Phase transition between hidden and antiferromagnetic order in URu2Si2.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Heavy fermion compounds like URu2Si2 exhibit complex electronic behaviors.
• Understanding the interplay between different electronic orders is key to materials science.
• URu2Si2 is known for its 'hidden order' phase, a subject of intense research.

Purpose of the Study:

• To investigate the effects of pressure on the thermal expansion of URu2Si2.
• To identify and characterize new pressure-induced phase transitions in URu2Si2.
• To construct a temperature-pressure phase diagram for URu2Si2.

Main Methods:

• Precise thermal expansion measurements were performed on URu2Si2 single crystals.
• The experiments were conducted under varying pressure conditions.
• Temperature-pressure phase diagrams were constructed based on the observed anomalies.

Main Results:

• A novel pressure-dependent anomaly was observed in thermal expansion along both the a and c axes.
• A first-order phase transition boundary was identified, separating the hidden order and antiferromagnetic phases.
• Significant changes in lattice constants (shrinking along 'a', elongating along 'c') were noted upon entering the antiferromagnetic phase.

Conclusions:

• The heavy fermion compound URu2Si2 exhibits a distinct pressure-induced phase transition.
• The observed lattice changes indicate a strong coupling between electronic order and lattice degrees of freedom.
• URu2Si2 is positioned near a bicritical point, influencing the nature of its phase transitions.