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A. Mourachkine

Publications and source records attributed to A. Mourachkine.

At least 37 records · Page 2Linked to original sources
arXiv2001

Evidence for a Quasi-1D Topological-Excitation Liquid in Bi2212 by Tunneling Spectroscopy

Tunneling measurements have been carried out on heavily underdoped and slightly overdoped Bi2212 single crystals by using a break-junction technique. We find that in-plane tunneling spectra below Tc are the combination of incoherent part from the pseudogap and coherent quasiparticle peaks. There is a correlation between the magnitude of the pseudogap and the magnitude of the superconducting gap in Bi2212. We find that the quasiparticle conductance peaks are caused by condensed solitonlike excitations.

cond-mat.supr-con↗
arXiv2001

c-Axis Phase Coherence and Spin Fluctuations in Cuprates

There is a consensus that superconductivity (SC) in cuprates is two-dimensional. It is widely believed that the long-range phase coherence appears at T_{c} due to the Josephson coupling between SC CuO_{2} (bi-, tri-, >...)layers. Recent T_{c} and resistivity measurements in Tl2212 as a function of applied pressure (Salvetat J.-P. et al., Europhys. Lett., 52 (2000) 584) show that the interlayer Josephson-coupling mechanism does not fit the data. Here we analyze data obtained in Andreev reflection, neutron scattering, microwave, muon spin relaxation, tunneling and resistivity measurements performed on different cuprates, mainly, on YBCO, Bi2212 and LSCO. The analysis of the data shows that the long-range phase coherence in the cuprates intimately relates to antiferromagnetic interactions along the c axis. At the same time, it seems that the in-plane mechanism of the SC has no or little relations to the magnetic interactions along the c axis.

cond-mat.supr-con↗
arXiv2000

Phenomenological model of high-Tc superconductivity

We present a phenomenological model of high-Tc superconductivity in hole-doped cuprates: a Magnetic Coupling between Stripes (MCS) model. The MCS model is based upon experimental facts, namely, the presence of (i) stripes, (ii) spin fluctuations, and (iii) two order parameters (for pairing and long-range phase coherence) in hole-doped cuprates. We discuss also the superconductivity in electron-doped cuprates.

cond-mat.supr-con↗
arXiv2000

Andreev reflections and tunneling spectroscopy on underdoped NCCO (x = 0.15)

Andreev-reflection and tunneling studies have been carried out on a single crystal of underdoped Nd1.85Ce0.15CuO4-d (NCCO) by using Ag, Pt-Ir and Nb tips to clarify the symmetry of its order parameter. Surprisingly, we observed in the NCCO, on the one hand, the Josephson current (with Nb tip) which indicates the presence of s-wave order parameter, on the other hand, a zero-bias conductance peak (with Ag tip) which is a manifestation of d-wave order parameter. In addition, we find the presence of two distinct energy scales in the underdoped NCCO: the smallest energy scale is associated with the Andreev gap and c-axis tunneling gap, and the second scale corresponds to the maximum in-plane tunneling gap. It seems that the phenomenon of superconductivity in electron- and hole-doped cuprates can be understood within a common scheme.

cond-mat.supr-con↗
arXiv1999

CDW Ordering in Stripe Phase of Underdoped Cuprates

The in-plane resistivity and out-of-plane resistivity of non-superconducting RBCO (R = Y, Tm) and Fe-doped Bi2212 single crystals are discussed. The comparison of electrical transport properties of the cuprates and quasi-one dimensional (1D) (TMTSF)2PF6 organic conductor suggests that RBCO and Bi2212 exhibit 1D transport properties, and the step rise at low temperatures in the resistivities of the cuprates and quasi-1D organic conductor is due to charge-density-wave ordering. We discuss also phonon-electron interactions in cuprates at low temperatures.

cond-mat.supr-con↗
arXiv1999

Interpretation of Inelastic Neutron Scattering Data Using the Phase Diagram of Hole-Doped Cuprates

Inelastic Neutron Scattering (INS) data in LSCO, YBCO and Bi2212 are discussed. In the literature, the INS spectra remain far from being comprehensively understood. We show that local (Q-integrated) susceptibility data and the energy dependence of the spin susceptibility at antiferromagnetic vector, Q = (p,p), can be interpreted by using the phase diagram for hole-doped cuprates. We analyze also the origin of the resonant peak which relates to the order parameter for long-range phase coherence in hole-doped cuprates. Thus, we present an interpretation of neutron data in LSCO, YBCO and Bi2212 published so far.

cond-mat.supr-con↗
arXiv1999

Phenomenological model of high-Tc superconductivity: a MCS model

Since the introduction of a MCS (Magnetic Coupling between Stripes) phenomenological model [cond-mat/9902355, to be published in J. Superconductivity] for hole-doped cuprates many new experimental data have been presented in the literature as evidence in support of the MCS model. We consider here recent data and the MCS model which is based upon experimental facts, namely, the presence of (i) stripes; (ii) spin fluctuations, and (iii) two order parameters (for pairing and for long-phase coherence) in hole-doped cuprates. We discuss also the superconductivity in the s-wave NdCeCuO cuprate.

cond-mat.supr-con↗
arXiv1999

The pseudogap in Bi2212 single crystals from tunneling measurements: a possible evidence for the Cooper pairs above Tc

We present electron-tunneling spectroscopy of slightly overdoped Bi2212 single crystals with Tc = 87 - 90 K in a temperature range between 14 K and 290 K using a break-junction technique. The pseudogap which has been detected above Tc appears at T* = 280 K. The analysis of the spectra shows that there is a contribution to the pseudogap above Tc, which disappears approximately at 110 - 115 K. We associate this contribution with the presence of incoherent Cooper pairs.

cond-mat.supr-con↗
arXiv1999

The Symmetries and Origins of the Order Parameters for Pairing and Phase Coherence in Cuprates

The symmetries and origins of the order parameters (OPs) for pairing and long-range phase coherence in hole-doped cuprates are discussed. By analyzing tunneling, inelastic neutron scattering and torque measurements we conclude that the Cooper pairs in cuprates consist of spinons, and the pairing OP has an anisotropic s-wave symmetry, whereas the OP for long-range phase coherence has the magnetic origin due to spin fluctuations and, has the d-wave symmetry. All conclusions are based exclusively on experimental facts.

cond-mat.supr-con↗
arXiv1999

Two energy gaps observed in tunneling measurements on hole-doped cuprates: pairing gap and coherent gap

There is a clear discrepancy among the energy-gap values for different 90 K cuprates, inferred from tunneling measurements. By using the phase diagram for hole-doped cuprates we show that tunneling measurements performed on 90 K cuprates, simply, detect two different energy gaps: the pairing gap and the coherent gap, which are identical in conventional superconductors. We find that there are two reasons why tunneling measurements show in one cuprate exclusively the coherent gap while, in another cuprate, they show the pairing gap: (i) the number of CuO2 planes per unit cell in the cuprate, and (ii) the directionality of the tunneling current (along c-axis or ab-plane).

cond-mat.supr-con↗
arXiv1999

The Order Parameters for Pairing and Phase Coherence in Cuprates; the Magnetic Origin of the Coherent Gap. The MCS Model of High-Tc Superconductivity

The phase diagram of order parameters for pairing and phase coherence in hole-doped cuprates is discussed. By examining carefully some recent inelastic neutron scattering data obtained on hole-doped cuprates and heavy fermion compound UPd2Al3 in which the superconductivity is mediated by spin fluctuations, we conclude that the coherent gap in hole-doped cuprates has most likely the magnetic origin and scales with Tc, on average, as 2Dc/kBTc = 5.4. We discuss a model of the superconductivity in hole-doped cuprates and the symmetries of two order parameters.

cond-mat.supr-con↗
arXiv1999

The Magnetic Origin of the Coherent Order Parameter in Hole-Doped Cuprates

The phase diagram for hole-doped cuprates is discussed. By examining some recent inelastic neutron scattering data obtained on hole-doped cuprates we conclude that the coherent gap in hole-doped cuprates has most likely the magnetic origin and scales with Tc, on average, as 2Delta/kTc = 5.4.

cond-mat.supr-con↗
arXiv1999

The Symmetries of the Order Parameters for Pairing and Phase Coherence in Hole-Doped Cuprates

The symmetries of the order parameter (OP) responsible for pairing and the OP responsible for phase coherence in hole-doped cuprates are discussed. We analyze angle-resolved tunneling, ARPES, Raman scattering and torque measurements performed on hole-doped cuprates. We conclude that, most likely, the OP responsible for phase coherence has the d-wave symmetry whereas the OP responsible for pairing has an anisotropic s-wave symmetry.

cond-mat.supr-con↗
arXiv1999

The MCS Model of the Superconductivity in Hole-Doped Cuprates: an Experimental Evidence

We present experimental data obtained by different techniques. Some of them are not easy to explain by any theoretical model presented in the literature. However, a MCS model of the superconductivity in hole-doped cuprates, proposed in our previous work, is capable to explain them. Thus, we present an evidence in favor of the MCS model.

cond-mat.supr-con↗
arXiv1999

The Effect of Ni and Zn Doping in Bi2212 from Tunneling Measurements. The MCS model of the High-Tc Superconductivity in hole-doped cuprates

We use Ni and Zn impurities doped into Bi2212 to test the MS (Magnetic polaron - Spinon) model proposed earlier. We present electron-tunneling spectroscopy of pure, Ni- and Zn-doped Bi2212 single crystals below Tc using a break-junction technique. We show that the magnetic (Ni) and nonmagnetic (Zn) impurities doped into CuO2 planes affect both Tc and the density of states in Bi2212 but do it differently. In order to explain the data, we had to modify the MS model. Thus, we present a Magnetic Coupling of Stripes (MCS) model. In the MCS model, there is only one superconductivity - a spinon superconductivity along charged stripes. The coherent state of the spinon superconductivity is established by magnons which are excited by motions of charged stripes. So, in the MCS model, the superconductivity has two mechanisms: along charged stripes and perpendicular to stripes.

cond-mat.supr-con↗
arXiv1999

The Coexistence of Spinon Superconductivity and d-wave Superconductivity in Bi-2212 from Tunneling Measurements

We present electron-tunneling spectroscopy of slightly overdoped Bi2212 single crystals at low temperature using a break-junction technique. Below Tc, we observe, at least, two different superconducting gaps. We show that (i) the largest superconducting gap occurs due to pairing of spinons; (ii) the second superconducting gap has the d-wave symmetry; (iii) the d-wave gap is smaller than the spinon gap, however, predominant and occurs due to pairing of fermionic excitations carrying charge; (iv) the spinon gap has either a s-wave or (s+d) mixed symmetry with the maximum located in (p, p) direction on the Fermi surface. It is possible that there exists the third superconducting gap having a g-wave symmetry, which is approximately twice smaller in magnitude than the d-wave gap. Thus, there are two different types of superconductivity and two different types of carriers in Bi2212.

cond-mat.supr-con↗