We experimentally explore the phenomenon of electron tunneling across a modulated tunneling barrier which is created between an STM tip and an Au film deposited on a vibrating piezo surface.Measurements of the time series of the quantum mechanical tunneling current across the modulating barrier show large fluctuations. Analysis of the average work done in establishing tunneling current in finite time interval shows a distribution of both positive and negative work events. The negative work events suggest tunneling against the bias voltage direction. We show that these distributions obey the Gallavotti Cohen Non-equilibrium Fluctuation Relations (GC-NEFR) valid for systems driven through a dissipating environment. Typically, while the GC-NEFR has been shown for non -equilibrium classical systems we show its validity for the quantum mechanical tunneling process too. The GC-NEFR analysis also gives us a way to measure the dissipation present in this quantum tunneling system.We propose the modulated barrier behaves like a lossy scattering medium for the tunneling electrons resulting in a tendency to randomize of the tunneling process.

Study of the formation and evolution of large scale, ordered structures is an enduring theme in science. Generation, evolution and control of large sized magnetic domains are challenging tasks, given the complex nature of competing interactions in a magnetic system. Here, we demonstrate large scale non-coplanar ordering of spins, driven by picosecond, megagauss magnetic pulses derived from a high intensity, femtosecond laser. Our studies on a specially designed yttrium iron garnet (YIG) dielectric/metal film sandwich target, show the creation of complex, large, concentric, elliptical shaped magnetic domains which resemble the layered shell structure of an onion. The largest shell has a major axis over hundreds of micrometers, in stark contrast to sub micrometer scale polygonal, striped or bubble shaped magnetic domains in magnetic materials, or large dumbbell shaped domains produced in magnetic films irradiated with accelerator based relativistic electron beams. Micromagnetic simulations show that the giant magnetic field pulses create ultrafast terahertz (THz) spin waves and a snapshot of these fast-propagating spin waves is stored as the layered onion shell shaped domains in the YIG film. Typically, information transport via spin waves in magnonic devices occurs in the gigahertz regime, where devices are susceptible to thermal disturbances at room temperature. Our intense laser light pulse—YIG sandwich target combination, paves the way for room temperature table-top THz spin wave devices, operating just above or in the range of the thermal noise floor. This dissipation-less device offers ultrafast control of spin information over distances of few hundreds of microns.

We report the observation of magnetic domain formation and reorientation in a Fe 2 O 3 magnetic tape by intense laser induced high magnetic field. Earlier reports have shown that high intensity lasers (femtosecond, terawatt) can create relativistic electron jets in a solid which can generate Mega Gauss magnetic field pulses. Irradiation of such laser pulse on pre-magnetized iron/iron-oxide films creates large domain formation. The magnetic domains are imaged through Magneto-optical imaging technique based on Faraday Effect. We see that the intense laser induced domain formation depends on the laser power and that a threshold laser power is required for nucleating the large domain. With micro-magnetic simulations involving LLG equations we study the magnetization dynamics of the magnetic films under high magnetic pulse. Comparison of the results with the simulations indicates the formation of the observed domain patterns due to the transient effect of the azimuthal magnetic field pulse. We believe our work holds the potential to explore different routes towards efficient ways of encoding magnetic information which may be useful for magnetic memory devices.