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Research Center for Quantum Information
Institute of Physics, Slovak Academy of Sciences
Dúbravská cesta 9, 84511 Bratislava, Slovakia
Tel: (+421 +2) 20910701
Fax: (+421 +2) 54776085

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23.08.2016 Research publication
Phase diagram of a truncated tetrahedral model
Phase diagram of a discrete counterpart of the classical Heisenberg model, the truncated tetrahedral model, is analyzed on the square lattice, when the interaction is ferromagnetic. Each spin is represented by a unit vector that can point to one of the 12 vertices of the truncated tetrahedron, which is a continuous interpolation between the tetrahedron and the octahedron. Phase diagram of the model is determined by means of the statistical analog of the entanglement entropy, which is numerically calculated by the corner transfer matrix renormalization group method. The obtained phase diagram consists of four different phases, which are separated by five transition lines. In the parameter region, where the octahedral anisotropy is dominant, a weak firstorder phase transition is observed.
by
Roman Krcmar, Andrej Gendiar, and Tomotoshi Nishino
Phys. Rev. E 94, 022134 (2016)
+++
APVV140878 (QETWORK),
VEGA2/0130/15 (OAQS)

23.08.2016 Research publication
Boundaryfielddriven control of discontinuous phase transitions on hyperbolic lattices
The multistate Potts models on twodimensional hyperbolic lattices are studied with respect to various boundary effects. The free energy is numerically calculated using the corner transfer matrix renormalization group method. We analyze phase transitions of the Potts models in the thermodynamic limit with respect to contracted boundary layers. A false phase transition is present even if a couple of the boundary layers are contracted. Its significance weakens, as the number of the contracted boundary layers increases, until the correct phase transition (deep inside the bulk) prevails over the false one. For this purpose, we derive a thermodynamic quantity, the socalled bulk excess free energy, which depends on the contracted boundary layers and memorizes additional boundary effects. In particular, the magnetic field is imposed on the outermost boundary layer. While the boundary magnetic field does not affect the secondorder phase transition in the bulk if suppressing all the boundary effects on the hyperbolic lattices, the firstorder (discontinuous) phase transition is significantly sensitive to the boundary magnetic field. Contrary to the phase transition on the Euclidean lattices, the discontinuous phase transition on the hyperbolic lattices can be continuously controlled (within a certain temperature coexistence region) by varying the boundary magnetic field.
by
Yoju Lee, Frank Verstraete, and Andrej Gendiar
Phys. Rev. E 94, 022133 (2016)
+++
APVV080812 (QIMABOS),
VEGA2/0130/15 (OAQS)


S E M I N A R S
 more 
09/08 11:00
Christian Schilling (Oxford, United Kingdom)
Fermionic Exchange Symmetry: Quantifying its Influence beyond Pauli's Exclusion Principle
??/?? 11:00
Martin Schwarz (Berlin, Germany)
Approximating local observables on projected entangledpair states

V I S I T O R S
 history 
07.0811.08 Christian Schilling
(University of Oxford, United Kingdom)
08.0826.08 David Davalos
(National Autonomous University of Mexico, Mexico City)


