scholarly journals Spin symmetry of the bilayer graphene ground state

2013 ◽  
Vol 87 (16) ◽  
Author(s):  
Frank Freitag ◽  
Markus Weiss ◽  
Romain Maurand ◽  
Jelena Trbovic ◽  
Christian Schönenberger
Keyword(s):  
Ground State ◽  
Spin Symmetry ◽  
Bilayer Graphene

scholarly journals Electronic ground state in bilayer graphene with realistic Coulomb interactions

2019 ◽  
Vol 100 (12) ◽  
Author(s):  
Jia Ning Leaw ◽  
Ho-Kin Tang ◽  
Pinaki Sengupta ◽  
Fakher F. Assaad ◽  
Igor F. Herbut ◽  
...  
Keyword(s):  
Ground State ◽  
Bilayer Graphene ◽  
Electronic Ground State ◽  
Coulomb Interactions ◽  
Electronic Ground

scholarly journals The ground state construction of bilayer graphene

2016 ◽  
Vol 28 (08) ◽  
pp. 1650018
Author(s):  
Alessandro Giuliani ◽  
Ian Jauslin
Keyword(s):  
Ground State ◽  
Short Range ◽  
Interaction Strength ◽  
Bilayer Graphene ◽  
The Other ◽  
Group Methods ◽  
Effective Dispersion ◽  
State Construction ◽  
Strength Formula ◽  
Renormalization Group Methods

We consider a model of half-filled bilayer graphene, in which the three dominant Slonczewski–Weiss–McClure hopping parameters are retained, in the presence of short-range interactions. Under a smallness assumption on the interaction strength [Formula: see text] as well as on the inter-layer hopping [Formula: see text], we construct the ground state in the thermodynamic limit, and prove that the pressure and two-point Schwinger function, away from its singularities, are analytic in [Formula: see text], uniformly in [Formula: see text]. The interacting Fermi surface is degenerate, and consists of eight Fermi points, two of which are protected by symmetries, while the locations of the other six are renormalized by the interaction, and the effective dispersion relation at the Fermi points is conical. The construction reveals the presence of different energy regimes, where the effective behavior of correlation functions changes qualitatively. The analysis of the crossover between regimes plays an important role in the proof of analyticity and in the uniform control of the radius of convergence. The proof is based on a rigorous implementation of fermionic renormalization group methods, including determinant estimates for the renormalized expansion.

Molecular Doping of PCPDT-BT Copolymers: Comparison of Molecular Complexes with and Without Integer Charge Transfer

2019 ◽  
Author(s):  
Chuanding Dong ◽  
Stefan Schumacher
Keyword(s):  
Charge Transfer ◽  
Ground State ◽  
Spin Symmetry ◽  
Molecular Complexes ◽  
Molecular Geometry ◽  
Electronic System ◽  
Electronic Density ◽  
Specific Geometry ◽  
Molecular Doping ◽  
System Properties

<div> <div> <div> <p>Molecular doping in conjugated polymers is a crucial process for their application in organic photovoltaics and optoelectronics. In the present work we theoretically investigate p-type molecu- lar doping in a series of (poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b”]dithiophene)-alt- 4,7-(2,1,3-benzothiadiazole)] (PCPDT-BT) conjugated oligomers with different lengths and three widely-used dopants with different electron affinities, namely F4TCNQ, F6TCNNQ, and CN6-CP. We study in detail the molecular geometry of possible oligomer-dopant complexes and its influence on the doping mechanisms and electronic system properties. We find that the mechanisms of dop- ing and charge transfer observed sensitively depend on the specific geometry of the oligomer-dopant complexes. For a given complex different geometries may exist, some of which show transfer of an entire electron from the oligomer chain onto the dopant molecule resulting in an integer-charge transfer complex, leaving the system in a ground state with broken spin symmetry. In other ge- ometries merely hybridization of oligomer and dopant frontier orbitals occurs with partial charge transfer but spin-symmetric ground state. Considering the resulting electronic density of states both cases may well contribute to an increased electrical conductivity of corresponding film samples while the underlying physical mechanisms are entirely different. </p> </div> </div> </div>

Ground state superconducting pair correlations in twisted bilayer graphene

2019 ◽  
Vol 34 (01) ◽  
pp. 2050016 ◽  
Author(s):  
Lufeng Zhang ◽  
Tongyun Huang ◽  
Ying Liang ◽  
Tianxing Ma
Keyword(s):  
Ground State ◽  
Quantum Monte Carlo ◽  
Bilayer Graphene ◽  
Pairing Symmetry ◽  
Honeycomb Lattice ◽  
Magic Angle ◽  
Pairing Interaction ◽  
Twisted Bilayer Graphene ◽  
Effective Pairing Interaction ◽  
Effective Pairing

Motivated by the recent novel electronic features extracted from the magic-angle graphene superlattices, we studied the ground state superconducting pairing correlations within the Hubbard model on a twisted bilayer honeycomb lattice. Using Constrained-Path Quantum Monte Carlo method, we found that the [Formula: see text] pairing correlation dominates over other pairing patterns among various electron fillings and interaction strengths, and the effective pairing interaction was enhanced as the on-site Coulomb interaction increased. We further examined the effect of the nearest neighbor interaction [Formula: see text], and the effective pairing interaction with [Formula: see text] pairing symmetry was also enhanced by either a repulsive or attractive interaction. Our intensive numerical results confirm the interaction driven superconductivity with a dominant [Formula: see text] pairing symmetry in twisted bilayer graphene.

Molecular Doping of PCPDT-BT Copolymers: Comparison of Molecular Complexes with and Without Integer Charge Transfer

2019 ◽  
Author(s):  
Chuanding Dong ◽  
Stefan Schumacher
Keyword(s):  
Charge Transfer ◽  
Ground State ◽  
Spin Symmetry ◽  
Molecular Complexes ◽  
Molecular Geometry ◽  
Electronic System ◽  
Electronic Density ◽  
Specific Geometry ◽  
Molecular Doping ◽  
System Properties

<div> <div> <div> <p>Molecular doping in conjugated polymers is a crucial process for their application in organic photovoltaics and optoelectronics. In the present work we theoretically investigate p-type molecu- lar doping in a series of (poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b”]dithiophene)-alt- 4,7-(2,1,3-benzothiadiazole)] (PCPDT-BT) conjugated oligomers with different lengths and three widely-used dopants with different electron affinities, namely F4TCNQ, F6TCNNQ, and CN6-CP. We study in detail the molecular geometry of possible oligomer-dopant complexes and its influence on the doping mechanisms and electronic system properties. We find that the mechanisms of dop- ing and charge transfer observed sensitively depend on the specific geometry of the oligomer-dopant complexes. For a given complex different geometries may exist, some of which show transfer of an entire electron from the oligomer chain onto the dopant molecule resulting in an integer-charge transfer complex, leaving the system in a ground state with broken spin symmetry. In other ge- ometries merely hybridization of oligomer and dopant frontier orbitals occurs with partial charge transfer but spin-symmetric ground state. Considering the resulting electronic density of states both cases may well contribute to an increased electrical conductivity of corresponding film samples while the underlying physical mechanisms are entirely different. </p> </div> </div> </div>

scholarly journals Absence of Spontaneous Spin Symmetry Breaking in 1D and 2D Quantum Ferromagnetic Systems with Bilinear and Biquadratic Exchange Interactions

Symmetry ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 2061
Author(s):  
Roberto Zivieri
Keyword(s):  
Symmetry Breaking ◽  
Exchange Interaction ◽  
Ground State ◽  
Short Range ◽  
Exchange Interactions ◽  
Spin Symmetry ◽  
Second Order ◽  
Biquadratic Exchange ◽  
Heisenberg Hamiltonian ◽  
Quantum Spins

Some measurements have shown that the second-order exchange interaction is non-negligible in ferromagnetic compounds whose microscopic interactions are described by means of half-odd integer quantum spins. In these spin systems the ground state is either ferromagnetic or antiferromagnetic when the bilinear exchange interaction is dominant. Instead, in ferromagnetic systems characterized by bilinear and biquadratic exchange interactions of comparable magnitude, the energy minimum occurs when spins are in a canting ground-state. To this aim, a one-dimensional (1D) quantum spin chain and a two-dimensional (2D) lattice of quantum spins subjected to periodic boundary conditions are modeled via the generalized quantum Heisenberg Hamiltonian containing, in addition to the isotropic and short-range bilinear exchange interaction of the Heisenberg type, a second-order interaction, the isotropic and short-range biquadratic exchange interaction between nearest-neighbors quantum spins. For these 1D and 2D quantum systems a generalization of the Mermin–Wagner–Hohenberg theorem (also known as Mermin–Wagner–Berezinksii or Coleman theorem) is given. It is demonstrated, by means of quantum statistical arguments, based on Bogoliubov’s inequality, that, at any finite temperature, (1) there is absence of long-range order and that (2) the law governing the vanishing of the order parameter is the same as in the bilinear case for both 1D and 2D quantum ferromagnetic systems. The physical implications of the absence of a spontaneous spin symmetry breaking in 1D spin chains and 2D spin lattices modeled via a generalized quantum Heisenberg Hamiltonian are discussed.

Sign in / Sign up

Export Citation Format

Share Document