Direct photoluminescence probing of ferromagnetism in monolayer two-dimensional CrBr3

Atomically thin magnets are the key element to build up spintronics based on two-dimensional materials. The surface nature of two-dimensional ferromagnet opens up opportunities to improve the device performance efficiently. Here, we report the intrinsic ferromagnetism in atomically thin monolayer CrBr3, directly probed by polarization resolved magneto-photoluminescence. The spontaneous magnetization persists in monolayer CrBr3 with a Curie temperature of 34 K. The development of magnons by the thermal excitation is in line with the spin-wave theory. We attribute the layer-number dependent hysteresis loops in thick layers to the magnetic domain structures. As a stable monolayer material in air, CrBr3 provides a convenient platform for fundamental physics and pushes the potential applications of the two-dimensional ferromagnetism.Comment: 27 pages, 10 figure

Optical spin pumping induced pseudo-magnetic field in two dimensional heterostructures

Two dimensional heterostructures are likely to provide new avenues for the manipulation of magnetization that is crucial for spintronics or magnetoelectronics. Here, we demonstrate that optical spin pumping can generate a large effective magnetic field in two dimensional MoSe2/WSe2 heterostructures. We determine the strength of the generated field by polarization-resolved measurement of the interlayer exciton photoluminescence spectrum: the measured splitting exceeding 10 milli-electron volts (meV) between the emission originating from the two valleys corresponds to an effective magnetic field of ~ 30 T. The strength of this optically induced field can be controlled by the excitation light polarization. Our finding opens up new possibilities for optically controlled spintronic devices based on van der Waals heterostructures

Bright room temperature single photon source at telecom range in cubic silicon carbide

Single photon emitters (SPEs) play an important role in a number of quantum information tasks such as quantum key distributions. In these protocols, telecom wavelength photons are desired due to their low transmission loss in optical fibers. In this paper, we present a study of bright single-photon emitters in cubic silicon carbide (3C-SiC) emitting in the telecom range. We find that these emitters are photostable and bright at room temperature with a count rate of ~ MHz. Together with the fact that SiC is a growth and fabrication-friendly material, our result may pave the way for its future application in quantum communication technology applications.Comment: Accepted by Nature Communication

The transfer space

The coordinates of the transfer space are loss of the source, gain of the sink and cost to both sides and compares the coupled gain and loss of two single parties to gain or loss of the ensemble of both, the invisible third party. Whenever two not identically equipped parties meet with the potential to exchange substrates one party will become a source and the other a sink. The outcome depends on the relation between fix cost, variable cost, productivity and affinity. The selfishly transferred substrate will optimize productivity of one or both sides and will lead under certain conditions to a productivity increase of the ensemble. This increase roots in the transfer of substrates from saturated to unsaturated production conditions. Brute force and educational conditioning take advantage of emotions to hide the real size of the cost to the exploited party. In case the transfer of substrates leads to increased productivity parts of the productivity might be reinvested to keep the exploited party. The lasting relationship is called wise exploitation. Wise exploitation may last for one or many generations depending on the use of brute force, education or breeding. To maintain a stable system the benefit must always exceed the cost. The transfer space views group (ensemble) selection as egoism based exploitation from catalytic networks to societies and interprets the decision process under external influence in a single economic entity

Light-matter interaction in 2D transition metal dichalcogenide heterostructure : magneto photoluminescence, lasing, and photocurrent

The two-dimensional (2D) transition metal dichalcogenide (TMD) features many properties that are desirable for applications in spintronics and valleytronics, as well as in excitonic devices, all of which aims for more energy-efficient devices. Moreover, even richer physical phenomena involving interlayer interaction can be observed when two TMD monolayers are stacked together creating, the 2D TMD heterostructure. This thesis presents the study of several aspects of the interaction between matter and light in the two-dimensional TMD heterostructure. First, the study regarding the MoSe2/WSe2 interlayer exciton dynamics under circularly polarized excitation and magnetic field influence is presented. We show that the interlayer exciton dynamic is affected by the dark WSe2 exciton. Moreover, we found that the interlayer exciton transition energy corresponding to maximum transition strength depends on the excitation polarization indicating a large optically induced pseudomagnetic field. Next, the study of the interaction between the MoS2/WSe2 interlayer exciton with light inside a cavity is presented. We show that the long interlayer exciton lifetime enables an excitonic laser with ultralow threshold power even with a low Q-factor cavity. Lastly, we show that the circular photogalvanic effect (CPGE) can be generated at the boundary between the 2D MoS2/WSe2 heterostructure and a metal electrode. The observed CPGE is due to the valley-dependent shift of the valence band induced by the combination of the built-in electric field and the optical selection rule of the valley as well as the different effective relaxation times between electron and hole in the 2D heterostructure. The findings presented in this thesis may be useful for realizing opto-valleytronics, opto-spintronics, as well as excitonic device applications which is based on 2D TMD heterostructure as a platform. We discuss several possible future research directions based on these findings.Doctor of Philosoph

RF circuit and antenna optimization using space mapping technique

The use of EM simulation in circuit optimization in RF domain is very common. There are some problems with this kind of optimization. Firstly, in many cases EM simulations are expensive process. Another problem is the relationship between circuit response and design variable is not an easy function in many cases. In order to overcome these problems a technique named space mapping (SM) was suggested. This technique has been experimentally proved as effective and efficient technique to do optimization including RF circuit optimization. From large number of SM algorithm variants there are only a few that are designed specially for constrained optimization. In this report some constrained SM algorithms using projection method are investigated. These algorithms are variants of Aggressive Space Mapping (ASM) and Aggressive Output Space Mapping (AOSM) and designed to handle convex constraints. The methods are used to optimize multilayer LTCC bandpass filter. The numerical results shows good convergence rate. All of the constrained SM algorithms designed in this report use equivalent circuit and embedded knowledge in coarse model. Parameter extraction is done using circuit tuning based on physical augmentation. In order to test the efficiency of the tuning method, this tuning method is used to tune multilayer LTCC bandpass filter equivalent circuit. The result shows this tuning algorithm is effective and efficient. This circuit tuning algorithm is a derivative of a modeling algorithm based on physical augmentation. The use of this modeling technique in producing equivalent circuit for antenna is investigated. It is shown experimentally that this modeling algorithm is effective and efficient. Although some of proposed constrained SM algorithms are designed to provide global convergence, the author can not prove the global convergence mathematically. The author can only provide the proof for local convergence of some constrained SM algorithms. Further developments may be done in the direction of finding the mathematical analysis of these SM algorithms, refining the methods especially the AOSM based methods and combining the ASM and AOSM.Bachelor of Engineerin

Accessos directes a adiabaticity per al transport de les ones de matèria

Treball final de màster oficial fet en col·laboració amb Universitat Autònoma de Barcelona (UAB), Universitat de Barcelona (UB) i Institut de Ciències Fotòniques (ICFO)[ANGLES] In this master thesis we investigate the quantum transport of a single neutral atom between double-well and triple-well potentials. In particular, we study and implement the Fast-Forward technique to speed up the quantum dynamics of the Three-Level Atom Optics (TLAO) based transport. We show that the resulting technique is faster and, against certain experimentaimperfections, more robust than the usual TLAO-based transport. Moreover, we address different shortcuts to adiabaticity examples. First, we derive a more general shortcut to adiabaticity for adiabatic translation than the one reported in the literature. Also, we obtain a criterion for the realization of a shortcut to adiabaticity and we show that, under this criterion, it is impossible to derive a realizable shortcut to adiabaticity using the Fast-Forward technique for the TLAO-based transport.[CASTELLÀ] Esta tesis de maestría se investiga el transporte cuántico de un átomo neutro entre los potenciales de doble-well y triple-well. En particular, estudiamos y aplicamos la técnica de Fast-Forward para acelerar la dinámica cuántica de la Three-Level Atom Optics (TLAO) transporte basado. Se demuestra que la técnica es que resulta más rápido y, en contra de ciertas imperfecciones experimentales, más robusto que el transporte TLAO basado habitual. Por otra parte, abordamos diferentes accesos directos a ejemplos adiabaticity. En primer lugar, derivamos un acceso más general a adiabaticity para su traducción adiabática que la reportada en la literatura. Además, se obtiene un criterio para la realización de un acceso directo a adiabaticity y mostramos que, bajo este criterio, no se puede derivar un acceso directo a adiabaticity realizable mediante la técnica de Fast-Forward para el transporte TLAO basado.[CATALA] En aquesta tesi de mestratge s'investiga el transport quàntic d'un àtom neutre entre els potencials de doble-well i triple-well. En particular, estudiem i apliquem la tècnica de Fast-Forward per accelerar la dinàmica quàntica de la Three-Level Atom Optics (TLAO) transport basat. Es demostra que la tècnica és que resulta més ràpid i, en contra de certes imperfeccions experimentals, més robust que el transport TLAO basat habitual. D'altra banda, abordem diferents accessos directes a exemples adiabaticity. En primer lloc, derivem un accés més general adiabaticity per a la seva traducció adiabàtica que la considerada en la literatura. A més, s'obté un criteri per a la realització d'un accés directe a adiabaticity i mostrem que, sota aquest criteri, no es pot derivar un accés directe a adiabaticity realitzable mitjançant la tècnica de Fast-Forward per al transport TLAO basat

Accessos directes a adiabaticity per al transport de les ones de matèria

Treball final de màster oficial fet en col·laboració amb Universitat Autònoma de Barcelona (UAB), Universitat de Barcelona (UB) i Institut de Ciències Fotòniques (ICFO)[ANGLES] In this master thesis we investigate the quantum transport of a single neutral atom between double-well and triple-well potentials. In particular, we study and implement the Fast-Forward technique to speed up the quantum dynamics of the Three-Level Atom Optics (TLAO) based transport. We show that the resulting technique is faster and, against certain experimentaimperfections, more robust than the usual TLAO-based transport. Moreover, we address different shortcuts to adiabaticity examples. First, we derive a more general shortcut to adiabaticity for adiabatic translation than the one reported in the literature. Also, we obtain a criterion for the realization of a shortcut to adiabaticity and we show that, under this criterion, it is impossible to derive a realizable shortcut to adiabaticity using the Fast-Forward technique for the TLAO-based transport.[CASTELLÀ] Esta tesis de maestría se investiga el transporte cuántico de un átomo neutro entre los potenciales de doble-well y triple-well. En particular, estudiamos y aplicamos la técnica de Fast-Forward para acelerar la dinámica cuántica de la Three-Level Atom Optics (TLAO) transporte basado. Se demuestra que la técnica es que resulta más rápido y, en contra de ciertas imperfecciones experimentales, más robusto que el transporte TLAO basado habitual. Por otra parte, abordamos diferentes accesos directos a ejemplos adiabaticity. En primer lugar, derivamos un acceso más general a adiabaticity para su traducción adiabática que la reportada en la literatura. Además, se obtiene un criterio para la realización de un acceso directo a adiabaticity y mostramos que, bajo este criterio, no se puede derivar un acceso directo a adiabaticity realizable mediante la técnica de Fast-Forward para el transporte TLAO basado.[CATALA] En aquesta tesi de mestratge s'investiga el transport quàntic d'un àtom neutre entre els potencials de doble-well i triple-well. En particular, estudiem i apliquem la tècnica de Fast-Forward per accelerar la dinàmica quàntica de la Three-Level Atom Optics (TLAO) transport basat. Es demostra que la tècnica és que resulta més ràpid i, en contra de certes imperfeccions experimentals, més robust que el transport TLAO basat habitual. D'altra banda, abordem diferents accessos directes a exemples adiabaticity. En primer lloc, derivem un accés més general adiabaticity per a la seva traducció adiabàtica que la considerada en la literatura. A més, s'obté un criteri per a la realització d'un accés directe a adiabaticity i mostrem que, sota aquest criteri, no es pot derivar un accés directe a adiabaticity realitzable mitjançant la tècnica de Fast-Forward per al transport TLAO basat

Accessos directes a adiabaticity per al transport de les ones de matèria

Treball final de màster oficial fet en col·laboració amb Universitat Autònoma de Barcelona (UAB), Universitat de Barcelona (UB) i Institut de Ciències Fotòniques (ICFO)[ANGLES] In this master thesis we investigate the quantum transport of a single neutral atom between double-well and triple-well potentials. In particular, we study and implement the Fast-Forward technique to speed up the quantum dynamics of the Three-Level Atom Optics (TLAO) based transport. We show that the resulting technique is faster and, against certain experimentaimperfections, more robust than the usual TLAO-based transport. Moreover, we address different shortcuts to adiabaticity examples. First, we derive a more general shortcut to adiabaticity for adiabatic translation than the one reported in the literature. Also, we obtain a criterion for the realization of a shortcut to adiabaticity and we show that, under this criterion, it is impossible to derive a realizable shortcut to adiabaticity using the Fast-Forward technique for the TLAO-based transport.[CASTELLÀ] Esta tesis de maestría se investiga el transporte cuántico de un átomo neutro entre los potenciales de doble-well y triple-well. En particular, estudiamos y aplicamos la técnica de Fast-Forward para acelerar la dinámica cuántica de la Three-Level Atom Optics (TLAO) transporte basado. Se demuestra que la técnica es que resulta más rápido y, en contra de ciertas imperfecciones experimentales, más robusto que el transporte TLAO basado habitual. Por otra parte, abordamos diferentes accesos directos a ejemplos adiabaticity. En primer lugar, derivamos un acceso más general a adiabaticity para su traducción adiabática que la reportada en la literatura. Además, se obtiene un criterio para la realización de un acceso directo a adiabaticity y mostramos que, bajo este criterio, no se puede derivar un acceso directo a adiabaticity realizable mediante la técnica de Fast-Forward para el transporte TLAO basado.[CATALA] En aquesta tesi de mestratge s'investiga el transport quàntic d'un àtom neutre entre els potencials de doble-well i triple-well. En particular, estudiem i apliquem la tècnica de Fast-Forward per accelerar la dinàmica quàntica de la Three-Level Atom Optics (TLAO) transport basat. Es demostra que la tècnica és que resulta més ràpid i, en contra de certes imperfeccions experimentals, més robust que el transport TLAO basat habitual. D'altra banda, abordem diferents accessos directes a exemples adiabaticity. En primer lloc, derivem un accés més general adiabaticity per a la seva traducció adiabàtica que la considerada en la literatura. A més, s'obté un criteri per a la realització d'un accés directe a adiabaticity i mostrem que, sota aquest criteri, no es pot derivar un accés directe a adiabaticity realitzable mitjançant la tècnica de Fast-Forward per al transport TLAO basat