[Paper Review] Eliminating Orbital Selectivity from the Metal-Insulator Transition by Strong Magnetic Fluctuations

Е. А. Степанов|arXiv (Cornell University)|Apr 6, 2022

Advanced Condensed Matter PhysicsPhysics and Astronomy88 references31 citations

TL;DR

This paper demonstrates that strong spatially collective magnetic fluctuations suppress orbital-selective Mott transitions (OSMT) in a three-dimensional two-orbital Hubbard-Kanamori model. Using the D-TRILEX diagrammatic extension of DMFT, it shows that magnetic fluctuations become orbital-independent near the Néel transition, leading to a simultaneous, non-selective Mott transition for both orbitals.

ABSTRACT

The orbital-selective electronic behavior is one of the most remarkable manifestations of strong electronic correlations in multi-orbital systems. A prominent example is the orbital-selective Mott transition (OSMT), which is characterized by the coexistence of localized electrons in some orbitals, and itinerant electrons in other orbitals. The state-of-the-art theoretical description of the OSMT in two- and three-dimensional systems is based on local non-perturbative approximations to electronic correlations provided by dynamical mean-field theory or slave spin method. In this work we go beyond this local picture and focus on the effect of spatial collective electronic fluctuations on the OSMT. To this aim, we consider a half-filled Hubbard-Kanamori model on a cubic lattice with two orbitals that have different bandwidths. We show that strong magnetic fluctuations that are inherent in this system prevent the OSMT and favor the N\'eel transition that occurs at the same critical temperature for both orbitals.

Motivation & Objective

• To investigate the impact of non-local electronic fluctuations on orbital-selective Mott transitions (OSMT) beyond local approximations.
• To determine whether strong magnetic fluctuations, inherent in multi-orbital systems, can suppress OSMT and alter the metal-insulator transition scenario.
• To examine the role of orbital-dependent magnetic fluctuations in driving a non-orbital-selective Néel transition in a 3D cubic lattice.
• To assess the stability of OSMT against interorbital hopping in the presence of collective electronic fluctuations.

Proposed method

• Employing the D-TRILEX diagrammatic approach, a non-perturbative, self-consistent extension of dynamical mean-field theory (DMFT), to include non-local two-particle fluctuations.
• Using the dual triply irreducible local expansion (D-TRILEX) to couple single-particle and collective electronic fluctuations via lowest-order three-point vertex corrections.
• Applying the method to a half-filled two-orbital Hubbard-Kanamori model on a cubic lattice with different orbital bandwidths (D1 = 1, D2 = 2).
• Implementing Kanamori interaction parameters: U = 2.4, U′ = 1.6, J = 0.4, with interorbital hopping t12 introduced to probe stability of OSMT.
• Calculating the spin susceptibility, self-energy, and polarization operators to track the onset of magnetic order and metal-insulator transitions.
• Analyzing orbital-resolved spectral functions and spin susceptibility to detect orbital selectivity or isotropy in the transition.

Experimental results

Research questions

• RQ1 Can strong spatially collective magnetic fluctuations suppress the orbital-selective Mott transition (OSMT) in a 3D multi-orbital system?
• RQ2 Does the Néel transition occur simultaneously across all orbitals when non-local fluctuations are included, or does it retain orbital selectivity?
• RQ3 How do orbital-dependent magnetic fluctuations evolve with decreasing temperature, and do they become orbital-independent near the Néel transition?
• RQ4 What is the effect of interorbital hopping on the stability of the OSMT in the presence of non-local fluctuations?
• RQ5 Does the inclusion of non-local correlations via D-TRILEX alter the critical interaction strength for the metal-insulator transition compared to local DMFT?

Key findings

• Strong magnetic fluctuations develop at relatively high temperatures and are initially orbital-dependent, with different orbital contributions to the spin susceptibility.
• As temperature decreases, the contributions from both orbitals to the spin susceptibility mix efficiently, leading to orbital-independent magnetic fluctuations near the Néel transition.
• The Néel transition occurs before the OSMT and is characterized by the simultaneous divergence of spin susceptibility in both orbitals, indicating a non-orbital-selective transition.
• The OSMT is suppressed by strong magnetic fluctuations, and the system instead undergoes a simultaneous Mott transition at the Néel temperature.
• The presence of interorbital hopping (t12) destroys the OSMT at low temperatures, favoring a metallic ground state, consistent with previous DMFT findings but now stabilized by non-local fluctuations.
• The D-TRILEX approach successfully captures the feedback of collective fluctuations on single-particle properties, revealing a transition scenario fundamentally different from local DMFT.