Browsing by Author "Ran, Sheng"
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Item Nature of the spin resonance mode in CeCoIn5(Springer Nature, 2020) Song, Yu; Wang, Weiyi; Van Dyke, John S.; Pouse, Naveen; Ran, Sheng; Yazici, Duygu; Schneidewind, A.; Čermák, Petr; Qiu, Y.; Maple, M.B.; Morr, Dirk K.; Dai, PengchengSpin-fluctuation-mediated unconventional superconductivity can emerge at the border of magnetism, featuring a superconducting order parameter that changes sign in momentum space. Detection of such a sign-change is experimentally challenging, since most probes are not phase-sensitive. The observation of a spin resonance mode (SRM) from inelastic neutron scattering is often seen as strong phase-sensitive evidence for a sign-changing superconducting order parameter, by assuming the SRM is a spin-excitonic bound state. Here we show that for the heavy fermion superconductor CeCoIn5, its SRM defies expectations for a spin-excitonic bound state, and is not a manifestation of sign-changing superconductivity. Instead, the SRM in CeCoIn5 likely arises from a reduction of damping to a magnon-like mode in the superconducting state, due to its proximity to magnetic quantum criticality. Our findings emphasize the need for more stringent tests of whether SRMs are spin-excitonic, when using their presence to evidence sign-changing superconductivity.Item Tuning magnetic confinement of spin-triplet superconductivity(Springer Nature, 2020) Lin, Wen-Chen; Campbell, Daniel J.; Ran, Sheng; Liu, I.-Lin; Kim, Hyunsoo; Nevidomskyy, Andriy H.; Graf, David; Butch, Nicholas P.; Paglione, JohnpierreElectrical magnetoresistance and tunnel diode oscillator measurements were performed under external magnetic fields up to 41 T applied along the crystallographic b axis (hard axis) of UTe2 as a function of temperature and applied pressures up to 18.8 kbar. In this work, we track the field-induced first-order transition between superconducting and magnetic field-polarized phases as a function of applied pressure, showing suppression of the transition with increasing pressure until the demise of superconductivity near 16 kbar and the appearance of a pressure-induced ferromagnetic-like ground state that is distinct from the field-polarized phase and stable at zero field. Together with evidence for the evolution of a second superconducting phase and its upper critical field with pressure, we examine the confinement of superconductivity by two orthogonal magnetic phases and the implications for understanding the boundaries of triplet superconductivity.