Inequivalent routes across the Mott transition in V$_{2}$O$_{3}$ explored by X-ray absorption $^{1}$Laboratoire de Physique des Solides, CNRS-UMR 8502, Universit´e Paris-Sud, F-91405 Orsay, France $^{2}$Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, France $^{3}$Institut for Solid State Physics, Vienna University of Technology, 1040 Vienna, Austria $^{4}$Max-Planck-Institut f¨ ur Festk¨ orperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany $^{5}$Laboratoire de Chimie Physique–Mati`ere et Rayonnement, CNRS-UMR 7614, Universit´e Pierre et Marie Curie, F-75005 Paris, France $^{6}$Department of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima 739-8530, Japan $^{7}$S.N.Bose Center for Basic Sciences, Salt Lake, Kolkata, India $^{8}$ESRF, 6 rue Jules Horowitz, BP 220, 38043 Grenoble Cedex, France $^{9}$CEA/DSM/INAC/NRS 17 avenue des Martyrs 38000 Grenoble $^{10}$Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA (Dated: November 2, 2018) F. Rodolakis, 1, 2 P. Hansmann, 3, 4 J.-P. Rueff, 2, 5 A. Toschi, 3 M.W. Haverkort, 4 G. Sangiovanni, 3 A. Tanaka, 6 T. Saha-Dasgupta, 7 O.K. Andersen, 4 K. Held, 3 M. Sikora, 8 I. Alliot, 8, 9 J.-P. Iti´ e, 2 F. Baudelet, 2 P. Wzietek, 1 P. Metcalf, 10 and M. Marsi 1 The changes in the electronic structure of V 2 O 3 across the metal-insulator transition induced by temperature, doping and pressure are identified using high resolution x-ray absorption spectroscopy at the V pre K -edge. Contrary to what has been taken for granted so far, the metallic phase reached under pressure is shown to differ from the one obtained by changing doping or temperature. Using a novel computational scheme, we relate this effect to the role and occupancy of the a$_{1}$$_{g}$ orbitals. This finding unveils the inequivalence of different routes across the Mott transition in V 2 O 3 . PACS numbers: 78.70.En; 71.27.+a; 71.20.Eh Some materials present metal-insulator transitions (MIT) without any changes in crystal structure or long- range magnetic order. These phenomena, known as Mott-Hubbard transitions, constitute a fundamental sig- nature of strong electronic correlations. The physics emerging in the vicinity of these transitions is highly non-trivial and the properties of such materials depend on small changes in the electronic structure induced by external parameters [1, 2]. Several features of the MIT have been successfully clarified by resorting to realistic many-body calculations [3]. Yet, contrary to common as- sumptions, a growing number of experimental facts are revealing that this physical process is also strongly de- pendent on the route followed through the MIT. Here we show this to be the case for vanadium sesquioxide (V$_{2}$O$_{3}$). The isostructural MIT in Cr-doped V$_{2}$O$_{3}$ is considered as the textbook example of a Mott transition, which occurs between a paramagnetic insulator (PI) and a paramagnetic metallic (PM) phase by changing dop- ing level ( x ), temperature (T) or pressure (P) [4]. As such V$_{2}$O$_{3}$ has served as a test bed for many theoretical models [5–11] and a sustained experimental effort. Among the different experimental methods recently employed to study the electronic properties of the Mott transition in Cr-doped V$_{2}$O$_{3}$ [12–15], X-ray absorption spectroscopy (XAS) has played a crucial role. It was the detailed investigation of the V L$_{2}$$_{,}$$_{3}$ absorption edges [16] that demonstrated the necessity of abandoning the sim- ple one band, S = 1 / 2, model to obtain a realistic de- scription of the changes in the electronic structure at the phase transition. XAS can also be performed at the V The experiments were performed on the inelastic x-ray scattering (IXS) beamlines ID-26 and BM-30 at the Eu- ropean Synchrotron Radiation Facility (ESRF). We used We used V K -edge XAS to explore extensively the MIT in V$_{2}$O$_{3}$ by changing temperature, doping and apply- ing an external pressure. The pre K -edges were ana- lyzed by a novel computational scheme combining local density approximation and dynamical mean field theory (LDA+DMFT) [17] with configuration interaction (CI) full multiplet ligand field calculations to interpret subtle differences at the PM-PI transition. This allowed us to: (i) observe in detail the changes in the electronic exci- tations, providing also a direct estimate of the Hund’s coupling J ; (ii) analyze the physical properties of the PI and PM phase on both sides of the MIT, leading to the main result of our work: (iii) understand the difference between P, T or doping-induced transitions. This dif- ference is mainly related to the occupancy of the a$_{1}$$_{g}$ or- bitals, suggesting the existence of a new “pressure” path- way between PI and PM in the phase diagram. K -edge in the hard x-ray range: in this case, the pre- edge will carry most of the physical information we are interested in, as it is predominantly due to 1 s → 3 d tran- sitions. The excitations in this spectral region are influ- enced by the core hole and should be considered to be of an excitonic nature. The advantages over the L$_{2}$$_{,}$$_{3}$ edge studies are (i) a more straightforward interpretation (due to the simple symmetry of the s -core hole, the multiplet structure reveals a direct view on the d -states) and (ii) the possibility of applying external pressure as diamond anvil cells are compatible with hard X-rays. arXiv:1001.0477v1 [cond-mat.str-el] 4 Jan 2010