Mechanism of the insulator-to-metal transition and superconductivity in the spin liquid candidate NaYbSe$_2$ under pressure

• Main Authors: Xu, Yuanji, Sheng, Yutao, Yang, Yi-feng
• Format: Journal Article
• Language: English
• Published: 06-08-2021
• Subjects: Physics - Strongly Correlated Electrons; Physics - Superconductivity
• DOI: 10.48550/arxiv.2108.03218

npj Quantum Mater. 7, 21 (2022) The quantum spin liquid candidate NaYbSe$_2$ was recently reported to exhibit
a Mott transition under pressure. Superconductivity was observed in the
high-pressure metallic phase, raising the question concerning its relation with
the low-pressure quantum spin liquid ground state. Here we combine the density
functional theory and the dynamical mean-field theory to explore the underlying
mechanism of the insulator-to-metal transition and superconductivity and
establish an overall picture of its electronic phases under pressure. Our
results suggest that NaYbSe$_2$ is a charge-transfer insulator at ambient
pressure. Upon increasing pressure, however, the system first enters a
semi-metallic state with incoherent Kondo scattering against coexisting
localized Yb-$4f$ moments, and then turns into a heavy fermion metal. In
between, there may exist a delocalization quantum critical point responsible
for the observed non-Fermi liquid region with linear-in-$T$ resistivity. The
insulator-to-metal transition is therefore a two-stage process.
Superconductivity emerges in the heavy fermion phase with well-nested Yb-4$f$
Fermi surfaces, suggesting that spin fluctuations may play a role in the Cooper
pairing. NaYbSe$_2$ might therefore be the 3rd Yb-based heavy-fermion
superconductor with a very "high" $T_c$ than most heavy fermion
superconductors.