Time-resolved quasiparticle dynamics of the itinerant antiferromagnet UPtGa${}_5$

Time-resolved photoinduced reflectivity is measured in the spin-density-wave phase of the itinerant antiferromagnet UPtGa${}_5$. Two relaxation components were seen: (a) a slow component whose amplitude appears below $T_N$, and relaxation time ${\tau }_{\text{slow}}$ exhibits an upturn near $T_N$, and (b) the fast component persists at all temperatures, with the relaxation time ${\tau }_{\text{fast}}$ also exhibiting an upturn near $T_N$. Comparing with pump-probe data on UNiGa${}_5$, the differences are explained in the context of UPtGa${}_5$ having A-type (rather than G-type) antiferromagnetism, resulting in partial Fermi surface nesting, partial gapping, and consequently finite density of states at the Fermi surface.

Figure 1

Transient reflection $\Delta R/R$ after photoexcitation by a 50 fs laser pulse above and below $T_N$ for UPtGa${}_5$. (a) For time delays up to 500 ps (logarithmic scale). (b) Blowup of data at short time delays up to 20 ps. Thick black (red) curves denote two-exponential fits of data at $T=7.4$ K (14.8 K).

Figure 2

(a) Temperature dependence of relaxation amplitudes $A_{\text{fast}}$ and $A_{\text{slow}}$, and thermally excited QP densities $n_T$ (inset). Solid lines are fits using the RT model. (b) Temperature dependence of relaxation times ${\tau }_{\text{fast}}$ and $A{\tau }_{\text{slow}}$. Solid line is the fit using the RT model.

Figure 3

Calculated temperature dependence of the order parameter $M_Q\left(T\right)$ for a tetragonal lattice for $Q=(\pi ,\pi ,\pi )$ (solid circles), and $Q=(0,0,\pi )$ (solid squares). Experimental neutron scattering intensity for ($+$) UPtGa${}_5$, and ($\times$) UNiGa${}_5$, taken from Ref.7.

Figure 4

Calculated temperature dependence of the DOS in the SDW state for (a) $Q=(\pi ,\pi ,\pi )$, and (b) $Q=(0,0,\pi )$. The curves A–F represents DOS calculated from the values of $T$ and $M_Q\left(T\right)$ in Fig. 3. $E=0$ is the Fermi level.

Figure 5

Band structure using the LAPW method of (a) UNiGa${}_5$ and (b) UPtGa${}_5$ in the SDW state. Notice the in UPtGa${}_5$ a flat band runs between $\Gamma$ and $Z$ near the Fermi energy.

Figure 6

Total DOS calculated from the LAPW method for UNiGa${}_5$ and UPtGa${}_5$ in the magnetic unit cell in the energy range (a) ($-$2,2) eV and (b) ($-$0.5,0.5) eV. $E=0$ is the Fermi level. Notice at the Fermi level DOS is strongly suppressed in UNiGa${}_5$.