Magnetic-field-induced superconductivity in the antiferromagnetic organic superconductor $\kappa \text{−}{\left(\mathrm{BETS}\right)}_2\mathrm{Fe}{\mathrm{Br}}_4$

The high magnetic field electronic state of the quasi-two-dimensional organic superconductor,$\kappa \text{−}{\left(\mathrm{BETS}\right)}_2\mathrm{Fe}{\mathrm{Br}}_4$ was investigated by the resistance measurements. At very low temperatures, magnetic-field-induced superconductivity (FISC) was observed under high magnetic field parallel to the conducting layers. The obtained magnetic phase diagrams are well reproduced by Fisher’s theory based on the Jaccarino-Peter compensation mechanism, where the external field and internal field caused by the magnetic moments are canceled out. The analyses of the phase diagram show that the orbital effect is not so small in this compound, which makes the Fulde-Ferrell-Larkin-Ovchinnikov state less likely.

Figure 1

(a) Field dependence of the interlayer resistance at various temperatures for $H\Vert a$. Inset shows the data in low field region. (b) Magnetic phase diagram for $H\Vert a$. Closed circles, open circles, and closed triangles shows the superconducting, metamagnetic and the field induced superconducting transitions, respectively. Open squares shows the metamagnetic transition determined from the SQUID and transport measurements (Ref. 8). Dotted line is the guide to the eyes. Shaded areas show the calculated superconducting phases by using Fisher’s theory (Ref. 14).

Figure 2

(a) Field dependence of the interlayer resistance at various temperatures for $H\Vert c$. Inset shows the data in low field region. (b) Magnetic phase diagram for $H\Vert c$. Closed circle, open circle, and closed triangle shows the superconducting, canted antiferromagnetic and the field induced superconducting transitions, respectively. Shaded areas show the calculated superconducting phases by using Fisher’s theory (Ref. 14).

Figure 3

Interlayer resistance as a function of the magnetic field for various field angles tilted from the $a$-axis. Inset shows the$H_b\text{−}{H}_a$ phase diagram at $25\mathrm{mK}$.