Signature of superconductivity in $\mathrm{U}{\mathrm{Be}}_{13}$ as seen by neutron scattering: Superconducting and magnetic energy scales

Signature of superconductivity in $U {Be}_{13}$ as seen by neutron scattering: Superconducting and magnetic energy scales

A. Hiess, A. Schneidewind, O. Stockert, and Z. Fisk

Phys. Rev. B 89, 235118 – Published 17 June 2014

Abstract

We here present inelastic neutron scattering results on the strongly correlated cubic superconductor $U {Be}_{13}$ ( $T_{c}$ = 0.85 K) obtained on a large single crystal by high-resolution cold neutron three-axis spectroscopy. We observed spin dynamics at a unique momentum space position building up below $T \sim 50$ K and changing significantly on entering the superconducting state. The observed short-range longitudinal character of the correlations can be understood as a result of competing magnetic interactions. The energy dependence in the normal state reflects the energy scales determined from specific heat, whereas the low-temperature data suggest the opening of a superconducting gap. Our findings are consistent with a superconducting order parameter exhibiting $s \pm$ or $d$ -wave symmetry and placing pure UBe $_{13}$ in the strong coupling regime.

Received 21 May 2013
Revised 2 June 2014

DOI:https://doi.org/10.1103/PhysRevB.89.235118

Authors & Affiliations

A. Hiess^1,2,*, A. Schneidewind^3,4, O. Stockert⁵, and Z. Fisk⁶

¹European Spallation Source ESS AB, P.O. Box 176, SE-22100 Lund, Sweden
²Institut Max von Laue, Paul Langevin, 6 rue Jules Horowitz, BP 156, F-38042 Grenoble Cedex 9, France
³Jülich Centre for Neutron Science-MLZ, FZ Juelich GmbH, Outstation at MLZ, Lichtenbergstrasse 1, 85747 Garching, Germany
⁴Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany
⁵Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Strasse 40, D-01187 Dresden, Germany
⁶University of California Irvine, 2186 Frederick Reines Hall, Irvine, California 92697, USA

^*arno.hiess@esss.se

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Vol. 89, Iss. 23 — 15 June 2014

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Figure 1
(a) Sketch of the (H, H, L) scattering plane. Green dots indicate nuclear Bragg peak positions. Fuzzy magenta dots indicate the position of the broad signal observed. The open dot indicates the background position. (b) Intensity map of the normal state dynamic response of UBe $_{13}$ in the ( $H, H, L$ ) plane at constant energy transfer $Δ E = 0.6$ meV and $T = 1.5$ K using IN14 FlatCone. The observed neutron-scattering intensity is color-coded varying from black (low) to white (high). The red and white circles indicate the momentum space positions $Q_{0} = (1 / 2, 1 / 2, 2)$ and $Q_{bckgrd} = (1, 1, 3 / 2)$ , respectively. (c) Cut through the data along the ( $H, H$ , 2) direction with an integration width $Δ L = \pm 0.5$ as indicated by the rectangle in the middle panel. The nuclear Bragg peak intensity is outside the scale shown.
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Figure 2
Temperature dependence of the neutron scattering intensity at $Q = (1 / 2, 1 / 2, 2)$ after subtracting the background contribution at $Q = (1, 1, 3 / 2)$ . Integrating the response over energies $0.15 meV < Δ E < 1.2$ meV (closed symbols) or averaging single measurements at $Δ E$ = 0.3 meV and $Δ E$ = 0.6 meV (open symbols) indicate an accelerated increase of intensity on lowering temperature. Data taken on PANDA with $k_{f} = 1.15 Å^{- 1}$ . The solid line shows the temperature dependence of bulk molar susceptibility published by Tou et al. [29] (scaled to the units of the plot).
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Figure 3
(a) Neutron scattering intensity at $Q = (1 / 2, 1 / 2, 2)$ in the normal state (red dots) of UBe $_{13}$ as function of energy transfer. (b) Neutron scattering intensity at $Q = (1 / 2, 1 / 2, 2)$ in the superconducting state (blue dots) of UBe $_{13}$ as function of energy transfer. (c) Background corrected neutron scattering intensity at $Q = (1 / 2, 1 / 2, 2)$ in the normal (red dots) and superconducting (blue dots) state of UBe $_{13}$ as function of energy transfer. The red line in panels (a) and (c) is a fit of the magnetic signal in the normal state as described in the text. In panel (b), this fit with unchanged parameters has been scaled by the temperature Bose factor to be compared with the data taken in the superconducting state. The dashed black line shows the fit of the temperature-independent intensities at a background position $Q_{bckgrd} = (1, 1, 3 / 2)$ . Data taken on IN14 with $k_{f} = 1.15 Å^{- 1}$ .
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Figure 4
Neutron scattering intensity in the superconducting state subtracted by the neutron scattering intensity in the normal state as a function of energy transfer. Green dots show the $T$ difference $I (T = 0.1 K) - I (T = 1.5 K)$ in zero magnetic field. Three or four data points from the raw data presented in Fig. 2 have been binned together and corrected for the Bose temperature factor. Orange diamonds show the magnetic field difference $I (B = 0 T) - I (B = 13 T)$ at $T = 0.1$ K. Data taken on IN14. The light green bar indicates the average intensity I = $- 2.5$ $\pm$ 5.2 of all data taken at neutron energy gain (negative energies). Arrows indicate the energy transfer investigated as a function of temperature in Fig. 5.
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Figure 5
(a) $T$ dependence of the AC susceptibility measured on the same UBe $_{13}$ single crystal used for the INS experiments (open symbols) and compared to literature [10] (closed symbols). $T_{c}$ indicated by dotted line. (b) $T$ dependence of the neutron scattering intensity at $Q = (1 / 2, 1 / 2, 2)$ and different energy transfers. All data are corrected by the Bose temperature factor and for the background contribution at $Q = (1, 1, 3 / 2)$ . Data taken on PANDA.
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Figure 6
Sketch of the magnetic structure in different rare-earth-based REBe $_{13}$ and actinide-based ANBe $_{13}$ compounds projected onto the $(h, k, 0)$ plane. (a) Incommensurate regular helical structure of GdBe $_{13}$ , (b) irregular helical structure of other REBe $_{13}$ compounds, (c) collinear antiferromagnetic structure of NpBe $_{13}$ , and (d) short-range correlations in UBe $_{13}$ . Different colors indicate different layers along the propagation axis $[0, 0, 1]$ .
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Physical Review B

covering condensed matter and materials physics

Signature of superconductivity in $U {Be}_{13}$ as seen by neutron scattering: Superconducting and magnetic energy scales

A. Hiess, A. Schneidewind, O. Stockert, and Z. Fisk

Phys. Rev. B 89, 235118 – Published 17 June 2014

Abstract

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Physical Review B

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Signature of superconductivity in UBe13 as seen by neutron scattering: Superconducting and magnetic energy scales

A. Hiess, A. Schneidewind, O. Stockert, and Z. Fisk

Phys. Rev. B 89, 235118 – Published 17 June 2014

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Signature of superconductivity in $U {Be}_{13}$ as seen by neutron scattering: Superconducting and magnetic energy scales