Enhanced paramagnetic limit of the upper critical magnetic field for superconductors with charge-density waves

Войтенко

Advances in Condensed Matter Physics

et al. 2010

Explicit and implicit experimental evidence for charge density wave (CDW) presence in high-Tcsuperconducting oxides is analyzed. The theory of CDW superconductors is presented. It is shown that the observed pseudogaps and dip-hump structures in tunnel and photoemission spectra are manifestations of the same CDW gapping of the quasiparticle density of states. Huge pseudogaps are transformed into modest dip-hump structures at low temperatures,T, when the electron spectrum superconducting gapping dominates. Heat capacity jumps at the superconducting critical temperature and the paramagnetic limit are calculated for CDW superconductors. For a certain range of parameters, the CDW state in ad-wave superconductor becomes reentrant withT, the main control quantity being a portion of dielectrcally gapped Fermi surface. It is shown that in the weak-coupling approximation, the ratio between the superconducting gap at zero temperatureΔ(T=0)andTchas the Bardeen-Cooper-Schrieffer value fors-wave Cooper pairing and exceeds the corresponding value ford-wave pairing of CDW superconductors. Thus, large experimentally found values2Δ(T=0)/Tc≈5÷8are easily reproduced with reasonable input parameter values of the model. The conclusion is made that CDWs play a significant role in cuprate superconductivity.

Section: Enhancement Of the Paramagnetic Limit In S-wave Cdw Superconmentioning

confidence: 81%

Section: Enhancement Of the Paramagnetic Limit In S-wave Cdw Superconmentioning

confidence: 99%

Section: Enhancement Of the Paramagnetic Limit In S-wave Cdw Superconmentioning

confidence: 99%

See 1 more Smart Citation

Competition of Superconductivity and Charge Density Waves in Cuprates: Recent Evidence and Interpretation

Войтенко

Advances in Condensed Matter Physics

et al. 2010

“…This is a feature distinguishing the CDW case from the superconducting one. One should also note that H p in normal and superconducting CDWMs substantially differs [3] from its Clogston-Chandrasekhar superconducting analog [1]. We predict one more effect to be observed in symmetrical (or non-symmetrical) junctions involving CDWMs only.…”

mentioning

confidence: 66%

Spin-dependent splitting of the tunnel conductivity peaks in the magnetic field for junctions involving CDW metals

Physica B: Condensed Matter

et al. 2006

Current-voltage characteristics for junctions involving normal and superconducting charge-density-wave metals in the magnetic field were calculated. Spin splitting was found both for symmetrical and non-symmetrical junctions. r Tunneling between s-wave superconductors (S) and ferromagnets (FM) in the external magnetic field H is a powerful method for studying both electron properties of the paired states and the spin-split band structure of the itinerant electron spectrum [1]. The main practical goal of those investigations consists in the determination of the electron spin polarization P inside the ferromagnet at its Fermi level. The spin splitting of the gap-like maxima in the voltage, V, dependence of the dynamical conductance GðV Þ ¼ dJ=dV , where J is the quasiparticle current, into two components, GðV Þ ¼ G þ ðV Þ þ G À ðV Þ, corresponding to the contributions of current carriers with different spin orientations with respect to the applied field H, is the origin of the effect obtained in the junction device. There is an obstacle, which always acts harmfully in such experiments. It is a strong orbital Meissner effect. To overcome it, a thin-film geometry is used, so that the paramagnetic influence of H on Cooper pairs may manifest itself. The smearing of the G AE ðV Þ maxima by a spin-orbital scattering constitutes another prominent difficulty negatively influencing the method. In this situation, any supplement in the set of gap-possessing objects suitable for probing P would be highly desirable.As those, we propose charge-density-wave (CDW) normal metals and superconductors. Indeed, their paramagnetic properties are very similar to those of s-wave superconductors because due to the electron-hole and electron-electron attraction, respectively, both are in the spin-singlet paired state. That is why the spin splitting of GðV Þ should be like. Nevertheless, one can expect substantial differences since the CDW metals (CDWMs) are gapped only partially, i.e. the nested (d) sections of the Fermi surface (FS) are gapped by the CDW order parameter S ¼ jSje ij , whereas the other FS sections (nd) remain intact at temperatures, T, below the structural transition one, T d [2]. The relative portion of the gapped FS is determined by the parameter 0pmp1.In the magnetic field H, which is large enough to conspicuously move apart the gap-induced maxima G AE ðV Þ but substantially smaller than the so-called paramagnetic limit, H p , one may expect to observe the effect depending also on j. This is a feature distinguishing the CDW case from the superconducting one. One should also note that H p in normal and superconducting CDWMs substantially differs [3] from its Clogston-Chandrasekhar superconducting analog [1]. ARTICLE IN PRESSwww.elsevier.com/locate/physb 0921-4526/$ -see front matter r

“…Here, ∆ 0 is the value of the superconducting gap in the hypothetical case where CDWs are switched off (T d = Σ = 0). Let us note that H is smaller here than the paramagnetic limit for CDW superconductors [15]. One sees that both the square-root singularities are split.…”

Section: Non-symmetrical Junctionsmentioning

confidence: 89%

Spin-Dependent Tunneling in a Magnetic Field for Junctions Involving Normal and Superconducting CDW Metals

et al. 2006

Acta Phys. Pol. A

The voltage, V , dependences of the differential tunnel conductance G(V ) were calculated for two kinds of junctions involving normal and superconducting charge-density-wave metals (CDWMs) in the external magnetic field H. The first is a non-symmetrical junction with a CDWM electrode being biased with respect to a ferromagnet. Calculations show that the paramagnetic splitting occurs between spin-up and spin-down components of G(V ), similar to what is observed when a superconducting electrode is used instead of the CDWM one. The second setup is symmetric (CDWM-I-CDWM), where I denotes an insulator. If at least one of the CDWM electrodes is normal and H = 0, G(V ) will also be spin-split.