Nodeless versus nodal scenarios of possible triplet superconductivity in the quasi-one-dimensional layered conductor Li_0.9Mo₆O ₁₇

We consider the problem of the orbital upper critical magnetic field, parallel to the most conducting axis of a quasi-one-dimensional layered superconductor. It is shown that superconductivity can be destroyed through orbital effects at fields much higher than the so-called Clogston-Chandrasekhar paramagnetic limiting field H_p, provided that superconducting pairing of electrons are of a triplet nature. We demonstrate that the superconducting state of the quasi-one-dimensional layered conductor Li_0.9Mo ₆O₁₇ is well described by the suggested theory. To this end, we consider two competing scenarios: (1) a superconducting order parameter without zeros on the Fermi surface, and (2) one with zeros on the Fermi surface - both are shown to lead to destruction of superconductivity at a magnetic field Hc₂x, five times higher than H_p. With recent experimental measurements on the Li_0.9Mo₆O₁₇ favoring the nodeless order parameter, we present a strong argument supporting triplet pairing in this compound.