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arXiv:cond-mat/9302022 · Modern Physics Letters B

VARIOUS CONDENSED MATTER HAMILTONIANS IN TERMS OF U(2/2) OPERATORS AND THEIR SYMMETRY STRUCTURES

Ko Okumura

Published Feb 20, 1993• 2 citations
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Abstract

We rewrite various lattice Hamiltonians in condensed matter physics in terms of U(2/2) operators that we introduce. In this representation the symmetry structure of the models becomes clear. Especially, the Heisenberg, the supersymmetric t-J and a newly proposed high-T c superconducting Hamiltonian reduce to the same form [Formula: see text]. This representation also gives us a systematic way of searching for the symmetries of the system.

DOI
10.1142/s0217984993000266

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We rewrite various lattice Hamiltonians in condensed matter physics in terms of U(2/2) operators that we introduce. In this representation the symmetry structure of the models becomes clear. Especially, the Heisenberg, the supersymmetric t-J and a newly proposed high-T c superconducting Hamiltonian reduce to the same form [Formula: see text]. This representation also gives us a systematic way of searching for the symmetries of the system.
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In many condensed-matter systems, it is very useful to introduce a quasi-particle approach, which is based on some sort of linearization around a suitable background state. In order to be a systematic and controlled approximation, this linearization should be justified by an expansion into powers of some small control parameter. Here, we present a method for general lattice Hamiltonians with large coordination numbers Z >> 1, which is based on an expansion into powers of 1/Z. In order to demonstrate the generality of our method, we apply it to various spin systems, as well as the Bose and Fermi Hubbard model.
We present a systematic method to construct the spin models of Heisenberg type in higher dimensions with nearest and non-nearest neighbour interactions. These models constructed in this way are of Temperley-Lieb-Jones (TLJ) algebraic structures and -invariances. The TLJ algebra is generalized to adjusting the lattice spin models. The Hamiltonians of Heisenberg spin models in one dimension (including second nearest neighbour interactions) and in two-dimensional triangular lattice (with nearest interaction) are constructed explicitly. The hidden symmetries are shown to be the group, and the terms in Hamiltonian for different lattice cells are explicitly shown to be the representations of elements of (TLJ) algebra.
In many condensed-matter systems, it is very useful to introduce a quasi-particle approach, which is based on some sort of linearization around a suitable background state. In order to be a systematic and controlled approximation, this linearization should be justified by an expansion into the powers of some small control parameter. Here, we present a method for general lattice Hamiltonians with large coordination numbers Z 1, which is based on an expansion into the powers of 1/Z. In order to demonstrate the generality of our method, we apply it to various spin systems, as well as the Bose and Fermi–Hubbard model.
CPT{\mathcal{CPT}}CPT-CONSERVING HAMILTONIANS AND THEIR NONLINEAR SUPERSYMMETRIZATION USING DIFFERENTIAL CHARGE-OPERATORS C{\mathcal C}C
A brief overview is given of recent developments and fresh ideas at the intersection of [Formula: see text]- and/or [Formula: see text]-symmetric quantum mechanics with supersymmetric quantum mechanics (SUSY QM). Within the framework of the resulting supersymmetric version of [Formula: see text]-symmetric quantum mechanics we study the consequences of the assumption that the "charge" operator [Formula: see text] is represented in a differential-operator form of the second or higher order. Besides the freedom allowed by the Hermiticity constraint for the operator [Formula: see text], encouraging results are obtained in the second-order case. In particular, the integrability of intertwining relations proves to match the closure of our nonlinear (viz., polynomial) SUSY algebra. In a particular illustration, our form of [Formula: see text]-symmetric SUSY QM leads to a new class of non-Hermitian polynomial oscillators with real spectrum which turn out to be [Formula: see text]-asymmetric.