Real-space coherent manipulation of electrons in a single tunnel junction by single-cycle terahertz electric fields

Graphene is conceivably the most nonlinear optoelectronic material we know. Its nonlinear optical coefficients in the terahertz frequency range surpass those of other materials by many orders of magnitude. Here, we show that the terahertz nonlinearity of graphene, both for ultrashort single-cycle and quasi-monochromatic multicycle input terahertz signals, can be efficiently controlled using electrical gating, with gating voltages as low as a few volts. For example, optimal electrical gating enhances the power conversion efficiency in terahertz third-harmonic generation in graphene by about two orders of magnitude. Our experimental results are in quantitative agreement with a physical model of the graphene nonlinearity, describing the time-dependent thermodynamic balance maintained within the electronic population of graphene during interaction with ultrafast electric fields. Our results can serve as a basis for straightforward and accurate design of devices and applications for efficient electronic signal processing in graphene at ultrahigh frequencies.

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Investigation of the Carrier Movement through the Tunneling Junction in the InGaP/GaAs Dual Junction Solar Cell Using the Electrically and Optically Biased Photoreflectance Spectroscopy

Energies ◽

10.3390/en14030638 ◽

2021 ◽

Vol 14 (3) ◽

pp. 638

Author(s):

Sanam SaeidNahaei ◽

Hyun-Jun Jo ◽

Sang Jo Lee ◽

Jong Su Kim ◽

Sang Jun Lee ◽

...

Keyword(s):

Solar Cell ◽

Electric Field ◽

Electric Fields ◽

Bias Voltage ◽

Tunnel Junction ◽

Photogenerated Carrier ◽

Internal Electric Field ◽

Junction Solar Cell ◽

Photoreflectance Spectroscopy ◽

Dc Bias

For examining the carrier movements through tunnel junction, electrically and optically-biased photoreflectance spectroscopy (EBPR and OBPR) were used to investigate the internal electric field in the InGaP/GaAs dual junction solar cell at room temperature. At InGaP and GaAs, the strength of p-n junction electric fields (Fpn) was perturbed by the external DC bias voltage and CW light intensity for EBPR and OBPR experiments, respectively. Moreover, the Fpn was evaluated using the Fast Fourier Transform (FFT) of the Franz—Keldysh oscillation from PR spectra. In the EBPR, the electric field decreased by increasing the DC bias voltage, which also decreased the potential barrier. In OBPR, when incident CW light is absorbed by the top cell, the decrement of the Fpn in the GaAs cell indicates that the photogenerated carriers are accumulated near the p-n junction. Photogenerated carriers in InGaP can pass through the tunnel junction, and the PR results show the contribution of the modification of the electric field by the photogenerated carriers in each cell. We suggest that PR spectroscopy with optical-bias and electrical-bias could be analyzed using the information of the photogenerated carrier passed through the tunnel junction.

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Nonlinear nanoelectrodynamics of a Weyl metal

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2116366118 ◽

2021 ◽

Vol 118 (48) ◽

pp. e2116366118

Author(s):

Yinming Shao ◽

Ran Jing ◽

Sang Hoon Chae ◽

Chong Wang ◽

Zhiyuan Sun ◽

...

Keyword(s):

Electric Fields ◽

Mirror Symmetry ◽

Density Functional ◽

Near Field ◽

Surface States ◽

Real Space ◽

Resonance Structure ◽

Nonlinear Conductivity ◽

Weyl Semimetal ◽

Photocurrent Spectroscopy

Chiral Weyl fermions with linear energy-momentum dispersion in the bulk accompanied by Fermi-arc states on the surfaces prompt a host of enticing optical effects. While new Weyl semimetal materials keep emerging, the available optical probes are limited. In particular, isolating bulk and surface electrodynamics in Weyl conductors remains a challenge. We devised an approach to the problem based on near-field photocurrent imaging at the nanoscale and applied this technique to a prototypical Weyl semimetal TaIrTe4. As a first step, we visualized nano-photocurrent patterns in real space and demonstrated their connection to bulk nonlinear conductivity tensors through extensive modeling augmented with density functional theory calculations. Notably, our nanoscale probe gives access to not only the in-plane but also the out-of-plane electric fields so that it is feasible to interrogate all allowed nonlinear tensors including those that remained dormant in conventional far-field optics. Surface- and bulk-related nonlinear contributions are distinguished through their “symmetry fingerprints” in the photocurrent maps. Robust photocurrents also appear at mirror-symmetry breaking edges of TaIrTe4 single crystals that we assign to nonlinear conductivity tensors forbidden in the bulk. Nano-photocurrent spectroscopy at the boundary reveals a strong resonance structure absent in the interior of the sample, providing evidence for elusive surface states.

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Sub-cycle Manipulation of Electrons in a Tunnel Junction with Phase-controlled Single-cycle THz Near-fields

EPJ Web of Conferences ◽

10.1051/epjconf/201920508007 ◽

2019 ◽

Vol 205 ◽

pp. 08007

Author(s):

Katsumasa Yoshioka ◽

Ikufumi Katayama ◽

Yusuke Arashida ◽

Atsuhiko Ban ◽

Yoichi Kawada ◽

...

Keyword(s):

Tunnel Junction ◽

Phase Shifter ◽

Electron Tunneling ◽

Near Field ◽

Scanning Tunneling ◽

Electron Dynamics ◽

Tunneling Microscopy ◽

Single Cycle ◽

Carrier Envelope Phase ◽

Tunneling Dynamics

By utilizing terahertz scanning tunneling microscopy (THz-STM) with a carrier envelope phase shifter for broadband THz pulses, we could successfully control the near-field-mediated electron dynamics in a tunnel junction with sub-cycle precision. Measurements of the phase-resolved sub-cycle electron tunneling dynamics revealed an unexpected large carrier-envelope phase shift between far-field and near-field single-cycle THz waveforms.

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Attosecond coherent manipulation of electrons in tunneling microscopy

Science ◽

10.1126/science.aaz1098 ◽

2019 ◽

Vol 367 (6476) ◽

pp. 411-415 ◽

Cited By ~ 12

Author(s):

M. Garg ◽

K. Kern

Keyword(s):

Tunnel Junction ◽

Coherent Control ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Optical Pulses ◽

Nanoelectronic Devices ◽

Electronic Current ◽

And Control ◽

Coherent Manipulation ◽

Manipulation And Control

Nanoelectronic devices operating in the quantum regime require coherent manipulation and control over electrons at atomic length and time scales. We demonstrate coherent control over electrons in a tunnel junction of a scanning tunneling microscope by means of precise tuning of the carrier-envelope phase of two-cycle long (<6-femtosecond) optical pulses. We explore photon and field-driven tunneling, two different regimes of interaction of optical pulses with the tunnel junction, and demonstrate a transition from one regime to the other. Our results show that it is possible to induce, track, and control electronic current at atomic scales with subfemtosecond resolution, providing a route to develop petahertz coherent nanoelectronics and microscopy.

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An eigenstate formulation of the magnetotelluric impedance tensor

Geophysics ◽

10.1190/1.1441383 ◽

1982 ◽

Vol 47 (8) ◽

pp. 1204-1214 ◽

Cited By ~ 55

Author(s):

Dwight E. Eggers

Keyword(s):

Electric Fields ◽

Degrees Of Freedom ◽

Homogeneous Medium ◽

Real Space ◽

Conventional Approach ◽

Impedance Tensor ◽

Electric And Magnetic Fields ◽

Coordinate Rotation ◽

Rotation Methods ◽

Transverse Electromagnetic

An important step in the interpretation of magnetotelluric (MT) data is the extraction of scalar parameters from the impedance tensor Z, the transfer function which relates the observed horizontal magnetic and electric fields. The conventional approach defines parameters in terms of elements of a coordinate‐rotated tensor. The rotation angle is chosen such that Z′(θ) approximates in some sense the form for a two‐dimensional (2-D) subsurface conductivity distribution, with zero elements on the diagonal. There are two major problems with this approach. (1) Apparent resistivities, defined from the off‐diagonal elements of the rotated tensor, are independent of the trace of Z. It is problematic that apparent resistivities, the parameters for which we have physical analogs and which are most heavily used in interpretation, are insensitive to the addition of an arbitrary constant on the diagonal of Z. (2) The conventional parameter set is incomplete; there are two degrees of freedom in Z which are transparent to all parameters. Through a variation of the classical eigenstate formulation of a matrix, it is shown that in general there exist two, and only two, polarization states for which the electric and magnetic fields have the same polarization at perpendicular orientations. For each eigenstate the magnetic and electric fields are related by a scalar, the eigenvalue for that state. This scalar relationship between fields is of identical form to the solution for transverse electromagnetic (TEM) waves in a homogeneous medium and thus provides a physically more satisfactory basis for defining apparent resistivity than the conventional approach using the off‐diagonal elements of the coordinate‐rotated impedance tensor. The eigenstate and coordinate‐rotation methods yield identical results in the limited cases of 1-D and 2-D subsurface conductivity distributions. The eigenstates provide the basis for new definitions of parameters as concise, closed expressions which are complete and more amenable to interpretational insight. The polarization ellipses defined by the eigenstates provide a concise display in real space of all the information contained in the impedance tensor.

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