29Si NMR and hidden order in URu2Si2

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

• URu2Si2 is a canonical heavy fermion compound exhibiting complex magnetic behavior.
• Understanding the nature of its hidden order parameter is a long-standing challenge in condensed matter physics.
• Previous studies have focused on magnetic ordering and its effects on electronic properties.

Purpose of the Study:

• To investigate the low-temperature behavior of the 29Si NMR linewidth in URu2Si2.
• To identify the microscopic origin of the previously unobserved field-independent contribution to the linewidth.
• To explore potential coupling mechanisms between nuclear spins and the hidden order parameter.

Main Methods:

• Utilizing 29Si Nuclear Magnetic Resonance (NMR) spectroscopy.
• Measuring the NMR linewidth as a function of temperature and applied magnetic field.
• Analyzing the field-independent and isotropic nature of the observed linewidth contribution.

Main Results:

• Observed a previously uncharacterized field-independent, nearly isotropic contribution to the 29Si NMR linewidth below approximately 17 K.
• This contribution increases to about 12 G as temperature approaches 0 K.
• The observed behavior is inconsistent with static freezing of uranium (U) spin magnetization.

Conclusions:

• The observed NMR linewidth anomaly is attributed to coupling between 29Si nuclear spins and the hidden order parameter in URu2Si2.
• Possible coupling mechanisms include time-reversal symmetry-breaking orbital antiferromagnetism and indirect nuclear spin-spin interactions.
• Further NMR experiments and theoretical calculations are recommended to elucidate the precise nature of this coupling and the hidden order.