49 research outputs found
Terahertz Radiation Detection by Field Effect Transistor in Magnetic Field
We report on terahertz radiation detection with InGaAs/InAlAs Field Effect
Transistors in quantizing magnetic field. The photovoltaic detection signal is
investigated at 4.2 K as a function of the gate voltage and magnetic field.
Oscillations analogous to the Shubnikov-de Haas oscillations, as well as their
strong enhancement at the cyclotron resonance, are observed. The results are
quantitatively described by a recent theory, showing that the detection is due
to rectification of the terahertz radiation by plasma waves related
nonlinearities in the gated part of the channel.Comment: 4 pages, 3 figure
Temperature-driven single-valley Dirac fermions in HgTe quantum wells
We report on temperature-dependent magnetospectroscopy of two HgTe/CdHgTe
quantum wells below and above the critical well thickness . Our results,
obtained in magnetic fields up to 16 T and temperature range from 2 K to 150 K,
clearly indicate a change of the band-gap energy with temperature. The quantum
well wider than evidences a temperature-driven transition from
topological insulator to semiconductor phases. At the critical temperature of
90 K, the merging of inter- and intra-band transitions in weak magnetic fields
clearly specifies the formation of gapless state, revealing the appearance of
single-valley massless Dirac fermions with velocity of
ms. For both quantum wells, the energies extracted from
experimental data are in good agreement with calculations on the basis of the
8-band Kane Hamiltonian with temperature-dependent parameters.Comment: 5 pages, 3 figures and Supplemental Materials (4 pages
Massless Dirac fermions in III-V semiconductor quantum wells
We report on the clear evidence of massless Dirac fermions in two-dimensional
system based on III-V semiconductors. Using a gated Hall bar made on a
three-layer InAs/GaSb/InAs quantum well, we restore the Landau levels fan chart
by magnetotransport and unequivocally demonstrate a gapless state in our
sample. Measurements of cyclotron resonance at different electron
concentrations directly indicate a linear band crossing at the point
of Brillouin zone. Analysis of experimental data within analytical Dirac-like
Hamiltonian allows us not only determing velocity m/s of
massless Dirac fermions but also demonstrating significant non-linear
dispersion at high energies.Comment: Main text and Supplemental Materials, 14 pages, 9 figure
Temperature Dependent Zero-Field Splittings in Graphene
Graphene is a quantum spin Hall insulator with a 45 eV wide non-trivial
topological gap induced by the intrinsic spin-orbit coupling. Even though this
zero-field spin splitting is weak, it makes graphene an attractive candidate
for applications in quantum technologies, given the resulting long spin
relaxation time. On the other side, the staggered sub-lattice potential,
resulting from the coupling of graphene with its boron nitride substrate,
compensates intrinsic spin-orbit coupling and decreases the non-trivial
topological gap, which may lead to the phase transition into trivial band
insulator state. In this work, we present extensive experimental studies of the
zero-field splittings in monolayer and bilayer graphene in a temperature range
2K-12K by means of sub-Terahertz photoconductivity-based electron spin
resonance technique. Surprisingly, we observe a decrease of the spin splittings
with increasing temperature. We discuss the origin of this phenomenon by
considering possible physical mechanisms likely to induce a temperature
dependence of the spin-orbit coupling. These include the difference in the
expansion coefficients between the graphene and the boron nitride substrate or
the metal contacts, the electron-phonon interactions, and the presence of a
magnetic order at low temperature. Our experimental observation expands
knowledge about the non-trivial topological gap in graphene.Comment: Main text with figures (20 pages) and Supplementary Information (14
pages) Accepted in Phys. Rev.
Helicity sensitive terahertz radiation detection by field effect transistors
Terahertz light helicity sensitive photoresponse in GaAs/AlGaAs high electron
mobility transistors. The helicity dependent detection mechanism is interpreted
as an interference of plasma oscillations in the channel of the
field-effect-transistors (generalized Dyakonov-Shur model). The observed
helicity dependent photoresponse is by several orders of magnitude higher than
any earlier reported one. Also linear polarization sensitive photoresponse was
registered by the same transistors. The results provide the basis for a new
sensitive, all-electric, room-temperature and fast (better than 1 ns)
characterisation of all polarization parameters (Stokes parameters) of
terahertz radiation. It paves the way towards terahertz ellipsometry and
polarization sensitive imaging based on plasma effects in
field-effect-transistors.Comment: 7 pages, 4 figure