Temperature-dependent Fermi surface evolution in heavy fermion CeIrIn5

We address theoretically the evolution of the heavy fermion Fermi surface (FS) as a function of temperature (T), using a first principles dynamical mean-field theory approach combined with density functional theory. We focus on the archetypical heavy electrons in CeIrIn{5}. Upon cooling, both the quantum oscillation frequencies and cyclotron masses show logarithmic scaling behavior [～ln(T{0}/T)] with different characteristic temperatures T{0}=130 and 50 K, respectively. The enlargement of the electron FSs at low T is accompanied by topological changes around T=10-50 K. The resistivity coherence peak observed at T?50 K is the result of the competition between the binding of incoherent 4f electrons to the spd conduction electrons at Fermi level (E{F}) and the formation of coherent 4f electrons.     

Phase Separation in the Neutral Falicov–Kimball Model

The Falicov–Kimball model consists of spinless electrons and classical particles (ions) on a lattice. The electrons hop between nearest neighbor sites, while the ions do not. We consider the model with equal numbers of ions and electrons and with a large on-site attractive force between ions and electrons. For densities 1/4 and 1/5, the ion configuration in the ground state had been proved to be periodic. We prove that for density 2/9 it is periodic as well. However, for densities between 1/4 and 1/5 other than 2/9 we prove that the ion configuration in the ground state is not periodic. Instead there is phase separation. For densities in (1/5, 2/9) the ground-state ion configuration is a mixture of the density 1/5 and 2/9 ground-state ion configurations. For the interval (2/9, 1/4) it is a mixture of the density 2/9 and 1/4 ground states.     

Superconducting fluctuations and the pseudogap in the slightly overdoped high- T(c) superconductor TlSr2CaCu2O6.8: high magnetic field NMR studies

From measurements of the 63Cu Knight shift ( K) and the nuclear spin-lattice relaxation rate ( 1/T1) under magnetic fields from zero up to 28 T in the slightly overdoped high- T(c) superconductor TlSr2CaCu2O6.8 ( T(c) = 68 K), we find that the pseudogap behavior, i.e., the reductions of 1/T1T and K above T(c) from the values expected from the normal state at high T, is strongly field dependent and follows a scaling relation. We show that this scaling is consistent with the effects of the Cooper pair density fluctuations. The present finding contrasts sharply with the pseudogap property reported previously in the underdoped regime where no field effect was seen up to 23.2 T. The implications are discussed.     

Kondo effect of single Co adatoms on Cu surfaces

The Kondo resonance of Co adatoms on the Cu(100) and Cu(111) surfaces has been studied by scanning tunneling spectroscopy. We demonstrate the scaling of the Kondo temperature T(K) with the host electron density at the magnetic impurity. The quantitative analysis of the tunneling spectra reveals that the Kondo resonance is dominated by the Cu bulk electrons. While at the Cu(100) surface both tunneling into the hybridized localized state and into the substrate conduction band contribute to the Kondo resonance, the latter channel is found to be dominant for Cu(111).     

The effective gauge field action of a system of non-relativistic electrons

We consider a system of free, non-relativistic electrons at zero temperature and positive density, coupled to an arbitrary, external electromagnetic vector potential,A. By integrating out the electron degrees of freedom we obtain the effective action forA. We show that, in the scaling limit, this effective action is quadratic inA and can be viewed as an integral over the Fermi sphere of effective actions of (1+1)-dimensional, chiral schwinger models. We use this result to elucidate Luther-Haldane bosonization of systems of non-relativistic electrons. We also study systems of weakly coupled interacting electrons for which the BCS channel is turned off. Using the quadratic dependence of the effective action onA, we show that, in the scaling limit, the RPA yields the dominant contribution.     

Theory of a Fermi-liquid to non-Fermi-liquid quantum phase transition in dimensions d>1

We develop a theory for a generic instability of a Fermi liquid in dimension d>1 against the formation of a Luttinger-liquid-like state. The density of states at the Fermi level is the order parameter for the ensuing quantum phase transition, which is driven by the effective interaction strength. A scaling theory in conjunction with an effective field theory for clean electrons is used to obtain the critical behavior of observables. In the Fermi-liquid phase the order-parameter susceptibility, which is measurable by tunneling, is predicted to diverge for 1相似文献   

The 3-D electrostatic potential surrounding a square array of surface charges

Simple scaling laws have been derived which relate the 3-D potential to the inter-surfacestate spacing, the field-plate spacing, the dielectric constants of both insulators bordering the interface, and the dimensions x,y,z. This 3-D potential, obtained by using a pair of images and Neumann boundary conditions, contains the usual 1-D potential as the zeroth harmonic in a Fourier series. The 3-D and 1-D potentials give equivalent densities of conduction electrons in an accumulation layer only for a surface state density σ < 3 × 10¹¹/cm². For higher σ, the 1-D potential seriously underestimates the amount of space charge possible. There is a low saddle point in the 3-D potential configuration which allows surface conduction electrons to transport laterally in the presence of a transverse field.     

Spin-wave contribution to the nuclear spin-lattice relaxation in triplet superconductors

We discuss collective spin-wave excitations in triplet superconductors with an easy axis anisotropy for the order parameter. Using a microscopic model for interacting electrons, we estimate the frequency of such excitations in Bechgaard salts and ruthenate superconductors to be 1 and 20 GHz, respectively. We introduce an effective bosonic model to describe spin-wave excitations and calculate their contribution to the nuclear spin-lattice relaxation rate. We find that, in the experimentally relevant regime of temperatures, this mechanism leads to the power law scaling of 1/T1 with temperature. For two- and three-dimensional systems, the scaling exponents are 3 and 5, respectively. We discuss experimental manifestations of the spin-wave mechanism of the nuclear spin-lattice relaxation.     

Shell model description of the 14C dating beta decay with Brown-Rho-scaled NN interactions

We present shell model calculations for the beta decay of 14C to the 14N ground state, treating the states of the A=14 multiplet as two 0p holes in an 16O core. We employ low-momentum nucleon-nucleon (NN) interactions derived from the realistic Bonn-B potential and find that the Gamow-Teller (GT) matrix element is too large to describe the known lifetime. By using a modified version of this potential that incorporates the effects of Brown-Rho scaling medium modifications, we find that the GT matrix element vanishes for a nuclear density around 85% that of nuclear matter. We find that the splitting between the (J(pi),T)=(1(+),0) and (J(pi),T)=(0(+),1) states in 14N is improved using the medium-modified Bonn-B potential and that the transition strengths from excited states of 14C to the 14N ground state are compatible with recent experiments.     

Numerical finite size scaling approach to many-body localization

We develop a numerical technique to study Anderson localization in interacting electronic systems. The ground state of the disordered system is calculated with quantum Monte Carlo simulations while the localization properties are extracted from the "Thouless conductance" g, i.e., the curvature of the energy with respect to an Aharonov-Bohm flux. We apply our method to polarized electrons in a two-dimensional system of size L. We recover the well-known universal beta(g)=dlogg/dlogL one parameter scaling function without interaction. Upon switching on the interaction, we find that beta(g) is unchanged while the system flows toward the insulating limit. We conclude that polarized electrons in two dimensions stay in an insulating state in the presence of weak to moderate electron-electron correlations.     

强脉冲磁场冲击处理对铝基复合材料塑性的影响机制

铝基复合材料在加入颗粒相之后, 延伸率和塑性变形能力明显降低. 为改善其塑性变形能力, 通过对比强脉冲磁场冲击处理前后试样内部组织和残余应力的变化特征, 研究了磁致塑性效应对铝基复合材料塑性变形能力的影响机理. 结果表明: 当磁感应强度从2 T变化到4 T时, 铝基复合材料中位错密度显著增加, 4 T时的位错密度是未加磁场时的3.1倍; 3 T, 30个脉冲处理后的复合材料中残余应力值从未加磁场时的41 MPa减小为-1 MPa. 从原子尺度来看, 强磁场导致了磁致塑性效应, 从而引起了位错的运动, 并促进了位错的退钉扎和可移动位错数量的增加; 从材料内部整体结构变化来看, 磁场加速了材料内应力的释放速率, 降低了材料内部的残余应力, 从而改善了铝基复合材料的塑性变形能力.     

Density fluctuations in strongly stratified two-dimensional turbulence

We present a study of density fluctuations in two-dimensional soap-film convection. When the temperature difference (DeltaT) imposed vertically along the film is smaller than a critical value (DeltaT(C) approximately 48 K), the convective motion is in a strongly stratified state and the frequency power spectrum of density fluctuations shows a Bolgiano-like scaling f(-7/5) in the buoyancy subrange. When DeltaT>DeltaT(C), the fluid motion crosses over to a strongly mixed state characterized by the emergence of a large-scale circulation. The density power spectrum in this state has a passive-scalar-like scaling f(-1.0).     

Calculation of profile of charge carrier concentration in modulation doped structure with a wide potential well

We investigate the equilibrium state of interacting electron system with Fermi statistics in modulation doped structure with a wide quantum well. The model is formulated for the carrier system with a sufficiently high density, such that the de Broglie wavelength of electrons is smaller than the width of the quantum well. Due to a significant interaction of electrons with electric field of the doped layer, a state with strongly‐inhomogeneous density of electrons is formed. Within the hydrodynamic approach, we set up formalism for calculating the electron density across the width of the potential well. We have obtained the exact solution of the equations, which is expressed in terms of hypergeometric functions. Based on the deduced formulas, we performed numerical computations for the profile of carriers' concentrations in a potential well in the modulation doped Si/SiGe/Si structures.     

Power spectrum crossover in sediments of a paleolake disturbed by volcanism

We study density fluctuations from sediments of a paleolake in central Mexico that was subjected to volcanic perturbations by means of computed tomography (CT) measurements on blocks chiselled out of mines at the lake's bed. The mine walls show laminations corresponding to the alternation of low density diatom sediments and high density volcanic ash depositions. We have previously shown that there is a range of scales where these fluctuations present a self-similar behavior [1]. Here we relate density correlation calculations to the power spectrum of the fluctuations. We show that a scaling region in the power spectrum coincides with the scaling region in the correlations produced by relaxation from intense volcanic perturbations to steady state fluctuations. There appears to be a kink-like crossover in the power spectrum from mid range scaling to a shorter range scale invariance. This, together with the density probability distribution of the fluctuations, draws attention to the dominant role of rare events. We believe that our analysis may be useful for the understanding of other phenomena with similar power spectrum properties, in which a scale invariance in the unperturbed system is altered by external perturbations that induce an additional scaling behavior.     

Quantum criticality and percolation in dimer-diluted two-dimensional antiferromagnets

The S = 1/2 Heisenberg model is considered on bilayer and single-layer square lattices with couplings J1, J2, with each spin belonging to one J2-coupled dimer. A transition from a Néel to disordered ground state occurs at a critical value of g = J2/J1. The systems are here studied at their dimer-dilution percolation points p*. The multicritical point (g*,p*) previously found for the bilayer is not reproduced for the single layer. Instead, there is a line of critical points (g < g*, p*) with continuously varying exponents. The uniform magnetic susceptibility diverges as T(-alpha) with alpha element of [1/2,1]. This unusual behavior is attributed to an effective free-moment density approximately T(1-alpha). The susceptibility of the bilayer is not divergent but exhibits remarkably robust quantum-critical scaling.     

Magnetic impurity in hybrid and type-Ⅱ nodal line semimetals

We study the Kondo screening of a spin-1/2 magnetic impurity in the hybrid nodal line semimetals(NLSMs) and the type-Ⅱ NLSMs by using the variational method. We mainly study the binding energy and the spin–spin correlation between magnetic impurity and conduction electrons. We find that in both the hybrid and type-Ⅱ cases, the density of states(DOS) is always finite, so the impurity and the conduction electrons always form bound states, and the bound state is more easily formed when the DOS is large. Meanwhile, due to the unique dispersion relation and the spin–orbit couplings in the NLSMs, the spatial spin–spin correlation components show very interesting features. Most saliently, various components of the spatial spin–spin correlation function decay with 1/r~2 in the hybrid NLSMs, while they follow 1/r~3 decay in the type-Ⅱ NLSMs. This property is mainly caused by the special band structures in the NLSMs, and it can work as a fingerprint to distinguish the two types of NLSMs.     

Spin density wave and ferromagnetism in a quasi-one-dimensional organic polymer

The spin density wave(SDW) — charge density wave(CDW) phase transition and the magnetic properties in a half-filled quasi-one-dimensional organic polymer are investigated by the world line Monte Carlo simulations. The itinerant π electrons moving along the polymer chain are coupled radically to localized unpaired d electrons, which are situated at every other site of the polymer chain. The results show that both ferromagnetic and anti-ferromagnetic radical couplings enhance the SDW phase and the ferromagnet order of the radical spins, but suppress the CDW phase. By finite size scaling, we are able to obtain the phase transition line in the parameter space. The ferromagnetic order of the radical spins are observed to coexist with the SDW phase. As compared to the system being free of the radical coupling, the phase transition line is shifted upward in the U-V parameter space in favor of larger V, where U is the on-site repulsion and V is the nearest-neighbor interaction between the π electrons. All of these findings can be understood qualitatively by a second-order perturbation theory starting from the classical state at zero temperature in the strong coupling limit. We also address the consequences of the radical coupling for the persistent current if the polymer chain is fabricated as a mesoscopic ring.     

Critical scaling of shear viscosity at the jamming transition

We carry out numerical simulations to study transport behavior about the jamming transition of a model granular material in two dimensions at zero temperature. Shear viscosity eta is computed as a function of particle volume density rho and applied shear stress sigma, for diffusively moving particles with a soft core interaction. We find an excellent scaling collapse of our data as a function of the scaling variable sigma/|rho(c)-rho|(Delta), where rho(c) is the critical density at sigma=0 ("point J"), and Delta is the crossover scaling critical exponent. We define a correlation length xi from velocity correlations in the driven steady state and show that it diverges at point J. Our results support the assertion that jamming is a true second-order critical phenomenon.     

Thermoelectric Coefficients of Silicon MOSFETS in Quantizing Magnetic Field

The phonon drag and electron diffusion contribution to the tensor M which determines 3 the heat flux U = M·E is calculated for a silicon MOSFETS in a perpendicular magnetic field B. We used nearly the same theoretical formalism as Ref [6], but improvements are made in several respects. First of all the dielectric function of Fermi-Thomas approximation which has been proved to result in overscreening of the interaction is replaced by rigorous Lindhard-type dielectric function to take account of the screening between electrons and phonons. Secondly the contributions of localized electrons are separated from those of the free state electrons which are the only part that contributes to both conductivity tensor and magnetothermopower tensor. The calculated M_yx and S_xx reveal magneto-oscillationsoriginating Gom oscillations in the density of states at the Fermi level. At T = 5.02 K, our new results show that the diffusion components of thermopower are negligibly small compared with those due to phonon drag. All the theoretical values of M_yx, S_xx and S_yx are in accordance with the experimental data better than previous theoretical results.     

空间波函数的对称性对氦原子双光子双电离过程中电子关联的影响

通过数值求解含时薛定谔方程,研究了氦原子具有对称空间波函数的1s2s 1S态和具有反对称空间波函数的1s2s 3S态分别作为初态的双光子双电离过程. 结果表明,对于初态为单重态1s2s 1S的双光子双电离过程,两个电离电子的能量分布随激光脉冲持续时间的增加呈现由单峰到双峰的变化,这里的单峰和双峰分别意味着两个电离电子主要携带相等和不等的能量;然而对于初态为三重态1s2s 3S的双光子双电离过程,两个电离电子的能量分布随激光脉冲持续时间的增加总是保持双峰结构. 这些结果表明当原子的初态处于反对称空间波函数时,两电子的空间密度分布具有较少的重叠,从而导致电子在超短激光脉冲中电离时电子关联能无法平均分配.