Fig. 3: Enhanced superconductivity under an in-plane magnetic field.
From: Lithium intercalated FeSe as a high-temperature superconducting ferromagnet
a Hall resistance as a function of magnetic field at selected tilting angles for sample S2. Inset illustrates the definition of the tilting angle. Curves are vertically offset, with the dashed lines representing zero Hall resistances. Arrows on the curves indicate the sweeping directions. The hysteresis loop at the nominal 0 degree looks clockwise, whereas other loops are counterclockwise, indicating that the real in-plane direction is between nominally 0° and 0.1°. b Temperature-dependent longitudinal resistances \({R}_{{xx}}\) at a set of in-plane magnetic fields for sample S2. The magnetic field increases in a step of 2 T from 0 T to 12 T. Gray and red arrows indicate the conventional and anomalous field responses, respectively. The inset illustrates two effects involved when applying an in-plane magnetic field: 1. Enhanced superconductivity (SC); 2. Increased broadening. c \({R}_{{xx}}\) as a function of magnetic field at a set of temperature points for sample S4. The temperature increases in a step of 0.25 K from 42 K to 46 K. d, e Color-plot of \({R}_{{xx}}\) at 12 T as a function of temperature and tilting angle for sample S2. Black dashed line represents the superconducting transition temperature defined by the mid-point criterion at zero magnetic field: \({T}_{{sc}}^{50\%}\left(B=0\right)\). White dashed curve represents the transition temperature at 12 T: \({T}_{{sc}}^{50\%}\left(B=12\right)\). Arrows in e indicate the critical angles. Within this small range, \({T}_{{sc}}^{50\%}\left(B=12\right) > {T}_{{sc}}^{50\%}\left(B=0\right)\). f Upper critical fields as a function of normalized temperature at different tilting angles. Here we apply the mid-point criterion to the data from S2 and S4. Squares are the in-plane upper critical field data of [(Li,Fe)OH]FeSe35. g Upper critical fields as a function of temperature at different tilting angles. Solid lines are fits employing the 2D Ginzburg–Landau formula. Purple dashed line represents the Pauli limit.
