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The heavy-fermion superconductor CeCoIn₅, whose order parameter is known to have d_x²_-y² symmetry [1], manifests an interesting spin density wave-like Q-phase [2]. Despite several recent scanning tunneling spectroscopic measurements [3], there are no phase-sensitive measurements in the Q-phase. Our planer tunneling spectroscopy data at 20 mK show sharp coherence peaks and the estimated gap size is 0.65 meV. Quite intriguingly, the superconducting gap-like features evolve into a pseudogap as superconductivity is destroyed with temperature and magnetic fields. The field-induced pseudogap is enhanced further with increasing fields up to the highest measurements field of 18 T. The possible origin of the pseudogap and implications of our results will be discussed.

[1]J. D. Thompson et al.,JPSJ 81, 011002 (2012); W.K. Park, et al. PRL 100, 177001 (2008).
[2]M. Kenzelmann, et al.,Science, 321, 1652 (2008).
[3]Y. Fasano, et al.,Physica B 536, 798 (2018); A. Gyenis, et al.,Nat. Commun. 9, 549 (2018); M. P. Allan, et al.,Nat. Phys. 9, 468 (2013); B. B. Zhou, et al.,Nat. Phys. 9, 474 (2013).