The influence of intermolecular interactions involving molecular chiral centers on two-dimensional organization in the limit of a weak adsorbate-surface interaction has been studied with low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT). A model system composed of a chiral organic molecule, tartaric acid, and an inert metallic surface, Ag(111), was employed. Dual component films formed from the serial deposition of (S,S)-and (R,R)-tartaric acid enantiomers onto this surface exhibit homochiral domain formation as revealed by molecularly resolved STM images. In contrast, a unique tartaric acid enantiomeric heteropair is experimentally and computationally verified as the basis unit of films formed via the deposition of both enantiomers simultaneously from a racemic (1:1) mixture. The molecular adsorption geometry relative to the Ag(111) lattice in both enantiomerically pure and racemic domains is determined primarily by the interaction of chiral centers between nearest neighbors.

Here we present a model for a small system combined with an explicit entropy bath that is comparably small. The dynamics of the model is defined by a simple matrix, M. Each row of M corresponds to a macrostate of the system, e.g. net alignment, while the elements in the row represent microstates. The constant number of elements in each row ensures constant entropy, which allows reversible fluctuations, similar to information theory where a constant number of bits allows reversible computations. Many elements in M come from the microstates of the system, but many others come from the bath. Bypassing the bath states yields fluctuations that exhibit standard white noise; whereas with bath states the power spectral density varies as S(f) ∝ 1/f over a wide range of frequencies, f. Thus, the explicit entropy bath is the mechanism of 1/f noise in this model. Both forms of the model match Crooks' fluctuation theorem exactly, indicating that the theorem applies not only to infinite reservoirs, but also to finite-sized baths.The model is used to analyze measurements of 1/f-like noise from a sub-micron tunnel junction.

Disordered systems show deviations from the standard Debye theory of specific heat at low temperatures. These deviations are often attributed to two-level systems of uncertain origin. We find that a source of excess specific heat comes from correlations between quanta of energy if phonon-like excitations are localized on an intermediate length scale. We use simulations of a simplified Creutz model for a system of Ising-like spins coupled to a thermal bath of Einstein-like oscillators. One feature of this model is that energy is quantized in both the system and its bath, ensuring conservation of energy at every step. Another feature is that the exact entropies of both the system and its bath are known at every step, so that their temperatures can be determined independently. We find that there is a mismatch in canonical temperature between the system and its bath. In addition to the usual finite-size effects in the Bose-Einstein Experimental evidence for this model comes from its ability to characterize the excess specific heat of imperfect crystals at low temperatures.

The primary low-frequency noise in superconducting quantum interference devices (SQUIDs) at low temperature is flux noise with a power spectral density of the form with . Experiments show this noise is due to independent clusters of interacting spins at the metal-insulator interface of the Josephson junction. The temperature dependences of the amplitude and the spectral exponent α are such that the noise spectra of devices taken at different temperatures cross each other at a common crossing frequency fc, so that S(fc) is constant over a wide range of temperatures. Presented here are Monte Carlo simulations of a Heisenberg spin model modified with a type of dynamic constraint that depends on the configurational entropy of clusters of spins. The constraint arises from assuming that coupling between clusters of spins and the thermal reservoir is mediated by a local bath. Noise in the alignment of this model shows similarities to the temperature-dependent flux noise of SQUIDs, reproducing the relationship between α and the amplitude that leads to the existence of a crossing frequency fc of spectra at different temperatures.