Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session L25: Universality of Spin Glass Dynamics: Recent AdvancesInvited

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Sponsoring Units: DCMP DMP Chair: E. Dan Dahlberg Room: LACC 403B 
Wednesday, March 7, 2018 11:15AM  11:51AM 
L25.00001: Glassy Dynamics: Spin Glasses at the Mesoscale Invited Speaker: Raymond Orbach Spin glasses are an exemplar of glassy dynamics, exhibiting aging, freezing, and other correlation properties. The lower critical dimension is < 3 so that, by working with CuMn/Cu multilayers at the mesoscale (CuMn thicknesses L less than ~ 20 nm), the spin glass can be frozen into a metastable state. The perpendicular component of the correlation length grows to L but the parallel component of the correlation length grows to the d = 2 correlation length. The combination of the two conditions leads to a “pancakelike” correlated volume. Comparison of mesoscale and bulk waiting time effects supports this interpretation. Sessation of correlation length growth results in a largest free energy barrier of height independent of T. Metastable states occupancies cause the largest barrier to dominate, leading to glassy dynamics. The Ldependence of the largest barrier height distinguishes between two competing theories for spin glass dynamics: activated vs power law dynamics, the latter in better agreement with experiment. The largest barrier height’s change with temperature and magnetic field exhibits temperature chaos and determines the size of the correlated regions, respectively. 
Wednesday, March 7, 2018 11:51AM  12:27PM 
L25.00002: Matching Microscopic and Macroscopic Responses in Glasses Invited Speaker: Beatriz Seoane We use Janus and Janus II supercomputers to revisit two successful experimental approaches to detect the glass correlation length from macroscopic observables [1]. On the one hand, we reproduce a milestone experiment to measure spinglass coherence length, ξ_{max}, through the lowering of freeenergy barriers induced by the Zeeman effect [2], and on the other hand, we explore the relationship between the spinglass coherence length and the macroscopic nonlinear susceptibilities, the latter recently measured in supercooled glasses [3] to support the existence of a growth of thermodynamic amorphous order upon approaching the ideal glass transition. We compare these macroscopic measures, with the microscopic spinglass coherence length ξ_{mic} (as extracted from the fourpoint spatial correlation function), concluding that (i) ξ_{max} and ξ_{mic }are mutually consistent, and (ii) the nonlinear susceptibilities scale as powers of ξ_{mic}, so they can be used to describe the growth of an amorphous order in glass formers. In addition, we propose scaling laws on the applied field that have allowed a quantitative analysis of new experiments [4]. 
Wednesday, March 7, 2018 12:27PM  1:03PM 
L25.00003: Time and length for spin glasses Invited Speaker: Victor MartinMayor The dynamics of glass formers (such as spinglasses) is so slow that they never reach equilibrium in macroscopic samples: in analogy with 
Wednesday, March 7, 2018 1:03PM  1:39PM 
L25.00004: Fifthorder susceptibility unveils growth of thermodynamic amorphous order in glassformers. Invited Speaker: François Ladieu Glasses are ubiquitous in daily life and technology. However the microscopic mechanisms generating this state of matter are still controversially debated: glasses are considered either as merely hyperviscous liquids or as resulting from a genuine thermodynamic phase transition towards a rigid state. We show that third and fifth order susceptibilities provide a smokinggun answer to this longstanding controversy. Performing the corresponding highprecision nonlinear dielectric experiments for supercooled glycerol and propylene carbonate, we find strong support for theories based upon thermodynamic amorphous order. Moreover, when lowering temperature, we find that the growing transient domains are compact, i.e. their fractal dimension d_{f }= 3. The glass transition may thus represent a new class of critical phenomena, different from canonical secondorder phase transitions for which d_{f }< 3. Time permitting, I will shortly review some experimental results obtained recently in spin glasses and in colloids, explaining why nonlinear responses directly test amorphous order in glassy matter. 
Wednesday, March 7, 2018 1:39PM  2:15PM 
L25.00005: Can Analog Quantum Computers Solve Spin Glasses? Invited Speaker: Itay Hen Recent developments in quantum technology have led to the manufacture of experimental programmable quantum annealing optimizers that contain thousands of quantum bits. These optimizers, also known as the ‘DWave’ processors, promise to solve practical optimization problems potentially faster than conventional computers. The claimed superiority of these annealers over traditional solvers and the degree to which they exploit their quantum capabilities is currently the center of a heated debate. In this context, specifically of importance is the question of how well these quantum annealers perform on hard problems with rugged freeenergy landscapes for which classical methods are known to fail. I will describe attempts to identify such hard problems and characterize these devices by means of stateoftheart methods borrowed from spinglass theory, and present results pertaining to the performance of various classical algorithms and the Dwave processors on these. 
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