Evidence of a pseudogap driven by competing orders of multi-band origin in the ferromagnetic superconductor Sr$_{0.5}$Ce$_{0.5}$FBiS$_2$

Mohammad Aslam; Arpita Paul; Gohil S. Thakur; Sirshendu Gayen; Ritesh Kumar; Avtar Singh; Shekhar Das; Ashok K. Ganguli; Umesh V. Waghmare; Goutam Sheet

doi:10.1088/0953-8984/28/19/195701

arXiv · 1603.08814

Evidence of a pseudogap driven by competing orders of multi-band origin in the ferromagnetic superconductor Sr$_{0.5}$Ce$_{0.5}$FBiS$_2$

Mohammad Aslam·Arpita Paul·Gohil S. Thakur·Sirshendu Gayen·Ritesh Kumar·Avtar Singh·Shekhar Das·Ashok K. Ganguli·Umesh V. Waghmare·Goutam Sheet

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Abstract

From temperature and magnetic field dependent point-contact spectroscopy on the ferromagnetic superconductor Sr$_{0.5}$Ce$_{0.5}$FBiS$_2$ (bulk superconducting $T_c$ = 2.5 K) we observe (a) a pseudogap in the normal state that sustains to a remarkably high temperature of 40 K and (b) two-fold enhancement of $T_c$ upto 5 K in the point-contact geometry. In addition, Andreev reflection spectroscopy reveals a superconducting gap of 6 meV for certain point-contacts suggesting that the mean field $T_c$ of this system could be approximately 40 K, the onset temperature of pseudo-gap. Our results suggest that quantum fluctuations originating from other competing orders in Sr$_{0.5}$Ce$_{0.5}$FBiS$_2$ forbid a global phase coherence at high temperatures thereby suppressing $T_c$. Apart from the known ordering to a ferromagnetic state, our first-principles calculations reveal nesting of a multi-band Fermi surface and a significant electron-phonon coupling that could result in charge density wave-like instabilities.

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Mohammad Aslam, Arpita Paul, Gohil S. Thakur, Sirshendu Gayen, Ritesh Kumar, Avtar Singh, Shekhar Das, Ashok K. Ganguli, Umesh V. Waghmare, Goutam Sheet. 2016-03-29. Evidence of a pseudogap driven by competing orders of multi-band origin in the ferromagnetic superconductor Sr$_{0.5}$Ce$_{0.5}$FBiS$_2$. https://doi.org/10.1088/0953-8984%2F28%2F19%2F195701

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