Scaling and data collapse from local moments in frustrated disordered quantum spin systems

Area of Science:

• Condensed Matter Physics
• Quantum Magnetism
• Materials Science

Background:

• Experimental measurements on diverse spin-1/2 quantum magnets (e.g., H3LiIr2O6, LiZn2Mo3O8) exhibit universal low-temperature scaling.
• These materials share magnetic frustration and quenched disorder, but lack other commonalities, suggesting an underlying universal mechanism.

Purpose of the Study:

• To develop a theoretical framework explaining the observed universal scaling collapse in the heat capacity of quantum magnets.
• To incorporate spin-orbit coupling and Dzyaloshinskii-Moriya interactions into the theoretical model.

Main Methods:

• Theoretical modeling based on an emergent random-singlet regime.
• Derivation of scaling relations for heat capacity C[H, T] as a function of temperature T and magnetic field H.
• Analysis of scaling exponents (q) dependent on spatial symmetries.

Main Results:

• A theoretical scaling relation C[H, T]/T ~ H^-γ * F_q[T/H] is derived, with F_q[x] = x^q for small x.
• The exponent q can take integer values {0, 1, 2}, determined by spatial symmetries.
• Experimental data agreement supports a model where spins form random valence bonds within a quantum paramagnetic phase.

Conclusions:

• The random-singlet theory successfully explains the universal scaling collapse observed in various quantum magnets.
• The presence of random valence bonds and a surrounding quantum paramagnetic phase is indicated.
• Distinct scaling behaviors for magnetization are discussed, including q-dependent subdominant terms.