Temperature and angular dependences of upper critical fields for the layer structure superconductor 2H-NbSe2

In-plane and transverse superconducting fluctuation diamagnetism in the presence of charge-density waves in2H−NbSe2single crystals

“…For T CDW ≫ T C (a case well adapted for 2H-NbSe 2 ) this functional just differs from the conventional one by a coupling term K cos ( Q · r), where K is a dimensionless constant which amplitude is expected to decrease with T C /T CDW , and Q is the CDW wavevector. For 2H- (6) and (8)]. Nevertheless, these data show that the FD in both directions vanishes at H ≈ H ⊥, C2 , in agreement with the total energy cutoff prediction.…”

“…The moderate uniaxial anisotropy of 2H-NbSe 2 (γ ≈ 3), 8 together with its accessible critical temperature (T C ≈ 7.15 K) and the possibility of growing large and very homogeneous single crystals, makes this material and excellent candidate to study the FD anisotropy. In fact, the interest of 2H-NbSe 2 to study superconducting fluctuations was early recognized by Prober, Beasley and Schwall (PBS).…”

The stress tensor for the mixed phase of uniaxial anisotropic superconductors

“…This can be considered as the lowest term in the expansion *The stress tensor of Ref. 10 differs from (6) because the authors did not take into account that (a) not all of the Ulk are independent of Bi and (b) identity (5) can be used to get the symmetric form of the O'k.…”

“…1 In an isotropic material the rotation of a volume element and of B through the same angle 8,p 6B~ = (8~ x B); = eikt t~qOgBl, 8Vik = eUk 6~Ot (4) under a fixed structure (6S~k = 0) cannot change the free energy density. This gives a 8~ 3F/ 6vik = BiHk -BkHi (5) Now, one can find a variation of the free energy due to a small displacement ~ of the vortex system in the form 6,.~=S6FdV= -~ (i(O0"ik/OXk) dV and the corresponding stress tensor 1'9"t~ O-,k=(6F/6S, k)+(F-B " lt/4rr) 6,k +(B,Hk + BkI-I~)/8rr (6) This tensor gives the stresses in the system of vortices, but not in the crystal lattice of the material itself; the latter plays in this theory only the role of a "container" or an "isotropic and homogeneous space" for the superconducting condensate.…”

Resistivity anisotropy of the Bi‐based misfit layer compounds (BiS)1.11(NbS2) and (BiSe)1.10(NbSe2) down to the liquid nitrogen temperature

“…The two compounds (BiS) 1.11 (NbS 2 ) and (BiSe) 1.10 (NbSe 2 ) undergo a superconducting transition at 0.415 K and 2.37 K respectively and the anisotropies of their critical magnetic fields is respectively 2.4 and 1.29 [3]. This anisotropy is lower than the anisotropy of the mother compounds NbX 2 which is slightly higher than 3 [4]. We investigate in this work the resistivity anisotropy of these two compounds down to the liquid nitrogen temperature.…”