52 research outputs found
A Microscopic View on the Mott transition in Chromium-doped V2O3
V2O3 is the prototype system for the Mott transition, one of the most
fundamental phenomena of electronic correlation. Temperature, doping or
pressure induce a metal to insulator transition (MIT) between a paramagnetic
metal (PM) and a paramagnetic insulator (PI). This or related MITs have a high
technological potential, among others for intelligent windows and field effect
transistors. However the spatial scale on which such transitions develop is not
known in spite of their importance for research and applications. Here we
unveil for the first time the MIT in Cr-doped V2O3 with submicron lateral
resolution: with decreasing temperature, microscopic domains become metallic
and coexist with an insulating background. This explains why the associated PM
phase is actually a poor metal. The phase separation can be associated with a
thermodynamic instability near the transition. This instability is reduced by
pressure which drives a genuine Mott transition to an eventually homogeneous
metallic state.Comment: Paper plus supplementary materia
Dynamical Mean-Field Theory
The dynamical mean-field theory (DMFT) is a widely applicable approximation
scheme for the investigation of correlated quantum many-particle systems on a
lattice, e.g., electrons in solids and cold atoms in optical lattices. In
particular, the combination of the DMFT with conventional methods for the
calculation of electronic band structures has led to a powerful numerical
approach which allows one to explore the properties of correlated materials. In
this introductory article we discuss the foundations of the DMFT, derive the
underlying self-consistency equations, and present several applications which
have provided important insights into the properties of correlated matter.Comment: Chapter in "Theoretical Methods for Strongly Correlated Systems",
edited by A. Avella and F. Mancini, Springer (2011), 31 pages, 5 figure
Ultrafast evolution and transient phases of a prototype out-of-equilibrium Mott-Hubbard material
The study of photoexcited strongly correlated materials is attracting growing interest since their rich phase diagram often translates into an equally rich out-of-equilibrium behaviour. With femtosecond optical pulses, electronic and lattice degrees of freedom can be transiently decoupled, giving the opportunity of stabilizing new states inaccessible by quasi-adiabatic pathways. Here we show that the prototype Mott-Hubbard material V2O3 presents a transient non-thermal phase developing immediately after ultrafast photoexcitation and lasting few picoseconds. For both the insulating and the metallic phase, the formation of the transient configuration is triggered by the excitation of electrons into the bonding a1g orbital, and is then stabilized by a lattice distortion characterized by a hardening of the A1g coherent phonon, in stark contrast with the softening observed upon heating. Our results show the importance of selective electron-lattice interplay for the ultrafast control of material parameters, and are relevant for the optical manipulation of strongly correlated systems. \ua9 The Author(s) 2017
The Hubbard model within the equations of motion approach
The Hubbard model has a special role in Condensed Matter Theory as it is
considered as the simplest Hamiltonian model one can write in order to describe
anomalous physical properties of some class of real materials. Unfortunately,
this model is not exactly solved except for some limits and therefore one
should resort to analytical methods, like the Equations of Motion Approach, or
to numerical techniques in order to attain a description of its relevant
features in the whole range of physical parameters (interaction, filling and
temperature). In this manuscript, the Composite Operator Method, which exploits
the above mentioned analytical technique, is presented and systematically
applied in order to get information about the behavior of all relevant
properties of the model (local, thermodynamic, single- and two- particle ones)
in comparison with many other analytical techniques, the above cited known
limits and numerical simulations. Within this approach, the Hubbard model is
shown to be also capable to describe some anomalous behaviors of the cuprate
superconductors.Comment: 232 pages, more than 300 figures, more than 500 reference
RESONANT MAGNETIC-X-RAY SCATTERING FROM MIXED-VALENCE TMSE
The mixed-valent compound TmSe has been studied in its antiferromagnetic state (T <T(N) = 3.2) by resonant magnetic x-ray scattering. The (003) magnetic reflection shows two peaks as a function of incident energy corresponding to the L(III) absorption edges of its Tm2+ and Tm2+ configurations. This unambiguously establishes that long-range magnetic order is present for both valence states. An Anderson impurity model including multiplet and core-hole effects gives a good description of the data
Recommended from our members
Oscillatory magnetic fluctuations near the superconductor-to-ferromagnet transition in ErRh4B4
Small-angle neutron experiments show that near the transition from superconductor to ferromagnet in ErRh4B4 scattering peaks occur at a wave vector |q's|=0.06 -1. The temperature and wave-vector dependence suggest this signal is due to oscillatory magnetization fluctuations caused by the electromagnetic coupling of magnetic and superconducting order parameters. The ferromagnetic Bragg scattering shows a 5% hysteresis and transition-temperature-smearing effects which are also due to magnetic-superconducting interactions. © 1980 The American Physical Society
- …