اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدPhotoexcitation Cascade and Quantum-Relativistic Jets in Graphene
325
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
In Dirac materials linear band dispersion blocks momentum-conserving interband transitions, creating a bottleneck for electron-hole pair production and carrier multiplication in the photoexcitation cascade. Here we show that the decays are unblocked and the bottleneck is relieved by subtle many-body effects involving multiple off-shell e-h pairs. The decays result from a collective behavior due to emission of many soft pairs. We discuss characteristic signatures of the off-shell pathways, in particular the sharp angular distribution of secondary carriers, resembling relativistic jets in high-energy physics. The jets can be directly probed using solid-state equivalent of particle detectors. Collinear scattering enhances carrier multiplication, allowing for emission of as many as ${sim}10$ secondary carriers per single absorbed photon.
قيم البحث
اقرأ أيضاً
The conversion of light into free electron-hole pairs constitutes the key process in the fields of photodetection and photovoltaics. The efficiency of this process depends on the competition of different relaxation pathways and can be greatly enhance
d when photoexcited carriers do not lose energy as heat, but instead transfer their excess energy into the production of additional electron-hole pairs via carrier-carrier scattering processes. Here we use Optical pump - Terahertz probe measurements to show that in graphene carrier-carrier scattering is unprecedentedly efficient and dominates the ultrafast energy relaxation of photoexcited carriers, prevailing over optical phonon emission in a wide range of photon wavelengths. Our results indicate that this leads to the production of secondary hot electrons, originating from the conduction band. Since hot electrons in graphene can drive currents, multiple hot carrier generation makes graphene a promising material for highly efficient broadband extraction of light energy into electronic degrees of freedom, enabling high-efficiency optoelectronic applications.
We theoretically study the population inversion and negative dynamic conductivity in intrinsic graphene in the terahertz (THz) frequency range upon pulse photoexcitation with near-/mid-infrared wavelength. The threshold pulse energy required for the
population inversion and negative dynamic conductivity can be orders-of-magnitude lower when the pulse photon energy is lower, due to the inverse proportionality of the photoexcited carrier concentration to the pulse photon energy and to the weaker carrier heating. We also investigate the dependence of the dynamic conductivity on the momentum relaxation time. The negative dynamic conductivity takes place either in high- or low-quality graphene, where the Drude absorption by carriers in the THz frequency is weak.
We propose and evaluate the vertical cascade terahertz and infrared photodetectors based on multiple-graphene-layer (GL) structures with thin tunnel barrier layers (made of tungsten disulfide or related materials). The photodetector operation is asso
ciated with the cascaded radiative electron transitions from the valence band in GLs to the conduction band in the neighboring GLs (interband- and inter-GL transitions). We calculate the spectral dependences of the responsivity and detectivity for the vertical cascade interband GL- photodetectors (I-GLPDs) with different number of GLs and doping levels at different bias voltages in a wide temperature range. We show the possibility of an effective manipulation of the spectral characteristics by the applied voltage. The spectral characteristics depend also on the GL doping level that opens up the prospects of using I-GLPDs in the multi-color systems. The advantages of I-GLPDs under consideration are associated with their sensitivity to the normal incident radiation, weak temperature dependence of the dark current as well as high speed of operation. The comparison of the proposed I-GLDs with the quantum-well intersubband photodectors demonstrates the superiority of the former, including a better detectivity at room temperature and a higher speed. The vertical cascade I-GLDs can also surpass the lateral p-i-n GLDs in speed.
We study a relativistic quantum cavity system realized by etching out from a graphene sheet by quantum transport measurements and theoretical calculations. The conductance of the graphene cavity has been measured as a function of the back gate voltag
e (or the Fermi energy) and the magnetic field applied perpendicular to the graphene sheet, and characteristic conductance contour patterns are observed in the measurements. In particular, two types of high conductance contour lines, i.e., straight and parabolic-like high conductance contour lines, are found in the measurements. The theoretical calculations are performed within the framework of tight-binding approach and Greens function formalism. Similar characteristic high conductance contour features as in the experiments are found in the calculations. The wave functions calculated at points selected along a straight conductance contour line are found to be dominated by a chain of scars of high probability distributions arranged as a necklace following the shape of cavity and the current density distributions calculated at these point are dominated by an overall vortex in the cavity. These characteristics are found to be insensitive to increasing magnetic field. However, the wave function probability distributions and the current density distributions calculated at points selected along a parabolic-like contour line show a clear dependence on increasing magnetic field, and the current density distributions at these points are characterized by the complex formation of several localized vortices in the cavity. Our work brings a new insight into quantum chaos in relativistic particle systems and would greatly stimulate experimental and theoretical efforts towards this still emerging field.
Electrons in graphene, behaving as massless relativistic Dirac particles, provide a new perspective on the relation between condensed matter and high-energy physics. We discuss atomic collapse, a novel state of superheavy atoms stripped of their disc
rete energy levels, which are transformed into resonant states. Charge impurities in graphene provide a convenient condensed matter system in which this effect can be explored. Relativistic dynamics also manifests itself in another system, graphene p-n junctions. We show how the transport problem in the presence of magnetic field can be solved with the help of a Lorentz transformation, and use it to investigate magnetotransport in p-n junctions. Finally, we review recent proposal to use Fabry-Perot resonances in p-n-p structures as a vehicle to investigate Klein scattering, another hallmark phenomenon of relativistic dynamics.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
