Understanding the charge pumping and relaxation of the chiral anomaly in a Dirac semimetal (original) (raw)
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Electron energy relaxation under terahertz excitation in (Cd1− x Zn x )3As2 Dirac semimetals
Beilstein Journal of Nanotechnology, 2017
We demonstrate that measurements of the photo-electromagnetic effect using terahertz laser radiation provide an argument for the existence of highly conductive surface electron states with a spin texture in Dirac semimetals (Cd1− x Zn x )3As2. We performed a study on a range of (Cd1− x Zn x )3As2 mixed crystals undergoing a transition from the Dirac semimetal phase with an inverse electron energy spectrum to trivial a semiconductor with a direct spectrum in the crystal bulk by varying the composition x. We show that for the Dirac semimetal phase, the photo-electromagnetic effect amplitude is defined by the number of incident radiation quanta, whereas for the trivial semiconductor phase, it depends on the laser pulse power, irrespective of wavelength. We assume that such behavior is attributed to a strong damping of the interelectron interaction in the Dirac semimetal phase compared to the trivial semiconductor, which may be due to the formation of surface electron states with a spin...
Strong tunable photomixing in semi-Dirac materials in the terahertz regime
Journal of the Optical Society of America B, 2019
We demonstrate a strong and anisotropic photomixing effect in an electronic system whose energy-momentum dispersion is parabolic in the ? direction and linear in the ? direction, such as a TiO 2 /VO 2 multilayered structure. The third-order photoresponses along the linear and parabolic directions have been analyzed and determined quantitatively. We have found a remarkable tunability of the mixing efficiency along the parabolic direction by a small electric field in the linear direction, up to two orders of magnitude. In the terahertz (THz) regime, the third-order response is comparable to the linear response under an applied field of 10 3-10 4 V/cm. Additionally, the nonlinear response persists at room temperature. The results may have applications where different current responses are required along different directions in the THz regime. We demonstrate a strong and anisotropic photomixing effect in an electronic system whose energy-momentum dispersion is parabolic in the ? direction and linear in the ? direction, such as a TiO2/VO2 multilayered structure. The third-order photoresponses along the linear and parabolic directions have been analyzed and determined quantitatively. We have found a remarkable tunability of the mixing efficiency along the parabolic direction by a small electric field in the linear direction, up to two orders of magnitude. In the terahertz (THz) regime, the third-order response is comparable to the linear response under an applied field of 103-104 V/cm. Additionally, the nonlinear response persists at room temperature. The results may have applications where different current responses are required along different directions in the THz regime.
Signature of the chiral anomaly in a Dirac semimetal: a current plume steered by a magnetic field
In this talk, we describe recent experimental progress in detecting the chiral anomaly in the Dirac semimetal Na$_3$Bi in the presence of a magnetic field. The chiral anomaly, which plays a fundamental role in chiral gauge theories, was predicted to be observable in crystals by Nielsen and Ninomiya in 1983 [1]. Theoretical progress in identifying and investigating Dirac and Weyl semimetals has revived strong interest in this issue [2-6]. In the Dirac semimetal, the breaking of time-reversal symmetry by a magnetic field bfB\bf BbfB splits each Dirac node into two chiral Weyl nodes. If an electric field bfE\bf EbfE is applied parallel to bfB\bf BbfB, charge is predicted to flow between the Weyl nodes. We report the observation in the Dirac semimetal Na$_3$Bi of a novel, negative and highly anisotropic magnetoresistance (MR). We show that the enhanced conductivity has the form of a narrowly defined plume that can be steered by the applied field. The novel MR is acutely sensitive to deviations of $...
Three-dimensional Dirac semimetal and magnetic quantum oscillations in Cd3As2
Journal of Physics: Conference Series
Single crystals of topological Dirac semimetal Cd 3 As 2 were synthesized using a modified vapour transport technique. The magnetization of Cd 3 As 2 single crystals was measured in the temperature range from 4.2-300 K and magnetic field up to 5 T along [001] and [100] directions. In the low temperature region we observed the de Haas van Alphen (dHvA) oscillations which allow us to characterize the three dimensional Fermi surface by extracting its relevant parameters. The dHvA oscillations show the existence of two different Fermi surface cross sections and nontrivial Berry's phase, which is the signature of Dirac fermion in Cd 3 As 2 .
Electric field, Magnetic field and Magnetization: THz time-domain spectroscopy studies
2015
Terahertz radiation is electromagnetic waves with frequencies from 0.1-10 THz. THz radiation can pass through cardboard, paper, plastics, ceramics and many other materials. Hence, it can be used for non-destructive imaging. Another important application of THz radiation is spectroscopy. Many organic molecules absorb light at THz frequencies and these absorption lines can be used for the identification of the molecules. This spectroscopic technique is called terahertz time domain spectroscopy (THz-TDS). It is a valuable tool for studying the properties of the material. In THz-TDS we measure the amplitude and phase of the THz pulse in the time domain using coherent detection techniques. Usually, in THz-TDS technique we measure the THz electric field using electro-optic detention technique. However, in thesis, the main goal is to focus on the magnetic aspect of THz generation and detection using THz-TDS. This thesis is divided into three research problems, in which THz-TDS plays the ke...
Journal of Applied Physics, 2016
The amplification coefficient α of acoustic phonons is theoretically investigated in a three-dimensional Dirac semimetal (3DDS) driven by a dc electric field E causing the drift of the electrons. It is numerically studied as a function of the frequency ωq, drift velocity vd, electron concentration ne, and temperature T in the Dirac semimetal Cd3As2. We find that the amplification of acoustic phonons (α ∼ hundreds of cm-1) takes place when the electron drift velocity vd is greater than the sound velocity vs. The amplification is found to occur at small E (∼few V/cm) due to large electron mobility. The frequency dependence of α shows amplification in the THz regime with a maximum αm occurring at the same frequency ωqm for different vd. The αm is found to increase with increasing vd. α vs ωq for different ne also shows a maximum, with αm shifting to higher ωq for larger ne. Each maximum is followed by a vanishing α at nearly “2kf cutoff,” where kf is the Fermi wave vector. It is found ...
Large transverse Hall-like signal in topological Dirac semimetal Cd3As2
Scientific reports, 2016
Cadmium arsenide (Cd3As2) is known for its inverted band structure and ultra-high electron mobility. It has been theoretically predicted and also confirmed by ARPES experiments to exhibit a 3D Dirac semimetal phase containing degenerate Weyl nodes. From magneto-transport measurements in high quality single crystals of Cd3As2, a small effective mass m(*) ≈ 0.05 me is determined from the Shubnikov-de Haas (SdH) oscillations. In certain field orientations, we find a splitting of the SdH oscillation frequency in the FFT spectrum suggesting a possible lifting of the double degeneracy in accord with the helical spin texture at outer and inner Fermi surfaces with opposite chirality predicted by our ab initio calculations. Strikingly, a large antisymmetric magnetoresistance with respect to the applied magnetic fields is uncovered over a wide temperature range in needle crystal of Cd3As2 with its long axis along [112] crystal direction. It reveals a possible contribution of intrinsic anomalo...