Mott transition

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

Mott transition in the Hubbard model on the hyper-kagome lattice

Abstract: =12 combined with the continuous-timequantum Monte Carlo (CT QMC) method. The system undergoes a Mott transition if the Hubbardinteraction U/W (W is the bandwidth) exceeds the value of 1.2 for T=0.1 and displays reentrantbehavior due to competition between the magnetic correlation and the kinetic energy of electronsdue to the geometrical frustration. We observe a “critical slowing down” of the double occupancywhich shows evidence of a continuous transition. The nearest-neighbor and next nearest-neighborspin-spin correlations indicate a paramagnetic metallic state in the weak-coupling regime and anantiferromagnetic (AF) Mott insulator in the strong-coupling regime within the temperature rangewhich we can access with our numerical tools.

Mechanism of electrically driven metal-insulator phase transition in vanadium dioxide nanowires

Abstract: Vanadium dioxide (VO2) is well known for its metal-insulator transition (MIT) at 341 K.Normally,the VO2 presents a metallic rutile (R) phase above the Tc,but an insulator (monoclinic,M) phase below the Tc.Besides the thermally driven mode,the phase transition can also be triggered electrically,which is common in electron devices like field effect transistors and actuators.Due to the electron correlation,the Mott transition associated with electronelectron interaction as well as the Peierls transition involving electron-lattice interaction are both believed to drive the transition of VO2,although the actual MIT mechanism is still under debate in condensed matter physics.The Coulomb screening of the electron hopping can be broken by injecting enough carriers.However,the issue is more complicated in the electrically-triggered MIT of VO2 due to the Joule heat of current and the carrier injection of field effect.In this work, we study the electrically induced MIT in VO2 nanowires by in-situ transmission electron microscopy (TEM).We build a closed circuit under the TEM by using in-situ electric TEM holder to capture the changes of VO2 in electron structure and phase structure simultaneously.An alternating bias voltage is applied to the VO2 nanowire while the selected area electron diffraction (SAED) patterns of VO2 nanowire are recorded using Gatan Oneview fast camera.The current rises or drops suddenly in the current-voltage curve (I-V curve),indicating a phase transition,through which the SAED pattern of nanowire is recoded every 5 ms.By correspondence analysis between the SAED patterns and the I-V data at every moment,a transition state of insulating R phase is observed,which is obviously different from the normal state of the metallic R phase or the insulating M phase.The existence of the insulating R phase indicates that electron structure transforms prior to the phase transition.The decoupling phenomenon reveals a predominant role of electron-electron interaction.Moreover,by feedback strategy of the circuit,the current through the metallic nanowire of VO2 remains unchanged,and thus keeping the Joule heating in the nanowire constant,the phase transition from metal to insulator does not happen until the voltage decreases to about 1 V.When phase transition to insulator happens in voltage stepdown,even stronger Joule heating is generated because of the increased resistance of VO2 nanowire.Therefore,the VO2 phase transition is triggered electrically by the carrier injection instead of the Joule heating.The injecting of enough carriers can break the screening effect to activate the electron hopping and initiate the phase transition.The deduction is confirmed by the decoupling phenomenon in the insulating R phase.Additionally,the polarized shift rather than the phase transition of the VO2 nanowire is observed in the non-contact electric field mode,which also supports the cause of the carrier injection for the electric induced MIT.The results prove the electron-correlation-driven MIT mechanism, or so called Mott mechanism,and open the new way for electron microscopy used to study the electron correlated MIT.

Effects of composite pions on the chiral condensate within the PNJL model at finite temperature

Abstract: We investigate the effect of composite pions on the behaviour of the chiral condensate at finite temperature within the Polyakov-loop improved NJL model. To this end we treat quark-antiquark correlations in the pion channel (bound states and scattering continuum) within a Beth-Uhlenbeck approach that uses medium-dependent phase shifts. A striking medium effect is the Mott transition which occurs when the binding energy vanishes and the discrete pion bound state merges the continuum. This transition is triggered by the lowering of the continuum edge due to the chiral restoration transition. This in turn also entails a modification of the Polyakov-loop so that the SU(3) center symmetry gets broken at finite temperature and dynamical quarks (and gluons) appear in the system, taking over the role of the dominant degrees of freedom from the pions. At low temperatures our model reproduces the chiral perturbation theory result for the chiral condensate while at high temperatures the PNJL model result is recovered. The new aspect of the current work is a consistent treatment of the chiral restoration transition region within the Beth-Uhlenbeck approach on the basis of mesonic phase shifts for the treatment of the correlations.

Thermodynamic properties of the Mott insulator-metal transition in a triangular lattice system without magnetic order

Abstract: The organic system $\ensuremath{\kappa}\text{\ensuremath{-}}{[{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{1\ensuremath{-}x}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{STF})}_{x}]}_{2}{\mathrm{Cu}}_{2}{(\mathrm{CN})}_{3}$, showing a Mott transition between a nonmagnetic Mott insulating (NMI) state and a Fermi liquid (FL), is systematically studied using calorimetric measurements. An increase in the electronic heat capacity at the transition from the NMI state to the FL state which keeps the triangular dimer lattice demonstrates that the charge sector lost in the Mott insulating state is recovered in the FL state. We observed that the remaining low-energy spin excitations in the Mott insulating state show a unique temperature dependence and that the NMI state has a larger lattice entropy originating from the frustrated lattice, which leads to a Pomeranchuk-like effect on the electron localization. Near the Mott boundary, an unexpected enhancement and magnetic field dependence of the heat capacity are observed. This anomalous heat capacity is different from the behavior in a typical first-order Mott transition and shows similarities with quantum critical behavior. To reconcile our results with previously reported scenarios about a spin gap and the first-order Mott transition, further studies are desired.

Liquid MnTe: An example of a Mott-Hubbard liquid semiconductor

Abstract: A series of experiments performed in our laboratory have shown that liquid alloy systems of the form MTe (M is a transition metal other than Mn) combine salt-like structural order with a high electrical conductivity. This apparent contradiction can be resolved in terms of the Mott transition, that is to say, the d-bands associated with M are delocalized and are therefore able to contribute significantly to the conductivity. The situation for liquid MnTe is totally different. Here, the salt-like structural order is associated with a very low electrical conductivity because the splitting of the two sub-d-bands is sufficiently large to give a deep pseudogap in the density of states. Furthermore, since the splitting of the d-bands is an intra-atomic effect, the pseudogap should be essentially independent of temperature. We therefore have an ideal system for checking the validity of the Mott formula for the conductivity σ of liquid semiconductor, σ = σOe−EC−EF/kT We can also determine σO by a combination of measurements of σ and the thermopower S. Results for S and are presented for a series of liquid alloys at and close to the stoichiometric composition MnTe and the results interpreted in terms of Eq. (1).