scholarly journals Strange metallicity in the doped Hubbard model

Science ◽  
2019 ◽  
Vol 366 (6468) ◽  
pp. 987-990 ◽  
Author(s):  
Edwin W. Huang ◽  
Ryan Sheppard ◽  
Brian Moritz ◽  
Thomas P. Devereaux
Keyword(s):  
Hubbard Model ◽  
Quantum Monte Carlo ◽  
High Temperature Superconductors ◽  
Linear Temperature Dependence ◽  
Strongly Correlated ◽  
Linear Temperature ◽  
Strongly Correlated Materials ◽  
Starting Point ◽  
Wide Range ◽  
Degenerate Regime

Strange or bad metallic transport, defined by incompatibility with the conventional quasiparticle picture, is a theme common to many strongly correlated materials, including high-temperature superconductors. The Hubbard model represents a minimal starting point for modeling strongly correlated systems. Here we demonstrate strange metallic transport in the doped two-dimensional Hubbard model using determinantal quantum Monte Carlo calculations. Over a wide range of doping, we observe resistivities exceeding the Mott-Ioffe-Regel limit with linear temperature dependence. The temperatures of our calculations extend to as low as 1/40 of the noninteracting bandwidth, placing our findings in the degenerate regime relevant to experimental observations of strange metallicity. Our results provide a foundation for connecting theories of strange metals to models of strongly correlated materials.

Parametric Models of Ultrasonic Piezoelectric Transducers over a Wide Temperature Range

2015 ◽  
Vol 2015 (HiTEN) ◽  
pp. 000266-000272 ◽  
Author(s):  
Steven A. Morris ◽  
Jeremy Townsend
Keyword(s):  
Dielectric Constant ◽  
Temperature Dependence ◽  
Coupling Coefficient ◽  
Thin Disk ◽  
Piezoelectric Transducers ◽  
Parametric Models ◽  
Model Parameters ◽  
Linear Temperature Dependence ◽  
Linear Temperature ◽  
Wide Range

Piezoelectric ultrasonic transducers are used extensively in well logging and logging-while-drilling applications for pulse-echo operation. We present a method of modeling the operation of ultrasonic thin-disk piezoelectric transducers over a wide range of temperatures. The model is based on using Redwood's version of Mason's model of thin-disk transducers. Laboratory measurements in the oven of non-backed transducers in air are used to extract the Mason model parameters as a function of temperature. Derived parameters are frequency-thickness constant, dielectric constant, and thickness mode coupling coefficient. A fourth parameter, bulk density, is measured independently and assumed constant over temperature. Temperature dependence of frequency thickness constant and coupling coefficient are modeled as linear temperature coefficients. Temperature dependence of the dielectric constant must be specified as a table because of the non-linear temperature dependence of that parameter.

scholarly journals Metallic and insulating stripes and their relation with superconductivity in the doped Hubbard model

2019 ◽  
Vol 7 (2) ◽  
Author(s):  
Luca Fausto Tocchio ◽  
Arianna Montorsi ◽  
Federico Becca
Keyword(s):  
Hubbard Model ◽  
Quantum Monte Carlo ◽  
Variational Approach ◽  
Wave Functions ◽  
Density Matrix Renormalization Group ◽  
Strongly Correlated ◽  
Density Matrix Renormalization ◽  
Spin Modulation ◽  
Stripe Order ◽  
Superconducting Correlations

The dualism between superconductivity and charge/spin modulations (the so-called stripes) dominates the phase diagram of many strongly-correlated systems. A prominent example is given by the Hubbard model, where these phases compete and possibly coexist in a wide regime of electron dopings for both weak and strong couplings. Here, we investigate this antagonism within a variational approach that is based upon Jastrow-Slater wave functions, including backflow correlations, which can be treated within a quantum Monte Carlo procedure. We focus on clusters having a ladder geometry with MM legs (with MM ranging from 22 to 1010) and a relatively large number of rungs, thus allowing us a detailed analysis in terms of the stripe length. We find that stripe order with periodicity \lambda=8λ=8 in the charge and 2\lambda=162λ=16 in the spin can be stabilized at doping \delta=1/8δ=1/8. Here, there are no sizable superconducting correlations and the ground state has an insulating character. A similar situation, with \lambda=6λ=6, appears at \delta=1/6δ=1/6. Instead, for smaller values of dopings, stripes can be still stabilized, but they are weakly metallic at \delta=1/12δ=1/12 and metallic with strong superconducting correlations at \delta=1/10δ=1/10, as well as for intermediate (incommensurate) dopings. Remarkably, we observe that spin modulation plays a major role in stripe formation, since it is crucial to obtain a stable striped state upon optimization. The relevance of our calculations for previous density-matrix renormalization group results and for the two-dimensional case is also discussed.

scholarly journals Spin transport in a Mott insulator of ultracold fermions

Science ◽  
2018 ◽  
Vol 363 (6425) ◽  
pp. 383-387 ◽  
Author(s):  
Matthew A. Nichols ◽  
Lawrence W. Cheuk ◽  
Melih Okan ◽  
Thomas R. Hartke ◽  
Enrique Mendez ◽  
...  
Keyword(s):  
Hubbard Model ◽  
Spin Transport ◽  
Spin Diffusion ◽  
Quantum Limit ◽  
Strong Interactions ◽  
Strongly Correlated ◽  
Strongly Correlated Materials ◽  
Fermionic Atoms ◽  
And Diffusion ◽  
Shed Light

Strongly correlated materials are expected to feature unconventional transport properties, such that charge, spin, and heat conduction are potentially independent probes of the dynamics. In contrast to charge transport, the measurement of spin transport in such materials is highly challenging. We observed spin conduction and diffusion in a system of ultracold fermionic atoms that realizes the half-filled Fermi-Hubbard model. For strong interactions, spin diffusion is driven by super-exchange and doublon-hole–assisted tunneling, and strongly violates the quantum limit of charge diffusion. The technique developed in this work can be extended to finite doping, which can shed light on the complex interplay between spin and charge in the Hubbard model.

Computer simuations for the nano-scale

2007 ◽  
Vol 57 (1) ◽  
pp. 1-176 ◽  
Author(s):  
I. Štich
Keyword(s):  
Quantum Monte Carlo ◽  
Density Functional ◽  
Large Scale ◽  
Hartree Fock ◽  
Monte Carlo Techniques ◽  
Nano Scale ◽  
Scale Modeling ◽  
Starting Point ◽  
Wide Range ◽  
Weak Points

Computer simuations for the nano-scaleA review of methods for computations for the nano-scale is presented. The paper should provide a convenient starting point into computations for the nano-scale as well as a more in depth presentation for those already working in the field of atomic/molecular-scale modeling. The argument is divided in chapters covering the methods for description of the (i) electrons, (ii) ions, and (iii) techniques for efficient solving of the underlying equations. A fairly broad view is taken covering the Hartree-Fock approximation, density functional techniques and quantum Monte-Carlo techniques for electrons. The customary quantum chemistry methods, such as post Hartree-Fock techniques, are only briefly mentioned. Description of both classical and quantum ions is presented. The techniques cover Ehrenfest, Born-Oppenheimer, and Car-Parrinello dynamics. The strong and weak points of both principal and technical nature are analyzed. In the second part we introduce a number of applications to demonstrate the different approximations and techniques introduced in the first part. They cover a wide range of applications such as non-simple liquids, surfaces, molecule-surface interactions, applications in nanotechnology, etc. These more in depth presentations, while certainly not exhaustive, should provide information on technical aspects of the simulations, typical parameters used, and ways of analysis of the huge amounts of data generated in these large-scale supercomputer simulations.

Ferromagnetism in the two-dimensional Hubbard model with long-range hopping

Open Physics ◽  
2013 ◽  
Vol 11 (1) ◽  
Author(s):  
Pavol Farkašovský ◽  
Hana Čenčariková
Keyword(s):  
Hubbard Model ◽  
Long Range ◽  
Quantum Monte Carlo ◽  
Ferromagnetic State ◽  
Critical Value ◽  
Exact Diagonalization ◽  
Two Dimensional ◽  
Wide Range ◽  
Quantum Monte Carlo Method ◽  
Generalized Type

AbstractThe combination of small-cluster exact-diagonalization calculations and the quantum Monte Carlo method is used to examine ferromagnetism in the two-dimensional Hubbard model with a generalized type of hopping. It is found that the long-range hopping with exponentially decaying hopping amplitudes t ij ∼ − q Ri−Rj stabilizes the ferromagnetic state for a wide range of electron interactions U and electron concentrations n > 1. The critical value of the hopping parameter q c above which the ferromagnetic state becomes stable is calculated numerically and the ground-state phase diagram of the model is discussed for physically the most interesting cases.

Discovery of Antibacterial Agents Inhibiting the Energy-Coupling Factor (ECF) Transporters by Structure-Based Virtual Screening

2020 ◽  
Author(s):  
Eleonora Diamanti ◽  
Inda Setyawati ◽  
Spyridon Bousis ◽  
leticia mojas ◽  
lotteke Swier ◽  
...  
Keyword(s):  
Virtual Screening ◽  
Antibacterial Agents ◽  
Antimicrobial Agents ◽  
Energy Coupling ◽  
Coupling Factor ◽  
Design Synthesis ◽  
Screening Design ◽  
Starting Point ◽  
Wide Range ◽  
Vitamin Uptake

Here, we report on the virtual screening, design, synthesis and structure–activity relationships (SARs) of the first class of selective, antibacterial agents against the energy-coupling factor (ECF) transporters. The ECF transporters are a family of transmembrane proteins involved in the uptake of vitamins in a wide range of bacteria. Inhibition of the activity of these proteins could reduce the viability of pathogens that depend on vitamin uptake. Because of their central role in the metabolism of bacteria and their absence in humans, ECF transporters are novel potential antimicrobial targets to tackle infection. The hit compound’s metabolic and plasma stability, the potency (20, MIC Streptococcus pneumoniae = 2 µg/mL), the absence of cytotoxicity and a lack of resistance development under the conditions tested here suggest that this scaffold may represent a promising starting point for the development of novel antimicrobial agents with an unprecedented mechanism of action.<br>

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