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  • Letter

Possible coexistence of antiferromagnetic and ferromagnetic spin fluctuations in the spin-triplet superconductor UTe2 revealed by Te125 NMR under pressure

Devi V. Ambika, Qing-Ping Ding, Khusboo Rana, Corey E. Frank, Elizabeth L. Green, Sheng Ran, Nicholas P. Butch, and Yuji Furukawa
Phys. Rev. B 105, L220403 – Published 17 June 2022
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    Abstract

    A spin-triplet superconducting state mediated by ferromagnetic (FM) spin fluctuations has been suggested to occur in the newly discovered heavy-fermion superconductor UTe2. However, the recent neutron scattering measurements revealed the presence of antiferromagnetic (AFM) spin fluctuations in UTe2. Here, we report the Te125 nuclear magnetic resonance studies of a single-crystal UTe2, suggesting the coexistence of FM and AFM spin fluctuations in UTe2. Owing to the two different Te sites in the compound, we conclude that the FM spin fluctuations are dominant within ladders and the AFM spin fluctuations originate from the interladder magnetic coupling. Although AFM spin fluctuations exist in the system, the FM spin fluctuations in the ladders may play an important role in the appearance of the spin-triplet superconducting state of UTe2.

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    • Received 15 April 2022
    • Revised 7 June 2022
    • Accepted 8 June 2022

    DOI:https://doi.org/10.1103/PhysRevB.105.L220403

    ©2022 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    High-pressure studiesSpin fluctuationsSpin-triplet pairing
    1. Physical Systems
    Heavy-fermion systemsStrongly correlated systemsUnconventional superconductors
    1. Techniques
    Nuclear magnetic resonance
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Devi V. Ambika1,2, Qing-Ping Ding1,2, Khusboo Rana1,2, Corey E. Frank3,4, Elizabeth L. Green5, Sheng Ran3,4,*, Nicholas P. Butch3,4, and Yuji Furukawa1,2

    • 1Ames Laboratory, U.S. DOE, Ames, Iowa 50011, USA
    • 2Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
    • 3NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
    • 4Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
    • 5National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA

    • *Present address: Department of Physics, Washington University, St.Louis, Missouri 63130, USA.

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    Issue

    Vol. 105, Iss. 22 — 1 June 2022

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    Images

    • Figure 1
      Figure 1

      (a) Crystal structure of UTe2. The U atoms (blue circles) form a two-leg ladder structure. The light blue circles representing the U atom outside the unit cell are shown to emphasize the ladder structure. The local environment of Te1 and Te2 sites are shown on the right. (b) Pressure dependence of the H-swept Te125-NMR spectra of a single crystal UTe2 at T = 30 K for H∥b where the horizontal axis is Knight shift K defined by K = (H0 – H)/H where H0 = 2πf/γN, f is NMR resonance frequency, and H is the external magnetic field. For p = 0, 0.52 and 1.0 GPa, the spectra were measured at f = 41 MHz (H0 = 3.0472 T). f = 45.35 MHz (H0 = 3.3717 T) was used at p = 1.57 GPa. (c) T and p dependences of FWHMs of Te1 and Te2 sites estimated from Te125-NMR spectra.

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    • Figure 2
      Figure 2

      (a) T dependences of Ks for both Te1 and Te2 under different pressures. Open and closed symbols are for Te1 and Te2, respectively. (b) T dependence of the ratio K(Te2)/K(Te1) under various pressures. The solid lines are guides for the eye. (c) K versus magnetic susceptibility χ plots with T as an implicit parameter. Solid and open symbols show the data above and below Tmax = 35–40 K, respectively. The black solid line is a linear fit for Te2 for the whole temperature range. The red solid line is a linear fit for Te1 for T≥Tmax and the red broken line represents a fit using the lowest temperature data while keeping a constant y intercept corresponding to the temperature independent part of Knight shift.

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    • Figure 3
      Figure 3

      T dependence of 1/T1T for Te1 (red circles) and Te2 (black circles) at p = 0 (a), 0.5 (b), 1.0 (c) and 1.5 GPa (d). (e)–(h) T dependence of 1/T1 for Te1 (red circles) and Te2 (black circles) at p = 0, 0.5, 1.0 and 1.5 GPa. The solid lines show 1/T1T = constant, expected for a heavy-fermion state.

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    • Figure 4
      Figure 4

      Images of the local spin fluctuations at the Te1 and Te2 sites. The dark blue circles represent the nearest-neighbor U atoms for each Te site and the ladder structures along the a axis are illustrated by the light blue circles.

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