Mechanism of the insulator-to-metal transition and superconductivity in the spin liquid candidate NaYbSe2 under pressure

Abstract

The quantum spin liquid candidate NaYbSe2 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 NaYbSe2 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-4f Fermi surfaces, suggesting that spin fluctuations may play a role in the Cooper pairing. NaYbSe2 might therefore be the 3rd Yb-based heavy-fermion superconductor with a very “high” Tc than most heavy-fermion superconductors.

Pressure induced insulator to metal transition in quantum spin liquid candidate NaYbS2

“…[9] Yang et al' DFT calculation indicated that the resistance should be dominated by incoherent Kondo scattering. [15] Here, we find both NaYbS 2 and NaYbSe 2 show similar behavior, suggesting that it may be the intrinsic physical property related to the 4f electron. The piezochromism of the NaYbS 2 single crystal also coincides with that transport properties, reflecting the narrowing of the band gap.…”

“…Recently, Yang et al explored the underlying mechanism of the insulator-to-metal transition and superconductivity of NaYbSe 2 and established an overall picture of its electronic phases under pressure utilizing density functional theory and the dynamical mean-field theory. [15] They found the superconductivity emerged in the heavy fermion phase with well-nested Yb-4f Fermi surfaces, suggesting that spin fluctuations may play a role in the Cooper pairing. Moreover, they pointed out that NaYbSe 2 might be the third Yb-based heavy-fermion superconductor with a very high T c than most heavy fermion superconductors.…”

An emerging global picture of heavy fermion physics

“…Our DFT plus dynamical mean-field theory (DFT+DMFT) calculations confirmed that the insulator-to-metal transition is induced by gap close of conduction bands, so it becomes first a lowcarrier Kondo system after the transition and then a heavy fermion metal above about 75 GPa [143]. Its superconductivity emerges when the itinerant f electron Fermi surfaces become well-nested on one of the inequivalent Yb layers, while the other Yb layer remains a spin liquid due to its large Yb-Se distance.…”

Configuration-Mixing-Driven Quasiparticle Multiplets in Curium Trichloride: Insights from Single-Particle Approximations and a Many-Body Approach

“…Consequently, the DFT+ U method, equivalent to the static limit of the DMFT scheme, is more appropriate for strongly correlated systems with static spin and orbital correlations, e.g., Mott insulators with large bandwidths. , In addition, DFT-based methods, in the essence of 0 K ground-state theories, fail to simultaneously capture the excitation spectra at finite temperatures, as well as the screening and relaxation features, e.g., the lower Hubbard band (LHB) and upper Hubbard band (UHB) in the photoemission spectra (PES) . Fortunately, the recently introduced DMFT scheme could deal with the low-lying coherent and high-lying incoherent excitations on the same footing, and this picture is in favor of describing the finite temperature properties of correlated systems. ,,, For CmCl 3 in this work, as illustrated in Figure a,b, the DFT+DMFT calculation captures not only the intersite quantum fluctuations but also the local ones, e.g., the quasiparticle multiplets close to the Fermi level and Hubbard bands. , …”

“…44 Fortunately, the recently introduced DMFT scheme could deal with the lowlying coherent and high-lying incoherent excitations on the same footing, and this picture is in favor of describing the finite temperature properties of correlated systems. 15,16,45,46 For CmCl 3 in this work, as illustrated in Figure 4a,b, the DFT +DMFT calculation captures not only the intersite quantum fluctuations but also the local ones, 47 e.g., the quasiparticle multiplets close to the Fermi level and Hubbard bands. 21,48 3.3.2.…”