ترغب بنشر مسار تعليمي؟ اضغط هنا

Photoemission evidence for a Mott-Hubbard metal-insulator transition in VO$_2$

93   0   0.0 ( 0 )
 نشر من قبل Ritsuko Eguchi
 تاريخ النشر 2006
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

The temperature ($T$) dependent metal-insulator transition (MIT) in VO$_2$ is investigated using bulk sensitive hard x-ray ($sim$ 8 keV) valence band, core level, and V 2$p-3d$ resonant photoemission spectroscopy (PES). The valence band and core level spectra are compared with full-multiplet cluster model calculations including a coherent screening channel. Across the MIT, V 3$d$ spectral weight transfer from the coherent ($d^1underbar{it {C}}$ final) states at Fermi level to the incoherent ($d^{0}+d^1underbar{it {L}}$ final) states, corresponding to the lower Hubbard band, lead to gap-formation. The spectral shape changes in V 1$s$ and V 2$p$ core levels as well as the valence band are nicely reproduced from a cluster model calculations, providing electronic structure parameters. Resonant-PES finds that the $d^1underbar{it{L}}$ states resonate across the V 2$p-3d$ threshold in addition to the $d^{0}$ and $d^1underbar{it {C}}$ states. The results support a Mott-Hubbard transition picture for the first order MIT in VO$_2$.



قيم البحث

اقرأ أيضاً

Here we present experimental and computational evidences to support that rock-salt cubic VO is a strongly correlated metal with Non-Fermi-Liquid thermodynamics and an unusually strong spin-lattice coupling. An unexpected change of sign of metallic th ermopower with composition is tentatively ascribed to the presence of a pseudogap in the density of states. These properties are discussed as signatures of the proximity to a magnetic quantum phase transition. The results are summarized in a new electronic phase diagram for the 3d monoxides, which resembles that of other strongly correlated systems. The structural and electronic simplicity of 3d monoxides make them ideal candidates to progress in the understanding of highly correlated electron systems.
116 - J. Laverock , , A. R. H. Preston 2012
We present a spectroscopic study that reveals that the metal-insulator transition of strained VO$_2$ thin films may be driven towards a purely electronic transition, which does not rely on the Peierls dimerization, by the application of mechanical st rain. Comparison with a moderately strained system, which does involve the lattice, demonstrates the crossover from Peierls- to Mott-like transitions.
The insulator-to-metal transition (IMT) of the simple binary compound of vanadium dioxide VO$_2$ at $sim 340$ K has been puzzling since its discovery more than five decades ago. A wide variety of photon and electron probes have been applied in search of a satisfactory microscopic mechanistic explanation. However, many of the conclusions drawn have implicitly assumed a {em homogeneous} material response. Here, we reveal inherently {em inhomogeneous} behavior in the study of the dynamics of individual VO$_2$ micro-crystals using a combination of femtosecond pump-probe microscopy with nano-IR imaging. The time scales of the photoinduced bandgap reorganization in the ultrafast IMT vary from $simeq 40 pm 8$ fs, i.e., shorter than a suggested phonon bottleneck, to $sim 200pm20$ fs, with an average value of $80 pm 25$ fs, similar to results from previous studies on polycrystalline thin films. The variation is uncorrelated with crystal size, orientation, transition temperature, and initial insulating phase. This together with details of the nano-domain behavior during the thermally-induced IMT suggests a significant sensitivity to local variations in, e.g., doping, defects, and strain of the microcrystals. The combination of results points to an electronic mechanism dominating the photoinduced IMT in VO$_2$, but also highlights the difficulty of deducing mechanistic information where the intrinsic response in correlated matter may not yet have been reached.
Despite many efforts to rationalize the strongly correlated electronic ground states in doped Mott insulators, the nature of the doping induced insulator to metal transition is still a subject under intensive investigation. Here we probe the nanoscal e electronic structure of the Mott insulator Sr$_2$IrO$_{4-delta}$ with low-temperature scanning tunneling microscopy and find enhanced local density of states (LDOS) inside the Mott gap at the location of individual apical oxygen site defects. We visualize paths of enhanced conductance arising from the overlapping of defect states which induces finite LDOS at the Fermi level. By combining these findings with the typical spatial extension of isolated defects of about 2~nm, we show that the insulator to metal transition in Sr$_2$IrO$_{4-delta}$ is of percolative nature.
We examine the metal-insulator transition in a half-filled Hubbard model of electrons with random and all-to-all hopping and exchange, and an on-site non-random repulsion, the Hubbard $U$. We argue that recent numerical results of Cha et al. (arXiv:2 002.07181) can be understood in terms of a deconfined critical point between a disordered Fermi liquid and an insulating spin glass. We find a deconfined critical point in a previously proposed large $M$ theory which generalizes the SU(2) spin symmetry to SU($M$), and obtain exponents for the electron and spin correlators which agree with those of Cha et al. We also present a renormalization group analysis, and argue for the presence of an additional metallic spin glass phase at half-filling and small $U$.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا