In-Person
  CNLS Conference Room (TA-3, Bldg 1690)
 
Thursday, Jan. 5, 2022
3:45 – 4:45 pm (MT)
  Light refreshments  3:15 - 3:45 pm
 
 
 
Speaker: Dr. Michael Saccone

       Leon Heller Publication Prize Winner
          LANL                 
                     
“Direct observation of a dynamical glass transition in a nanomagnetic artificial Hopfield network”
 
Abstract: 
Spin glasses, generally defined as disordered systems with randomized competing interactions, are a widely investigated complex system. Theoretical models describing spin glasses are broadly used in other complex systems, such as those describing brain function, error-correcting codes or stock-market dynamics. This wide interest in spin glasses provides strong motivation to generate an artificial spin glass within the framework of artificial spin ice systems. Here we present the experimental realization of an artificial spin glass consisting of dipolar coupled single-domain Ising-type nanomagnets arranged onto an interaction network that replicates the aspects of a Hopfield neural network. Using cryogenic X-ray photoemission electron microscopy (XPEEM), we performed temperature-dependent imaging of thermally driven moment fluctuations within these networks and observed characteristic features of a two-dimensional Ising spin glass. Specifically, the temperature dependence of the spin glass correlation function follows a power-law trend predicted from theoretical models on two-dimensional spin glasses. Furthermore, we observe clear signatures of the hard-to-observe rugged spin glass free energy in the form of sub-aging, out-of-equilibrium autocorrelations and a transition from stable to unstable dynamics.
 
 
Bio: 
Michael Saccone began his academic journey at Cabrillo College, a community college overlooking the Monterey Bay. Encouraged by the enthusiasm of his instructions, he continued on to the University of Alaska Fairbanks to complete his undergraduate education in physics. He then returned to the Monterey Bay to attain his doctorate in physics from the University of California Santa Cruz, where he worked to advance the fundamental statistical physics of artificial spin ice. He now works with two outstanding theoreticians, Cristiano Nisoli and Francesco Caravelli, at Los Alamos. Through their guidance, his publication on embedding Hopfield networks in artificial spin systems has won the Leon Heller Publication Prize.

The Leon Heller Publication Prize is awarded every other year to celebrate the best article authored by a postdoc in theoretical physics.