Using electronic structure changes to map the $H-T$ phase diagram of ${\alpha }^{\prime }-{\mathrm{NaV}}_2{\mathrm{O}}_5$

We report polarized optical reflectance studies of ${\alpha }^{\prime }-{\mathrm{NaV}}_2{\mathrm{O}}_5$ as a function of temperature (4–45 K) and magnetic field (0–60 T). Rung directed electronic structure changes, as measured by near-infrared reflectance ratios $\Delta R\left(H\right)=R\left(H\right)/R(H=0\mathrm{}$ T), are especially sensitive to the phase boundaries. We employ these changes to map out an $H-T$ phase diagram. Topological highlights include the observation of an additional phase boundary slightly below $T_{\mathrm{SG}},$ enhanced curvature of the 34 K phase boundary above 35 T, and, surprisingly, strong hysteresis effects of both transitions with applied field.