Abstract-Terahertz magneto-optical spectroscopy of two-dimensional hole and electron systems

N. Kamaraju, W. Pan, U. Ekenberg, D. M. Gvozdić, S. Boubanga-Tombet, P. C. Upadhya, J. Reno, A. J. Taylor, R. P. Prasankumar

http://arxiv-web3.library.cornell.edu/abs/1412.5058

We have used terahertz (THz) magneto-optical spectroscopy to investigate the cyclotron resonance in high mobility two-dimensional electron and hole systems. Our experiments reveal long-lived (~20 ps) coherent oscillations in the measured signal in the presence of a perpendicular magnetic field. The cyclotron frequency extracted from the oscillations varies linearly with magnetic field for a two-dimensional electron gas (2DEG), as expected. However, we find that the complex non-parabolic valence band structure in a two-dimensional hole gas (2DHG) causes the cyclotron frequency and effective mass to vary nonlinearly with the magnetic field, as verified by multiband Landau level calculations. This is the first time that THz magneto-optical spectroscopy has been used to study 2DHG, and we expect that these results will motivate further studies of these unique 2D nanosystems.

Abstract-Current-driven detection of terahertz radiation using a dual-grating-gate plasmonic detector

S. Boubanga-Tombet^1,a), Y. Tanimoto¹, A. Satou¹, T. Suemitsu¹, Y. Wang²,H. Minamide², H. Ito², D. V. Fateev^3,4, V. V. Popov^3,4 and T. Otsuji¹
 HIDE AFFILIATIONS
1 Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-Ku, Sendai 980-8577, Japan
2 RIKEN Sendai, 519-1399 Aramaki Aoba, Aoba-ku, Sendai 980-0845, Japan
3 Kotelnikov Institute of Radio Engineering and Electronics (Saratov Branch), 410019 Saratov, Russia
4 Saratov State University, 410012 Saratov, Russia
a) Author to whom correspondence should be addressed. Electronic mail: stephanealbon@hotmail.com
Appl. Phys. Lett. 104, 262104 (2014); http://dx.doi.org/10.1063/1.4886763

We report on the detection of terahertz radiation by an on-chip planar asymmetric plasmonicstructure in the frequency region above one terahertz. The detector is based on a field-effect transistor that has a dual grating gate structure with an asymmetric unit cell, which provides a geometrical asymmetry within the structure. Biasing the detector with a dc source-to-drain current in the linear region of the current-voltage characteristic introduces an additional asymmetry (electrical asymmetry) that enhances the detector responsivity by more than one order of magnitude (by a factor of 20) as compared with the unbiased case due to the cooperative effect of the geometrical and electrical asymmetries. In addition to the responsivity enhancement, we report a relatively low noise equivalent power and a peculiar non-monotonic dependence of the responsivity on the frequency, which results from the multi-plasmonic-cavity structure of the device.

Abstract: Ultrafast carrier dynamics and terahertz emission in optically pumped graphene at room temperature

http://prb.aps.org/abstract/PRB/v85/i3/e035443

Received 5 April 2011; revised 11 November 2011; published 26 January 2012

We report, within a picosecond time scale, fast relaxation and relatively slow recombination dynamics of photogenerated electrons and holes in an exfoliated graphene under infrared pulse excitation. We conduct time-domain spectroscopic studies using an optical pump and terahertz probe with an optical probe technique and show that graphene sheet amplifies an incoming terahertz field. The graphene emission spectral dependency on laser pumping intensity shows a threshold-like behavior, testifying to the occurrence of the negative conductivity and the population inversion. The phase behavior of the measured terahertz electric field also shows clear Lorentzian-like normal dispersion around the gain peak, testifying to the amplification that can be attributed to stimulated emission of photocarriers in the inverted states. The emission spectra clearly narrow at a longer terahertz probe delay time, giving evidence that the quasi-Fermi energy moves closer to the equilibrium at this longer terahertz probe delay time.

©2012 American Physical Society

URL:

http://link.aps.org/doi/10.1103/PhysRevB.85.035443

DOI:

10.1103/PhysRevB.85.035443

PACS:

78.45.+h, 78.47.D-, 78.66.Tr, 78.70.-g

^*stephanealbon@hotmail.com

Abstract:Ultrafast carrier dynamics and terahertz emission in optically pumped graphene at room temperature

S. Boubanga-Tombet, S. Chan, A. Satou, V. Ryzhii, and T. Otsuji

http://prb.aps.org/accepted/B/8d071Y6cQf41b62629da6ff57cc914dfee7cb4880

We report within picosecond time scale, fast relaxation and relatively slow recombination dynamics of photogenerated electrons/holes in an exfoliated graphene under infrared pulse excitation. We conduct time domain spectroscopic studies using an optical pump/terahertz probe and optical probe technique and show that graphene sheet amplifies an incoming terahertz field. The graphene emission spectral dependency on laser pumping intensity shows a threshold like behavior, testifying the occurrence of the negative conductivity and the population inversion. The phase behavoir of the measured Terahertz electric field also show clear Lorentzian-like normal dispersion around the gain peak, testifying the occurrence of amplification that can be attributed to stimulated emission of photo-carriers in the inverted states. The emission spectra also show a clear narrowing at longer terahertz probe delay time giving a clear evidence of the quasi-fermi energy moving closer to the equilibrium at this longer terahertz probe delay time.