Search

We did extensive research for the nanolaminate Mn+1AXn (n = 1, 2, 3, etc.) ceramics on their structural stability, in which the “M”, “A” and “X” dependence of the phase transition pressure is concluded. Mo2GaC presents multi-phase co-existence status at high pressure. The hexagonal P63/mmc to tetragonal P4/mmm transition is the common direct route for the N-containing MAX due probably to the high transition pressure. P63/mmc (No.194, α, β) α → β → P4/mmm transition might be the common route for the C-containing MAX due probably to the low α → β transition pressure. Nb2InN/Nb2GaN and Mo2InN present c-axis abnormal elongation at low pressures.

The environment-induced decoherence of a quantum open system makes it fundamentally import to preserve the initial quantum information of the system in its steady state. Here we study information preservation of two maximally entangled qubits lying inside a photonic-crystal waveguide with semi-infinite cavity-array structure. We generalize our study to arbitrary position and arbitrary frequency detuning of the qubits. We find that for weak qubits-waveguide couplings, the information preservation greatly depends on the position and the frequency detuning of the qubits, while for strong couplings, both of these dependence is significantly weakened. Interestingly, by suitably choosing the position and the frequency of the qubits, high information preservation could be achieved for both weak and strong couplings, irrespective to Markovian or non-Markovian dynamics. Physically, we analytically verify that the ability of information preservation is indeed determined by the existence of the bound states of the entire system, but the probability of information preservation is closely related to the probability of the initial state of the qubits in the bound states. Our results provide an alternative route getting high information preservation without any external controls of the system.

The magnetism of Fe 2 MnAl and Mn 2 FeAl compounds are studied by first principles. Evolutions of magnetic moment of Fe 2 MnAl display distinct variation trends under pressure, showing three different slopes at different pressure intervals, 0~100 GPa, 100~250 GPa, 250-400 GPa, respectively, and the moment collapses finally at 450 GPa. The magnetic moment of Mn 2 FeAl shows an increasing tendency below 40 GPa and decreases subsequently with pressure, and collapses ultimately at about 175 GPa. Such non-continuing decrease of Fe 2 MnAl originates from the unusual charge transfer of Fe and Mn and bond populations rearrangement of Fe-Fe and Mn-Fe, whereas the distinct moment evolution of Mn 2 FeAl is attributed to the complicated distributions of bond populations. The half-metallicity of the compounds can be maintained at low pressure, below about 100 GPa in Fe 2 MnAl and 50 GPa in Mn 2 FeAl. The magnetic moment collapse process didn't induce volume and bond length anomalies in the two compounds, the unique anomaly is the elastic softening behaviour in elastic constant c 44 and shear (G) and Young's (E) moduli of Fe 2 MnAl at 270 GPa, where the second moment collapse occurs.

The electronic structure and thermodynamical properties of Cr 2 TiAlC 2 are studied by first principles under pressure. The obtained results observed that the ferromagnetic order is the most stable ground state and the magnetic moment will collapse at about 50 GPa. As a result, the lattice a axis becomes stiffer above about 420 GPa, ultimately presenting the same axial compressibility trends with those of nonmagnetic compounds Mo 2 TiAlC 2 and hypothetical Cr 2 TiAlC 2 . The elastic constants and phonon dispersion curves demonstrate the structural stability during the disappearance of magnetic moment and occurrence of axial alternative compressibility. The density of states and energy band calculations confirmed the existence of magnetic moment of Cr 2 TiAlC 2 at 0 GPa and disappearance at high pressures above 50 GPa. Evolutions of magnetic moment collapse with pressure are confirmed by a variety of properties. The obtained grüneisen parameter and thermal expansion coefficients show the maximum value among the known MAX phases, to date and to the author's knowledge.