scholarly journals Itinerant ferromagnetism in narrow-band metals

2021 ◽  
Vol 24 (4) ◽  
pp. 42701
Author(s):  
P. Farkašovský
Keyword(s):  
Hubbard Model ◽  
Long Range ◽  
Quantum Monte Carlo ◽  
Narrow Band ◽  
Lattice Structure ◽  
Ferromagnetic State ◽  
Charge Density Waves ◽  
Research Activity ◽  
Itinerant Ferromagnetism ◽  
Cooperative Phenomena

Since its introduction in 1963, the Hubbard model has becomes one of the most popular models used in the literature to study cooperative phenomena in narrow-band metals (ferromagnetism, metal-insulator transitions, charge-density waves, high-Tc superconductivity). Amongst all these cooperative phenomena, the problem of itinerant ferromagnetism in the Hubbard model has the longest history. However, in spite of an impressive research activity in the past, the underlying physics (microscopic mechanisms) that leads to the stabilization of itinerant ferromagnetism in Hubbard model (narrow-band metals) is still far from being understood. In this review we present our numerical results concerning this subject, which have been reached by small cluster exact diagonalization, density matrix renormalization group and quantum Monte Carlo calculations within various extensions of the Hubbard model. Particular attention is paid to a description of crucial mechanisms (interactions) that support the stabilization of the ferromagnetic state, and namely: (i) the long-range hopping, (ii) the correlated hopping, (iii) the long-range Coulomb interaction, (iv) the flat bands and (v) the lattice structure. Most of the presented results have been obtained for the one-dimensional case, but the influence of the increasing dimension of the system on the ferromagnetic state is also intensively discussed.

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.

scholarly journals SUPERCONDUCTIVITY IN THE 2D ATTRACTIVE HUBBARD MODEL WITHIN A FUNCTIONAL FIELD-THEORETICAL RG

2011 ◽  
Vol 25 (28) ◽  
pp. 3691-3706 ◽  
Author(s):  
EBERTH CORREA ◽  
HERMANN FREIRE ◽  
ALVARO FERRAZ
Keyword(s):  
Hubbard Model ◽  
Long Range ◽  
Quantum Monte Carlo ◽  
Mean Field Theory ◽  
Mean Field ◽  
S Wave ◽  
Energy Dynamics ◽  
Attractive Hubbard Model ◽  
Bare Interaction ◽  
Good Agreement

We apply the functional field-theoretical renormalization group methodology up to two-loop order to the 2D attractive Hubbard model for weak bare interaction. Since the momentum-resolved quasiparticle weight ZΛ(p) is always close to unity in the RG flow, higher-order quantum fluctuations do not affect crucially the low-energy dynamics in this case. As a result, we observe a s-wave singlet superconducting quasi-long-range order phase as a function of doping in good agreement with other numerical methods. To assess the role played by the fluctuations we compare the critical temperature Tc in which the quasi-long-range superconducting order phase takes place within our approach with mean-field theory and quantum Monte Carlo results.

scholarly journals The Influence of Long-Range Hopping on Ferromagnetism in the Hubbard Model

1998 ◽  
Vol 12 (07n08) ◽  
pp. 803-808 ◽  
Author(s):  
Pavol Farkašovský
Keyword(s):  
Magnetic Field ◽  
Phase Diagram ◽  
External Magnetic Field ◽  
Hubbard Model ◽  
Long Range ◽  
General Expression ◽  
Ferromagnetic State ◽  
Critical Value ◽  
Exact Diagonalization ◽  
Matrix Elements

The phase diagram of the Hubbard model in an external magnetic field is examined by extrapolation of small-cluster exact-diagonalization calculations. Using a general expression for the hopping matrix elements (tij ~ q|i-j|) the influence of long-range hopping (band asymmetry) on ferromagnetism in this model is studied. It is found that the long-range hopping (nonzero q) stabilizes ferromagnetism in an external magnetic field for n > 1. In the opposite limit n≤1 the fully polarized ferromagnetic state is generally suppressed with increasing q. The critical value of magnetic field h below which the ferromagnetic state becomes unstable is calculated numerically.

scholarly journals Manifestations of spin and charge fluctuations in spectra of the Hubbard model

2018 ◽  
Vol 32 (17) ◽  
pp. 1840032
Author(s):  
A. Sherman
Keyword(s):  
Hubbard Model ◽  
Long Range ◽  
Narrow Band ◽  
Transition Curve ◽  
Antiferromagnetic Order ◽  
Temperature Decrease ◽  
Metal Insulator Transition ◽  
Charge Fluctuations ◽  
Metal Insulator ◽  
Infinite Sequences

The influence of long-range spin and charge fluctuations on spectra of the two-dimensional (2D) fermionic Hubbard model is considered using the strong coupling diagram technique (SCDT). Infinite sequences of diagrams containing ladder inserts, which describe the interaction of electrons with these fluctuations, are summed, and obtained equations are self-consistently solved for the range of Hubbard repulsions 4t [Formula: see text]U [Formula: see text] 8t and temperatures 0.3t [Formula: see text] T [Formula: see text] t with t the intersite hopping constant. It was found that a metal–insulator transition curve goes from larger U and T to smaller values of these parameters. The temperature decrease causes the transition to the long-range antiferromagnetic order. It is responsible for the splitting out of a narrow band from a Hubbard subband with doping for U = 8t and low T. This segregated band is located near the Fermi level and forms a pseudogap here.

Phase transformation and Raman spectra in BaTiO3 nanocrystals

2002 ◽  
Vol 718 ◽  
Author(s):  
Jian Yu ◽  
X. J. Meng ◽  
J.L. Sun ◽  
G.S. Wang ◽  
J.H. Chu
Keyword(s):  
Particle Size ◽  
Phase Transformation ◽  
Low Temperature ◽  
Long Range ◽  
Lattice Expansion ◽  
Inversion Symmetry ◽  
Range Interaction ◽  
Cooperative Phenomena ◽  
Long Range Interaction ◽  
Hydrothermal Methods

AbstractIn this paper, size-induced ferroelectricit yweakening, phase transformation, and anomalous lattice expansion are observed in nanocrystalline BaTiO3 (nc-BaTiO3) deriv ed b y low temperature hydrothermal methods, and they are w ellunderstood using the terms of the long-range interaction and its cooperative phenomena altered by particle size in covalen t ionic nanocrystals. In cubic nc-BaTiO3, five modes centerd at 186, 254, 308, 512 and 716 cm-1 are observed Raman active in cubic nanophase, and they are attributed to local rhombohedral distortion breaking inversion-symmetry in cubic nanophase. The254 and 308 cm-1 modes are significantly affected not only by the concentration of hydroxyl defects, but also their particular configuration. And the 806 cm-1 modes found to be closely associated with OH - absorbed on grain boundaries.

scholarly journals Quantum-critical properties of the long-range transverse-field Ising model from quantum Monte Carlo simulations

2021 ◽  
Vol 103 (24) ◽  
Author(s):  
Jan Alexander Koziol ◽  
Anja Langheld ◽  
Sebastian C. Kapfer ◽  
Kai Phillip Schmidt
Keyword(s):  
Monte Carlo ◽  
Ising Model ◽  
Monte Carlo Simulations ◽  
Long Range ◽  
Quantum Monte Carlo ◽  
Transverse Field ◽  
Critical Properties ◽  
Quantum Critical ◽  
Transverse Field Ising Model ◽  
Quantum Monte Carlo Simulations

scholarly journals Recovery of long-range order in two-dimensional charge density waves at high temperatures

2021 ◽  
Vol 27 (S1) ◽  
pp. 952-954
Author(s):  
Suk Hyun Sung ◽  
Yin Min Goh ◽  
Noah Schnitzer ◽  
Ismail El Baggari ◽  
Kai Sun ◽  
...  
Keyword(s):  
Charge Density ◽  
Long Range ◽  
High Temperatures ◽  
Charge Density Waves ◽  
Range Order ◽  
Long Range Order ◽  
Two Dimensional ◽  
Density Waves

scholarly journals Phase separation in the two-dimensional Hubbard model: A fixed-node quantum Monte Carlo study

1998 ◽  
Vol 58 (22) ◽  
pp. R14685-R14688 ◽  
Author(s):  
A. C. Cosentini ◽  
M. Capone ◽  
L. Guidoni ◽  
G. B. Bachelet
Keyword(s):  
Monte Carlo ◽  
Phase Separation ◽  
Hubbard Model ◽  
Quantum Monte Carlo ◽  
Monte Carlo Study ◽  
Two Dimensional ◽  
Fixed Node

scholarly journals Scaling properties of the ferromagnetic state in the Hubbard model

1994 ◽  
Vol 50 (17) ◽  
pp. 12991-12994 ◽  
Author(s):  
K. Kusakabe ◽  
H. Aoki
Keyword(s):  
Hubbard Model ◽  
Ferromagnetic State ◽  
Scaling Properties
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