Classical Origins of Landau-Incompatible Transitions.

Area of Science:

• Condensed Matter Physics
• Statistical Mechanics
• Phase Transitions

Background:

• Continuous phase transitions with spontaneous symmetry breaking are common in physics.
• Landau-compatible transitions preserve subset symmetries, but deconfined quantum critical transitions between Landau-incompatible phases exist in quantum systems, often with anomalous symmetries.

Purpose of the Study:

• To investigate if special conditions are necessary for Landau-incompatible transitions.
• To explore Landau-incompatible transitions in classical statistical mechanical models with anomaly-free symmetries.

Main Methods:

• Studied anisotropic deformations of the classical 2D XY model, parameterized by an integer Q.
• Analyzed the phase diagrams of these models across various temperatures.

Main Results:

• For even Q (Q≥4), models exhibit two Landau-incompatible partial symmetry-breaking phases with a direct transition between them.
• Observed features of deconfined quantum criticality, like enhanced symmetries and melting of charged defects, in a classical context.
• For odd Q, two regions of a single partial symmetry-breaking phase are observed, separated by a critical line.

Conclusions:

• Landau-incompatible transitions can occur in classical statistical models with anomaly-free symmetries, challenging the need for special conditions.
• The findings suggest potential experimental realizations and provide insights for anomaly-free quantum models with similar phase diagrams.