Nature of the superconducting state in the new phase in $(\mathrm{TMTSF}{)}_2{\mathrm{PF}}_6$ under pressure

An unusual phase has recently been observed in the organic material $(\mathrm{TMTSF}{)}_2{\mathrm{PF}}_6$, where superconductivity (SC) may coexist with spin-density wave (SDW) in the whole pressure interval $p_{c1}<p<p_c$ below the first order transition into SC or normal metal phase. Assuming that the coexistence takes place on the microscopic scale, we consider the properties of the intermediate phase. We show that the new superconducting state inside SDW phase just above $p_{c1}$ must bear a triplet pairing.

Figure 1

The diagram equations for the functions $f_{\alpha \beta }^{LR}$ and $f_{\alpha \beta }^{RL}$ in the presence of SDW. The solid lines represent the electron Green functions $G_{i{\omega }_n}^{R\left(L\right)R\left(L\right)}$. The dashed lines represent the short-range interaction (in our case the backward scattering) of electrons.