Mott transition

About: Mott transition is a research topic. Over the lifetime, 2444 publications have been published within this topic receiving 78401 citations.

Structures of quantum 2D electron-hole plasmas

Abstract: We investigate structures of 2D quantum electron-hole (e-h) plasmas by the direct path integral Monte Carlo method (PIMC) in a wide range of temperature, density and hole-to-electron mass ratio. Our simulation includes a region of appearance and decay of the bound states (excitons and biexcitons), the Mott transition from the neutral e-h plasma to metallic-like clusters, formation from clusters the hexatic-like liquid and formation of the crystal-like lattice.

Conductivity Equations Based on Rate Process Theory and Free Volume Concept for Addressing Low Temperature Conductive Behaviors like Superconductivity

Abstract: New conduction equations are derived on the basis of Eyring’s rate process theory and free volume concept. The basic assumptions are that electrons traveling from one equilibrium position to the other may obey Eyring’s rate process theory; the traveling distance is governed by the free volume available to each electron by assuming that electrons may have a spherical physical shape with an imaginative effective radius. The obtained equations predict that the superconductivity happens only when electrons form certain structures of a relative small coordinate number like Cooper pair at low temperatures; If each electron has a large coordinate number such as 8 when electrons form the body-centered-cubic (bcc) lattice structure like Wigner crystal, the predicted conductivity decreases instead increases when temperatures approach to zero. The electron condensation structures have a big impact on the conductivity. A sharp conductivity decrease at low temperatures, probably due to an Anderson transition, is predicted even when the Cooper pair is formed and the electrons can only travel short distances; While the Mott transition appears when crystalline structures like Wigner crystal form. On the other hand, the electron pairing or called the strong spin-spin coupling is predicted to induce Kondo effect when electrons are assumed to travel a very short distance. The Anderson localization seems to have a lot of similarities as Kondo effect such as electron pairing and low traveling distances of electrons at low temperatures. The Cooper pair that is the essence of BCS theory for superconductivity and the spin-spin coupling that is the cause for Kondo effect seem to contradict each other, but are seamlessly united in our current conductivity equations. The topological insulators become the natural occurrences of our equations, as both Kondo insulator and superconductivity share a same physical origin–the electron pairs, but the electrons just travel different distances at these two cases. A material containing an element of a high electro-negativity (or high ionization energy) and an element of a low electro-negativity(or low ionization energy) may form a good topological insulator and superconductor. Any magnetic element, like Iron, Nickel, and Cobalt, that has unpaired electrons and can induce Kondo effect as a dopant, could be a very good superconductor candidate once it is synthesized together with other proper elements of low electro- negativity (for example forming pnictide superconductors). The numbers of both conduction and valence electrons and the volume of a material under investigation have positive impacts on the conductivity. Any method that may increase the numbers of both conduction and valence electrons may move the superconductivity transition temperatures to higher regions. Any method that may reduce the volume of the material like external pressure seems to lower transition temperatures, unless that the applied pressure is so high that the electron density between the chemical bonds increases. The derived equations are in good agreement with the currently observed experimental phenomena. The current work may shed light on the mechanisms of superconductivity, presenting clues on how to move the superconductivity transition temperatures to higher regions.

Superfluid State of Strongly-Correlated Bose–Fermi Mixtures on Optical Lattices at Commensurate Filling

Abstract: Confinement of atoms by laser technology has opened up a new field of physics. Following the realization of Bose– Einstein condensation (BEC) of bosonic atoms, fermionic atom systems and even boson–fermion mixture systems were successfully trapped and cooled. Application of a periodic potential, so called optical lattice, could also unveil interesting nature of the atoms. One of the interesting phenomena of the atoms on optical lattice is Mott transition. Although there is a long history of the study on bosons or fermions on lattice, coexistence of bosons and fermions on lattice is a rather new topic to study. In particular, we have little knowledge about strongly-correlated bosons and fermions on lattice. In our previous works we performed numerical simulations of Bose–Fermi mixtures to clarify the phase diagram and the effect of the confinement potential. When the total number of bosonic and fermionic atoms per site takes an integer value and interatomic interactions are sufficiently strong, the system would undergo Mott transition where the local atom density is fixed to the integer value. A characteristic of this Mott insulating phase is that a boson and fermion located next to each other can exchange their positions by going through a virtual doubly-occupied state with the atom exchange energy t ’ tbtf=Ubf where tb and tf are the hopping energy of the bosons and fermions respectively and Ubf denotes the on-site interaction between the boson and the fermion. Although there still remain a number of open questions on the Mott state of Bose–Fermi mixtures, the property of superfluid state of the strongly-correlated bosons and fermions has yet to be revealed. In this short note we would like to focus on strongly-correlated Bose–Fermi mixtures at commensurate filling in a three-dimensional periodical potential and see characteristic behaviors, if any, of the superfluid phase close to the phase boundary to the Mott insulating phase. In the following analysis we assume uniformity of the system and thus neglect the possibility of the emergence of so-called supersolid where superfluidity and structural long-range order coexist. For simplicity we ignore all the internal degree of freedom of the atoms and the influence of the trap potential which in fact creates a nonuniform density profile of the bosons and fermions. For the system at commensurate filling on optical lattice, we assume that the interatomic interactions are weak enough to avoid formation of Mott state but strong enough to allow us to expect that there are only few empty or doublyoccupied sites and most sites are singly occupied. Namely we analyze the system that stays in a superfluid phase but lies close to the boundary to the Mott phase. Since a boson and fermion located next to each other can exchange their positions as stated above, the energy of the superfluid state of the mixture system is given mostly by the kinetic energy of the bosons and fermions exchanging their positions. We therefore express the Hamiltonian in the following form, ignoring the kinetic energy of the atoms at the empty sites and the interaction energy at the doubly-occupied sites:

Correlation Mechanism of the Insulator–Metal Transition in V2O3 Films

Abstract: A complex character of the mechanism of thermal phase transformations from the insulating phase to the metallic phase has been revealed in thin V2O3 films The insulator–metal phase transition in V2O3 is shown to consist of two stages: the hysteresis-less temperature-extended electron Mott transition extended in temperature and the stepwise structural Peierls transition with temperature hysteresis The features of the insulator–metal phase transition revealed for V2O3 are discussed These features are analyzed on the base of their comparison with characteristic features of analogous phase transition in VO2 films