Evidence for a pressure-induced antiferromagnetic quantum critical point in intermediate-valence UTe2

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Science Advances  14 Oct 2020:
Vol. 6, no. 42, eabc8709
DOI: 10.1126/sciadv.abc8709
  • Fig. 1 Ac calorimetry and resistivity under pressure.

    (A) Heat capacity at zero pressure showing two superconducting transitions. The sample measured at zero pressure is different from the sample measured under pressure. (B) Ac calorimetry up to 1.32 GPa. Tc1 and Tc2 cross between 0.1 and 0.34 GPa. (C) Ac calorimetry between 1.40 and 1.57 GPa. Magnetic order emerges at 1.45 GPa, splitting into two magnetic transitions at higher pressure. The low-temperature tail observed in ac calorimetry for pressures above 1.25 GPa is of unknown origin, but it is unrelated to any superconducting transition as indicated by its presence even at 1.57 GPa where the low-temperature resistance does not approach zero. The curves in (B) and (C) were offset for clarity. (D) ΔC/T versus pressure for each of the superconducting transitions. ψ1 corresponds with Tc1, and ψ2 corresponds with Tc2. Specific heat jumps were determined by subtracting a baseline from each of the transitions and using the resulting peak value and temperature. (E) A comparison between ac calorimetry and resistivity at 1.47 GPa. The superconducting peak and the offset of the zero-resistance state differ by 0.5 K, as shown by dashed lines. (F) A comparison between ac calorimetry and resistivity at 1.49 GPa. A current density of 16 mA/cm2 was used for the resistivity measurements in (E) and (F). A.U., arbitrary units.

  • Fig. 2 Electrical resistivity measurements.

    (A) Critical current density versus temperature at 1.57 GPa. Inset shows resistivity versus temperature measured at different current densities. (B) Resistivity versus angle of applied field at 1.57 GPa as the field is rotated from parallel to [010] to perpendicular to [010]. Inset shows a comparison of resistivity versus temperature for 0 T and for 0.85 T applied either parallel or perpendicular to [010]. (C) Resistivity versus temperature at higher temperatures. Inset shows dρ/dT at 1.57 GPa. Current density was 160 mA/cm2. Circular markers indicate transition temperatures determined from ac calorimetry.

  • Fig. 3 Phase diagram and electrical resistivity exponent.

    (A) Temperature versus pressure phase diagram for UTe2. Shaded area indicates the region where heat capacity and resistivity show different superconducting temperatures. The dotted blue line for pressures below Pc2 is a guide to the eye. Below 1.25 GPa, the higher temperature superconducting transition had the same transition temperature in both heat capacity and resistivity. There is some uncertainty in the transition temperature for Tc2 at 1.18 GPa due to the potential for sample heating. Tc1 at 1.57 GPa in resistivity was determined using a current density of 16 mA/cm2. (B) A plot of the exponent in ρ(T) = ρ0 + ATn by taking d[ln(ρ − ρ0)]/d[ln(T)] = n. Dashed lines are a guide to the eye for boundaries of T-linear behavior, indicating a putative quantum critical point at a pressure near 1.3 GPa.

  • Fig. 4 Uranium L3 x-ray absorption near-edge spectroscopy spectra of UTe2.

    (A) Edge step–normalized x-ray absorption near-edge spectroscopy (XANES) data for UTe2 at 0.3 GPa and reference materials UCd11 and UF4 at ambient pressure. UF4 data were adapted from (24). (B) Edge step–normalized XANES data for UTe2 at the minimum and maximum pressures, showing a small shift toward 4+ at higher pressures. (C) Energy shift of UTe2 as a function of pressure. Right axis shows estimated valence shift by taking UCd11 and UF4 as U3+ and U4+ references, respectively. An apparent increase in valence starts at pressures higher than 1.25 GPa.

Supplementary Materials

  • Supplementary Materials

    Evidence for a pressure-induced antiferromagnetic quantum critical point in intermediate-valence UTe2

    S. M. Thomas, F. B. Santos, M. H. Christensen, T. Asaba, F. Ronning, J. D. Thompson, E. D. Bauer, R. M. Fernandes, G. Fabbris, P. F. S. Rosa

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