Tunneling spectroscopy with intrinsic Josephson junctions inBi2Sr2CaCu

Abstract

The paper presents a detailed discussion of the current-voltage characteristic of intrinsic Josephson junctions in Bi 2 Sr 2 CaCu 2 O 8ϩ␦ and Tl 2 Ba 2 Ca 2 Cu 3 O 10ϩ␦ . In these materials Josephson tunnel junctions are formed naturally between adjacent superconducting CuO 2 bilayers or trilayers. A typical sample consists of a stack of Josephson junctions. We explicitly show that all junctions inside a given sample have identical tunneling characteristics. We discuss the shape ͑general curvature͒ of the current-voltage characteristic in terms of a superconducting order parameter that has a predominant d x 2 Ϫy 2 symmetry. The I c R n product of the intrinsic Josephson junctions turns out to be 2-3 mV, about 10% of the maximum energy gap ⌬ 0 /e. The currentvoltage characteristic of every individual junction exhibits pronounced structures in the subgap regime. They are best explained by a recently proposed resonant coupling mechanism between infrared active optical c-axis phonons and oscillating Josephson currents.

Theory for the coupling between longitudinal phonons and intrinsic Josephson oscillations in layered superconductors

“…8: The position of the resonance is independent on temperature, magnetic field and the geometry of the probe, while the intensity of the structure varies ∼ j 2 c with the critical current density j c (T, B). Also the behaviour of the position and intensity of the structures in external pressure are in agreement with the phonon explanation and formula (1).…”

“…Next we want to relate the driving field to the average total electric field E n in the barrier because this field is connected with the phase difference γ n by the second Josephson-equation (8). The microscopic total electric field E z (x, z) is the sum of the fields set-up by both the charge-fluctuations and the displaced ionic charges:…”

“…1,2 Recently subgap structures in the I-V -characteristic have been discovered as intrinsic properties of the material, 3-5 which could be explained by the coupling between the intrinsic Josephson oscillations and phonons. [6][7][8] This interaction is mediated by the oscillating electric field in the Josephson junction, which excites vibrations of charged ions in the material. In our previous investigations 6,7 we used a simple model of a system of damped harmonic oscillators in order to describe the dynamics of oscillating ions in the barrier.…”

Plasma resonance in anisotropic layeredhigh−Tcsuperconductors

“…The voltage appearing per junction in the plasma analysis is smaller than the voltage jump ͑20-30 mV͒ per junction, and thus the chosen value of the loss parameter is not unrealistic from the estimation of conductances in such cases for BSCCO intrinsic Josephson junction. 15 The resonance intensity is evaluated by…”

Intrinsic tunneling spectroscopy: a look from the inside at HTSC

“…This method is specific to strongly anisotropic HTSC, like Bi 2 Sr 2 CaCu 2 O 8+δ (Bi-2212), in which mobile charge carriers are localized in double CuO 2 layers, while the transverse (c−axis) transport is due to interlayer tunneling [10,11]. Interlayer tunneling has become a powerful tool for studying both electron [12][13][14] and phonon [15] DOS of HTSC. It has several important advantages compared to surface tunneling techniques: (i) it probes bulk properties and is insensitive to surface deterioration or surface states; (ii) the current direction is well defined; (iii) the tunnel barrier is atomically perfect and has no extrinsic scattering centers; (iv) mesa structures are mechanically stable and can sustain high bias in a wide range of temperatures (T ) and magnetic fields (H).…”