Pressure effect on the charge-density-wave formation in2H−NbSe2and correlation between structural instabilities and superconductivity in unstable solids

Abstract

The hydrostatic pressure dependence of the charge-density-wave onset temperature To in 28-NbSe2 was measured up to 20 kbar. dT~/dP was found to be -{3. 3~0.2) g 10 Kbar '. An examination of existing high-pressure data concerning structural instabilities and superconductivity in both layered and isotropic compounds is made.2H-NbSe, is a trigonal prismatic coordinated layer compound. Qn cooling, it undergoes a structural transition' at the onset temperature T, = 32 K of a incommensurate charge-density-wave (CDW) state' and becomes supereonducting below -7. 2 K. ' 'The superconducting transition temperature To of 2H-NbSe, increases rapidly and nonlinearly with pressure up to -35 kbar, but slowly and linearly beyond -35 kbar. ' This pressure-enhanced superconductivity has been ascribed to the possible suppression of the structural transition by pressure' or to the band broadening due to pressure-promoted interlayer coupling' {it seems possible that the two are related). Our direct pressure mea.surements on T, show that T, decreases with pressure. However, recent results on 2H-TaSe, show that pressure increases T»' and also T,. '

Charge density wave and superconductivity in 2H- and 4H-NbSe2: A revisit

“…In 4H-NbSe 2 , the superconducting and CDW transitions are noticed at 6.5 and 42 K respectively. The correlation of these two transitions observed in our two single crystals is consistent with the pressure effect on 2H-NbSe 2 [10]. Room temperature resistivity of 4H-NbSe 2 is found to be 11.4 × 10 −4 -cm.…”

“…Its superconducting parameters such as critical fields (H c1 and H c2 ), coherence length (ξ ) and penetration depth (λ) are also reported in clean single crystals [9]. The existence of two transitions (CDW and superconducting) in 2H-NbSe 2 is explained in terms of the density of states (DOS) in conduction band by Chu et al [10].…”

High Pressure Effects on Superconductivity

“…The suggestion is also supported by the correlation between the structural instability and superconductivity as revealed by high-pressure experiments in layered charge-density-wave compounds, for example 2H-NbSe 2 [46]. …”

Superconductivity at 5.2 K in ZrTe3polycrystals and the effect of Cu and Ag intercalation

“…2H-NbSe 2 shows the CDW at 32 K and SC at 7 K, whereas Cu intercalation of 1T-TiSe 2 suppresses CDW and introduces SC at low temperature. [2,3] In the recent reports Copper and Nickel intercalated compounds of ZrTe 3 are shown to exhibit bulk superconducting properties at 3.8 K and 3.1 K respectively. [4,5] The parent compound ZrTe 3 shows SC transition below 2 K but the volume of SC fraction is very small (< 5 %).…”