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Abstract: We have studied the ground state and thermodynamic properties of the anisotropic 3-state Potts model on square lattice by means of the tensor network-based numerical method. The phase diagrams of this model in the ground state and at finite temperature are identified. The singular behavior at the critical endpoint along the phase boundary is carefully investigated. It is discovered that the sharp peaks appear in the second-order derivative of the field as well as the first-order derivative of the magnetization with respect to temperature on the phase boundary. Our numerical results confirm the prediction of Fisher et al. about the critical endpoint. [Copyright &y& Elsevier]

The electronic structures of haloform intercalated molecular solids C60·2CHX3 (X=Cl,Br) at low temperature are investigated by a first-principle calculation. It is found that the density of states of these solids at the Fermi level are quite low, and a phenomenon of hole doping induced insulator–metal transition in these systems is observed at low temperature. [Copyright &y& Elsevier]

We have investigated the current-induced spin transfer torque of a ferromagnet–insulator–ferromagnet tunnel junction by taking the spin-flip scatterings into account. It is found that the spin-flip scattering can induce an additional spin torque, enhancing the maximum of the spin torque and giving rise to an angular shift compared to the case when the spin-flip scatterings are neglected. The effects of the molecular fields of the left and right ferromagnets on the spin torque are also studied. It is found that τRx/Ie (τRx is the spin-transfer torque acting on the right ferromagnet and Ie is the tunneling electrical current) does vary with the molecular fields. At two certain angles, τRx/Ie is independent of the molecular field of the right ferromagnet, resulting in two crossing points in the curve of τRx/Ie versus the relevant orientation for different molecular fields. [Copyright &y& Elsevier]

By means of the nonequilibrium Green function technique, the effect of spin-flip scatterings on the spin-dependent electrical transport in ferromagnet–insulator–ferromagnet (FM–I–FM) tunnel junctions is investigated. It is shown that Jullie`re's formula for the tunnel conductance must be modified when including the contribution from the spin-flip scatterings. It is found that the spin-flip scatterings could lead to an angular shift of the tunnel conductance, giving rise to the junction resistance not being the largest when the orientations of magnetizations in the two FM electrodes are antiparallel, which may offer an alternative explanation for such a phenomenon observed previously in experiments in some FM–I–FM junctions. The spin-flip assisted tunneling is also observed. [Copyright &y& Elsevier]

Abstract: By comparing the recently obtained superconducting energy gaps from the scanning tunneling microscopy (STM) and the angle-resolved photoemission spectroscopy (ARPES) for underdoped superconductor Bi2Sr2CaCu2O8+ δ , significant distinctions were observed. By properly taking the effect of quasiparticle spectral weight in the STM spectra into account, good consistency between both energy gaps obtained by STM and ARPES is unveiled. [Copyright &y& Elsevier]

Abstract Spin caloritronics brings us new spin-thermal related effects, such as spin Seebeck effect, spin Nernst effect and their inverse effects. It is time to revisit the thermoelectric effects in ferromagnets by considering them. In this paper, a generalized Fourier law is derived and an anomalous Righi–Leduc effect is proposed for a ferromagnet when a temperature gradient is applied. A full description including particle current, spin current and heat current is necessarily taken into account and gives rise to novel contributions to the Righi–Leduc coefficient. This may shed more light on the spin caloritronics in ferromagnets. Highlights • A generalized Fourier law is derived. • The particle, spin and heat currents are taken into account fully. • Anomalous Righi–Leduc effect is studied for ferromagnets. • Spin caloritronic effects induce extra new terms to the Righi–Leduc coefficient. [ABSTRACT FROM AUTHOR]

Abstract: By means of the density matrix renormalization group (DMRG) method, the static spin structure factors and the magnetization plateaus of the trimerized Heisenberg ferromagnet–ferromagnet–antiferromagnet and antiferromagnet–antiferromagnet–ferromagnet spin chains in the presence of a magnetic field are elaborately studied. It is found that in the plateau states, the static structure factor with three peaks does not vary with the external magnetic field as well as the exchange couplings; the spin correlation function behaves as a perfect sequence and has a simple relation with the magnetization per site. An approximate wave function for the plateau states is proposed, and a picture based on the valence-bond-solid states is presented in order to understand the origin and the total number of the magnetization plateaus, which are shown to be in agreement with the DMRG results. [Copyright &y& Elsevier]

The current-induced magnetic switching of a single-molecule magnet (SMM) attached on the central region of a spin valve is explored, and the condition for the switching current is derived. Electrons flowing through the spin valve will interact with the SMM via the s–d exchange interaction, producing the spin accumulation that satisfies the spin diffusion equation. We further describe the spin motion of the SMM by a Heisenberg-like equation. Based on the linear stability analysis, we obtain the critical current from two coupled equations. The results of the critical current versus the external magnetic field indicate that one can manipulate the magnetic state of the SMM by an external magnetic field. [ABSTRACT FROM AUTHOR]

We study the effective manipulation of the Andreev bound states (ABS), zero mode Majorana fermion and Josephson current (JC) in a superconductor–normal–superconductor junction on the surface of a topological insulator in unexplored regime of parameters. It is found that the energy of the ABS changes dramatically with the phase difference between both superconductors (SCs) in a certain range of the incident angle of quasiparticles. It is shown that the velocity of Majorana fermion and the JC can be effectively tuned in a wide range of the chemical potential in the normal region ( μ N ) and the separation width ( L ) of the two SCs. In addition, we expose that the critical JC and its product with the normal resistance are, respectively, a quarter and the same to those in a graphene-based Josephson junction. The dependence of the critical JC on the chemical potential in the superconducting region is not monotonous: it increases (decreases) for small (large) μ N . [ABSTRACT FROM AUTHOR]

Abstract: The stable boron carbon nanotube superlattices (BCNTSLs) that are constructed by periodically connecting carbon nanotube (CNT) and boron nanotube (BNT) with different lengths and diameters are predicted by employing the density functional first-principles calculations. The geometrical and electronic structures as well as quantum conductance of BCNTSLs are studied. It is found that the superlattices can be metallic or semiconducting depending on tube diameters and the ratio of BNT to CNT segments in a periodic unit. The confined states in the superlattice are observed. The present study could offer a useful way for designing some functional nanodevices. [Copyright &y& Elsevier]

Abstract: The decorated Ising chain with pendants of arbitrary spin and the single-ion anisotropy is exactly solved by the transfer matrix method. The solutions reveal abundant novel properties than the conventional one-dimensional Ising model. It is compared with the experimental data of a necklace-like molecule-based magnet, that gives a qualitative consistency. [Copyright &y& Elsevier]

Abstract: The magnetic behaviors of a spin-1/2 alternating Heisenberg antiferromagnetic chain in a staggered transverse magnetic field is studied by means of the density-matrix renormalization group method and Jordan–Wigner transformation. Quantum phase transitions of different types are observed in the Néel and XY-like gapless phases, which result from the competitions between the staggered transverse field and magnetic orders induced by anisotropy and alternating interactions. The results are compared with the mean-field and some exactly resolved results. [Copyright &y& Elsevier]

Abstract: The effect of the spin accumulation on the spin-dependent transport properties in a ferromagnet–quantum dot (QD)–ferromagnet tunnel junction is reexamined in a self-consistent manner by means of Keldysh nonequilibrium Green function method. It has been found that when the spin and charge densities accumulated in the central QD are self-consistently treated, the electrical current and spin current differ from the previous results where the chemical potential shifts induced by the spin imbalance are not included, and the tunnel magnetoresistance is enhanced remarkably. The spin and charge accumulations in the QD are also discussed. [Copyright &y& Elsevier]

Abstract: Current-induced spin transfer torque through a marginal Fermi liquid (MFL) which is connected to two noncollinearly aligned ferromagnets via tunnel junctions is discussed in terms of the nonequilibrium Green function method. It is found that in the absence of the spin–flip scattering, the magnitude of the torque increases with the polarization and the coupling constant λ of the MFL, whose maximum increases with λ linearly, showing that the interactions between electrons tend to enhance the spin torque. When the spin–flip scattering is included, an additional spin torque is induced. It is found that the spin–flip scattering enhances the spin torque and gives rise to a nonlinear angular shift. [Copyright &y& Elsevier]

A recent elegant experimental realization [S. Yuasa et al., Science 297 (2002) 234] of the spin-polarized resonant tunneling in magnetic tunnel junctions is interpreted in terms of a two-band model. It is shown that the tunnel magnetoresistance (TMR) decays oscillatorily with the thickness of the normal metal (NM) layer, being fairly in agreement with the experimental observation. The tunnel conductance is found to decay with slight oscillations with the increase of the NM layer thickness, which is also well consistent with the experiment. In addition, when the magnetizations of both ferromagnet electrodes are not collinearly aligned, TMR is found to exhibit sharp resonant peaks at some particular thickness of the NM layer. The peaked TMR obeys nicely a Gaussian distribution against the relative orientation of the magnetizations. [Copyright &y& Elsevier]