An Unconventional Coherence Peak in the Quadrupole Relaxation of Cuprate Superconductors
First observation of a Hebel-Slichter-like coherence peak in an unconventional (cuprate) superconductor: in YBa2Cu4O8, NQR with 63Cu/65Cu isotopes separates magnetic (hyperfine) from quadrupole (electric-field-gradient / charge) relaxation, revealing a coherence peak in the quadrupole channel 1/T1(quad) but not the magnetic 1/T1(mag) — a consequence of the different coherence factors of charge versus magnetic fluctuations, and a new probe of unconventional pairing.
2501.00699
In conventional BCS superconductors the nuclear spin-lattice relaxation rate 1/T1 shows a Hebel-Slichter coherence peak just below Tc, a hallmark of the pairing symmetry; unconventional superconducto…