,4, W. Yu3,6, C. Q. Jin2,4, Z. Wang5, P. D. Johnson1, C. C. Homes1,*, and H. Ding2,4,†

  • 1Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
  • 2Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
  • 3Department of Physics, Renmin University of China, Beijing 100872, China
  • 4Collaborative Innovation Center of Quantum Matter, Beijing, China
  • 5Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, USA
  • 6Department of Physics and Astronomy, Collaborative Innovation Center of Advanced Microstructures, Shanghai Jiao Tong University, Shanghai 200240, China

  • *homes@bnl.gov
  • dingh@iphy.ac.cn

Popular Summary

A well-known, intriguing, and long-standing question in condensed-matter physics pertains to the origin of anomalous non-Fermi-liquid behavior and its relationship to high-temperature superconductivity. Here, we study single crystals of LiFe1xCoxAs with different Co concentrations to investigate the crossover from Fermi liquid to non-Fermi liquid and back. We find that this crossover is mediated by low-energy spin fluctuations in the material.

LiFe1xCoxAs, which is characterized by Tc=18K in its stoichiometric form, exhibits a decreased transition temperature when Fe is substituted with Co (i.e., superconductivity is suppressed with increasing Co concentration). We study the transport and spectroscopic properties of the compounds to reveal a Fermi-liquid to non-Fermi-liquid to Fermi-liquid crossover induced by low-energy spin fluctuations that evolve in parallel with Fermi-surface nesting. We note that this crossover occurs irrespective of impurities in the material.

We produce the temperature-doping phase diagram of LiFe1xCoxAs, and we demonstrate that the material is superconductive for parameters falling in the lower-left-hand corner of the phase diagram (which also happens to be free of long-range magnetic order). Our results provide a thorough understanding of the origin of the non-Fermi-liquid behavior in LiFe1xCoxAs. Our findings reveal, for the first time, an unusual phase diagram where the region of non-Fermi-liquid behavior and enhanced low-energy spin fluctuations is located at the boundary of the superconducting phase. This result, which is completely novel and unexpected, challenges the popular notion of Fermi-surface-driven pairing mediated by low-energy spin fluctuations.

We expect that our results will motivate additional studies of high-temperature superconductivity and its relationship to Fermi-liquid behavior.

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Vol. 5, Iss. 3 — July - September 2015

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