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Article
Efficiency of the microcanonical over-relaxation algorithm for vector spins analyzing first and second order transitions
We simulate vectorial spin systems solely with the microcanonical over-relaxation algorithm where the temperature is calculated by a formula of Nurdin and Schotte. We show that this procedure is the most effic...
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Article
Canonical local algorithms for spin systems: heat bath and Hasting’s methods
We introduce new fast canonical local algorithms for discrete and continuous spin systems. We show that for a broad selection of spin systems they compare favorably to the known ones except for the Ising ...
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Chapter
Real Structure of Perovskites Looked at From the Band Structure Point of View
Although perovskites can be viewed as a dense packing of ionic spheres of three different sizes in a cubic structure, there are several deviations from this ideal. Most common is the tilting of the corner shar...
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Article
Critical behavior of frustrated systems: Monte Carlo simulations versus renormalization group
We study the critical behavior of frustrated systems by means of the Padé-Borel resummed three-loop renormalization group expansions and numerical Monte Carlo simulations. Amazingly, for six-component spins, w...
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Article
A spin- \({1 \over 2}\) model for CsCuCl3 in an external magnetic field
CsCuCl3 is a ferromagnetically stacked triangular spin-1/2 antiferromagnet. We discuss models for its zero-temperature magnetization process. The models range from three antiferromagnetically coupled ferromagneti...
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Article
First and second order transition of frustrated Heisenberg spin systems
Starting from the hypothesis of a second order transition we have studied modifications of the original Heisenberg antiferromagnet on a stacked triangular lattice (STA-model) by the Monte Carlo technique. The ...
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Article
First and second order transition in frustrated XY systems
The nature of the phase transition for the XY stacked triangular antiferromagnet (STA) is a controversial subject at present. The field theoretical renormalization group (RG) in three dimensions predicts a first ...
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Article
Influence of twinning planes on upper critical fields
Within the framework of a Ginzburg-Landau theory for a scalar order parameter, we discuss the effect of the presence of twinning planes on the behavior of the upper critical field as function of the temperatur...
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Article
Correlated Huang scattering in hexagonal Jahn Teller compounds
This is a theoretical investigation on structural precursors in diffuse neutron scattering of disordered phases of cooperative Jahn-Teller compounds above their structural phase transitions. The theory is base...
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Article
Grüneisen parameter coupling in heavy fermion systems
We discuss thermodynamic consequences of a Grüneisenparameter electron-phonon coupling in heavy fermion systems. Characteristic features of sound propagation, thermal expansion and ultrasonic attenuation are g...
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Article
Can ultrasonic sound attenuation measurements elucidate the coupling of “Heavy electrons” to the lattice?
An unusual peak has been found by Müller et al. for the attenuation of longitudinal sound as a function of temperature around 12 K for UPt3. Breathing mode coupling of the volume strain to the electronic energy s...
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Article
Ice models and a lattice version of the Dirac equation
We study ice models as possible realizations for lattice versions of the Dirac equation. The starting point of this analysis is the close connection between the two dimensional ice model of Lieb and the Thirri...
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Article
Time correlations in quantum spin chains and the X-ray absorption problem
We study the isotropic spin one-half XY-chain with one arbitrarily modified coupling. The transverse auto-correlation functions of the spin at the modified bond are considered atT=0 and their asymptotic time depe...
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Article
Screening in a one dimensional plasma
We investigate the screening behavior of a neutral one dimensional plasma made up by two types of charges not necessarily of equal values. The thermodynamic potential is given by the lowest eigenvalue of a gen...
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Article
Specific heat of concentrated kondo systems: (La, Ce)Al2 and CeAl2
We report on specific heat measurements of (La1−x Ce x )Al2 samples, with 1.5 a/o≦x≦100 a/o, performed in magnetic fields of up to 5 T between 0.3 and 10 K. In the Ce rich alloys...
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Article
On the spin fluctuation approach to the anderson and Kondo hamiltonians
The free energy expression of the full Anderson model is derived in a similar way as has been done before for the Kondo model. Use is made of the “asymptotic time approximation” first invented to study the x-r...
