Experimental Determination of the Parisi Order Parameter x(q)
Abstract
Several crucial features of slow dynamics in spin glasses have already been reproduced in a model of barrier hopping between metastable states. Because the equilibrium population rates of these metastable states can be mapped onto the static overlap distribution x(q) of the Parisi mean-field spin glass, x(q) becomes experimentally accessible. The sensitivity of the thermoremanent magnetization (TRM) to the (squared) amplitude of the magnetic field change H gives access to the relative weights of states. A fit to the Sommers high temperature expansion (Tarrow T_g_-) allows precise calibration of TRM vs H^2 in terms of bar x vs q_EA-q (where 1-bar x is the length of the q(x)=q_EA plateau). Using this approach, we have extracted the Parisi Order Parameter, x(q) for single crystal Cu:Mn 1.5 at.% and polycrystalline Cu:Mn 6.0 at.% metallic alloys, and the insulating thiospinel CrCr_1.7In_0,3S_4. Very small magnetic field changes, as low as 8 mG, were used to probe q close to q_EA. Upper and lower limits on bar x, and an upper bound for the ``width'' of the delta function in P(q)=dx(q)/dq of ≈ 10-8q_EA, were established. The observation that x(q) increases with waiting time tw suggests that the amplitude for q(x) for q<q_EA remains finite for t_warrow ∞, supporting the Parisi argument that P(q) has finite amplitude for q<q_EA.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2001
- Bibcode:
- 2001APS..MARZ24003Z