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We have investigated the magnetocaloric effect in single and polycrystalline samples of quantum paraelectric EuTiO 3 by magnetization and heat capacity measurements. Single crystalline EuTiO 3 shows antiferromagnetic ordering due to Eu 2+ magnetic moments below T N = 5.6 K. This compound shows a giant magnetocaloric effect around its Néel temperature. The isothermal magnetic entropy change is 49 J kg −1 K −1 , the adiabatic temperature change is 21 K, and the refrigeration capacity is 500 J kg −1 for a field change of 7 T at T N . The single crystal and polycrystalline samples show similar values of the magnetic entropy and adiabatic temperature changes. The large magnetocaloric effect is due to suppression of the spin entropy associated with the localized 4f moment of Eu 2+ ions. The giant magnetocaloric effect, together with negligible hysteresis, suggest that EuTiO 3 could be a potential material for magnetic refrigeration below 40 K.

Graphene-enhanced polymer matrix nanocomposites are attracting ever increasing attention in the electromagnetic (EM) interference (EMI) shielding field because of their improved electrical property. Normally, the graphene is introduced into the matrix by chemical functionalization strategy. Unfortunately, the electrical conductivity of the nanocomposite is weak because the graphene nanosheets are not interconnected. As a result, the electromagnetic interference shielding effectiveness of the nanocomposite is not as excellent as expected. Interconnected graphene network shows very good electrical conduction property, thus demonstrates excellent electromagnetic interference shielding effectiveness. However, its brittleness greatly limits its real application. Here, we propose to directly infiltrate flexible poly(dimethylsiloxane) (PDMS) into interconnected reduced graphene network and form nanocomposite. The nanocomposite is superflexible, light weight, enhanced mechanical and improved electrical conductive. The nanocomposite is so superflexible that it could be tied as spring-like sucker. Only 1.07 wt % graphene significantly increases the tensile strengths by 64% as compared to neat PDMS. When the graphene weight percent is 3.07 wt %, the nanocomposite has the more excellent electrical conductivity up to 103 S/m, thus more outstanding EMI shielding effectiveness of around 54 dB in the X-band are achieved, which means that 99.999% EM has been shielded by this nanocomposite. Bluetooth communication testing with and without our nanocomposite confirms that our flexible nanocomposite has very excellent shielding effect. This flexible nanocomposite is very promising in the application of wearable devices, as electromagnetic interference shielding shelter.

We report the magnetic entropy change (S m ) in magnetoelectric Eu 1-x Ba x TiO 3 for 0.1 ≤ x ≤ 0.9. We find -S m = 11 (40) J/kg·K in x = 0.1 for a field change of 1 (5) Tesla respectively, which is the largest value among all Eu-based oxides. S m arises from the field-induced suppression of the spin entropy of Eu 2+ :4f 7 localized moments. While -S m decreases with increasing x, -S m  = 6.58 J/kg·K observed in the high spin diluted composition x = 0.9 is larger than that in many manganites. Our results indicate that these magnetoelectrics are potential candidates for cryogenic magnetic refrigeration.

Our new strategy is very promising in terms of controlling the thickness, density, and size of graphene paper.

We investigate electronic band structure and transport properties in bilayer graphene superlattices of Thue-Morse sequence. It is interesting to find that the zero-k gap center is sensitive to interlayer coupling t ′ , and the centers of all gaps shift versus t ′ at a linear way. Extra Dirac points may emerge at ky =0, and when the extra Dirac points are generated in pairs, the electronic conductance obeys a diffusive law, and the Fano factor tends to be 1/3 as the order of Thue-Morse sequence increases. Our results provide a flexible and effective way to control the transport properties in graphene.

Quantum open systems play an important role in the development of quantum sciences, therefore the study of corresponding numerical method is of great significance. For calculation of quantum open systems, the quasi-adiabatic propagator path integral, which was invented in 1990s, is one of the few numerically exact methods. However, its computational complexity scales exponentially with system size and correlation length, and due to this disadvantage its application is limited in practical calculation. In recent years, the study and application of tensor network has made rapid progress. Representing the path integral by tensor network makes scaling of the computational complexity polynomially, which greatly improve the computational efficiency. Such a new method is called time-evolving matrix product operators. At the very beginning, the reduced density matrix is represented as a matrix product state. Then the time evolution of the system can be achieved by iteratively applying matrix product operators on the matrix product state. The iterative process is amenable to the standard matrix product states compression algorithm, which keeps the computational cost at polynomial scales. The time-evolving matrix product operators is an efficient, numerically exact and fully non-Markovian method, which has a broad application prospect in the study of quantum open systems. For instance, it is already used in the study of the thermalization, heat statistic, heat transfer and optimal control of the quantum open systems, and conversely it can be also used to investigate the effect of the system on the environment. In addition, the TEMPO method is naturally connected to the process tensor which can be used to calculate the correlation function of the system efficiently. This article gives a review of this method and its applications.

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