Marat Gaifullin

Controlling high-frequency collective electron dynamics via single-particle complexity

We demonstrate, through experiment and theory, enhanced high-frequency current oscillations due to magnetically-induced conduction resonances in superlattices. Strong increase in the ac power originates from complex single-electron dynamics, characterized by abrupt resonant transitions between unbound and localized trajectories, which trigger and shape propagating charge domains. Our data demonstrate that external fields can tune the collective behavior of quantum particles by imprinting configurable patterns in the single-particle classical phase space.

Novel features of Josephson flux-flow in Bi-2212 : contribution of in-plane dissipation, coherent response to mm-wave radiation, size effect.

Abstract We studied Josephson flux flow (JFF) in Bi-2212 stacks fabricated from single crystal whiskers by focused ion beam technique. For long junctions with the in-plane sizes 30×2 μm 2 , we found considerable contribution of the in-plane dissipation to the JFF resistivity, ρ Jff , at low temperatures. According to recent theory [A. Koshelev, Phys. Rev. B 62 (2000) R3616] that results in quadratic type dependence of ρ Jff ( B ) with the following saturation. The I – V characteristics in the JFF regime also can be described consistently by that theory. In the JFF regime we found Shapiro-step response to the external mm-wave radiation. The step position is proportional to the frequency of applied microwaves and corresponds to the Josephson emission from all the 60 intrinsic junctions of the stack being synchronized. That implies the coherence of the JFF over the whole thickness of the stack and demonstrates the possibility of synchronization of intrinsic junctions by the magnetic field. We also found a threshold character of the appearance of the JFF branch on the I – V characteristic with the increase of magnetic field, the threshold field B t being scaled with the junction size perpendicular to the field L (L=30–1.4 μ m), as B t ≈ Φ 0 / Ls , where s is the interlayer spacing. On the I – V characteristics of small stacks in the JFF regime we found Fiske-step features associated with resonance of Josephson radiation with the main resonance cavity mode in transmission line formed by stacks.

Local measurement of microwave response with local tunneling spectra using near field microwave microscopy

We have designed and built a near-field scanning microwave microscope, which has been used to measure the local microwave response and the local density-of-states (LDOS) in the area including the boundary between the gold deposited and the non-deposited region on highly-orientated pyrolytic graphite at a frequency of about 7.3 GHz. We have succeeded in measuring the spatial variation of both the LDOS and the surface resistance. It can be observed that the surface resistance in gold deposited region with the metallic tunneling spectra is smaller than that in the non-deposited region with the U-shaped tunneling spectra.

Collective responses of Bi-2212 stacked junction to 100 GHz microwave radiation under magnetic field oriented along the c-axis

We studied a response of Bi-2212 mesa type structures to 100 GHz microwave radiation. We found that applying magnetic field of about 0.1 T across the layers enables to observe collective Shapiro step response corresponding to a synchronization of all 50 intrinsic Josephson junctions (IJJ) of the mesa. At high microwave power we observed up to 10th harmonics of the fundamental Shapiro step. Besides, we found microwave induced flux-flow step position of which is proportional to the square root of microwave power and that can exceed at high enough powers 1 THz operating frequency of IJJ oscillations.

Development of near-field microwave microscope with the functionality of scanning tunneling spectroscopy

We describe the details of an original near-field scanning microwave microscope, developed for simultaneous measurements of local density-of-states (LDOS) and local ohmic losses (LOL). Improving microwave detection systems, we have succeeded in distinguishing the LDOS and LOL even between two low resistance materials; gold and highly orientated pyrolitic graphite. The experimental data indicate that our microscope holds a capability to investigate both LDOS and LOL in nanoscale.

Vortex state of high-Tc superconductors studied by Josephson plasma resonance

Abstract The Josephson plasma resonance (JPR), which is a phase collective excitation mode representing the Cooper-pair oscillation mode, is a most powerful means to study the vortex state in Josephson coupled high-Tc superconductors (HTSC). In this paper, we report the detailed and quantitative study of the interlayer quantum phase coherence in the vortex liquid, Bragg glass and vortex glass phases of Bi2Sr2CaCu2O8+δ by the JPR. We also provide a quantitative discussion on the nature of the phase transitions among these vortex phases. On the basis of these results, we discuss the vortex phase diagram of HTSC.

The emergence of quantum capacitance in epitaxial graphene

We found an intrinsic redistribution of charge arises between epitaxial graphene, which has intrinsically n-type doping, and an undoped substrate. In particular, we studied in detail epitaxial graphene layers thermally elaborated on C-terminated

Spatial correlation between impurity states and energy gap distribution in Bi2Sr2Ca(Cu1-xZnx)2 O8+δ(x = 0.02)

4H

The c-axis coherent response of Bi-2212 Josephson flux-flow junction to mm-wave radiation

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Magnetic field tunable vortex diode made of YBa2Cu3O7−δ Josephson junction asymmetrical arrays

SiC