Kramers-Wannier Duality

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This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.

Kramers%E2%80%93Wannier Duality

The **Kramers-Wannier duality** is a symmetry in statistical physics. It relates the free energy of a two-dimensional square-lattice Ising model at a low temperature to that of another Ising model at a high temperature. It was discovered by Hendrik Kramers and Gregory Wannier in 1941. With the aid of this duality Kramers and Wannier found the exact location of the critical point for the Ising model on the square lattice.

Similar dualities establish relations between free energies of other statistical models. For instance, in 3 dimensions the Ising model is dual to an Ising gauge model.

The 2-dimensional Ising model exists on a lattice, which is a collection of squares in a chessboard pattern. With the finite lattice, the edges can be connected to form a torus. In theories of this kind, one constructs an involutive transform. For instance, Lars Onsager suggested that the Star-Triangle transformation could be used for the triangular lattice.^{[1]} Now the dual of the *discrete* torus is itself. Moreover, the dual of a highly disordered system (high temperature) is a well-ordered system (low temperature). This is because the Fourier transform takes a high bandwidth signal (more standard deviation) to a low one (less standard deviation). So one has essentially the same theory with an inverse temperature.

When one raises the temperature in one theory, one lowers the temperature in the other. If there is only one phase transition, it will be at the point at which they cross, at which the temperature is equal. Because the 2D Ising model goes from a disordered state to an ordered state, there is a near one-to-one mapping between the disordered and ordered phases.

The theory has been generalized, and is now blended with many other ideas. For instance, the square lattice is replaced by a circle,^{[2]} random lattice,^{[3]} nonhomogeneous torus,^{[4]} triangular lattice,^{[5]} labyrinth,^{[6]} lattices with twisted boundaries,^{[7]} chiral Potts model,^{[8]} and many others.

Define these variables.
The low temperature expansion for (K^{*},L^{*}) is

which by using the transformation

gives

where *v = tanh K* and * w = tanh L*. This yields a relation with the high-temperature expansion. The relations can be written more symmetrically as

With the free energy per site in the thermodynamic limit

the Kramers-Wannier duality gives

In the isotropic case where *K = L*, if there is a critical point at *K = K _{c}* then there is another at

**^**Somendra M. Bhattacharjee, and Avinash Khare,*Fifty Years of the Exact Solution of the Two-Dimensional Ising Model by Onsager (1995)*, arXiv:cond-mat/9511003**^**arXiv:cond-mat/9805301,*Self-dual property of the Potts model in one dimension*, F. Y. Wu**^**arXiv:hep-lat/0110063,*Dirac operator and Ising model on a compact 2D random lattice*, L.Bogacz, Z.Burda, J.Jurkiewicz, A.Krzywicki, C.Petersen, B.Petersson**^**arXiv:hep-th/9703037,*Duality of the 2D Nonhomogeneous Ising Model on the Torus*, A.I. Bugrij, V.N. Shadura**^**arXiv:cond-mat/0402420,*Selfduality for coupled Potts models on the triangular lattice*, Jean-Francois Richard, Jesper Lykke Jacobsen, Marco Picco**^**arXiv:solv-int/9902009,*A critical Ising model on the Labyrinth*, M. Baake, U. Grimm, R. J. Baxter**^**arXiv:hep-th/0209048,*Duality and conformal twisted boundaries in the Ising model*, Uwe Grimm**^**arXiv:0905.1924,*Duality and Symmetry in Chiral Potts Model*, Shi-shyr Roan

- H. A. Kramers and G. H. Wannier (1941). "Statistics of the two-dimensional ferromagnet".
*Physical Review*.**60**: 252-262. Bibcode:1941PhRv...60..252K. doi:10.1103/PhysRev.60.252. - J. B. Kogut (1979). "An introduction to lattice gauge theory and spin systems".
*Reviews of Modern Physics*.**51**(4): 659-713. Bibcode:1979RvMP...51..659K. doi:10.1103/RevModPhys.51.659.

This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.

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