Field-Angle-Resolved Specific Heat in Na_{2}Co_{2}TeO_{6}: Evidence against Kitaev Quantum Spin Liquid

Area of Science:

• Condensed Matter Physics
• Quantum Magnetism

Background:

• Kitaev quantum spin liquids (KSLs) are exotic states of matter hosting Majorana quasiparticles.
• Layered honeycomb magnets like α-RuCl_{3} show potential KSL behavior with field-dependent excitations.
• Na_{2}Co_{2}TeO_{6} (NCTO) is a candidate material for KSL studies.

Purpose of the Study:

• To investigate the low-energy excitations in NCTO using specific heat measurements.
• To determine if NCTO exhibits Majorana quasiparticle excitations characteristic of a KSL state.
• To compare the thermodynamic properties of NCTO with established KSL materials like α-RuCl_{3}.

Main Methods:

• Low-temperature specific heat measurements C(T) were performed on NCTO.
• Measurements were conducted under varying magnetic field strengths and angles within the honeycomb plane.
• Analysis focused on the field-angle dependence of the specific heat divided by temperature (C/T).

Main Results:

• Above the critical field for antiferromagnetic order, C/T exhibited minima along bond directions in NCTO.
• This behavior contrasts with the maxima observed in α-RuCl_{3}, a known KSL candidate.
• The excitations in NCTO were found to be nodeless and fully gapped, inconsistent with predicted Majorana excitations.

Conclusions:

• The observed excitations in NCTO are attributed to gapped magnon excitations, not Majorana quasiparticles.
• These findings provide thermodynamic evidence against NCTO being in a Kitaev quantum spin liquid state.
• The study highlights the importance of thermodynamic measurements in characterizing quantum spin liquid candidates.