The effect of a charge-density wave transition on the transport properties of 2H-NbSe₂

Abstract

Single crystals of two-dimensional 2H-NbSe2, which undergoes a superconducting transition at Tc = 7.2 K and a charge-density wave (CDW) transition at TCDW = 30 K, were synthesized. Measurements of the resistivity, Hall coefficient and magnetoresistance (MR) versus temperature were performed on NbSe2 crystals with different resistance residual ratios (RRR = R(300 K)/R(8 K)), chosen from different batches. The superconducting transition temperature hardly changes with the RRR, while the MR and Hall coefficient are strongly dependent on the RRR values of the samples. Moreover, the temperature and field dependence of the MR violate Kohler’s rule, indicating that the scattering times of the charge carriers are no longer isotropic. A steep decrease of the Hall coefficient RH below 50 K is only observed for the high quality sample; this can be interpreted in terms of a drastic increase of the mean free path for the electron-type charge carriers. The effect of the CDW transition on the Hall coefficient is discussed using a two-band model and a sharp change in the scattering rate on an electron-like orbit below TCDW is suggested.

Closer look at the low-frequency dynamics of vortex matter using scanning susceptibility microscopy

“…The sample under investigation is a 2H-NbSe 2 single crystal of approximate dimensions 2.5 × 2.5 × 0.5 mm 3 , grown by a standard iodine vapor transport method [29], which has a critical temperature of T c = 7.05 K at zero magnetic field.…”

Kondo-like behavior in ThAsSe and UAsSe

“…derived at room temperature does not contradict the observed plasma energy of 7.15 eV [1] as has been insinuated [3]; it only means that the effective mass is reduced compared to the free electron mass. In a twodimensional two-band model the Hall resistance R H is proportional to l + 2 Àl À 2 and inversely proportional to (k F + l + ) 2 +(k F À l À ) 2 , where l 7 and k F 7 are the mean free paths and Fermi vectors, respectively, for positively and negatively charged carriers [6]. The negative value of R H between 300 and 100 K [1] indicates the dominance of l À 2 .…”

“…The increase of the absolute value of R H going from 300 to 100 K may reflect an increase of l À 2 compared to l + 2 or a reduction of the Fermi surface. The former scenario applies for the charge-density wave transition in 2H-NbSe 2 [6], the second can be anticipated in general when the Brillouin zone is reduced due to the formation of superstructures.…”

Multi-band Superconductivity in a misfit layered compound (SnSe)1.16(NbSe2)2

“…Figure 4(b) displays corresponding carrier concentration of the two samples. Comparing with 2Ha-NbSe 2 [33], the electron-type charge transfer from the SnSe layers to the NbSe 2 layers decreases the holetype carrier concentration in the two MLCs. Comparing to n1, the charge transfer in n2 is reduced, hence the carrier concentration is enhanced.…”

“…Figure 4(a) shows the temperature dependence of Hall coefficient of (SnSe) 1.16 (NbSe 2 ) (n1), (SnSe) 1.16 (NbSe 2 ) 2 (n2) . In 2Ha-NbSe 2 , the positive Hall coefficient is reduced and finally changes to be negative below 50K due to the CDW transition [33]. This phenomenon is disappeared in n1 and n2 because of the absence of CDW transition.…”