The standard model of glasses is an ensemble of two-level systems interacting with a thermal bath. The general origin of memory effects in this model is a quasi-stationary but non-equilibrium state of a single two-level system, which is realized due to a finite-rate cooling and very slow thermally activated relaxation. We show that single particle memory effects, such as negativity of the specific heat under reheating, vanish for a sufficiently disordered ensemble. In contrast, a disordered ensemble displays a collective memory effect [similar to that described by Kovacs for glassy polymers], where non-equilibrium features of the ensemble are monitored via a macroscopic observable. An experimental realization of the effect can be used to further assess the consistency of the model.
当自旋玻璃冷却时，冷却过程的记忆被印刻在自旋结构中。这种记忆可以在交流磁化率的连续加热测量中公开。例如，在一个示例中，如果连续冷却过程在一个或两个中间温度下在一定的老化时间内间歇性停止，则当样品被连续再加热时，先前停止的痕迹会恢复[1]。然而，将样品加热到高于老化温度，但保持其低于Tg，会消除较低温度下的热历史记忆。我们还表明，在较高温度下烙印的记忆可以通过在较低温度下等待足够长的时间来擦除。预测从两个互补的自旋玻璃的描述，分层相空间模型和一个真正的空间液滴图片与这些记忆现象和干扰效应的争议。[1]K. Jonason，E. Vincent，J. Hammann，J. P. Bouchaud and P. Nordblad，Phys. Rev. Lett. 31，3243（1998）中所述。
The Mpemba effect occurs when a hot system cools faster than an initially colder one, when both are refrigerated in the same thermal reservoir. Using the custom built supercomputer Janus II, we study the Mpemba effect in spin glasses and show that it is a non-equilibrium process, governed by the coherence length ξof the system. The effect occurs when the bath temperature lies in the glassy phase, but it is not necessary for the thermal protocol to cross the critical temperature. In fact, the Mpemba effect follows from a strong relationship between the internal energy and ξthat turns out to be …
Spin glasses are notoriously difficult to study both analytically and numerically due to the presence of frustration and metastability. Their highly non-convex landscapes require collective updates to explore efficiently. Currently, most state-of-the-art algorithms rely on stochastic spin clusters to perform non-local updates, but such "cluster algorithms" lack general efficiency. Here, we introduce a non-equilibrium approach for simulating spin glasses based on classical dynamics with memory. By simulating various classes of 3d spin glasses (Edwards-Anderson, partially-frustrated, and fully-f…
We show numerically that a three-dimensional model for structural glass displays aging, rejuvenation and memory effects when submitted to a temperature cycle. These effects indicate that the free energy landscape of structural glasses may possess the complex hierarchical structure that characterize materials such as spin and polymer glasses. We use the theoretical concept of marginal stability to interpret our results, and explain in which physical conditions a complex aging dynamics can emerge in dense supercooled liquids, paving the way for future experimental studies of complex aging dynami…
The relative influences of disorder and of frustration on the glassy dynamics in magnetic systems
本文用与自旋玻璃相同的实验方法研究了三种不同几何阻挫磁系统的磁化弛豫。所研究的材料是Y $_2$ Mo $_2$ O $_7$（烧绿石系统）、SrCr $_{8.6}$ Ga $_{3.4}$ O $_{19}$（堆叠的Kagomé层对）和（H $_3$ O）Fe $_3$（SO $_4$）$_2$（OH）$_6$（黄钾铁矾化合物）。尽管有非常少量的无序，所有的样品表现出许多特征的自旋玻璃动力学低于冻结温度$T_g$，远小于他们的居里-外斯温度$θ$。它们的热释磁磁化强度的老化特性可以用与自旋玻璃相同的标度律很好地解释，标度指数的值非常接近。老化过程中的温度变化的影响进行了专门研究。在烧绿石和双-Kagomé化合物中，在某一温度下等待一段时间后温度降低，$T_p$重新老化，并且在新温度下的演变与系统刚刚从$T_g$以上淬火相同。然而，当温度升高回到$T_p$时，样品恢复其先前在该温度下达到的状态。这些特征在自旋眼镜中被称为复原和记忆效应。它们是自旋玻璃动力学的明显特征。在Kagomé化合物中，也有一些恢复和记忆，但需要更大的温度变化才能观察到效果。从这个意义上说，这种化合物的行为与自旋玻璃的行为在数量上是不同的。
We present a novel view of the standard model of tunneling two level systems (TLS) to explain the puzzling universal value of a quantity, $C\sim 3\times 10^{-4}$, that characterizes phonon scattering in glasses below 1 K as reflected in thermal conductivity, ultrasonic attenuation, internal friction, and the change in sound velocity. Physical considerations lead to a broad distribution of phonon-TLS couplings that (1) exponentially renormalize tunneling matrix elements, and (2) reduce the TLS density of states through TLS-TLS interactions. We find good agreement between theory and experiment f…
Recent experimental results showing untypical nonlinear absorption and marked deviations from well known universality in the low temperature acoustic and dielectric losses in amorphous solids prove the need for improving the understanding of the nature of two-level systems (TLSs) in these materials. Here we suggest the study of TLSs focused on their properties which are nonuniversal. Our theoretical analysis shows that the standard tunneling model and the recently suggested Two-TLS model provide markedly different predictions for the experimental outcome of these studies. Our results may be di…
