共查询到20条相似文献,搜索用时 0 毫秒
1.
Josephson junctions were photogenerated in underdoped thin films of the YBa2Cu3O6+x family using a near-field scanning optical microscope. The observation of the Josephson effect for separations as large as 100 nm between two wires indicates the existence of an anomalously large proximity effect and shows that the underdoped insulating material in the gap of the junction is readily perturbed into the superconducting state. The critical current of the junctions was found to be consistent with the conventional Josephson relationship. This result appears to constrain the applicability of SO(5) theory to explain the phase diagram of high critical temperature superconductors. 相似文献
2.
V. F. Gantmakher G. E. Tsydynzhapov L. P. Kozeeva A. N. Lavrov 《Journal of Experimental and Theoretical Physics》1999,88(1):148-156
A superconducting transition in the temperature dependence of the ab-plane resistivity of underdoped YBa2Cu3O6+x
crystals in the range T
c≲30 K has been investigated. Unlike the case of samples with the optimal level of doping, the transition width increased insignificantly
with magnetic field, and in the range T≲13 K it decreased with increasing magnetic field. The transition point T
c(B) was determined by analyzing the fluctuation conductivity. The curves of B
c2(T) measured in the region T/T
c≳0.1 did not show a tendency to saturation and had a positive second derivative everywhere, including the immediate neighborhood
of T
c. The only difference among the curves of B
c2(T) for different crystal states is the scales of Tand B, so they can be described in terms of a universal function, which fairly closely follows Alexandrov’s model of boson superconductivity.
Zh. éksp. Teor. Fiz. 115, 268–284 (January 1999) 相似文献
3.
4.
5.
6.
The lower critical field H(c1) for highly underdoped YBa2Cu3O(6+x) with T(c) between 8.9 and 22 K has been determined by measurements of magnetization M(H) curves with applied field parallel to the c axis. H(c1) is linear in temperatures below about 0.6T(c), and H(c1)(0) is proportional to T(1.64+/-0.04)(c), clearly violating the proportionality between rho(s)(0) and T(c). Moreover, the slope -dH(c1)/dT decreases steeply toward zero as T(c) approaches zero, indicating that the effective charge of the quasiparticles vanishes as the doping is decreased toward the insulating phase. 相似文献
7.
V. N. Samovarov 《Physics of the Solid State》1997,39(10):1556-1558
Optical absorption in YBa2Cu3O6+x
metal films carrying a direct current up to 100 mA is investigated. For films with a highly nonlinear I-V curve the current is observed to have a strong influence on interband absorption. The effect is not observed in the region
of optical transitions at local levels. The results are analyzed from the standpoint of carrier localization and delocalization
processes.
Fiz. Tverd. Tela (St. Petersburg) 39, 1747–1749 (October 1997) 相似文献
8.
A. Weidinger Ch. Niedermayer H. Glückler A. Golnik G. Nowitzke E. Recknagel H. Eickenbusch W. Paulus R. Schöllhorn J. I. Budnick 《Hyperfine Interactions》1991,63(1-4):147-153
Oxygen-deficient YBa2Cu3O6+x
samples were investigated by the muon spin rotation technique in zero external field. In an intermediate oxygen concentration
region we find strongly relaxing μSR signals indicating the existence of internal magnetic fields. The strongly relaxing signals
were observed only in samples with superconducting transition temperatures below 50 K. As an interpretation of the data we
suggest that magnetic ordering and superconductivity coexist in these samples within regions of extensions of a few lattice
constants, but not necessarily on the same sites. 相似文献
9.
10.
11.
12.
The muon is a useful probe of magnetic fields in superconductors, but knowing the field seen by the muon is often of limited
value until we know where the muon is in the crystal lattice. Here we employ two independent theoretical methods to search
for candidate muon sites:the potential energy field method, which seeks the minimum of the electrostatic potential of theμ
+, and themagnetic dipolar field method, which compares the calculated magnetic field (due to host electronic or nuclear dipolar fields) with the observed
local fields at the muon.
Work supported by Canadian NRC and NSERC. 相似文献
13.
14.
15.
Govind A. Pratap Ajay R.S. Tripathi 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(2):153-158
In the present paper, we study the magnetic properties of bilayer cuprate antiferromagnets. In order to evaluate the expressions
for spin-wave dispersion, sublattice magnetization, Néel temperature and the magnetic contribution to the specific heat, the
double time Green's function technique has been employed in the random phase approximation (RPA). The spin wave dispersion
curve for a bilayer antiferromagnetic system is found to consist of one acoustic and one optic branch. The “optical magnon
gap” has been attributed solely to the intra-bilayer exchange coupling (J
⊥
) as its magnitude does not change significantly with the inter-bilayer exchange coupling (Jz). However Jz is essential to obtain the acoustic mode contribution to the magnetization. The numerical calculations show that the Néel
temperature (T
N
) of the bilayer antiferromagnetic system increases with the Jz and a small change in Jz gives rise to a large change in the Néel temperature of the system. The magnetic specific heat of the system follows a T2 behaviour but in the presence of Jz it varies faster than T2.
Received 13 July 2000 and Received in final form 14 May 2001 相似文献
16.
17.
18.
B. Keimer 《Hyperfine Interactions》1997,105(1-4):3-12
A review is given of recent developments in inelastic neutron scattering experiments on the high temperature superconductor
YBa_2Cu_3O_7 and its antiferromagnetic precursor YBa_2Cu_3O6.2. These include the detection of high energy “optical” spin waves and the determination of the full spin Hamiltonian in YBa_2Cu_3O6.2, a detailed study of the 40 meV magnetic resonance peak in the superconducting state of YBa_2Cu_3O_7, and experiments on
the effect of superconductivity on phonon lifetimes in YBa_2Cu_3O_7.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
Hiroshi Yasuoka Susumu Sasaki Takashi Imai Tadashi Shimizu Yutaka Ueda Koji Kosuge 《Phase Transitions》2013,86(4):183-199
The nuclear quadrupole resonance (NQR) technique has been utilized to characterize the local oxygen coordination of inequivalent Cu sites in YBa2Cu3O6+x(0 ≤ x ≤ 0.91). Essentially, four distinct NQR lines which correspond to 2, 3,4 oxygen coordinated Cu sites in the Cu-O chains and 5 oxygen coordinated Cu sites in the Cu-O planes have been observed. The zero-field NQR frequencies of these are centered at about 30.1, 24.0, 22.0 and 31.5 MHz for 63Cu, respectively. For the antiferromagnetic ordered state (x ≤ 0.3), antiferromagnetic nuclear resonance (AFNR) has been observed at 90 MHz with quadrupole splittings associated with the moment-bearing Cu sites in the Cu-O planes. The relative intensities of these resonance lines depend on the oxygen content, and this gives us a microscopic understanding of the Cu chemistry of this system. 相似文献
20.
We report measurements of the ab-plane superfluid density n(s) (magnetic penetration depth lambda) of heavily underdoped films of YBa2Cu3O6+x, with T(C)'s from 6 to 50 K. We find the characteristic length for vortex unbinding transition equal to the film thickness, suggesting strongly coupled CuO2 layers. At the lowest dopings, T(C) is as much as 5 times larger than the upper limit set by the 2D Kosterlitz-Thouless-Berezinskii transition temperature calculated for individual CuO2 bilayers. Our main finding is that T(C) is not proportional to n(s)(0); instead, we find T(C) proportional to ns(1/2.3+/-0.4). This conflicts with a popular point of view that quasi-2D thermal phase fluctuations determine the transition temperature. 相似文献