Figure 1

(a) Sheet resistance vs $T$ for Ta 2 at various $B$ in the range 0–0.5 T. (b) $I\text{−}V$ curves of Ta 1 at $T=0.1\text{K}$ at the indicated $B$. Filled (open) circles are for current increasing (decreasing) branch. The solid lines are to indicate the electronic instabilities, and the arrows show the direction of the change. (c) $dV/dI$ vs $I$ of Ta 1 at $B=0.6\text{T}$ at the indicated $T$. The solid lines are the fit to the quadratic function. (d) The quadratic coefficients from the fitting are plotted for Ta 1. The solid lines are a guide to the eye, and the dashed line corresponds to the metal-normal conductor phase boundary. (e) $dV/dI$ vs $I$ for Ta 2 at $B=2.0\text{T}$ at the indicated $T$. Solid lines are fit to the quadratic function. (f) Quadratic coefficients vs $T$ for sample Ta 2. The dashed line corresponds to the insulator-normal conductor boundary.Reuse & Permissions

Figure 2

(a) Phase diagram of Ta 1 in the $B\text{−}T$ plane. Symbols are experimental data and solid lines are to guide the eye. The superconducting phase is marked by S, the metallic phase by M, the insulating phase by I, and the normal conducting phase by N. (b) Phase diagram of Ta 2. (c) The topology of the 3D phase diagram in $T\text{−}B$-disorder space is shown. Disorder is represented by ${\rho }_n$ and the disorder axis indicates only the direction of increasing disorder. The illustrated phase diagram does not include the clean limit.Reuse & Permissions

Figure 3

(a) $T$ dependence of $\rho$ for samples Ta 3–9 at $B=0$ is shown. All these samples are grown in a single batch. (Inset) A blowup view of resistance behavior at low $T$ for samples Ta 5–7. (b) $dV/dI$ vs $I$ for samples Ta 5–8. The arrows indicate the corresponding scale for each trace.Reuse & Permissions

Figure 4

(a) Phase diagram of Ta 10 in the $T\text{−}B$ plane. Insulating phase is marked by I and the normal conducting phase by N. Solid lines are to guide the eye. (b) Phase diagram of Ta 11, which is more disordered than Ta 10 by the measure of ${\rho }_n$. (c) The same 3D phase diagram shown in Fig. 2c, but includes the corresponding cross-sectional views for Ta 10 ($T_{d3}\text{−}{B}_{d3}$ plane) and Ta 11 ($T_{d4}\text{−}{B}_{d4}$ plane).Reuse & Permissions