**2. Materials and Methods**

All films in this study were deposited by the pulsed laser deposition (PLD) method using a Nd:YAG laser (*λ* = 266 nm). We first grew a CeO<sup>2</sup> layer with a thickness of about 80–100 nm on SrTiO<sup>3</sup> single-crystal substrate at a substrate temperature of 600–650 ◦C and oxygen partial pressure of ~115 mTorr. Then, 100–130 nm thick FST films were grown on CeO<sup>2</sup> buffer layers. During the deposition of FST films, the substrate temperature and oxygen partial pressure were kept at 300–360 ◦C and ~1 <sup>×</sup> <sup>10</sup>–6 Torr, respectively.

Superconducting transport properties were measured using the conventional fourprobe method in a physical property measurement system (PPMS, Quantum Design). *T*c,10 and *J*<sup>c</sup> were determined from the *ρT* and *I*–*V* curves using 0.1 *ρ*<sup>n</sup> and 1 µV/cm criteria, respectively. Here, *ρ*<sup>n</sup> means the normal state resistivity above the transition temperature. The current was applied perpendicularly to the magnetic field. The magnetization was measured using a superconducting quantum interference device (SQUID, Quantum Design) magnetometer. Two FST films (sample A and B) were fabricated under the same deposition condition for different irradiation conditions. Each FST film was cut into 3 pieces: one for magnetization measurement before and after irradiation with same film, another for transport measurement before irradiation (pristine) and the other for transport measurement after irradiation (irradiated).

The FST films were irradiated with 1.5 MeV proton doses of 1 <sup>×</sup> <sup>10</sup><sup>15</sup> and <sup>1</sup> <sup>×</sup> <sup>10</sup><sup>16</sup> p/cm<sup>2</sup> in vacuum at room temperature using the 5 MV tandem accelerator of the Wakasa Wan Energy Research Center (WERC). The samples were mounted on a copper plate with a double-faced carbon tape. The incident angle of ions was set as normal to the film surface. The flux was kept around 3.2 <sup>×</sup> <sup>10</sup><sup>12</sup> p/cm<sup>2</sup> ·s, corresponding to a beam current density of ~500 nA/cm<sup>2</sup> . The surface temperature was monitored by a thermocouple. The surface temperature during the irradiation remained below 40 ◦C.

Prior to the ion irradiation experiment, we ran Stopping and Range of Ions in Matter (SRIM) [18] to estimate ion range and damage profile in our experiment. Based on the simulation results, 1 <sup>×</sup> <sup>10</sup><sup>15</sup> and 1 <sup>×</sup> <sup>10</sup><sup>16</sup> p/cm<sup>2</sup> are estimated to be ~3.2 <sup>×</sup> <sup>10</sup>–5 and ~3.2 <sup>×</sup> <sup>10</sup>–4 dpa (displacement per atm), respectively.
