PSEUDO-GAP FEATURES OF INTRINSIC TUNNELING IN (HgBr 2 )-Bi2212 SINGLE CRYSTALS (original) (raw)
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The technology for making a specified (1-100) number of intrinsic Josephson junctions in Bi-2212 is reported. Measurements of the resistance during the fabrication process made it possible to avoid the in-plane contribution. The c-axis resistivity p,: was about 30 f~ cm at 90 K and it obeyed an exponential law pc(T)ct exp(A/T), with A-~ 43 meV, suggesting a thermally activated hopping mechanism of the c-axis transport. The c-axis gap parameter of an individual junction is about one half of that reported elsewhere and is strongly temperature dependent, suggesting proximity induced superconductivity of the intermediate Bi-O layers in Bi-2212.
Physica C: Superconductivity, 2001
From intrinsic tunneling spectroscopy, superconducting-and pseudo-gaps could be separated within a wide range of temperatures. We have found that the two gaps have dierent temperature (T) and magnetic ®eld (H) dependencies. The superconducting gap closes both as T 3 T c and H 3 H c2 , while the pseudo-gap does not change neither with T, or H. This would speak in favor of two coexisting phenomena and against the precursor superconductivity scenario of the pseudo-gap.
Bi2Sr2CaCu2O8+x Single Crystals Probed by c-Axis Tunneling Measurements
1998
We fabricated small-size stacks on the surface of Bi2Sr2CaCu2O8+x (BSCCO-2212) single crystals with the bulk transition temperature Tc≃90 K, each containing a few intrinsic Josephson junctions. Below a critical temperature T ′ c ( ≪ Tc), we have observed a weakened Josephson coupling between the CuO2 superconducting double layer at the crystal surface and the adjacent one located deeper inside a stack. The quasiparticle branch in the IV data of the weakened Josephson junction (WJJ) fits well to the tunneling characteristics of a d-wave superconductor ( ′)/insulator/d-wave superconductor (D ′ ID) junction. Also, the tunneling resistance in the range T ′ c<T<Tc agrees well with the tunneling in a normal metal/insulator/d-wave superconductor (NID) junction. In spite of the suppressed superconductivity at the surface layer the symmetry of the order parameter appears to remain unaffected. I.
Tunneling studies on single crystals of superconducting Bi2Ca1−xYxSr2Cu2O8+δ
Physica C: Superconductivity, 1992
Tunneling studies have been carried out on single crystals of Bi>Ca, ,Sr,Cu& x+,> over a wide range of compositions wherein the hole concentration varies by a factor of 2.5. The 23 value varies between 25 meV and 75 meV over the composition range studied, but scales with 2A/k,T,=9.5 throughout
Break junction tunnelling on Bi2Sr2CaCu2O8+?-single crystals
Zeitschrift f�r Physik B Condensed Matter, 1992
Break junction tunnelling experiments on Bi2Sr2Ca-Cu20 s +o-single crystals were performed at different temperatures. Carefully adjusted samples exhibited conductance curves showing only one large peak at positive and negative bias voltages. From these measurements a gap value A=(21.2_2.8)meV, i.e. 2A/kBTc=(5.5+_0.8), was inferred. The behaviour of the conductance curves is similar to that of conventional superconductors but with a much larger broadening of the tunnelling characteristic. Therefore, several models which could explain this smearing are compared with the experimental data. However, it is found that none of them is capable of fitting the conductance curves convincingly. In some cases tunnel characteristics similar to those predicted by a charging effect model or a multigap model were obtained.
Interlayer tunneling of quasiparticles and Cooper pairs in Bi-2212 from experiments on small stacks
Physica C: Superconductivity, 2001
The interlayer tunneling has been studied on high quality Bi-2212 stacks of micron to the submicron lateral size. We found that low temperature and low voltage tunneling I±V characteristics can be self-consistently described by Fermiliquid model for a d-wave superconductor with a signi®cant contribution from coherent interlayer tunneling. For micron-sized stacks we found very clear Fraunhofer type dependence of critical current across the stack on parallel magnetic ®eld with periodicity corresponding to one¯ux quantum per elementary junction. The gap and pseudogap interplay with variation of temperature and magnetic ®eld has been extracted from the I±V characteristics. We consider also the role of charging eects for submicron stacks.
Fizika Nizkikh Tempreratur, 2020
Conductance-voltage characteristics (CVCs) of tunnel break junctions made of Bi 2 Sr 2 CaCu 2 O 8+δ crystals were measured. It was demonstrated that the CVCs have a V-shaped inner gap region, similar to those typical of CVCs for tunnel junctions between d-wave superconductors. The CVCs have different forms for different junctions, but all of them reveal weak dip-hump structures outside the inner gap region. Calculations of the tunnel current in the ab plane of the break junctions were carried out in the model of the inhomogeneous d-wave superconductor partially gapped by charge density waves (CDWs). The averaging of the tunnel current over the statistical distributions of both the superconducting and CDW order parameters was carried out. The theoretical results qualitatively reproduce the behavior of experimental curves. A conclusion was made that tunnel direc-tionality and the statistical distributions of both order are crucial factors governing the observed CVC shapes for break junctions made of high-T c oxides.
Physical Review B, 2007
The tunnel conductance G͑V͒ for break junctions made of single-crystal as-grown Bi 2 Sr 2 CaCu 2 O 8+␦ samples with T c Ϸ 86-89 K were measured and clear-cut dip-hump structures ͑DHSs͒ were found in the range 80-120 mV of the bias voltage V. A theory of tunneling in symmetrical junctions between inhomogeneous charge-density-wave ͑CDW͒ superconductors, considered in the framework of the s-pairing model, has been developed. CDWs have been shown to be responsible for the appearance of the DHS in the tunnel currentvoltage characteristics and properly describe the experimental results.
Superconducting properties of La-substituted Bi2201 crystals
2001
The superconducting gap Delta has been measured in Bi2Sr2-xLaxCuO6+d single crystals in a wide range of temperatures 4.2 K < T < Tc by point-contact and tunnelling spectroscopy for current in c-direction. The value of Delta(4.2 K) was found to scale with the critical temperature Tc in the whole range of doping levels with the ratio 2D/kTc = 12.5 +/- 2. The closing of the gap Ds at T = Tc has been registered in the underdoped, optimally doped as well as in the overdoped sam-ples.