Spin Polarons in the Correlated Metallic Pyrochlore ${\mathrm{Cd}}_2{\mathrm{Re}}_2{\mathbf{O}}_7$

Muon spin rotation spectroscopy reveals localized electron states in the geometrically frustrated metallic pyrochlore ${\mathrm{Cd}}_2{\mathrm{Re}}_2{\mathrm{O}}_7$ at temperatures from 2 to 300 K in transverse magnetic fields up to 7 T. Two distinctive types of localized states, with characteristic radii of about 0.5 and 0.15 nm, are detected at high and low temperature, respectively. These states may be spin polarons, formed due to strong exchange interaction between itinerant electrons and the magnetic $5d$ electrons of Re ions, which may determine the peculiar electronic and magnetic properties of ${\mathrm{Cd}}_2{\mathrm{Re}}_2{\mathrm{O}}_7$.

Figure 1

Frequency spectra of muon spin precession in ${\mathrm{Cd}}_2{\mathrm{Re}}_2{\mathrm{O}}_7$ in a transverse magnetic field of $H=5\mathrm{T}$ at $T=150\mathrm{K}$ (a) and $T=2.4\mathrm{K}$ (b). The two-frequency or four-frequency precession patterns characteristic of the electron bound state occur at frequencies on either side of the narrower background signal. Note different frequency scales for (a) and (b).

Figure 2

Frequency spectra of muon spin precession in ${\mathrm{Cd}}_2{\mathrm{Re}}_2{\mathrm{O}}_7$ in a transverse magnetic field of $H=5\mathrm{T}$ at different temperatures. The large splitting decreases towards high $T$ and disappears above about 60 K.

Figure 3

Temperature dependences of hyperfine splittings in ${\mathrm{Cd}}_2{\mathrm{Re}}_2{\mathrm{O}}_7$ at $H=5\mathrm{T}$.

Figure 4

Magnetic field dependence of hyperfine splittings at $T=2.4\mathrm{K}$, from fast Fourier transform. Error bars represent apparent peak widths.