scholarly journals Interplay between field-induced and frustration-induced quantum criticalities in the frustrated two-leg Heisenberg ladder

2008 ◽  
Vol 86 (9) ◽  
pp. 1125-1132 ◽  
Author(s):  
B Ramakko ◽  
M Azzouz
Keyword(s):  
Magnetic Field ◽  
Field Theory ◽  
External Magnetic Field ◽  
Mean Field Theory ◽  
Mean Field ◽  
Spin Susceptibility ◽  
The Other ◽  
Wigner Transformation ◽  
75.10 Jm ◽  
Physical Quantities

The antiferromagnetic Heisenberg two-leg ladder in the presence of frustration and an external magnetic field is a system that is characterized by two sorts of quantum criticalities, not only one. One criticality is the consequence of intrinsic frustration, and the other one is a result of the external magnetic field. So the behaviour of each of them in the presence of the other deserves to be studied. Using the Jordan–Wigner transformation in dimensions higher than one and the bond-mean-field theory we examine the interplay between the field-induced and frustration-induced quantum criticalities in this system. The present work could constitute a prototype for those systems showing multiple, perhaps sometimes competing, quantum criticalities. We calculate several physical quantities such as magnetization and spin susceptibility as functions of field and temperature.PACS Nos.: 75.10.Jm 73.43.Nq 75.10.Pq 75.10.Dg

VERTEX CORRECTIONS IN THE NUCLEAR SCHWINGER–DYSON FORMALISM

2002 ◽  
Vol 11 (04) ◽  
pp. 321-333 ◽  
Author(s):  
MASAHIRO NAKANO ◽  
HIROYUKI MATSUURA ◽  
TAISUKE NAGASAWA ◽  
KEN-ICHI MAKINO ◽  
NOBUO NODA ◽  
...  
Keyword(s):  
Field Theory ◽  
Correlation Energy ◽  
Mean Field Theory ◽  
Mean Field ◽  
The Other ◽  
Vertex Correction ◽  
Hartree Fock ◽  
Vertex Corrections ◽  
Negative Correlation Energy ◽  
Self Consistent

We develop the Nuclear Schwinger–Dyson (NSD) formalism to include the effects of ladder diagrams by modifying the vertex. In this extension, the NSD equation sums up both ring diagrams and ladder diagrams self-consistently. The results are compared with mean field theory, Hartree Fock and bare-vertex NSD calculations. It is shown that the vertex correction is important from the following viewpoints. First, the vertex correction greatly modifies the meson propagators, and we can avoid the ghost-pole from meson propagators in a self-consistent way. Secondly, it gives a large negative correlation-energy compared with the other calculations; as a result, it gives a softer equation of state which is preferable according to the experimental data.

Tunneling Spectra of Inhomogeneous d-Wave Superconductor

2003 ◽  
Vol 17 (18n20) ◽  
pp. 3484-3492
Author(s):  
Jung Hoon Han
Keyword(s):  
Field Theory ◽  
Mean Field Theory ◽  
Mean Field ◽  
Low Energy ◽  
The Other ◽  
Tunneling Spectrum ◽  
Self Consistent ◽  
Underlying Disorder ◽  
D Wave ◽  
Good Agreement

The tunneling spectrum of an inhomogeneous d-wave superconductor is discussed in the framework of self-consistent slave-boson mean-field theory. Distinct from the usual BCS-type mean-field theory, an electron is now described using both fermionic and bosonic degree of freedom. We show that one can define two types of tunneling spectra in this theory, which also corresponds to two ways of calibrating the STM spectra. In good agreement with the experimental observation, we show that one type of tunneling spectrum remains inhomogeneous while the other type shows a remarkable degree of homogeneity at low energy, despite the underlying disorder. Physical implications of this result, in particular in relation to thermodynamic measurement such as heat capacity, are discussed.

scholarly journals Quantum and classical criticalities in the frustrated two-leg Heisenberg ladder

2008 ◽  
Vol 86 (4) ◽  
pp. 509-513 ◽  
Author(s):  
M Azzouz ◽  
B Ramakko
Keyword(s):  
Heisenberg Model ◽  
Mean Field Theory ◽  
Mean Field ◽  
Exchange Interactions ◽  
Thermal Fluctuations ◽  
Temperature Dependences ◽  
Wigner Transformation ◽  
75.10 Jm ◽  
75.50 Ee ◽  
Antiferromagnetic Heisenberg Model

This paper is about the frustration-induced criticality in the antiferromagnetic Heisenberg model on the two-leg ladder with exchange interactions along the chains, rungs, and diagonals, and also about the effect of thermal fluctuations on this criticality. The method used is the bond-mean-field theory, which is based on the Jordan–Wigner transformation in dimensions higher than one. In this paper, we will summarize the main results presented in a talk, and report on new results about the couplings and temperature dependences of the spin susceptibility.PACS Nos.: 75.10.Jm, 75.10.Dg, 75.50.Ee

High temperature superconductivity from magnetism - The Resonating Valence Bond State

1987 ◽  
Vol 01 (03n04) ◽  
pp. 697-719 ◽  
Author(s):  
G. BASKARAN
Keyword(s):  
Field Theory ◽  
High Temperature ◽  
High Temperature Superconductivity ◽  
Mean Field Theory ◽  
Mean Field ◽  
Valence Bond ◽  
The Other ◽  
Superconducting Properties ◽  
Bond State ◽  
Resonating Valence Bond

In this talk the Resonating Valence Bond (RVB) state of the Mott- Hubbard insulator and the high temperature superconductivity resulting from doping are described as the possible mechanisms for the insulating and high temperature superconducting properties of undoped and doped La2CuO4 and other high Tc oxides. We describe in detail two microscopic approaches to the understanding of the RVB superconductivity- one is a simple mean field theory and the other is a gauge theory.

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