Proposal for THz lasing from a topological quantum dot

Abstract Topological quantum dots (TQDs) are 3D topological insulator (TI) nanoparticles, displaying symmetry-protected surface states with discretized energies. We present a theoretical proposal to harness these energy levels in a closed lasing scheme operating in the terahertz (THz) frequency range. In this scheme, a single TQD lases from its topological surface states in the THz regime when pumped with low intensity, incoherent THz frequency light. The time scales associated with the system are unusually slow, and we find that lasing occurs with a very low threshold. THz lasers are often bulky or require intricately engineered nanostructures. Topological quantum dots present a new, compact and simple platform for THz lasing. The lasing threshold is so low, we predict that the room-temperature blackbody radiation can substantially contribute to population inversion, providing a route to room-temperature THz lasing pumped via blackbody radiation.

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Vapour Sensitivity of InP Surface Quantum Dots

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.605.177 ◽

2014 ◽

Vol 605 ◽

pp. 177-180 ◽

Cited By ~ 3

Author(s):

Roberta de Angelis ◽

Mauro Casalboni ◽

Liliana D’Amico ◽

Fabio de Matteis ◽

Fariba Hatami ◽

...

Keyword(s):

Quantum Dots ◽

Room Temperature ◽

Near Infrared ◽

Surface Recombination ◽

Surface States ◽

Infrared Emission ◽

Polar Solvents ◽

Solvent Type ◽

Near Infrared Emission ◽

Inp Surface

We studied the effect of solvent vapours on the photoluminescent emission of self-assembled InP surface quantum dots (SQDs). Their room temperature near infrared emission undergoes a fully reversible intensity enhancement when the dots were exposed to vapours of polar solvents since polar molecules are likely to be adsorbed onto intrinsic surface states and thus reducing non radiative surface recombination. The shape and position of the emission band does not change. The observed effect is dependent on solvent type and concentration with linear law over a limited concentration range.

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A Chemical Theory of Topological Insulators

10.26434/chemrxiv.7637009 ◽

2019 ◽

Author(s):

Angel Martín Pendás ◽

Julia Contreras-García ◽

Fernanda Pinilla ◽

José Daniel Mella ◽

Carlos Cárdenas ◽

...

Keyword(s):

Topological Insulators ◽

Surface States ◽

Chemical Theory ◽

Protected Surface ◽

Symmetry Protected ◽

Chemical Description

This article presents a chemical description of a simple topological insulators model in order to translate concepts such as "symmetry protected", "surface states" to the chemistry vocabulary

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Three-Dimensional Topological States of Phonons with Tunable Pseudospin Physics

Research ◽

10.34133/2019/5173580 ◽

2019 ◽

Vol 2019 ◽

pp. 1-8 ◽

Cited By ~ 3

Author(s):

Yizhou Liu ◽

Yong Xu ◽

Wenhui Duan

Keyword(s):

Degrees Of Freedom ◽

Three Dimensional ◽

Surface States ◽

Phonon Transport ◽

Efficient Control ◽

Topological States ◽

Topological Surface ◽

Symmetry Protected ◽

Energy Information ◽

Crystalline Symmetry

Efficient control of phonons is crucial to energy-information technology, but limited by the lacking of tunable degrees of freedom like charge or spin. Here we suggest to utilize crystalline symmetry-protected pseudospins as new quantum degrees of freedom to manipulate phonons. Remarkably, we reveal a duality between phonon pseudospins and electron spins by presenting Kramers-like degeneracy and pseudospin counterparts of spin-orbit coupling, which lays the foundation for “pseudospin phononics”. Furthermore, we report two types of three-dimensional phononic topological insulators, which give topologically protected, gapless surface states with linear and quadratic band degeneracies, respectively. These topological surface states display unconventional phonon transport behaviors attributed to the unique pseudospin-momentum locking, which are useful for phononic circuits, transistors, antennas, etc. The emerging pseudospin physics offers new opportunities to develop future phononics.

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Spin-polarized Weyl cones and giant anomalous Nernst effect in ferromagnetic Heusler films

Communications Materials ◽

10.1038/s43246-020-00088-w ◽

2020 ◽

Vol 1 (1) ◽

Author(s):

Kazuki Sumida ◽

Yuya Sakuraba ◽

Keisuke Masuda ◽

Takashi Kono ◽

Masaaki Kakoki ◽

...

Keyword(s):

Photoelectron Spectroscopy ◽

Remanent Magnetization ◽

Room Temperature ◽

High Efficiency ◽

Quantum Critical Point ◽

Surface States ◽

Flat Band ◽

Zero Field ◽

Topological Quantum ◽

Spin Polarized

AbstractWeyl semimetals are characterized by the presence of massless band dispersion in momentum space. When a Weyl semimetal meets magnetism, large anomalous transport properties emerge as a consequence of its topological nature. Here, using in−situ spin- and angle-resolved photoelectron spectroscopy combined with ab initio calculations, we visualize the spin-polarized Weyl cone and flat-band surface states of ferromagnetic Co2MnGa films with full remanent magnetization. We demonstrate that the anomalous Hall and Nernst conductivities systematically grow when the magnetization-induced massive Weyl cone at a Lifshitz quantum critical point approaches the Fermi energy, until a high anomalous Nernst thermopower of ~6.2 μVK−1 is realized at room temperature. Given this topological quantum state and full remanent magnetization, Co2MnGa films are promising for realizing high efficiency heat flux and magnetic field sensing devices operable at room temperature and zero-field.

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Natural van der Waals heterostructural single crystals with both magnetic and topological properties

Science Advances ◽

10.1126/sciadv.aax9989 ◽

2019 ◽

Vol 5 (11) ◽

pp. eaax9989 ◽

Cited By ~ 43

Author(s):

Jiazhen Wu ◽

Fucai Liu ◽

Masato Sasase ◽

Koichiro Ienaga ◽

Yukiko Obata ◽

...

Keyword(s):

Magnetic Properties ◽

Hall Effect ◽

Exchange Coupling ◽

Van Der Waals ◽

Surface States ◽

Anomalous Hall Effect ◽

Topological Quantum ◽

Magnetic Layers ◽

Topological Surface ◽

Ferromagnetic Hysteresis

Heterostructures having both magnetism and topology are promising materials for the realization of exotic topological quantum states while challenging in synthesis and engineering. Here, we report natural magnetic van der Waals heterostructures of (MnBi2Te4)m(Bi2Te3)n that exhibit controllable magnetic properties while maintaining their topological surface states. The interlayer antiferromagnetic exchange coupling is gradually weakened as the separation of magnetic layers increases, and an anomalous Hall effect that is well coupled with magnetization and shows ferromagnetic hysteresis was observed below 5 K. The obtained homogeneous heterostructure with atomically sharp interface and intrinsic magnetic properties will be an ideal platform for studying the quantum anomalous Hall effect, axion insulator states, and the topological magnetoelectric effect.

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Photoemission Spectroscopic Evidence of Multiple Dirac Cones in Superconducting BaSn3

Chinese Physics Letters ◽

10.1088/0256-307x/38/10/107403 ◽

2021 ◽

Vol 38 (10) ◽

pp. 107403

Author(s):

Zhe Huang ◽

Xianbiao Shi ◽

Gaoning Zhang ◽

Zhengtai Liu ◽

Soohyun Cho ◽

...

Keyword(s):

Surface States ◽

Photoemission Spectroscopy ◽

Rotational Axis ◽

Type I ◽

Dirac Fermions ◽

First Principles Calculations ◽

Angle Resolved Photoemission Spectroscopy ◽

Topological Quantum ◽

Topological Surface ◽

Single Material

Signatures of topological superconductivity (TSC) in superconducting materials with topological nontrivial states prompt intensive researches recently. Utilizing high-resolution angle-resolved photoemission spectroscopy and first-principles calculations, we demonstrate multiple Dirac fermions and surface states in superconductor BaSn3 with a critical transition temperature of about 4.4 K. We predict and then unveil the existence of two pairs of type-I topological Dirac fermions residing on the rotational axis. Type-II Dirac fermions protected by screw axis are confirmed in the same compound. Further calculation for the spin helical texture of the observed surface states originating from the Dirac fermions gives an opportunity for realization of TSC in one single material. Hosting multiple Dirac fermions and topological surface states, the intrinsic superconductor BaSn3 is expected to be a new platform for further investigation of topological quantum materials as well as TSC.

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Weyl-like points from band inversions of spin-polarised surface states in NbGeSb

Nature Communications ◽

10.1038/s41467-019-13464-z ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 1

Author(s):

I. Marković ◽

C. A. Hooley ◽

O. J. Clark ◽

F. Mazzola ◽

M. D. Watson ◽

...

Keyword(s):

Mirror Symmetry ◽

Density Functional ◽

Three Dimensional ◽

Surface States ◽

Nodal Line ◽

Surface Band ◽

Spin Orbital ◽

Band Inversion ◽

Topological Surface ◽

Symmetry Protected

AbstractBand inversions are key to stabilising a variety of novel electronic states in solids, from topological surface states to the formation of symmetry-protected three-dimensional Dirac and Weyl points and nodal-line semimetals. Here, we create a band inversion not of bulk states, but rather between manifolds of surface states. We realise this by aliovalent substitution of Nb for Zr and Sb for S in the ZrSiS family of nonsymmorphic semimetals. Using angle-resolved photoemission and density-functional theory, we show how two pairs of surface states, known from ZrSiS, are driven to intersect each other near the Fermi level in NbGeSb, and to develop pronounced spin splittings. We demonstrate how mirror symmetry leads to protected crossing points in the resulting spin-orbital entangled surface band structure, thereby stabilising surface state analogues of three-dimensional Weyl points. More generally, our observations suggest new opportunities for engineering topologically and symmetry-protected states via band inversions of surface states.

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Photocharging dynamics in colloidal CdS quantum dots visualized by electron spin coherence

Физика и техника полупроводников ◽

10.21883/ftp.2018.04.45838.27 ◽

2018 ◽

Vol 52 (4) ◽

pp. 489

Author(s):

D.R. Yakovlev ◽

D.H. Feng ◽

V.V. Pavlov ◽

A.V. Rodina ◽

E.V. Shornikova ◽

...

Keyword(s):

Quantum Dots ◽

Room Temperature ◽

Spin Dynamics ◽

Surface States ◽

Laser Pulses ◽

Spin Coherence ◽

Core Electron ◽

Time Resolved ◽

Hole Trapping ◽

Colloidal Cds

AbstractWe use a time-resolved technique with three laser pulses (pump, orientation and probe) to study the photocharging dynamics with picosecond resolution on a long timescale ranging from ps to ms in CdS colloidal quantum dots. The detection is based on measuring the coherent spin dynamics of electrons, allowing us to distinguish the type of carrier in the dot core (electron or hole). We find that although initially negative photocharging happens because of fast hole trapping on surface states, eventually it evolves to positive photocharging due to electron trapping and hole detrapping. The positive photocharging lasts up to hundreds of microseconds at room temperature.

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Simulation of the luminescence spectrum of CdSe quantum dots

Science and Technology Development Journal ◽

10.32508/stdj.v16i4.1597 ◽

2013 ◽

Vol 16 (4) ◽

pp. 61-67

Author(s):

Cuong Chi Huynh ◽

Luan Nguyen Thanh Huynh ◽

Vinh Quang Lam ◽

Dat Thanh Huynh

Keyword(s):

Quantum Dots ◽

Room Temperature ◽

Surface States ◽

Thiol Group ◽

Experimental Investigations ◽

Cdse Quantum Dots ◽

Nano Particle ◽

Small Quantum ◽

Organic Capping ◽

Matlab Programming

CdSe quantum dots were prepared via a colloidal route using an organic capping agent consist thiol group (SH). We explicitly calculated the exciton binding energy and we incorporate the exciton contribution then combined it with quantum confinement model and surface states to see its effect on photoluminescence. The results obtained by using MATLAB programming. Calculations took place at room temperature on small quantum dots (1 - 5 nm). In conclusion, our results are quite new and it effect some of the feature that has quite close correspondence with the experimental. The results are also in conformity with other theoretical and experimental investigations. This study shows the applications of photoluminescence spectrum in determination the size of nano particle, distribution of size and surface energy level of CdSe quantum dots.

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