Multilayer transition in a spin-1 Blume Capel model with RKKY interaction and quantum transverse anisotropy

Using mean-field theory, we have studied the effect of quantum transverse anisotropies with RKKY interaction on the multi-layer transition and magnetic properties of the spin-1 Blume-Capel model of a system formed by two magnetic multi-layer materials, of different thicknesses, separated by a non-magnetic spacer of thickness M. It is found that the multilayer magnetic order-disorder transition temperature depends strongly on the value of the transverse anisotropy. The multilayer transition temperature decreases when increasing the transverse anisotropy. Furthermore, there exists a critical quantum transverse anisotropy △xL beyond which the separate transitions occur in the two magnetic layers. The critical transverse anisotropy AxL decreases （increases） on increasing the non-magnetic spacer of thickness M （on increasing the crystal field）, and AxL undergoes oscillations as a function of the Fermi level.

Uniaxial stress effect on quasi-one-dimensional Kondo lattice CeCo_(2)Ga_(8)

Quantum critical phenomena in the quasi-one-dimensional limit remain an open issue.We report the uniaxial stress effect on the quasi-one-dimensional Kondo lattice CeCo_(2)Ga_(8) by electric transport and AC heat capacity measurements.CeCo_(2)Ga_(8) is speculated to sit in close vicinity but on the quantum-disordered side of a quantum critical point.Upon compressing the c axis,parallel to the Ce-Ce chain,the onset of coherent Kondo effect is enhanced.In contrast,the electronic specific heat diverges more rapidly at low temperature when the intra-chain distance is elongated by compressions along a or b axis.These results suggest that a tensile intra-chain strain(ε_(c)>0)pushes CeCo_(2)Ga_(8) closer to the quantum critical point,while a compressive intra-chain strain(ε_(c)<0)likely causes departure.Our work provides a rare paradigm of manipulation near a quantum critical point in a quasi-1D Kondo lattice by uniaxial stress,and paves the way for further investigations on the unique feature of quantum criticality in the quasi-1D limit.

Kondo Effect Versus Magnetic Coupling in Indirectly Coupled Double Quantum Dots

We theoretically investigate a device consisting of two quantum dots （QDs） side-coupled to a quantum wire which has many physical ingredients of an artificial heavy fermion system. An extra parameter, the distance L between the two QDs, is introduced and it plays an important role on the competition of the Kondo temperature and magnetic coupling. Three different phases are found： antiferromagnetic phase, Kondo phase with spin S = 1/2, and Kondo phase with S = 1, depending on the distance L, the magnetic properties are qualitatively different for different phases： conductance tends to the unitary value 2e2 /h; for the S ： the distance. coupling, and the Kondo temperature. Quantum transport for the S = 1 Kondo and the antiferromagnetic phases, the 1/2 Kondo phase the conductance is strongly dependent onthe distance.

Competition between axial anomaly and ferromagnetic ordering in Bi_(2-x)Fe_(x)Se_(3-x)S_(x) topological insulator:A study of magnetic and magnetotransport properties

The topological insulators Bi_(2-x)Fe_(x)Se_(3-x)S_(x) have been investigated by the dc-magnetization,magnetotransport and angle resolved photoemission spectroscopy(ARPES)techniques.With doping of Fe and S,a negative giant magneto-resistance(MR)is observed for parallel electric and magnetic fields(H||E).The MR behavior at lower magnetic field can be explained with the semi-classical theory whereas the MR behavior at higher field has been attributed to the axial anomaly.Interestingly,the system reached to the quantum limit at low magnetic field(~4.5T).The magnetic ordering can be explained with the presence of both the RKKY(surface)and van-Vleck(bulk)interaction.The ARPES study reveals that a surface gap is suppressed when the magnetic ordering changes from ferromagnetic to anti-ferromagnetic ordering.The ARPES study and the appearance of quantum oscillations(SdH)in the resistivity pattern reveal that the topological surface property is preserved with the co-doping of Fe and S.