arXiv subjects

R. J. Baxter

Publications and source records attributed to R. J. Baxter.

At least 19 recordsLinked to original sources

arXiv2019

Bulk, surface and corner free energies of the anisotropic triangular Ising model: series expansions and critical behaviour

We consider the anisotropic Ising model on the triangular lattice with finite boundaries, and use Kaufman's spinor method to calculate low-temperature series expansions for the partition function to high order. From these we can obtain 108-term series expansions for the bulk, surface and corner free energies. We extrapolate these to all terms and thereby conjecture the exact results for each. Our results agree with the exactly known bulk free energy. For the isotropic case, they also agree with Vernier and Jacobsen's conjecture for the $60^{\circ}$ corners, and with Cardy and Peschel's conformal invariance predictions for the dominant behaviour at criticality.

math-ph↗

arXiv2017

Surface and corner free energies of the self-dual Potts model

We consider the bulk, vertical surface, horizontal surface and corner free energies $f_b, f_s, f'_s, f_c$ of the anisotropic self-dual $Q$-state Potts model for $Q > 4$. $f_b$ was calculated in 1973[1]. For $Q<4$, $f_s, f'_s$ were calculated in 1989[2]. Here we extend this last calculation to $Q>4$ and find agreement with the conjectures made in 2012 by Vernier and Jacobsen (VJ)[3] for the isotropic case. All these four free energies satisfy inversion and rotation relations. Together with some plausible analyticity assumptions, these provide a less rigorous, but much simpler, way of determining $f_b, f_s, f'_s$. They also imply that $f_c$ is independent of the anisotropy, being a function only of $Q$, in which respect they resemble the order parameters of the associated six-vertex model. Hence VJ's conjecture for $f_c$ should apply to the full anisotropic model.

math-ph↗

arXiv2016

The bulk, surface and corner free energies of the square lattice Ising model

We use Kaufman's spinor method to calculate the bulk, surface and corner free energies $f_b, f_s, f_s', f_c$ of the anisotropic square lattice zero-field Ising model for the ordered ferromagnetic case. For $f_b, f_s, f'_s$ our results of course agree with the early work of Onsager, McCoy and Wu. We also find agreement with the conjectures made by Vernier and Jacobsen (VJ) for the isotropic case. We note that the corner free energy $f_c$ depends only on the elliptic modulus $k$ that enters the working, and not on the argument $v$, which means that VJ's conjecture applies for the full anisotropic model. The only aspect of this paper that is new is the actual derivation of $f_c$, but by reporting all four free energies together we can see interesting structures linking them.

math-ph↗

arXiv2014

The $τ_2$ model and parafermions

Paul Fendley has recently found a "parafermionic" way to diagonalise a simple solvable hamiltonian associated with the chiral Potts model. Here we indicate how this method generalizes to the $τ_2$ model with open boundaries and make some comments.

cond-mat.stat-mech↗

arXiv2012

Onsager and Kaufman's calculation of the spontaneous magnetization of the Ising model: II

In 2011 I reviewed the calculation by Onsager and Kaufman of the spontaneous magnetization of the square-lattice Ising model, which Onsager announced in 1949 but never published. I have recently been alerted to further original papers that bear on the subject. It is quite clear that the draft paper on which I relied was indeed written by Onsager, who was working on the problem with Kaufman, and that they had two derivations of the result.

cond-mat.stat-mech↗

arXiv2011

Onsager and Kaufman's calculation of the spontaneous magnetization of the Ising model

Lars Onsager announced in 1949 that he and Bruria Kaufman had proved a simple formula for the spontaneous magnetization of the square-lattice Ising model, but did not publish their derivation. It was three years later when C. N. Yang published a derivation in Physical Review. In 1971 Onsager gave some clues to his and Kaufman's method, and there are copies of their correspondence in 1950 now available on the Web and elsewhere. Here we review how the calculation appears to have developed, and add a copy of a draft paper, almost certainly by Onsager and Kaufman, that obtains the result.

cond-mat.stat-mech↗

arXiv2010

Some comments on developments in exact solutions in statistical mechanics since 1944

Lars Onsager and Bruria Kaufman calculated the partition function of the Ising model exactly in 1944 and 1949. Since then there have been many developments in the exact solution of similar, but usually more complicated, models. Here I shall mention a few, and show how some of the latest work seems to be returning once again to the properties observed by Onsager and Kaufman.

cond-mat.stat-mech↗

arXiv2010

Spontaneous magnetization of the superintegrable chiral Potts model: calculation of the determinant D_PQ

For the Ising model, the calculation of the spontaneous magnetization leads to the problem of evaluating a determinant. Yang did this by calculating the eigenvalues in the large-lattice limit. Montroll, Potts and Ward expressed it as a Toeplitz determinant and used Szego's theorem: this is almost certainly the route originally travelled by Onsager. For the corresponding problem in the superintegrable chiral Potts model, neither approach appears to work: here we show that the determinant D_PQ can be expressed as that of a product of two Cauchy-like matrices. One can then use the elementary exact formula for the Cauchy determinant. One of course regains the known result, originally conjectured in 1989.

cond-mat.stat-mech↗

arXiv2010

Proof of the determinantal form of the spontaneous magnetization of the superintegrable chiral Potts model

The superintegrable chiral Potts model has many resemblances to the Ising model, so it is natural to look for algebraic properties similar to those found for the Ising model by Onsager, Kaufman and Yang. The spontaneous magnetization M_r can be written in terms of a sum over the elements of a matrix S_r. The author conjectured the form of the elements, and this conjecture has been verified by Iorgov et al. The author also conjectured in 2008 that this sum could be expressed as a determinant, and has recently evaluated the determinant to obtain the known result for M_r. Here we prove that the sum and the determinant are indeed identical expressions.

cond-mat.stat-mech↗

arXiv2009

Some remarks on a generalization of the superintegrable chiral Potts model

The spontaneous magnetization of a two-dimensional lattice model can be expressed in terms of the partition function $W$ of a system with fixed boundary spins and an extra weight dependent on the value of a particular central spin. For the superintegrable case of the chiral Potts model with cylindrical boundary conditions, W can be expressed in terms of reduced hamiltonians H and a central spin operator S. We conjectured in a previous paper that W can be written as a determinant, similar to that of the Ising model. Here we generalize this conjecture to any Hamiltonians that satisfy a more general Onsager algebra, and give a conjecture for the elements of S.

cond-mat.stat-mech↗

arXiv2008

Algebraic reduction of the Ising model

We consider the Ising model on a cylindrical lattice of L columns, with fixed-spin boundary conditions on the top and bottom rows. The spontaneous magnetization can be written in terms of partition functions on this lattice. We show how we can use the Clifford algebra of Kaufman to write these partition functions in terms of L by L determinants, and then further reduce them to m by m determinants, where m is approximately L/2. In this form the results can be compared with those of the Ising case of the superintegrable chiral Potts model. They point to a way of calculating the spontaneous magnetization of that more general model algebraically.

cond-mat.stat-mech↗

arXiv2008

A conjecture for the superintegrable chiral Potts model

We adapt our previous results for the ``partition function'' of the superintegrable chiral Potts model with open boundaries to obtain the corresponding matrix elements of e^{-αH}, where H is the associated hamiltonian. The spontaneous magnetization M_r can be expressed in terms of particular matrix elements of e^{-αH} S^r_1 \e^{-βH}, where S_1 is a diagonal matrix.We present a conjecture for these matrix elements as an m by m determinant, where m is proportional to the width of the lattice. The author has previously derived the spontaneous magnetization of the chiral Potts model by analytic means, but hopes that this work will facilitate a more algebraic derivation, similar to that of Yang for the Ising model.

cond-mat.stat-mech↗

arXiv2007

Hard Squares for z = -1

The hard square model in statistical mechanics has been investigated for the case when the activity z is -1. For cyclic boundary conditions, the characteristic polynomial of the transfer matrix has an intriguingly simple structure, all the eigenvalues $x$ being zero, roots of unity, or solutions of x^3 = 4 cos^2 (pi*m/N). Here we tabulate the results for lattices of up to 12 columns with cyclic or free boundary conditions and the two obvious orientations. We remark that they are all unexpectedly simple and that for the rotated lattice with free or fixed boundary conditions there are obvious likely generalizations to any lattice size.

cond-mat.stat-mech↗

arXiv2006

Corner transfer matrices in statistical mechanics

Corner transfer matrices are a useful tool in the statistical mechanics of simple two-dimensinal models. They can be very effective way of obtaining series expansions of unsolved models, and of calculating the order parameters of solved ones. Here we review these features and discuss the reason why the method fails to give the order parameter of the chiral Potts model.

cond-mat.stat-mech↗

arXiv2006

Free energy of the three-state $τ_2(t_q)$ model as a product of elliptic functions

{We show that the free energy of the three-state $τ_2(t_q)$ model can be expressed as products of Jacobi elliptic functions, the arguments being those of an hyperelliptic parametrization of the associated chiral Potts model. This is the first application of such a parametrization to the $N$-state chiral Potts free energy problem for $N > 2$.

cond-mat.stat-mech↗

arXiv2006

Hyperelliptic parametrization of the generalized order parameter of the N=3 chiral Potts model

It has been known for some time that the Boltzmann weights of the chiral Potts model can be parametrized in terms of hyperelliptic functions, but as yet no such parametrization has been applied to the partition and correlation functions. Here we show that for N=3 the function $S(t_p)$ that occurs in the recent calculation of the order parameters can be expressed quite simply in terms of such a parametrization.

cond-mat.stat-mech↗

arXiv2005

The challenge of the chiral Potts model

The chiral Potts model continues to pose particular challenges in statistical mechanics: it is ``exactly solvable'' in the sense that it satisfies the Yang-Baxter relation, but actually obtaining the solution is not easy. Its free energy was calculated in 1988 and the order parameter was conjectured in full generality a year later. However, a derivation of that conjecture had to wait until 2005. Here we discuss that derivation.

cond-mat.stat-mech↗

arXiv2005

The order parameter of the chiral Potts model

An outstanding problem in statistical mechanics is the order parameter of the chiral Potts model. An elegant conjecture for this was made in 1983. It has since been successfully tested against series expansions, but as far as the author is aware there is as yet no proof of the conjecture. Here we show that if one makes a certain analyticity assumption similar to that used to derive the free energy, then one can indeed verify the conjecture. The method is based on the ``broken rapidity line'' approach pioneered by Jimbo, Miwa and Nakayashiki.

cond-mat.stat-mech↗