Charge density fluctuations with enhanced superconductivity at the proposed quantum critical point of Sr0.77Ba0.23Ni2As2

Y. Chen; N. Giles-Donovan; J. Guo; R. Chen; Y. Xie; H. Fukui; T. Manjo; D. Ishikawa; A. Q.R. Baron; A. A. Aczel; P. Dai; Y. Song; R. J. Birgeneau

doi:10.1103/6rl6-w746

Charge density fluctuations with enhanced superconductivity at the proposed quantum critical point of Sr_0.77Ba_0.23Ni₂As₂

Y. Chen
, N. Giles-Donovan
, J. Guo
, R. Chen
, Y. Xie
, H. Fukui
, T. Manjo
, D. Ishikawa
, A. Q.R. Baron
, A. A. Aczel
, P. Dai
, Y. Song
, R. J. Birgeneau

Triple-Axis

Research output: Contribution to journal › Review article › peer-review

Abstract

A quantum critical point (QCP) represents a continuous phase transition at absolute zero. In unconventional superconductors, enhanced superconducting transition temperature and magnetic fluctuation strength are often observed together, indicating magnetism-mediated superconductivity. This raises the question of whether quantum fluctuations in other degrees of freedom, such as charge, could similarly boost superconductivity. However, because charge is frequently intertwined with magnetism, isolating and understanding its specific role in Cooper pair formation pose a significant challenge. Here, we report persistent charge density fluctuations (CDFs) down to 15 K in the nonmagnetic superconductor Sr_0.77Ba_0.23Ni₂As₂, which lie near a proposed nematic QCP associated with a sixfold enhancement of superconductivity. Our results show that the quasielastic CDFs do not condense into resolution-limited Bragg peaks but, rather, display nonsaturated strength. The phonons associated with CDFs completely soften at 25 K, with their critical behavior described by the same mathematical framework as the antiferromagnetic Fermi liquid model, yielding a fitted Curie-Weiss temperature of θ ≈ 0 K. Additionally, we find that the nematic fluctuations are weakly coupled to the lattice, as evidenced by the absence of softening in nematic-coupled in-plane transverse acoustic phonons. Our discovery positions Sr_xBa_1−xNi₂As₂ as a promising candidate for charge-fluctuation-driven superconductivity.

Original language	English
Article number	075119
Pages (from-to)	1-8
Number of pages	8
Journal	Physical Review B
Volume	112
Issue number	7
DOIs	https://doi.org/10.1103/6rl6-w746
State	Published - Aug 8 2025

Funding

The work at UC Berkeley and LBNL was funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Material Sciences and Engineering Division under Contract No. DE-AC02-05-CH11231 (Quantum Materials program KC2202). The single-crystal synthesis and characterization work at Rice were supported by the U.S. DOE under Contract No. DE-SC0012311 and the Robert A. Welch Foundation under Grant No. C-1839, respectively. The of China (Grants No. 12350710785 and No. 12274363), and the Fundamental Research Funds for the Central Universities (Grant No. 226-2024-00068). single-crystal XRD experiment was conducted at BL02B1 of SPring-8, Hyogo, Japan (Proposal No. 2023B2105). The inelastic x-ray scattering experiments were performed at BL35XU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) under Proposal No. 2023B1149. The neutron scattering work used resources at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The beam time was allocated to VERITAS on Proposal No. 32621.1. The work at Zhejiang University was supported by the National Key R&D Program of China (Grant No. 2022YFA1402200), the National Natural Science Foundation The work at UC Berkeley and LBNL was funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Material Sciences and Engineering Division under Contract No. DE-AC02-05-CH11231 (Quantum Materials program KC2202). The single-crystal synthesis and characterization work at Rice were supported by the U.S. DOE under Contract No. DE-SC0012311 and the Robert A. Welch Foundation under Grant No. C-1839, respectively. single-crystal XRD experiment was conducted at BL02B1 of SPring-8, Hyogo, Japan (Proposal No. 2023B2105). The inelastic x-ray scattering experiments were performed at BL35XU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) under Proposal No. 2023B1149. The neutron scattering work used resources at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The beam time was allocated to VERITAS on Proposal No. 32621.1. The work at Zhejiang University was supported by the National Key R&D Program of China (Grant No. 2022YFA1402200), the National Natural Science Foundation of China (Grants No. 12350710785 and No. 12274363), and the Fundamental Research Funds for the Central Universities (Grant No. 226-2024-00068).

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Chen, Y., Giles-Donovan, N., Guo, J., Chen, R., Xie, Y., Fukui, H., Manjo, T., Ishikawa, D., Baron, A. Q. R., Aczel, A. A., Dai, P., Song, Y., & Birgeneau, R. J. (2025). Charge density fluctuations with enhanced superconductivity at the proposed quantum critical point of Sr_0.77Ba_0.23Ni₂As₂. Physical Review B, 112(7), 1-8. Article 075119. https://doi.org/10.1103/6rl6-w746

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title = "Charge density fluctuations with enhanced superconductivity at the proposed quantum critical point of Sr0.77Ba0.23Ni2As2",

abstract = "A quantum critical point (QCP) represents a continuous phase transition at absolute zero. In unconventional superconductors, enhanced superconducting transition temperature and magnetic fluctuation strength are often observed together, indicating magnetism-mediated superconductivity. This raises the question of whether quantum fluctuations in other degrees of freedom, such as charge, could similarly boost superconductivity. However, because charge is frequently intertwined with magnetism, isolating and understanding its specific role in Cooper pair formation pose a significant challenge. Here, we report persistent charge density fluctuations (CDFs) down to 15 K in the nonmagnetic superconductor Sr0.77Ba0.23Ni2As2, which lie near a proposed nematic QCP associated with a sixfold enhancement of superconductivity. Our results show that the quasielastic CDFs do not condense into resolution-limited Bragg peaks but, rather, display nonsaturated strength. The phonons associated with CDFs completely soften at 25 K, with their critical behavior described by the same mathematical framework as the antiferromagnetic Fermi liquid model, yielding a fitted Curie-Weiss temperature of θ ≈ 0 K. Additionally, we find that the nematic fluctuations are weakly coupled to the lattice, as evidenced by the absence of softening in nematic-coupled in-plane transverse acoustic phonons. Our discovery positions SrxBa1−xNi2As2 as a promising candidate for charge-fluctuation-driven superconductivity.",

author = "Y. Chen and N. Giles-Donovan and J. Guo and R. Chen and Y. Xie and H. Fukui and T. Manjo and D. Ishikawa and Baron, \{A. Q.R.\} and Aczel, \{A. A.\} and P. Dai and Y. Song and Birgeneau, \{R. J.\}",

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AU - Chen, Y.

AU - Giles-Donovan, N.

AU - Guo, J.

AU - Chen, R.

AU - Xie, Y.

AU - Fukui, H.

AU - Manjo, T.

AU - Ishikawa, D.

AU - Baron, A. Q.R.

AU - Aczel, A. A.

AU - Dai, P.

AU - Song, Y.

AU - Birgeneau, R. J.

PY - 2025/8/8

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N2 - A quantum critical point (QCP) represents a continuous phase transition at absolute zero. In unconventional superconductors, enhanced superconducting transition temperature and magnetic fluctuation strength are often observed together, indicating magnetism-mediated superconductivity. This raises the question of whether quantum fluctuations in other degrees of freedom, such as charge, could similarly boost superconductivity. However, because charge is frequently intertwined with magnetism, isolating and understanding its specific role in Cooper pair formation pose a significant challenge. Here, we report persistent charge density fluctuations (CDFs) down to 15 K in the nonmagnetic superconductor Sr0.77Ba0.23Ni2As2, which lie near a proposed nematic QCP associated with a sixfold enhancement of superconductivity. Our results show that the quasielastic CDFs do not condense into resolution-limited Bragg peaks but, rather, display nonsaturated strength. The phonons associated with CDFs completely soften at 25 K, with their critical behavior described by the same mathematical framework as the antiferromagnetic Fermi liquid model, yielding a fitted Curie-Weiss temperature of θ ≈ 0 K. Additionally, we find that the nematic fluctuations are weakly coupled to the lattice, as evidenced by the absence of softening in nematic-coupled in-plane transverse acoustic phonons. Our discovery positions SrxBa1−xNi2As2 as a promising candidate for charge-fluctuation-driven superconductivity.

AB - A quantum critical point (QCP) represents a continuous phase transition at absolute zero. In unconventional superconductors, enhanced superconducting transition temperature and magnetic fluctuation strength are often observed together, indicating magnetism-mediated superconductivity. This raises the question of whether quantum fluctuations in other degrees of freedom, such as charge, could similarly boost superconductivity. However, because charge is frequently intertwined with magnetism, isolating and understanding its specific role in Cooper pair formation pose a significant challenge. Here, we report persistent charge density fluctuations (CDFs) down to 15 K in the nonmagnetic superconductor Sr0.77Ba0.23Ni2As2, which lie near a proposed nematic QCP associated with a sixfold enhancement of superconductivity. Our results show that the quasielastic CDFs do not condense into resolution-limited Bragg peaks but, rather, display nonsaturated strength. The phonons associated with CDFs completely soften at 25 K, with their critical behavior described by the same mathematical framework as the antiferromagnetic Fermi liquid model, yielding a fitted Curie-Weiss temperature of θ ≈ 0 K. Additionally, we find that the nematic fluctuations are weakly coupled to the lattice, as evidenced by the absence of softening in nematic-coupled in-plane transverse acoustic phonons. Our discovery positions SrxBa1−xNi2As2 as a promising candidate for charge-fluctuation-driven superconductivity.

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Charge density fluctuations with enhanced superconductivity at the proposed quantum critical point of Sr_0.77Ba_0.23Ni₂As₂

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