Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session W24: Dynamical properties of complex systemsInvited
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Sponsoring Units: DCMP Chair: Dan Dahlberg, University of Minnesota Room: Room 237 |
Thursday, March 9, 2023 3:00PM - 3:36PM |
W24.00001: Temperature Chaos in Spin Glasses Invited Speaker: Qiang Zhai The problem of temperature chaos in spin glasses, which predicts the sensitivity of the spin configuration to the external temperature perturbations in equilibrium, has been formalized, debated and studied for nearly four decades. Although its theoretical existence has been proved, its physical observation remains elusive due to the non-equilibrium nature of a real spin glass system. In our study, by separating and comparing two length scales, the correlation length and the chaos length and by utilizing a high-quality CuMn single crystal sample, we traced the dynamics of spin glass with and without external temperature perturbations. Our experimental results strongly suggest the presence of temperature chaos in a real spin glass system with the calibrated chaos exponent matching theoretical predictions. |
Thursday, March 9, 2023 3:36PM - 4:12PM |
W24.00002: Memory and rejuvenation in spin glasses: numerical simulations meet experiments. Invited Speaker: Ilaria Paga Memory and rejuvenation effects in the magnetic response of off-equilibrium spin glasses have been widely regarded as the doorway into the experimental exploration of ultrametricity and temperature chaos (maybe the most exotic features in glassy free-energy landscapes). Unfortunately, despite more than twenty years of theoretical efforts following the experimental discovery of memory and rejuvenation, these effects have thus far been impossible to simulate reliably. Yet, three recent developments convinced us to accept this challenge: first, the custom-built Janus II supercomputer makes it possible to carry out ``numerical experiments'' in which the very same quantities that can be measured in single crystals of CuMn are computed from the simulation, allowing for parallel analysis of the simulation/experiment data. Second, Janus II simulations have taught us how numerical and experimental length scales should be compared. Third, we have recently understood how temperature chaos materializes in aging dynamics. All three aspects have proved crucial for reliably reproducing rejuvenation and memory effects on the computer. Our analysis shows that (at least) three different length scales play a key role in aging dynamics, while essentially all theoretical analyses of the aging dynamics emphasize the presence and the crucial role of a single glassy correlation length. |
Thursday, March 9, 2023 4:12PM - 4:48PM |
W24.00003: What rejuvenation and memory tell us about non-equilibrium spin glass dynamics Invited Speaker: Jennifer Freedberg The spin glass problem is interesting because of its unique dynamical properties [1], the most famous of these being aging, rejuvenation, and memory. Aging is a relaxation of the susceptibility at fixed temperature [2]. Rejuvenation occurs when the sample is cooled after an aging process and returns to a reference cooling curve taken without any aging procedures – seemingly “forgetting” that it aged [2]. In the memory effect, a sample starts from a temperature below the aging temperature and upon warming the sample “remembers” its previous cooling history [2]. In this talk, we discuss our ac susceptibility experiments studying rejuvenation and memory in a single crystal of CuMn with 7.92 at.% Mn (grown by Deborah Schlagel at Ames National Laboratory). To do this, a “double waiting time” experiment is conducted where the sample is first aged at high temperature (T1) for some time (t1). The temperature is then lowered by 4 kelvin (T2) and aged again for a second time (t2). Our results show that the amount of memory retained upon heating back to T1 depends on the aging time at each temperature – the longer t1 is, the more memory is retained, but the longer t2 is, the less memory is retained. While seemingly contradictory, we explain our results using the framework of temperature chaos – or the temperature change required to make the energy landscape unrecognizable [3]. At each waiting temperature, correlated regions develop, but due to temperature chaos, they are independent. Thus, waiting longer at T1 will improve memory, but waiting longer at T2 will reduce it. |
Thursday, March 9, 2023 4:48PM - 5:24PM |
W24.00004: The Eminuscent Phase in Geometrically Frustrated Magnets - a challenge to quantum spin liquids Invited Speaker: Arthur P Ramirez Some geometrically frustrated magnets are claimed to host a quantum spin liquid (QSL) state. The QSL is a theoretically-proposed many-body state that is fully quantum coherent and, if achievable, may offer a new route to quantum computation. We show that the response of such materials to small amounts of disorder cannot be explained in terms of the canonical source-field construct and suggests a temperature-dependent permeability with a hidden energy scale where short-range order among spins is established. This particular type of short range order mediates long range interactions and is called the eminuscent phase, best described within the Coulomb representation. The instability of the eminuscent phase to spin glass formation in 3D and random singlets in 2D, in addition to the short range order itself, pose serious challenges to the viability of the QSL state. We will also discuss ways to study this unique phase of magnetism. |
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