Comment on "Phase separation in a two-species Bose mixture"

In an article in 2007, Mishra, Pai, and Das [Phys. Rev. A 76, 013604 (2007)] investigated the two-component Bose-Hubbard model using the numerical DMRG procedure. In the regime of inter-species repulsion $U^{ab}$ larger than the intra-species repulsion $U$, they found a transition from a uniform miscible phase to phase-separation occurring at a finite value of $U$ , e.g., at around $U = 1.3$ for $\Delta = U^{ab}/U = 1.05$ and $\rho_{a} = \rho_{b} = 1/2$. In this comment, we show that this result is not correct and in fact the two-component Bose-Hubbard model is unstable to phase-separation for any $U^{ab} > U > 0$.Comment: 2 pages, 3 figures, submitted to Phys. Rev.

Electronic Heat Transport Across a Molecular Wire: Power Spectrum of Heat Fluctuations

With this study we analyze the fluctuations of an electronic only heat current across a molecular wire. The wire is composed of a single energy level which connects to two leads which are held at different temperatures. By use of the Green function method we derive the finite frequency power spectral density (PSD) of the emerging heat current fluctuations. This result assumes a form quite distinct from the power spectral density of the accompanying electric current noise. The complex expression simplifies considerably in the limit of zero frequency, yielding the heat noise intensity. The heat noise intensity still depends on the frequency in the zero-temperature limit, assuming different asymptotic behaviors in the low- and high-frequency regimes. These findings evidence that heat transport across molecular junctions can exhibit a rich structure beyond the common behavior which emerges in the linear response limit

Interpretable Machine learning based coordination motif identification scheme from X-ray absorption near-edge structure spectroscopy XANES

XANES is an important experimental method to probe the local three dimensional geometry and electronic structure of the system. The quantitative analysis of XANES data is very important to obtain the above mentioned structure. Because XANES contains a lot of information and complexity, the quantitative analysis of XANES is also a challenging task.Interpretable Machine learning(IML) approach: Shapley additive explanations(SHAP) based interpretable machine learning(ML) approach is adopted in two types of ML XANES data analysis methods respectively. These two methods are "spectrum to parameters" and "parameters to spectrum" methods.We used the TreeSHAP method to explain the mechanism of our models and of a specific prediction example. The model mechanism is explained from the physical perspective as much as possible, which expands the methodological perspective of machine learning application in XAS data analysis. The "Parameters to spectrum" model in which structural parameters are input and theoretical XANES reconstructed by machine learning algorithm are output. Taking Fe complex system as an example. The analysis results quantitatively and systematically demonstrate the model mechanism, that is, how parameter changes affect the theoretical XANES reconstructed by machine learning. This is of practical value for determining the parameter variation trend using in the next XANES fitting and improving the model. In summary, we show the application of SHAP IML in two kinds of ML models in XANES analysis field, and expand the methodological perspective of XANES quantitative analysis

Shuttling heat across 1D homogenous nonlinear lattices with a Brownian heat motor

We investigate directed thermal heat flux across 1D homogenous nonlinear lattices when no net thermal bias is present on average. A nonlinear lattice of Fermi-Pasta-Ulam-type or Lennard-Jones-type system is connected at both ends to thermal baths which are held at the same temperature on temporal average. We study two different modulations of the heat bath temperatures, namely: (i) a symmetric, harmonic ac-driving of temperature of one heat bath only and (ii) a harmonic mixing drive of temperature acting on both heat baths. While for case (i) an adiabatic result for the net heat transport can be derived in terms of the temperature dependent heat conductivity of the nonlinear lattice a similar such transport approach fails for the harmonic mixing case (ii). Then, for case (ii), not even the sign of the resulting Brownian motion induced heat flux can be predicted a priori. A non-vanishing heat flux (including a non-adiabatic reversal of flux) is detected which is the result of an induced dynamical symmetry breaking mechanism in conjunction with the nonlinearity of the lattice dynamics. Computer simulations demonstrate that the heat flux is robust against an increase of lattice sizes. The observed ratchet effect for such directed heat currents is quite sizable for our studied class of homogenous nonlinear lattice structures, thereby making this setup accessible for experimental implementation and verification.Comment: 9 pages, 10 figures. Phys. Rev. E (in press