Aging, memory, and nonhierarchical energy landscape of spin jam

Samarakoon, Anjana; Sato, Taku; Chen, Tianran; Chern, Gai Wei; Yang, Junjie; Klich, Israel; Sinclair, R.; Zhou, H. D.; Lee, Seung Hun

doi:10.1073/pnas.1608057113

Cited by 42 publications

(41 citation statements)

References 40 publications

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“…Its landscape topography is that of a funnel, akin to the free energy landscape of proteins and the loss function of well-trained deep neural networks. (Credit: Reproduced from [94]. )…”

Section: Search Optimization and Funnel Topographymentioning

confidence: 99%

Search optimization, funnel topography, and dynamical criticality on the string landscape

Khoury

Parrikar

2019

J. Cosmol. Astropart. Phys.

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A striking feature of our universe is its near criticality. The cosmological constant and weak hierarchy problems, as well as the metastability of the electroweak vacuum, can all be understood as problems of criticality. This suggests a statistical physics approach, based on the landscape of string theory. In this paper we present a dynamical selection mechanism for hospitable vacua based on search optimization. Instead of focusing on late-time, stationary probability distributions for the different vacua, we are interested in the approach to equilibrium. This is particularly relevant if cosmological evolution on the multiverse has occurred for a finite time much shorter than the exponentially-long mixing time for the landscape. We argue this imposes a strong selection pressure among hospitable vacua, favoring those that lie in regions where the search algorithm is efficient. Specifically, we show that the mean first passage time is minimized for hospitable vacua lying at the bottom of funnel-like regions, akin to the smooth folding funnels of naturallyoccurring proteins and the convex loss functions of well-trained deep neural networks. The optimality criterion is time-reparametrization invariant and defined by two competing requirements: search efficiency, which requires minimizing the mean first passage time, and sweeping exploration, which requires that random walks are recurrent. Optimal landscape regions reach a compromise by lying at the critical boundary between recurrence and transience, thereby achieving dynamical criticality. Remarkably, this implies that the optimal lifetime of vacua coincides with the de Sitter Page time, τ crit ∼ M 2 Pl /H 3 . Our mechanism makes concrete phenomenological predictions: 1. The expected lifetime of our universe is 10 130 years, which is ∼ > 2σ from the Standard Model metastability estimate; 2. The supersymmetry breaking scale should be high, ∼ > 10 10 GeV. The present framework suggests a correspondence between the near-criticality of our universe and nonequilibrium critical phenomena on the landscape.

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“…Its landscape topography is that of a funnel, akin to the free energy landscape of proteins and the loss function of well-trained deep neural networks. (Credit: Reproduced from [94]. )…”

Section: Search Optimization and Funnel Topographymentioning

confidence: 99%

Search optimization, funnel topography, and dynamical criticality on the string landscape

Khoury

Parrikar

2019

J. Cosmol. Astropart. Phys.

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“…The TRM measurement is the most effective way to probe the memory effects in detail as explained in Supplementary Information and as shown most recently in the comparative study 35 of SCGO/BCGO and the canonical spin glass CuMn2%. While a dip-like memory effect with clear rejuvenation was observed, as expected, in CuMn2%, a shoulder-like memory effect seen in SCGO/BCGO implies lack of rejuvenation.…”

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confidence: 99%

Scaling of Memories and Crossover in Glassy Magnets

Samarakoon

Takahashi

Zhang

et al. 2017

Sci Rep

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Glassiness is ubiquitous and diverse in characteristics in nature. Understanding their differences and classification remains a major scientific challenge. Here, we show that scaling of magnetic memories with time can be used to classify magnetic glassy materials into two distinct classes. The systems studied are high temperature superconductor-related materials, spin-orbit Mott insulators, frustrated magnets, and dilute magnetic alloys. Our bulk magnetization measurements reveal that most densely populated magnets exhibit similar memory behavior characterized by a relaxation exponent of . This exponent is different from of dilute magnetic alloys that was ascribed to their hierarchical and fractal energy landscape, and is also different from of the conventional Debye relaxation expected for a spin solid, a state with long range order. Furthermore, our systematic study on dilute magnetic alloys with varying magnetic concentration exhibits crossovers among the two glassy states and spin solid.

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“…hrs [124] . , ranging from zero to 100hrs, at / ~ 0.7 where and are the waiting and the freezing temperature, respectively.…”

Section: Universal Memory Behaviormentioning

confidence: 99%

“…The aging effects of a spin jam prototype, SrCr9pGa12-9pO19 (SCGO(p=0.97)), and a spin glass prototype CuMn2% were taken from Ref. [124] , except the = 1.5 (5) data are new and are also plotted here for comparison. Each set of ∆ ( ) for each sample shown in panels It is interesting that the densely populated Y2Mo2O7 exhibits both spin glass and spin jam behaviors.…”

Section: Universal Memory Behaviormentioning

confidence: 99%

“…Authors: Tianran Chen, Gia-Wei Chern and Seung-Hun Lee [186] Understanding the dynamics of a glassy system via the energy landscape approach has led to promising insights into puzzling phenomena, such as temperature-dependent aging and memory effect. In this framework, the energy landscape is seen as a set of basins of attraction, and the system evolves through a succession of jumps between their local minima [187,188].…”

Section: Barrier Tree Models and Monte Carlo Simulationsmentioning

confidence: 99%

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Jamming in Spin Systems

Samarakoon¹

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Dedicated to my family and all my teachers.i "The true sign of intelligence is not knowledge but imagination." Albert Einsteinii Abstract Since the discovery of spin glasses in dilute magnetic systems, their study has been largely focused on understanding randomness and defects as the driving mechanism. The same paradigm has also been applied to explain glassy states found in dense frustrated systems. Recently, however, it has been theoretically suggested that different mechanisms, such as quantum fluctuations and topological features, may induce glassy states in defect-free spin systems, far from the conventional dilute limit. Here we report experimental evidence for the existence of a glassy state, that we call a spin jam, in the vicinity of the clean limit of a frustrated magnet, which shows unconventional spin glass properties, such as the quadratic low-temperature dependence of heatcapacity, a broad elastic neutron scattering peak centred around a non-zero wavevector ( ), and insensitivity to low-concentration of defects. We have mainly studied two isostructural frustrated magnets, SrCr9pGa12-9pO19 (SCGO(p)) and BaCr9pGa12-9pO19 (BCGO(p)), in which the magnetic Cr 3+ (s=3/2) ions form a quasi-two-dimensional (Q2D) triangular system of bi-pyramids, in comparison to several other magnetic glasses ranging from dilute magnetic alloys to threedimensional frustrated magnets.We performed both bulk susceptibility and neutron scattering experiments on both SCGO(p) and BCGO(p) systems as a function of dilution p in the range of 0.4 ≲ p ≲0.97. Our bulk susceptibility data exhibit glassy behavior at much lower temperatures ( ) than the absolute values of the Curie-Weiss temperature, | | ≈ -504(2) K for SCGO(p = 0.968(6)) and -695(1) K for BCGO(p = 0.902(8)). The frustration index = | |/ is as high as 130 for SCGO(p = 0.968(6)) and 190for BCGO(p = 0.902(8)) indicating strong frustration. Low-temperature susceptibility measurements of SCGO(p)/BCGO(p) reveals glass-like signatures such as zero-field cooled (ZFC) -field cooled (FC) hysteresis and frequency dependent AC susceptibility but the low-temperature magnetic phases found in the dense limit of magnetic ions show distinct properties from conventional spin glasses.Our inelastic neutron scattering data on SCGO(p = 0.968(6)) and BCGO(p = 0.902(8)) shows dispersionless magnetic excitations centered at ℏω = 18.6(1) meV and 16.5(1) meV respectively, due to singlet to triplet excitations of spin s = 3/2 dimers. The spin dimers are formed by Cr 3+ ions in two 4fvi layers that lie between 12k-2a-12k (kagome-triangle-kagome) trilayers. Moreover, a iii continuum spectrum centered around ≈ 1.5 Å , observed in time-of-flight (TOF) neutron scattering experiments for SCGO(p)/BCGO(p) magnets, confirm that the kagome−triangular−kagome trilayer is responsible for low-energy spin dynamics. The imaginary part of dynamical susceptibility ( ( )) for SCGO(p = 0.968(6)) or BCGO(p = 0.902 (8)) shows linear dependence at low-energies which is inconsistent with energy independent behavior of di...

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Aging, memory, and nonhierarchical energy landscape of spin jam

Cited by 42 publications

References 40 publications

Search optimization, funnel topography, and dynamical criticality on the string landscape

Search optimization, funnel topography, and dynamical criticality on the string landscape

Scaling of Memories and Crossover in Glassy Magnets

Jamming in Spin Systems

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