Electrocaloric effect in cubic Hubbard nanoclusters

Karol Szałowski,Tadeusz Balcerzak

doi:10.1038/s41598-018-23443-x

Abstract

In the paper a computational study of the electrocaloric effect is presented for a cubic nanocluster consisting of 8 sites. The system of interest is described by means of an extended Hubbard model in external electric field at half filling of the energy levels. The thermodynamic description is obtained within canonical ensemble formalism on the basis of exact numerical diagonalization of the system Hamiltonian. In particular, the entropy and the specific heat are determined as a function of temperature and external electric field. The electrocaloric effect is described quantitatively by isothermal entropy change. The behaviour of this quantity is thoroughly analysed as a function of extended Hubbard model parameters, temperature and electric field variation magnitude. The existence of direct and inverse electrocaloric effect is predicted for some range of model parameters. A high sensitivity to Hubbard model parameters is shown, what paves the way towards controlling and tuning the effect. A non-linear, quadratic dependence of isothermal entropy change on electric field variation magnitude is demonstrated. The potential for applications of electrocaloric effect in strongly correlated nanoclusters is shown.

Highlights

The dependence of the entropy in solids on such thermodynamic parameters as external fields or pressure gives rise to a variety of caloric effects[1,2,3]
In order to visualise the effect we present a contour plot in Fig. 5, showing the isothermal entropy change in the temperature-coulombic interaction energy plane
In the paper a theoretical study of the electrocaloric effect in a cubic nanocluster embedded in the electric field is presented

Summary

Introduction

The dependence of the entropy in solids on such thermodynamic parameters as external fields or pressure gives rise to a variety of caloric effects[1,2,3]. The less commonly explored phenomenon is the electrocaloric effect (ECE), which consists in the influence of the external electric field on the entropy of solid[6,7]. The situation is slightly different in the case of the magnetocaloric effect, which has been a subject of some theoretical studies for the exactly solvable model spin systems Such examples like zero-dimensional systems, in a form of nanoclusters[53,54,55,56,57], should be mentioned in this context. The aim of our study is theoretical characterization of the electrocaloric effect in a model nanostructure, being a zero-dimensional nanocluster of cubic shape

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Conclusion