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The density functional theory method is utilized to verify the electronic structures of SiC nanotubes (SiCNTs) and SiC nanoribbons (SiCNRs) one-dimensional (1D) van der Waals homojunctions (vdWh) under an applied axial strain and an external electric field. According to the calculated results, the SiCNTs/SiCNRs 1D vdWhs are direct semiconductors with a type-II band alignment and robust electronic structures with different diameters or widths. Furthermore, the SiCNTs/SiCNRs 1D vdWhs are direct semiconductors with a type-I band alignment, respectively, in a range of [–0.3, –0.1] V/Å and [0.1, 0.3] V/Å and change into metal when the electric field intensity is equal to or higher than 0.4 V/Å. Interestingly, the SiCNTs/SiCNRs 1D vdWhs have robust electronic structures under axial strain. These findings demonstrate theoretically that the SiCNTs/SiCNRs 1D vdWhs can be employed in nanoelectronics devices.

We investigate the quantum phase transition (QPT) and magnetocaloric effect (MCE) of a tetrameric chain with three-spin interaction using Green's function theory. The magnetization and gap analysis reveals a variety of quantum phases tuned by magnetic held and three-spin interaction, which can open up an energy gap, giving rise to the occurrence of zero magnetization plateau. However, strong three-spin couplings causing strong frustration will destroy the intermediate 1/2 plateau with emergence of a new gapless phase between two cusps. It favors achieving an enhanced MCE at the critical fields, where the minima of isoentropes as well as the valley-peak structure of Gruneisen ratio, signaling the accumulation of entropy, lead to cooling via adiabatic (de)magnetization processes. It is also found that the temperature dependence of specific heat combined with Gruneisen ratio can testify various quantum phases explicitly.

The finite-temperature entanglement entropy for an alternating spin-1/2 chain with multi-spin interactions is investigated by means of Green’s function theory combined with Jordan-Wigner transformation, to identify the spin-Peierls (SP) transition. It is found that the two-site thermal entanglement entropy is a useful tool to characterize theSPtransition. In addition, the competition between multi-spin interaction and Peierls-dimerization plays a central role in the critical phenomenon of the system.

The finite-temperature magnetic properties of an antiferromagnetic (AF) bond alternating S=1/2 zigzag spin chain with asymmetrical AF next-nearest-neighbor (NNN) exchange interactions in an external magnetic field are investigated by means of the many-body Greens function theory within random phase approximation. The results show that when the NNN exchange interactions are asymmetrical, the spin system exhibit a clear ferrimagnetic ordering at finite temperatures. It is shown that the ferrimagnetic behavior is attributed to asymmetrical elementary excitations, resulting from the competition between the spin frustrations and magnetic excitations reduced by the asymmetrical NNN interactions. The mechanism of this ferrimagnetism is much different from a common one which originates from mixed spins with different spin values through antiparallel spin alignments.

The zero- and low-temperature behaviors of spin-1/2 two-leg ladder with staggered dimerization are investigated by the Green’s function theory. At zero temperature, the ground state phase diagram is explored, wherein the leg-dimer and rung-singlet phases are revealed, which reflect two different intrinsic gapped behaviors. The former is attributed to the bond alternation along the legs, while the latter is due to the strong rung coupling. It is found that the quantum phase transition from one to another is of the first order, which can be clearly signaled by the rung entanglement entropy. At finite temperatures, the temperature dependence of thermodynamic quantities such as the magnetic susceptibility, specific heat, thermal Drude weight and rung entanglement entropy are calculated to characterize the corresponding quantum phases. It is shown that the magnetic behaviors clearly manifest a typical antiferromagnetism at low temperature, which is in accordance with the experimental results. It is also found that the intrinsic gapped low-lying excitations are responsible for the observed thermodynamic behaviors.

The thermodynamics and quantum phase transitions of two typically alternating double-chain systems are investigated by Green's function theory. (i) For the completely antiferromagnetic (AFM) alternating double-chain, the low-temperature antiferromagnetism with gapped behavior is observed, which is in accordance with the experimental result. In a magnetic field, we unveil the ground state phase diagram with zero plateau, 1/2 plateau, and polarized ferromagnetic (FM) phases, as a result of the intra-cluster spin-singlet competition. Furthermore, the Gruneisen ratio is an excellent tool to identify the quantum criticality and testify various quantum phases. (ii) For the antiferromagnetically coupled FM alternating chains, the 1/2 magnetization plateau and double-peak structure of specific heat appear, which are also observed experimentally. Nevertheless, the M—h curve shows an anomalous behavior in an ultra-low field, which is ascribed to the effectively weak Haldane-like state, demonstrated by the two-site entanglement entropy explicitly.