W.X. Gao

Relaxation behaviors in cluster-glass phase of itinerant magnetic FexTiS2 crystals studied by magnetotransport measurements using pulsed magnetic fields

Abstract Time decays of Hall resistivities ϱ H using pulsed magnetic fields up to 20 T for a cluster-glass phase of Fe x TiS 2 ( x = 1 4 , T g = 53 K) have been measured over the temperature ranges 4.2–45 K and time ranges 10 -1 –10 3 s. The temperature and peak field dependences of ϱ H are analyzed to obtain a universal relationship, mT α = C φ β , for the parameters characterizing the dynamical properties, where m is an exponent for the power law ϱ H ( t ) = At -m after a field is switched off, α = - 1 2 , and φ a newly introduced quantity, φ = [ M ( H p ) - M r (0)]/ M ( H p ) [ M ( H p ) is the magnetization at the peak field H p and M r (0) the remanent magnetization at time t = 0]. The exponent β has different values 0.60 and 2.9 for φ c and φ > φ c , respectively; φ c = 0.34, which corresponds to a three-dimensional ‘critical volume fraction’ in a site-percolation picture.

Oscillatory behavior of photogenerated carrier diffusion in γ-Mo4O11 under magnetic field

The pulsed-laser induced “transient thermoelectric effect (TTE)” under electric and magnetic fields has been measured for the CDW material γ-Mo4O11. The photo-induced TTE voltages decay with the characteristic relaxation times τi (i=2 and 3) for thermal diffusion of two types of holes. In the CDW state [T<Tc(=100 K)], the relaxation times τi oscillate periodically with the magnetic field, and the corresponding relaxation amplitudes aichange stepwise at the minima in the τi-Bcurves. These oscillation periods ΔBi(=0.56–0.68 T) are independent of the electric field E, and these increase appreciably with temperature above 40 K, while the initial phase differences θiincrease linearly with E.Possible mechanisms for such anomalous oscillations of the relaxation times are discussed from classical and conventional quantum mechanical viewpoints; however, its origin is uncertain at the moment.

Nonlinear response to pulsed electric field in η-Mo4O11 crystal under magnetic field

Abstract Pulsed electric field response for a charge-density-wave (CDW) material η-Mo 4 O 11 crystal along the b -axis (nesting direction) has been measured at 4.2 Kin magnetic field up to 3 T, Above a threshold electric field E T , we have observed a nonlinear response to the pulsed electric field, which is due to a deformation of CDW condensates, followed by a sliding motion. The former decay curve can be expressed by a simple exponential form a relaxation time τ D , while the latter obeys an extended exponential form with τ S . These characteristic relaxation times are dependent on both electric and magnetic field intensities, for which qualitative discussion is given.

Possibility of chiral-surface-state originated bulk quantum hall effect in η-mo4o11 crystal

Abstract Magnetotransport properties have been measured for quasi-two-dimensional oxide η-Mo 4 O 11 at low temperatures 0.3–4.2 K in magnetic fields up to 10 T using both bulk contacts and edge contacts methods. In the former case, normal Shubnikov-de Haas oscillations are observed. In the latter case, the Hall resistivity ρ H and transverse magnetoresistance along the c -axis exhibits clear plateaus and minima, respectively, while the longitudinal magnetoresistance along the a * -axis shows a profound peak around 9 T. At the plateaus ρ H is quantized as, ρ H ( v )/ρ H ( v =2) = 2/ v ( v : filling facter), which suggests that a 2D chiral-surface-state appears near the bulky crystal edge.

Anomalous oscillations in magnetic field of photogenerated carriers of quasi-two-dimensional γ-Mo4O11 crystal

Pulsed-laser induced “transient thermoelectric effect (TTE)” under electric and magnetic fields has been measured for the charge-density-wave (CDW) material γ-Mo4O11. The photoinduced TTE voltages decay with the characteristic relaxation times τi (i=2 and 3) for thermal diffusions of two types of holes. In the CDW state [T<Tc (=100 K)], τi is found to oscillate periodically with the magnetic field, whose periods ΔBi (=0.56–0.68 T) are independent of the electric fieldE. Such oscillatory behaviors may be due to any CDW-related quantum phenomenon of normal carriers; its origin is uncertain at the moment.

Nonlinear response to pulsed electric field of charge-density-waves in η-Mo4O11 under magnatic field

A resistive voltage response to a rectangular pulsed electric field has been measured for the charge-density-wave (CDW) material of η-Mo4O11 (Tc1=105 K andTc2=35 K) with and without a magnetic field. BelowTc2, a linear response due to normal carriers is observed when the applied fieldE is less than a threshold fieldET, while a nonlinear response appears forE>ET. The nonlinear response is due to two delayed processes; a deformation process of highly polarizable pinned CDW condensates that are screened by surrounding normal carriers, and a collective sliding motion of two kinds of CDW condensates formed atTc1 andTc2. The external magnetic field is also found to affect these phonomena.

Charge-density-wave induced multicarrier transport in quasi-two-dimensional η-Mo4O11

Abstract Both static and dynamic transport measurements for a quasi-two-dimensional η-Mo4O11, which undergoes metal-semiconductor transitions at Tc1=105K and Tc2=35K induced by “charge density wave (CDW)” instabilities, have been made over a wide temperature range 4.2–300 K. Based on our experimental results and existing tight-binding (block-band) model, we shall discuss the CDW induced multiband structure consisting of different kinds of electron and hole pockets that have remained after partial nesting of their Fermi surfaces.