Condensed Matter Seminars

UTe2 has drawn a lot of attention among the superconductivity (SC) community recently for the promising secondary evidence of spin-triplet Cooper pairing shown in this system through temperature-independent NMR Knight shift, the highly anisotropic and unusually large upper critical field, power-law behavior of the specific heat, and possible ferromagnetic spin fluctuation hinted by the magnetic susceptibility. Under an extremely large magnetic field (~30 T above Hc2 in the bc-plane) the system shows re-entrance of the superconducting phase. Our previous experiments at CNCS on a co-aligned UTe2 sample in its 0KL and HK0 plane showed two types of rod-like excitations at Brillouin zone boundary, and one of them develops a spin gap and a spin resonance upon entering the SC state. SEM study shows development of charge density wave (CDW) in the (011) cleaved edge at the Brillouin zone corner, which is similar to the other excitation we observed with neutron scattering. Because the resonance has only been found in spin-singlet unconventional superconductors near an AF instability, its observation in UTe2 suggests that AF spin fluctuations may also induce spin-triplet pairing24 or that electron pairing in UTe2 has a spin-singlet component.