128 citations · 793 across the 55 of their papers we have counts for
15 papers · 1 filter
Thermodynamics of the spin square
Heinz-Jürgen Schmidt, Christian Schröder
Small spin systems at the interface between analytical studies and experimental application have been intensively studied in recent decades. The spin ring consisting of four spins…
Thermodynamics of the classical spin triangle
Heinz-Jürgen Schmidt, Christian Schröder
The classical spin system consisting of three spins with Heisenberg interaction is an example of a completely integrable mechanical system. In this paper we explicitly calculate th…
Stochastic thermodynamics of a finite quantum system coupled to two heat baths
Heinz-Jürgen Schmidt, Jochen Gemmer
We consider a situation where an -level system (NLS) is coupled successively to two heat baths with different temperatures without being necessarily thermalized and approaches a…
Theory of ground states for classical Heisenberg spin systems VI
Heinz-Jürgen Schmidt, Wojciech Florek
We formulate part VI of a rigorous theory of ground states for classical, finite, Heisenberg spin systems. After recapitulating the central results of the parts I - V previously pu…
Dynamics and thermodynamics of a pair of interacting magnetic dipoles
Heinz-Jürgen Schmidt, Christian Schröder, Eva Hägele +1
We consider the dynamics and thermodynamics of a pair of magnetic dipoles interacting via their magnetic fields. We consider only the "spin" degrees of freedom; the dipoles are fix…
Moments of general Heisenberg Hamiltonians up to sixth order
Heinz-Juergen Schmidt, Andre Lohmann, Johannes Richter
We explicitly calculate the moments t_n of general Heisenberg Hamiltonians up to sixth order. They have the form of finite sums of products of two factors, the first factor being r…
Projection operator approach to transport in complex single-particle quantum systems
Robin Steinigeweg, Jochen Gemmer, Heinz-Peter Breuer +1
We discuss the time-convolutionless (TCL) projection operator approach to transport in closed quantum systems. The projection onto local densities of quantities such as energy, mag…
Symplectic integrators for classical spin systems
Robin Steinigeweg, Heinz-Jürgen Schmidt
We suggest a numerical integration procedure for solving the equations of motion of certain classical spin systems which preserves the underlying symplectic structure of the phase…
Spin systems with dimerized ground states
Heinz-Jürgen B. Schmidt
In view of the numerous examples in the literature it is attempted to outline a theory of Heisenberg spin systems possessing dimerized ground states (``DGS systems") which comprise…
A solvable model of a one-dimensional quantum gas with pair interaction
H. -J. Schmidt, J. Bartke
We propose a solvable model of a one-dimensional harmonic oscillator quantum gas of two sorts of particles, fermions or bosons, which allows to describe the formation of pairs due…
Quantum numbers for relative ground states of antiferromagnetic Heisenberg spin rings
K. Baerwinkel, P. Hage, H. -J. Schmidt +1
We suggest a general rule for the shift quantum numbers k of the relative ground states of antiferromagnetic Heisenberg spin rings. This rule generalizes well-known results of Mars…
Improved upper and lower energy bounds for antiferromagnetic Heisenberg spin systems
K. Baerwinkel, H. -J. Schmidt, J. Schnack
Large spin systems as given by magnetic macromolecules or two-dimensional spin arrays rule out an exact diagonalization of the Hamiltonian. Nevertheless, it is possible to derive u…
Symmetric polynomials in physics
Heinz-Juergen Schmidt, Juergen Schnack
We give two examples where symmetric polynomials play an important role in physics: First, the partition functions of ideal quantum gases are closely related to certain symmetric p…
Continuous families of isospectral Heisenberg spin systems and the limits of inference from measurements
Heinz-Juergen Schmidt, Marshall Luban
We investigate classes of quantum Heisenberg spin systems which have different coupling constants but the same energy spectrum and hence the same thermodynamical properties. To thi…
Investigations on finite ideal quantum gases
H. -J. Schmidt, J. Schnack
Recursion formulae of the N-particle partition function, the occupation numbers and its fluctuations are given using the single-particle partition function. Exact results are prese…