2,186 research outputs found
Terahertz quantum plasmonics at nanoscales and angstrom scales
Through the manipulation of metallic structures, light-matter interaction can enter into the realm of quantum mechanics. For example, intense terahertz pulses illuminating a metallic nanotip can promote terahertz field-driven electron tunneling to generate enormous electron emission currents in a subpicosecond time scale. By decreasing the dimension of the metallic structures down to the nanoscale and angstrom scale, one can obtain a strong field enhancement of the incoming terahertz field to achieve atomic field strength of the order of V/nm, driving electrons in the metal into tunneling regime by overcoming the potential barrier. Therefore, designing and optimizing the metal structure for high field enhancement are an essential step for studying the quantum phenomena with terahertz light. In this review, we present several types of metallic structures that can enhance the coupling of incoming terahertz pulses with the metals, leading to a strong modification of the potential barriers by the terahertz electric fields. Extreme nonlinear responses are expected, providing opportunities for the terahertz light for the strong light-matter interaction. Starting from a brief review about the terahertz field enhancement on the metallic structures, a few examples including metallic tips, dipole antenna, and metal nanogaps are introduced for boosting the quantum phenomena. The emerging techniques to control the electron tunneling driven by the terahertz pulse have a direct impact on the ultrafast science and on the realization of next-generation quantum devices
Phononics: Manipulating heat flow with electronic analogs and beyond
The form of energy termed heat that typically derives from lattice
vibrations, i.e. the phonons, is usually considered as waste energy and,
moreover, deleterious to information processing. However, with this colloquium,
we attempt to rebut this common view: By use of tailored models we demonstrate
that phonons can be manipulated like electrons and photons can, thus enabling
controlled heat transport. Moreover, we explain that phonons can be put to
beneficial use to carry and process information. In a first part we present
ways to control heat transport and how to process information for physical
systems which are driven by a temperature bias. Particularly, we put forward
the toolkit of familiar electronic analogs for exercising phononics; i.e.
phononic devices which act as thermal diodes, thermal transistors, thermal
logic gates and thermal memories, etc.. These concepts are then put to work to
transport, control and rectify heat in physical realistic nanosystems by
devising practical designs of hybrid nanostructures that permit the operation
of functional phononic devices and, as well, report first experimental
realizations. Next, we discuss yet richer possibilities to manipulate heat flow
by use of time varying thermal bath temperatures or various other external
fields. These give rise to a plenty of intriguing phononic nonequilibrium
phenomena as for example the directed shuttling of heat, a geometrical phase
induced heat pumping, or the phonon Hall effect, that all may find its way into
operation with electronic analogs.Comment: 24 pages, 16 figures, modified title and revised, accepted for
publication in Rev. Mod. Phy
Direct current generation due to harmonic mixing: From bulk semiconductors to semiconductor superlattices
We discuss an effect of dc current and dc voltage (stopping bias) generation
in a semiconductor superlattice subjected by an ac electric field and its
phase-shifted n-th harmonic. In the low field limit, we find a simple
dependence of dc voltage on a strength, frequency, and relative phase of mixing
harmonics for an arbitrary even value of n.
We show that the generated dc voltage has a maximum when a frequency of ac
field is of the order of a scattering constant of electrons in a superlattice.
This means that for typical semiconductor superlattices at room temperature
operating in the THz frequency domain the effect is really observable.
We also made a comparison of a recent paper describing an effect of a
directed current generation in a semiconductor superlattice subjected by ac
field and its second harmonic (n=2) [K.Seeger, Appl.Phys.Lett. 76(2000)82] with
our earlier findings describing the same effect [K.Alekseev et al., Europhys.
Lett. 47(1999)595; cond-mat/9903092 ].
For the mixing of an ac field and its n-th harmonic with n>=4, we found that
additionally to the phase-shift controlling of the dc current, there is a
frequency control. This frequency controlling of the dc current direction is
absent in the case of n=2. The found effect is that, both the dc current
suppression and the dc current reversals exist for some particular values of ac
field frequency. For typical semiconductor superlattices such an interesting
behavior of the dc current should be observable also in the THz domain.
Finally, we briefly review the history of the problem of the dc current
generation at mixing of harmonics in semiconductors and semiconductor
microstructures.Comment: 9 pages, 1 figure, RevTEX, EPS
Tunable transport with broken space-time symmetries
Transport properties of particles and waves in spatially periodic structures
that are driven by external time-dependent forces manifestly depend on the
space-time symmetries of the corresponding equations of motion. A systematic
analysis of these symmetries uncovers the conditions necessary for obtaining
directed transport. In this work we give a unified introduction into the
symmetry analysis and demonstrate its action on the motion in one-dimensional
periodic, both in time and space, potentials. We further generalize the
analysis to quasi-periodic drivings, higher space dimensions, and quantum
dynamics. Recent experimental results on the transport of cold and ultracold
atomic ensembles in ac-driven optical potentials are reviewed as illustrations
of theoretical considerations.Comment: Phys. Rep., in pres
Radiative Thermal Rectification between SiC and SiO2
By means of fluctuationnal electrodynamics, we calculate radiative heat flux
between two pla-nar materials respectively made of SiC and SiO2. More
specifically, we focus on a first (direct) situation where one of the two
materials (for example SiC) is at ambient temperature whereas the second
material is at a higher one, then we study a second (reverse) situation where
the material temperatures are inverted. When the two fluxes corresponding to
the two situations are different, the materials are said to exhibit a thermal
rectification, a property with potential applications in thermal regulation.
Rectification variations with temperature and separation distance are here
reported. Calculations are performed using material optical data experimentally
determined by Fourier transform emission spectrometry of heated materials
between ambient temperature (around 300 K) and 1480 K. It is shown that
rectification is much more important in the near-field domain, i.e. at
separation distances smaller than the thermal wavelength. In addition, we see
that the larger is the temperature difference, the larger is rectification.
Large rectification is finally interpreted due to a weakening of the SiC
surface polariton when temperature increases, a weakening which affects much
less SiO2 resonances
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