Prominent Quasiparticle Peak in the Photoemission Spectrum of the Metallic Phase ofV2O3

Abstract

We present the first observation of a prominent quasi-particle peak in the photoemission spectrum of the metallic phase of V2O3 and report new spectral calculations that combine the local density approximation with the dynamical mean-field theory (using quantum Monte Carlo simulations) to show the development of such a distinct peak with decreasing temperature. The experimental peak width and weight are significantly larger than in the theory.PACS numbers: PACS numbers: 71.20. Be, 71.30.+h, (V 1−x Cr x ) 2 O 3 displays a complex phase diagram with paramagnetic metal (PM), paramagnetic insulator (PI) and antiferromagnetic insulator (AFI) regions. The PM to PI transition serves as the paradigm of the MottHubbard (MH) metal-insulator transition (MIT) [1]. The MH scenario for (V 1−x Cr x ) 2 O 3 was put forth originally in the context of the half-filled one-band Hubbard model in which the tendency of the on-site Coulomb repulsion 'U ' to make a correlation gap insulator competes with the tendency of site to site hopping to make a broad band metal of bandwidth 'B'. A coherent thermodynamically consistent description of the MIT became possible with the development of the dynamical mean-field theory (DMFT) [2]. DMFT describes the strongly interacting metal in terms of Fermi liquid quasi-particles, i.e. single particle excitations near the Fermi energy E F which remain well defined as in a non-interacting system but have a self energy correction that increases their effective mass and reduces their spectral weight. In application to the Hubbard model, DMFT is significant as the best description that can be made by using a local (i.e. independent of momentum k) self energy. It may be formulated as a mapping of the lattice problem onto an effective Anderson impurity model coupled self-consistently to an effective conduction band bath [3]. In the metallic phase, although the large U value acts to separate much of the band's spectral weight away from E F into the so called upper and lower Hubbard bands, there remains at E F a distinctive quasi-particle (QP) peak, not accidentally reminiscent of the Kondo/Suhl-Abrikosov resonance [4] of the Anderson impurity model. The weight of the QPpeak decreases with increasing U/B and goes to zero at a critical value of U/B, which thus marks the MIT.Such a distinctive peak could in principle be seen in photoemission spectroscopy (PES). However, in spite of continuing efforts for over twenty years, literature [5,6,7,8,9, 10] V 3d PES spectra for the PM phase of (V 1−x Cr x ) 2 O 3 have shown at most a near E F feature that is the smallest part of the spectrum. One could hypothesize that the distinctive central peak of the halffilled one-band model is obscured and washed out by the multi-band complexity of the actual electronic structure of (V 1−x Cr x ) 2 O 3 in which the two 3d-electrons of the V 3+ ion must be distributed among singly degenerate a 1g and doubly degenerate e π g orbitals derived from a small trigonal crystal field splitting of the cubic t 2g manifold of the V 3d states....

Soft X-ray angle-resolved photoemission with micro-positioning techniques for metallic V2O3

“…The former peak is the so-called quasi particle peak, and the latter is due to the incoherent satellite originating from the lower Hubbard band. This spectral line shape is qualitatively consistent with the reported spectra 10 . The structures A and B are, however, not observed at position 2.…”

Soft X-ray angle-resolved photoemission with micro-positioning techniques for metallic V2O3

“…The former peak is the so-called quasi particle peak, and the latter is due to the incoherent satellite originating from the lower Hubbard band. This spectral line shape is qualitatively consistent with the reported spectra 10 . The structures A and B are, however, not observed at position 2.…”

Role of surface termination in the metal-insulator transition of V$_2$O$_3$(0001) ultrathin films

“…The QP is broad and less intense due to the lower photon energy (21.2 eV) used in our experiment, where we are extremely sensitive to the surface. Previous studies also show less intense QP at the surface than bulk due to the enhanced correlation at the surface region relative to the bulk [33]. This is also in line with the DFT+ dynamical mean-field theory (DMFT) results, where it has been shown that a dead layer forms below the surface of V 2 O 3 , where quasiparticles are exponentially suppressed [35].…”

Shining Light on Transition-Metal Oxides: Unveiling the Hidden Fermi Liquid

“…This is because in previous studies the relevant correlated orbitals are more extended due to downfolding or projection onto a small energy window and hence experience a reduced repulsion. With these parameters the calculated total spectra is consistent with experiment photoemission spectroscopy measurements [25][26][27]. The occupancies of e π g and a 1g orbitals at T = 200K are 1.60 and 0.50 respectively, in good agreement with X-ray absorption spectroscopy [41] measurements and previous LDA+DMFT calculations [35].…”

Soft X-ray angle-resolved photoemission with micro-positioning techniques for metallic V2O3

“…The former peak is the so-called quasi particle peak, and the latter is due to the incoherent satellite originating from the lower Hubbard band. This spectral line shape is qualitatively consistent with the reported spectra 10 . The structures A and B are, however, not observed at position 2.…”

Role of surface termination in the metal-insulator transition of V$_2$O$_3$(0001) ultrathin films

“…The QP is broad and less intense due to the lower photon energy (21.2 eV) used in our experiment, where we are extremely sensitive to the surface. Previous studies also show less intense QP at the surface than bulk due to the enhanced correlation at the surface region relative to the bulk [33]. This is also in line with the DFT+ dynamical mean-field theory (DMFT) results, where it has been shown that a dead layer forms below the surface of V 2 O 3 , where quasiparticles are exponentially suppressed [35].…”

Shining Light on Transition-Metal Oxides: Unveiling the Hidden Fermi Liquid

“…This is because in previous studies the relevant correlated orbitals are more extended due to downfolding or projection onto a small energy window and hence experience a reduced repulsion. With these parameters the calculated total spectra is consistent with experiment photoemission spectroscopy measurements [25][26][27]. The occupancies of e π g and a 1g orbitals at T = 200K are 1.60 and 0.50 respectively, in good agreement with X-ray absorption spectroscopy [41] measurements and previous LDA+DMFT calculations [35].…”

Soft X-ray angle-resolved photoemission with micro-positioning techniques for metallic V2O3

“…The former peak is the so-called quasi particle peak, and the latter is due to the incoherent satellite originating from the lower Hubbard band. This spectral line shape is qualitatively consistent with the reported spectra 10 . The structures A and B are, however, not observed at position 2.…”

Role of surface termination in the metal-insulator transition of V$_2$O$_3$(0001) ultrathin films

“…The QP is broad and less intense due to the lower photon energy (21.2 eV) used in our experiment, where we are extremely sensitive to the surface. Previous studies also show less intense QP at the surface than bulk due to the enhanced correlation at the surface region relative to the bulk [33]. This is also in line with the DFT+ dynamical mean-field theory (DMFT) results, where it has been shown that a dead layer forms below the surface of V 2 O 3 , where quasiparticles are exponentially suppressed [35].…”

Shining Light on Transition-Metal Oxides: Unveiling the Hidden Fermi Liquid

“…This is because in previous studies the relevant correlated orbitals are more extended due to downfolding or projection onto a small energy window and hence experience a reduced repulsion. With these parameters the calculated total spectra is consistent with experiment photoemission spectroscopy measurements [25][26][27]. The occupancies of e π g and a 1g orbitals at T = 200K are 1.60 and 0.50 respectively, in good agreement with X-ray absorption spectroscopy [41] measurements and previous LDA+DMFT calculations [35].…”