29 research outputs found
Low-energy excitations in strongly correlated materials: A theoretical and experimental study of the dynamic structure factor in V2O3
PACS number(s): 71.45.Gm, 71.15.−m, 71.30.+h.-- et al.This work contains an experimental and theoretical study of the dynamic structure factor at large momentum transfer |Q|∼4 Å−1 of the strongly correlated transition-metal oxide V2O3. We focus in particular on the transitions between d states that give rise to the spectra below 6 eV. We show that the main peak in this energy range is mainly due to t2g→egσ transitions, and that it carries a signature of the phase transition between the paramagnetic insulator and the paramagnetic metal that can already be understood from the joint density of states calculated at the level of the static local density approximation. Instead, in order to obtain theoretical spectra that are overall similar to the measured ones, we have to go beyond the static approximation and include at least crystal local field effects. The latter turn out to be crucial in order to eliminate a spurious peak and hence allow a safe comparison between theory and experiment, including an analysis of the strong anisotropy of the spectra.Use of the Advanced Photon Source at Argonne National Laboratory was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. We are grateful for support by ETSF-I3 Grant No. 211956. Computer time was granted by IDRIS (544). F.I. also acknowledges financial
support from the CEA program Transversal Nanosciences and M.G. from the European Research Council Advanced Grant DYNamo (ERC-2010-AdG Proposal No. 267374), Spanish
Grants No. FIS2011-65702-C02-01 and No. PIB2010US-00652, ACI-Promociona (ACI2009-1036), Grupos Consolidados
UPV/EHU del Gobierno Vasco (IT-319-07), Consolider nanoTHERM (Grant No. CSD2010-00044), and European Commission projects CRONOS (280879-2 CRONOS CPFP7)
and THEMA (FP7-NMP-2008-SMALL-2, 228539).Peer reviewe
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How Bulk Sensitive is Hard X-ray Photoelectron Spectroscopy: Accounting for the Cathode-Electrolyte Interface when Addressing Oxygen Redox.
Sensitivity to the "bulk" oxygen core orbital makes hard X-ray photoelectron spectroscopy (HAXPES) an appealing technique for studying oxygen redox candidates. Various studies have reported an additional O 1s peak (530-531 eV) at high voltages, which has been considered a direct signature of the bulk oxygen redox process. Here, we find the emergence of a 530.4 eV O 1s HAXPES peak for three model cathodes-Li2MnO3, Li-rich NMC, and NMC 442-that shows no clear link to oxygen redox. Instead, the 530.4 eV peak for these three systems is attributed to transition metal reduction and electrolyte decomposition in the near-surface region. Claims of oxygen redox relying on photoelectron spectroscopy must explicitly account for the surface sensitivity of this technique and the extent of the cathode degradation layer
Surface floating 2D bands in layered nonsymmorphic semimetals : ZrSiS and related compounds
Work at Argonne National Laboratory is supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357; additional support by National Science Foundation under Grant No. DMR-0703406. This work was partially supported by the DFG, proposal no. SCHO 1730/1-1.In this work, we present a model of the surface states of nonsymmorphic semimetals. These are derived from surface mass terms that lift the high degeneracy imposed on the band structure by the nonsymmorphic bulk symmetries. Reflecting the reduced symmetry at the surface, the bulk bands are strongly modified. This leads to the creation of two-dimensional floating or unpinned bands, which are distinct from Shockley states, quantum well states, or topologically protected surface states. We focus on the layered semimetal ZrSiS to clarify the origin of its surface states. We demonstrate an excellent agreement between density functional theory calculations and angle-resolved photoemission spectroscopy measurements and present an effective four-band model in which similar surface bands appear. Finally, we emphasize the role of the surface chemical potential by comparing the surface density of states in samples with and without potassium coating. Our findings can be extended to related compounds and generalized to other crystals with nonsymmorphic symmetries.Publisher PDFPeer reviewe
Quasiparticle characteristics of the weakly ferromagnetic Hund's metal MnSi
Hund's metals are multi-orbital systems with or electrons
exhibiting both itinerant character and local moments, and they feature
Kondo-like screenings of local orbital and spin moments, with suppressed
coherence temperature driven by Hund's coupling . They often exhibit
magnetic order at low temperature, but how the interaction between the
Kondo-like screening and long-range magnetic order is manifested in the
quasiparticle spectrum remains an open question. Here we present spectroscopic
signature of such interaction in a Hund's metal candidate MnSi exhibiting weak
ferromagnetism. Our photoemission measurements reveal renormalized
quasiparticle bands near the Fermi level with strong momentum dependence: the
ferromagnetism manifests through possibly exchange-split bands (Q1) below
, while the spin/orbital screenings lead to gradual development of
quasiparticles (Q2) upon cooling. Our results demonstrate how the
characteristic spin/orbital coherence in a Hund's metal could coexist and
compete with the magnetic order to form a weak itinerant ferromagnet, via
quasiparticle bands that are well separated in momentum space and exhibit
distinct temperature dependence. Our results imply that the competition between
the spin/orbital screening and the magnetic order in a Hund's metal bears
intriguing similarity to the Kondo lattice systems.Comment: accepted by PR