362 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
ENTRAPMENT NEUROPATHIES OF THE UPPER EXTREMITIES AND NEW TRENDS IN PHYSIOTHERAPY
Purpose. The purpose of this work was to highlight the importance of targeted physiotherapy in the treatment of nerve entrapment syndrome in the upper limb using the latest physiotherapeutic techniques.Material and methods. In this work, 56 patients are presented as diagnosed with nerve entrapment syndrome in the upper limb. 45 of them are women and 21 are men, ranging in age from 26–72 years old with an average age of 49 years. We evaluated the pain condition, pain intensity, and also functional deficits before and after rehabilitation treatment over a duration of four weeks.Conclusion. As a result of targeted therapy towards nerve entrapment syndrome in the upper limb, the functional condition of the majority of our patients has improved and their pain was reduced.The expected mechanism of this kind of physiotherapy is to improve blood circulation in the affected area, adjust the biomechanical forces that affect joint structures, improve the functional condition, and prevent a relapse of the disease from occurring.Keywords. Entrapment neuropathies, upper extremities, pain, physiotherapy
Atomistic defect states as quantum emitters in monolayer MoS
Quantum light sources in solid-state systems are of major interest as a basic
ingredient for integrated quantum device technologies. The ability to tailor
quantum emission through deterministic defect engineering is of growing
importance for realizing scalable quantum architectures. However, a major
difficulty is that defects need to be positioned site-selectively within the
solid. Here, we overcome this challenge by controllably irradiating
single-layer MoS using a sub-nm focused helium ion beam to
deterministically create defects. Subsequent encapsulation of the ion bombarded
MoS flake with high-quality hBN reveals spectrally narrow emission lines
that produce photons at optical wavelengths in an energy window of one to two
hundred meV below the neutral 2D exciton of MoS. Based on ab-initio
calculations we interpret these emission lines as stemming from the
recombination of highly localized electron-hole complexes at defect states
generated by the helium ion bombardment. Our approach to deterministically
write optically active defect states in a single transition metal
dichalcogenide layer provides a platform for realizing exotic many-body
systems, including coupled single-photon sources and exotic Hubbard systems.Comment: Main: 9 pages, 3 figures + SI: 19 pages, 10 figure
Spin-dynamic field coupling in strongly THz driven semiconductors : local inversion symmetry breaking
We study theoretically the optics in undoped direct gap semiconductors which
are strongly driven in the THz regime. We calculate the optical sideband
generation due to nonlinear mixing of the THz field and the near infrared
probe. Starting with an inversion symmetric microscopic Hamiltonian we include
the THz field nonperturbatively using non-equilibrium Green function
techniques. We find that a self induced relativistic spin-THz field coupling
locally breaks the inversion symmetry, resulting in the formation of odd
sidebands which otherwise are absent.Comment: 8 pages, 6 figure
Observation of magnon bound states in the long-range, anisotropic Heisenberg model
Over the recent years coherent, time-periodic modulation has been established
as a versatile tool for realizing novel Hamiltonians. Using this approach,
known as Floquet engineering, we experimentally realize a long-ranged,
anisotropic Heisenberg model with tunable interactions in a trapped ion quantum
simulator. We demonstrate that the spectrum of the model contains not only
single magnon excitations but also composite magnon bound states. For the
long-range interactions with the experimentally realized power-law exponent,
the group velocity of magnons is unbounded. Nonetheless, for sufficiently
strong interactions we observe bound states of these unconventional magnons
which possess a non-diverging group velocity. By measuring the configurational
mutual information between two disjoint intervals, we demonstrate the
implications of the bound state formation on the entanglement dynamics of the
system. Our observations provide key insights into the peculiar role of
composite excitations in the non-equilibrium dynamics of quantum many-body
systems
Non-Periodic Finite-Element Formulation of Orbital-Free Density Functional Theory
We propose an approach to perform orbital-free density functional theory calculations in a non-periodic setting using the finite-element method. We consider this a step towards constructing a seamless multi-scale approach for studying defects like vacancies, dislocations and cracks that require quantum mechanical resolution at the core and are sensitive to long range continuum stresses. In this paper, we describe a local real space variational formulation for orbital-free density functional theory, including the electrostatic terms and prove existence results. We prove the convergence of the finite-element approximation including numerical quadratures for our variational formulation. Finally, we demonstrate our method using examples
Geometrical Aberration Suppression for Large Aperture Sub-THz Lenses
Advanced THz setups require high performance optical elements with large numerical apertures and small focal lengths. This is due to the high absorption of humid air and relatively low efficiency of commercially available detectors. Here, we propose a new type of double-sided sub-THz diffractive optical element with suppressed geometrical aberration for narrowband applications (0.3 THz). One side of the element is designed as thin structure in non-paraxial approach which is the exact method, but only for ideally flat elements. The second side will compensate phase distribution differences between ideal thin structure and real volume one. The computer-aided optimization algorithm is performed to design an additional phase distribution of correcting layer assuming volume designing of the first side of the element. The experimental evaluation of the proposed diffractive component created by 3D printing technique shows almost two times larger performance in comparison with uncorrected basic diffractive lens
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
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