Dielectric catastrophe at the Mott transition

We study the Mott transition as a function of interaction strength in the half-filled Hubbard chain with next-nearest-neighbor hopping t' by calculating the response to an external electric field using the density matrix renormalization group. The electric susceptibility chi diverges when approaching the critical point from the insulating side. We show that the correlation length xi characterizing this transition is directly proportional to fluctuations of the polarization and that chi approximately xi2. The critical behavior shows that the transition is infinite order for all t', whether or not a spin gap is present, and that hyperscaling holds.     

Superconductivity in the americium metal as a function of pressure: probing the Mott transition

High-pressure measurements of the resistivity of americium metal are reported to 27 GPa and down to temperatures of 0.4 K. The unusual dependence of the superconducting temperature (T(c)) on pressure is deduced. The critical field [H(c)(0) extrapolated to T=0] increases dramatically from 0.05 to approximately 1 T as the pressure is increased, suggesting that the type of superconductivity is changing as pressure increases. At pressures of approximately 16 GPa the 5f electrons of Am are changing from localized to itinerant, and the crystal structure also transforms to a complex one. The role of a Mott-type transition in the development of the peak in T(c) above 16 GPa is postulated.     

Quantum critical transport near the Mott transition

We perform a systematic study of incoherent transport in the high temperature crossover region of the half filled one-band Hubbard model. We demonstrate that the family of resistivity curves displays characteristic quantum critical scaling of the form ρ(T, δU) = ρ(c)(T)f(T/T?(δU)), with T?(δU) ~ |δU|(zν), and ρ(c)(T) ~ T. The corresponding β function displays a "strong coupling" form β ~ ln(ρ(c)/ρ), reflecting the peculiar mirror symmetry of the scaling curves. This behavior, which is surprisingly similar to some experimental findings, indicates that Mott quantum criticality may be acting as the fundamental mechanism behind the unusual transport phenomena in many systems near the metal-insulator transition.     

Mott transition in anharmonic confinement

Two effects are identified that affect the visibility of the Mott transition in an atomic gas in an optical lattice confined in a power-law potential. The transition can be made more pronounced by increasing the power law, but at the same time, experimental uncertainty in the number of particles will induce corresponding fluctuations in the measured condensate fraction. Calculations in two dimensions indicate that a potential slightly more flat-bottomed than a quadratic one is to be preferred for a wide range of particle number fluctuation size.     

Mott transition of the electron-hole liquid in Ge

A treatment is given of the Mott transition of a gas of excitons in equilibrium with electron-hole droplets in Ge. We find that transition occurs near 4K. We can come to no firm conclusion whether the Mott transition is a first-order transition separate from the liquid-gas transition, as has been suggested.     

Mott transition in the two-dimensional Hubbard model

Spectral properties of the two-dimensional Hubbard model near the Mott transition are investigated by using cluster perturbation theory. The Mott transition is characterized by freezing of the charge degrees of freedom in a single-particle excitation that leads continuously to the magnetic excitation of the Mott insulator. Various anomalous spectral features observed in cuprate high-temperature superconductors are explained in a unified manner as properties near the Mott transition.     

完全由电子关联驱动的Mott型金属--绝缘体相变研究

Mott金属－绝缘体相变（MIT）是凝聚态物理中的一个非常基本的概念.长期以来,Mott型MIT的概念被广泛应用于凝聚态物理的许多领域,特别是用于描述强关联系统的电子结构特征.然而到目前为止,完全由电子关联驱动的MIT并没有被观察到.因此,是否存在着完全由于电子之间的强关联效应导致的Mott型MIT一直是科学家们感兴趣的重要问题.近日,中国科学院物理研究所方忠研究员组、郭建东研究员组和美国Florida International大学的Jiandi Zhang教授研究组及美国Tennessee大学及橡树岭国家实验室的E. W. Plummer教授研究组、Rong Ying Jin教授研究组合作,通过实验与理论相结合的研究,在Ca1.9Sr0.1RuO4表面首次实现了纯电子驱动的Mott型MIT,发生电子结构相变时并没有相应的结构畸变出现.该研究成果对于人们认识电子-电子关联效应引起的Mott转变具有非常重要的意义.     

Vanishing of the Mott transition in semiconductor nanocrystals

The dynamics of the system of photoexcited electron–hole pairs in semiconductor nanocrystals of different size with increasing excitation intensity was experimentally studied by utilizing the luminescence spectra of semiconductor-doped glasses in order to elucidate the peculiarities of many-body effects in structures approaching the zero-dimensional limit. Vanishing of effects causing the Mott transition in bulk crystals was observed with decreasing nanocrystal radius, and a new type of transformation of excitons to unbound electron–hole pairs was shown to take place in nanocrystals where the energy shift for electrons and holes due to quantum confinement becomes comparable with the exciton binding energy.     

Compressibility divergence and the finite temperature Mott transition

In the context of the dynamical mean-field theory (DMFT) of the Hubbard model, we study the behavior of the compressibility near the density driven Mott transition at finite temperatures. We demonstrate this divergence using DMFT and quantum Monte Carlo simulations in the one-band and the two-band Hubbard model. We supplement this result with considerations based on the Landau theory framework, and discuss the relevance of our results to the alpha-gamma end point in cerium.     

Mott insulation in transition metal compounds

The conditions for the occurance of Mott insulation and its disappearance in transition metal compounds are investigated. It is found, that transition metal compounds with less than fived-electrons may be good examples of Mott Insulators, while those with more than fived-electrons should more properly be termed charge transfer compounds.     

Subpicosecond time-resolved Mott transition in CuCl

The Mott transition in CuCl from a metallic phase of free electrons and holes towards an insulating phase of bound particles (excitons or biexcitons) has been studied by time-resolved luminescence with a resolution slightly better than 1 ps. The phase change takes place in a very short but finite time (about 3 ps) at a carrier density N 10¹⁹ cm^-3.     

The Mott transition in cold semiconductors

We discuss the Mott transition when a semiconductor is externally excited at low temperatures. We demonstrate that hysteresis is inevitable unless a phase separation occurs at higher temperatures or lower average excitation densities than necessary for the predicted ionization catastrophe. The critical temperature and pair density for hysteresis in Ge is of the order 6K and 3 · 10¹⁶ cm^-3, respectively, for a model involving dynamical screening.     

完全由电子关联驱动的Mott型金属-绝缘体相变研究

Mott金属-绝缘体相变(MIT)是凝聚态物理中的一个非常基本的概念.长期以来,Mott型MIT的概念被广泛应用于凝聚态物理的许多领域,特别是用于描述强关联系统的电子结构特征.然而到目前为止,完全由电子关联驱动的MIT并没有被观察到.因此,是否存在着完全由于电子之间的强关联效应导致的Mott型MIT一直是科学家们感兴趣的重要问题.近日,中国科学院物理研究所方忠研究员组、郭建东研究员组和美国Florida International大学的Jiandi Zhang教授研究组及美国Tennessee大学及橡树岭国家实验室的E.W.Plummer教授研究组、Rong Ying Jin教授研究组合作,通过实验与理论相结合的研究,在Ca1.9Sr0.1RuO4表面首次实现了纯电子驱动的Mott型MIT,发生电子结构相变时并没有相应的结构畸变出现.该研究成果对于人们认识电子-电子关联效应引起的Mott转变具有非常重要的意义.     

Excitonic absorption above the Mott transition in Si

We present experimental evidence for the existence of excitonic states above the excitonic Mott transition in both highly doped and highly excited silicon. Previous limitations to resolve the fundamental absorption edge of Si at dense carrier plasmas are overcome employing a novel spatially and time-resolved spectroscopy. We show that the obtained density dependent excess absorption at 75 K represents an excitonic enhancement effect, which is attributed to persisting many-body interactions.     

Theory of the excitonic Mott transition in quasi-two-dimensional systems

The excitonic Mott transition in single and double quantum wells is studied using the Green’s function technique. An abrupt jump in the value of the ionization degree, which happens with an increase of the carrier density or temperature, is found in a certain density–temperature region. The opposite effect–the collapse of the electron–hole plasma into an insulating exciton system–is predicted to occur at lower densities. The critical density of the Mott transition for spatially indirect excitons may be much smaller than that for direct excitons.     

Cluster dynamical mean field theory of the Mott transition

We address the nature of the Mott transition in the Hubbard model at half-filling using cluster dynamical mean field theory (DMFT). We compare cluster-DMFT results with those of single-site DMFT. We show that inclusion of the short-range correlations on top of the on-site correlations does not change the order of the transition between the paramagnetic metal and the paramagnetic Mott insulator, which remains first order. However, the short range correlations reduce substantially the critical U and modify the shape of the transition lines. Moreover, they lead to very different physical properties of the metallic and insulating phases near the transition point. Approaching the transition from the metallic side, we find an anomalous metallic state with very low coherence scale. The insulating state is characterized by the narrow Mott gap with pronounced peaks at the gap edge.