Pressure-induced multicriticality and electronic instability in the quasi-kagome ferromagnet URhSn

We report an unconventional class of pressure-induced quantum phase transitions, possessing two bicritical points at 6.25 GPa in URhSn. This unique transformation accompanies a Fermi surface reconstruction, demarcating competing ordered phases suitably described with a localized and itinerant description of the magnetic $5f$ electrons. Ferromagnetic fluctuations over a wide range of temperatures and pressures in the pressure-induced low temperature phase are evidenced by a robust $T^{5/3}$ temperature dependence of resistivity up to 11 GPa, which is a characteristic of an elusive marginal Fermi-liquid state.

Figure 1

(a) Crystal structure of URhSn. The triangular units of U atoms constitute a quasi-kagome lattice in the $c$ plane. A sandwiching mirror plane containing Rh and Sn atoms parallel to this quasi-kagome layer is shown with translucent green color. (b) Electrical resistivity of URhSn for the current along $\left[11\overline{2}0\right]$ direction along with of nonmagnetic analog ThRhSn. In ThRhSn case, the residual resistivity has been subtracted. The red curve is the difference of the two resistivities giving contribution from the $5f$ electrons, i.e., ${\rho }_{5f}$. (c) Pressure dependence of ${\rho }_{5f}\left(T\right)$ curves in URhSn on logarithmic temperature scale. The ${\rho }_{5f}\left(T\right)$ traces measured under pressure have been shifted vertically by 30 $\mu \mathrm{\Omega }\mathrm{cm}$ with respect to the adjacent ones for clarity. (d) Temperature derivative of resistivity with pressure in URhSn. Vertical arrows in (c) and (d) point to the transition temperatures. See Fig. S3 of Supplemental Material [20] for the criteria used in determining $T_{\mathrm{O}}$ and $T_{\mathrm{C}}$).

Figure 2

(a) $5f$-electron-derived resistivity of URhSn on quadratic temperature scale at selected pressures. (b) Variation of the $A$ coefficient (left axis) and ${\rho }_0$ derived from the least-squares linear fit to ${\rho }_{5f}\left(T^2\right)$ curves below 5 K. The error bars in fit results are smaller than size of the symbols. (c) $T^{5/3}$ dependence of ${\rho }_{5f}$ from 8 GPa to 11 GPa demonstrating a non-Fermi liquid behavior in URhSn over a large range of temperatures and pressures. Black lines are guides to the eyes to show the agreement.

Figure 3

(a) $P\text{−}T$ phase diagram of URhSn showing variation of $T_{\mathrm{C}}$ and $T_{\mathrm{O}}$ with pressure up to 11 GPa. The vertical grey double-line ABC represents a plausible first-order phase boundary, which is revealed by sharp anomalies in pressure dependence of resistivity in (b). This first-order phase boundary changes into a crossover above A, shown by a dashed line. Putatively, A and B are bicritical points, while C is a quantum phase transition point. (b) Traces showing isothermal variation of resistivity with pressure in URhSn derived from $\rho \left(T\right)$ scans. (c) An illustration showing plausible electronic and magnetic ground states in the two pressure regimes across the $P_{\mathrm{C}}$. The magnetic electrons attached nearly locally to the quasi-kagome uranium lattice become fully itinerant by pressure-induced $c\text{−}f$ hybridization above the $P_{\mathrm{C}}$. The blue enclosures represent size of the Fermi surfaces in the two regimes.