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materialsscienceandengineering · 8 days ago

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Insulator-to-metal transition achieved in iridate/manganate heterostructures

A research team has successfully achieved an atomically controlled insulator-to-metal transition in iridate/manganate heterostructures. Their findings were recently published in Nature Communications. Conductive interfaces in insulator-insulator heterostructures are central to modern electronics. Compared with a band insulator, a correlation insulator typically has a richer phase diagram that even covers both insulating and metallic states by itself. However, a conductive interface in heterostructures composed of two correlated insulators is rarely reported. In this research, the team investigated the heterostructure of a 5d iridate, CaIrO3 (CIO), and a 3d manganite, La0.67Sr0.33MnO3 (LSMO). While CaIrO3 is a Dirac semimetal and La0.67Sr0.33MnO3 a robust half-metal, both materials can be stabilized into insulating states under the right conditions. This combination forms a platform to explore emerging metallicity at their interface.

#Materials Science #Science #Heterostructures #Insulators #Interfaces #Semimetals

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deusvacuus · 2 months ago

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Quantum Well Competition

Once I saw you, I felt the specific valence of no longer having a position to rest in.

Maybe it was just the design of that specific nanometric infrastructure; too many unlike particles in too small a region.

Maybe it was my lowered excitation state; the background energy insufficient to escalate it.

Or maybe you were already residing in all the 1-dimensional wells wherein I could potentially rest; superposed in all the same outcomes as i was.

Maybe you were just dominating that heterostructure in a way that I probably have done in so many other wells; unknowingly making you feel less welcome inside them. All I can say for certain is that the experience did not tend well to my pre-existing restlessness.

When the song said: “you are the piece of me I wish I didn’t need,” I felt it like a dagger.

There were several daggers.

I’m just a momentary particle trying to disentangle instead of annihilate.

#spilled ink #prose #deusvacuus #personal

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sisiad · 2 months ago

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Effect of the underlayer on the elastic parameters of the CoFeB/MgO heterostructures

http://dlvr.it/TCd25r

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jobtendr · 4 months ago

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(17) PhD, Postdoc and Academic Jobs at Radboud University in the Netherlands

Radboud University invites application for vacant (17) PhD, Postdoc and Academic Jobs Radboud University invites application for vacant PhD, Postdoc and Academic Positions, a public university with a strong focus on research located in Nijmegen, the Netherlands. Postdoctoral Researchers: Environmental Science, Hydrology, Socioeconomics, Toxicology or Ecology of Pollutants Job opportunity 0.8 – 1.0 FTE Gross monthly salary: € 3,226 – € 5,090 Faculty of Science Are you eager to learn how emission, fate and effects of pollutants (and the water, material and biomass flows that carry them) are related to the size of cities, catchments, organisms and communities? Then join the ERC Advanced Grant project ’The… PhD Candidates: Environmental Science, Hydrology, Socioeconomics, Toxicology or Ecology of Pollutants Job opportunity 0.8 – 1.0 FTE Gross monthly salary: € 2,770 – € 3,539 Faculty of Science Are you eager to learn how emission, fate, and effects of pollutants (and the water, material and biomass flows that carry them) are related to the size of cities, catchments, organisms, and communities? Then join the ERC Advanced Grant project “The… PhD Candidate: The Conceptual History of Ethics in Modern Arabic Job opportunity 1.0 FTE Gross monthly salary: € 2,770 – € 3,539 Faculty of Philosophy, Theology and Religious Studies Are you fascinated by the history of ideas in the Arab world? By how the Arabic language developed in the modern age? By its discourse on ethics and how it has affected society? 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govindhtech · 4 months ago

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2D Devices: A Key to Keeping Quantum Computers Cool

There is great potential for revolutionising sectors such as drug discovery, artificial intelligence, and materials science with quantum computers. However, the requirement for extremely low temperatures is a considerable obstacle to their development. The basic building block of information in a quantum computer, known as a qubit, is extremely brittle and error-prone at even slightly higher temperatures. huge-scale quantum computers have historically been impractical due to the lack of access to these extremely cold settings, which has required the use of huge, energy-consuming dilution refrigerators.

Now for an innovative new development: 2D devices may be able to help cool quantum computers. Researchers at the Ecole Polytechnique Federale de Lausanne (EPFL) in Lausanne, Switzerland, created a gadget that converts heat into energy at temperatures below space. A smaller, more efficient cooling system could remove a major barrier to quantum computing development with this accomplishment.

The Quantum Computing Temperature Challenge

Quantum computers calculate via entanglement and superposition. Qubits must be delicate to deal with quantum information. This demands cold temperatures -273.15 degrees Celsius, or -459.67 degrees Fahrenheit often near absolute zero. Because thermal vibrations decrease, qubits stay stable and coherent longer at higher temperatures.

Maintaining such low temperatures is expensive, energy-intensive, and technically complex. Dilution refrigerators use various helium isotopes to cool. Because these systems are large and intricate, scaling quantum computers is an extremely difficult task.

2D devices Overview

Single-layer lattice materials like graphene, h-BN, and MoS2 are two-dimensional. These materials have different mechanical, thermal, and electrical properties than three-dimensional ones. The hexagonal lattice of carbon atoms in graphene gives it extraordinary electrical conductivity and strength.

Researchers have studied 2D devices in electronics, photonics, and energy storage. Due to their unique properties, quantum computing technologies benefit from them.

Thermal Control in Quantum Computing

Heat management is one of the most exciting uses of 2D devices in quantum computing. Metallic and semiconductor quantum computing materials can produce thermal noise and heat dissipation issues that influence qubit stability. Instead, 2D materials have many advantages.

High thermal conductivity: Graphene dissipates heat. This trait helps remove quantum processor heat, keeping qubit stability at low temperatures.

Diminished Electron-Phonon Interactions: In traditional materials, heat can be produced via the interaction of electrons with phonons, which are quantized crystal lattice vibrations. Because 2D devices have fewer electron-phonon interactions, they produce less heat and have better thermal management.

Electrical Insulation: A number of 2D devices, like h-BN, combine good electrical insulation with thermal conductivity. This combination can efficiently dissipate heat and help separate qubits from electrical noise.

Combining Quantum Devices with Two-Dimensional Materials

Several novel strategies are needed to incorporate 2D devices into quantum devices. To improve the performance and temperature control of quantum circuits, researchers are creating methods for fabricating and integrating two-dimensional materials.

Graphene-Based Cooling: One method for cooling quantum processors is to use graphene as a layer. Heat can be effectively transmitted away from the qubits by putting graphene layers in contact with the quantum devices, preserving the low temperatures necessary for their operation. Moreover, the strong electrical conductivity of graphene guarantees that it does not disrupt the quantum states of the qubits.

2D Heterostructures: Interfaces with specific qualities can be created by combining several 2D materials to generate heterostructures. For instance, graphene and h-BN together can offer superior electrical insulation and thermal management. Quantum devices can benefit from the integration of these heterostructures to improve their overall performance.

Phonon Engineering: Researchers can further minimise heat generation and thermal noise by manipulating the phonon characteristics of 2D devices. In order to reduce interactions with the quantum states of the qubits, this entails adjusting the vibrational modes of the materials.

Experimental Progress

Recent developments in experiments show that 2D materials have promise for use in quantum computing. For example, MIT researchers have created a way to add graphene to superconducting qubits, greatly enhancing their coherence times. The efficient heat dissipation of the graphene layers lowers thermal noise and prolongs the lifetime of the qubits in their quantum states.

Researchers at the University of California, Berkeley also looked into using h-BN as an insulating layer in quantum devices in another study. The findings demonstrated that h-BN effectively conducted heat away from the qubits, assisting in the maintenance of low temperatures in addition to offering superior electrical insulation.

Future challenges and prospects

2D materials in quantum computing have potential, but many challenges remain. One challenge is integrating these materials into quantum computing architectures. To guarantee compatibility and performance, new fabrication processes and techniques must be developed.

Furthermore, a detailed investigation is required into the long-term stability and scalability of quantum devices based on 2D materials. For these devices to be used in real applications, it is essential that they can function dependably for longer periods of time and can be scaled up for bigger quantum systems.

Prospective avenues for investigation could centre on investigating novel two-dimensional materials and their amalgamations to enhance the thermal and electrical characteristics for use in quantum computing. Furthermore, utilising 2D materials to their full potential in quantum technologies will depend heavily on developments in material science and nanofabrication methods.

Future Consequences for Quantum Computing

Some of the biggest obstacles facing the development of quantum computing may be solved by incorporating 2D materials into the devices. 2D materials can improve qubit performance and stability by lowering noise and managing heat better, opening the door to more dependable and scalable quantum computing.

Furthermore, previously unthinkable new kinds of quantum devices and architectures might be made possible by the special qualities of 2D materials. This could hasten the development of useful quantum technology by creating new opportunities for quantum computing research and innovation.

In summary

Two-dimensional materials present a viable resolution to the thermal management issues associated with quantum computing. Their distinct characteristics, such as elevated thermal conductivity and diminished electron-phonon interactions, provide them perfect options for enhancing the efficacy and durability of quantum devices. Even while incorporating these materials into current architectures still presents problems, current research and experimental advancements offer a solid platform for next innovations.

2D devices have a huge potential impact on quantum computing. These materials have the potential to be essential for achieving the full promise of quantum technologies, as they can facilitate more effective cooling and minimise thermal noise. The combination of 2D devices and quantum computing promises to open up new avenues for research and development in this industry, propelling the next wave of technological developments.

Read more on Govindhtech.com

#quatum #QuantumComputing #2ddevice #2Dmaterial #govindhtech #technologynews #technology #technologytrends #technews #news

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y2fear · 7 months ago

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Heterointerface engineering of layered double hydroxide/MAPbBr3 heterostructures enabling tunable synapse behaviors in a two-terminal optoelectronic device

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sunaleisocial · 7 months ago

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Propelling atomically layered magnets toward green computers

New Post has been published on https://sunalei.org/news/propelling-atomically-layered-magnets-toward-green-computers/

Propelling atomically layered magnets toward green computers

Globally, computation is booming at an unprecedented rate, fueled by the boons of artificial intelligence. With this, the staggering energy demand of the world’s computing infrastructure has become a major concern, and the development of computing devices that are far more energy-efficient is a leading challenge for the scientific community.

Use of magnetic materials to build computing devices like memories and processors has emerged as a promising avenue for creating “beyond-CMOS” computers, which would use far less energy compared to traditional computers. Magnetization switching in magnets can be used in computation the same way that a transistor switches from open or closed to represent the 0s and 1s of binary code.

While much of the research along this direction has focused on using bulk magnetic materials, a new class of magnetic materials — called two-dimensional van der Waals magnets — provides superior properties that can improve the scalability and energy efficiency of magnetic devices to make them commercially viable.

Although the benefits of shifting to 2D magnetic materials are evident, their practical induction into computers has been hindered by some fundamental challenges. Until recently, 2D magnetic materials could operate only at very low temperatures, much like superconductors. So bringing their operating temperatures above room temperature has remained a primary goal. Additionally, for use in computers, it is important that they can be controlled electrically, without the need for magnetic fields. Bridging this fundamental gap, where 2D magnetic materials can be electrically switched above room temperature without any magnetic fields, could potentially catapult the translation of 2D magnets into the next generation of “green” computers.

A team of MIT researchers has now achieved this critical milestone by designing a “van der Waals atomically layered heterostructure” device where a 2D van der Waals magnet, iron gallium telluride, is interfaced with another 2D material, tungsten ditelluride. In an open-access paper published March 15 in Science Advances, the team shows that the magnet can be toggled between the 0 and 1 states simply by applying pulses of electrical current across their two-layer device.

Play video

The Future of Spintronics: Manipulating Spins in Atomic Layers without External Magnetic Fields Video: Deblina Sarkar

“Our device enables robust magnetization switching without the need for an external magnetic field, opening up unprecedented opportunities for ultra-low power and environmentally sustainable computing technology for big data and AI,” says lead author Deblina Sarkar, the AT&T Career Development Assistant Professor at the MIT Media Lab and Center for Neurobiological Engineering, and head of the Nano-Cybernetic Biotrek research group. “Moreover, the atomically layered structure of our device provides unique capabilities including improved interface and possibilities of gate voltage tunability, as well as flexible and transparent spintronic technologies.”

Sarkar is joined on the paper by first author Shivam Kajale, a graduate student in Sarkar’s research group at the Media Lab; Thanh Nguyen, a graduate student in the Department of Nuclear Science and Engineering (NSE); Nguyen Tuan Hung, an MIT visiting scholar in NSE and an assistant professor at Tohoku University in Japan; and Mingda Li, associate professor of NSE.

Breaking the mirror symmetries

When electric current flows through heavy metals like platinum or tantalum, the electrons get segregated in the materials based on their spin component, a phenomenon called the spin Hall effect, says Kajale. The way this segregation happens depends on the material, and particularly its symmetries.

“The conversion of electric current to spin currents in heavy metals lies at the heart of controlling magnets electrically,” Kajale notes. “The microscopic structure of conventionally used materials, like platinum, have a kind of mirror symmetry, which restricts the spin currents only to in-plane spin polarization.”

Kajale explains that two mirror symmetries must be broken to produce an “out-of-plane” spin component that can be transferred to a magnetic layer to induce field-free switching. “Electrical current can ‘break’ the mirror symmetry along one plane in platinum, but its crystal structure prevents the mirror symmetry from being broken in a second plane.”

In their earlier experiments, the researchers used a small magnetic field to break the second mirror plane. To get rid of the need for a magnetic nudge, Kajale and Sarkar and colleagues looked instead for a material with a structure that could break the second mirror plane without outside help. This led them to another 2D material, tungsten ditelluride. The tungsten ditelluride that the researchers used has an orthorhombic crystal structure. The material itself has one broken mirror plane. Thus, by applying current along its low-symmetry axis (parallel to the broken mirror plane), the resulting spin current has an out-of-plane spin component that can directly induce switching in the ultra-thin magnet interfaced with the tungsten ditelluride.

“Because it’s also a 2D van der Waals material, it can also ensure that when we stack the two materials together, we get pristine interfaces and a good flow of electron spins between the materials,” says Kajale.

Becoming more energy-efficient

Computer memory and processors built from magnetic materials use less energy than traditional silicon-based devices. And the van der Waals magnets can offer higher energy efficiency and better scalability compared to bulk magnetic material, the researchers note.

The electrical current density used for switching the magnet translates to how much energy is dissipated during switching. A lower density means a much more energy-efficient material. “The new design has one of the lowest current densities in van der Waals magnetic materials,” Kajale says. “This new design has an order of magnitude lower in terms of the switching current required in bulk materials. This translates to something like two orders of magnitude improvement in energy efficiency.”

The research team is now looking at similar low-symmetry van der Waals materials to see if they can reduce current density even further. They are also hoping to collaborate with other researchers to find ways to manufacture the 2D magnetic switch devices at commercial scale.

This work was carried out, in part, using the facilities at MIT.nano. It was funded by the Media Lab, the U.S. National Science Foundation, and the U.S. Department of Energy.

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jcmarchi · 7 months ago

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Propelling atomically layered magnets toward green computers

New Post has been published on https://thedigitalinsider.com/propelling-atomically-layered-magnets-toward-green-computers/

Propelling atomically layered magnets toward green computers

Globally, computation is booming at an unprecedented rate, fueled by the boons of artificial intelligence. With this, the staggering energy demand of the world’s computing infrastructure has become a major concern, and the development of computing devices that are far more energy-efficient is a leading challenge for the scientific community.

Use of magnetic materials to build computing devices like memories and processors has emerged as a promising avenue for creating “beyond-CMOS” computers, which would use far less energy compared to traditional computers. Magnetization switching in magnets can be used in computation the same way that a transistor switches from open or closed to represent the 0s and 1s of binary code.

While much of the research along this direction has focused on using bulk magnetic materials, a new class of magnetic materials — called two-dimensional van der Waals magnets — provides superior properties that can improve the scalability and energy efficiency of magnetic devices to make them commercially viable.

Although the benefits of shifting to 2D magnetic materials are evident, their practical induction into computers has been hindered by some fundamental challenges. Until recently, 2D magnetic materials could operate only at very low temperatures, much like superconductors. So bringing their operating temperatures above room temperature has remained a primary goal. Additionally, for use in computers, it is important that they can be controlled electrically, without the need for magnetic fields. Bridging this fundamental gap, where 2D magnetic materials can be electrically switched above room temperature without any magnetic fields, could potentially catapult the translation of 2D magnets into the next generation of “green” computers.

A team of MIT researchers has now achieved this critical milestone by designing a “van der Waals atomically layered heterostructure” device where a 2D van der Waals magnet, iron gallium telluride, is interfaced with another 2D material, tungsten ditelluride. In an open-access paper published March 15 in Science Advances, the team shows that the magnet can be toggled between the 0 and 1 states simply by applying pulses of electrical current across their two-layer device.

Play video

The Future of Spintronics: Manipulating Spins in Atomic Layers without External Magnetic Fields Video: Deblina Sarkar

“Our device enables robust magnetization switching without the need for an external magnetic field, opening up unprecedented opportunities for ultra-low power and environmentally sustainable computing technology for big data and AI,” says lead author Deblina Sarkar, the AT&T Career Development Assistant Professor at the MIT Media Lab and Center for Neurobiological Engineering, and head of the Nano-Cybernetic Biotrek research group. “Moreover, the atomically layered structure of our device provides unique capabilities including improved interface and possibilities of gate voltage tunability, as well as flexible and transparent spintronic technologies.”

Sarkar is joined on the paper by first author Shivam Kajale, a graduate student in Sarkar’s research group at the Media Lab; Thanh Nguyen, a graduate student in the Department of Nuclear Science and Engineering (NSE); Nguyen Tuan Hung, an MIT visiting scholar in NSE and an assistant professor at Tohoku University in Japan; and Mingda Li, associate professor of NSE.

Breaking the mirror symmetries

When electric current flows through heavy metals like platinum or tantalum, the electrons get segregated in the materials based on their spin component, a phenomenon called the spin Hall effect, says Kajale. The way this segregation happens depends on the material, and particularly its symmetries.

“The conversion of electric current to spin currents in heavy metals lies at the heart of controlling magnets electrically,” Kajale notes. “The microscopic structure of conventionally used materials, like platinum, have a kind of mirror symmetry, which restricts the spin currents only to in-plane spin polarization.”

Kajale explains that two mirror symmetries must be broken to produce an “out-of-plane” spin component that can be transferred to a magnetic layer to induce field-free switching. “Electrical current can ‘break’ the mirror symmetry along one plane in platinum, but its crystal structure prevents the mirror symmetry from being broken in a second plane.”

In their earlier experiments, the researchers used a small magnetic field to break the second mirror plane. To get rid of the need for a magnetic nudge, Kajale and Sarkar and colleagues looked instead for a material with a structure that could break the second mirror plane without outside help. This led them to another 2D material, tungsten ditelluride. The tungsten ditelluride that the researchers used has an orthorhombic crystal structure. The material itself has one broken mirror plane. Thus, by applying current along its low-symmetry axis (parallel to the broken mirror plane), the resulting spin current has an out-of-plane spin component that can directly induce switching in the ultra-thin magnet interfaced with the tungsten ditelluride.

“Because it’s also a 2D van der Waals material, it can also ensure that when we stack the two materials together, we get pristine interfaces and a good flow of electron spins between the materials,” says Kajale.

Becoming more energy-efficient

Computer memory and processors built from magnetic materials use less energy than traditional silicon-based devices. And the van der Waals magnets can offer higher energy efficiency and better scalability compared to bulk magnetic material, the researchers note.

The electrical current density used for switching the magnet translates to how much energy is dissipated during switching. A lower density means a much more energy-efficient material. “The new design has one of the lowest current densities in van der Waals magnetic materials,” Kajale says. “This new design has an order of magnitude lower in terms of the switching current required in bulk materials. This translates to something like two orders of magnitude improvement in energy efficiency.”

The research team is now looking at similar low-symmetry van der Waals materials to see if they can reduce current density even further. They are also hoping to collaborate with other researchers to find ways to manufacture the 2D magnetic switch devices at commercial scale.

This work was carried out, in part, using the facilities at MIT.nano. It was funded by the Media Lab, the U.S. National Science Foundation, and the U.S. Department of Energy.

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testbank-zone · 8 months ago

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Solution Manuals For Diode Lasers and Photonic Integrated Circuits 2nd Edition By Larry A. Coldren

TABLE OF CONTENTS Preface xvii Acknowledgments xxi List of Fundamental Constants xxiii 1 Ingredients 1 1.1 Introduction 1 1.2 Energy Levels and Bands in Solids 5 1.3 Spontaneous and Stimulated Transitions: The Creation of Light 7 1.4 Transverse Confinement of Carriers and Photons in Diode Lasers: The Double Heterostructure 10 1.5 Semiconductor Materials for Diode Lasers 13 1.6 Epitaxial Growth Technology 20 1.7 Lateral Confinement of Current, Carriers, and Photons for Practical Lasers 24 1.8 Practical Laser Examples 31 References 39 Reading List 40 Problems 40 2 A Phenomenological Approach to Diode Lasers 45 2.1 Introduction 45 2.2 Carrier Generation and Recombination in Active Regions 46 2.3 Spontaneous Photon Generation and LEDs 49 2.4 Photon Generation and Loss in Laser Cavities 52 2.5 Threshold or Steady-State Gain in Lasers 55 2.6 Threshold Current and Power Out Versus Current 60 2.6.1 Basic P–I Characteristics 60 2.6.2 Gain Models and Their Use in Designing Lasers 64 2.7 Relaxation Resonance and Frequency Response 70 2.8 Characterizing Real Diode Lasers 74 2.8.1 Internal Parameters for In-Plane Lasers: ‹αi›, ηi , and g versus J 75 2.8.2 Internal Parameters for VCSELs: ηi and g versus J, ‹αi›, and αm 78 2.8.3 Efficiency and Heat Flow 79 2.8.4 Temperature Dependence of Drive Current 80 2.8.5 Derivative Analysis 84 References 86 Reading List 87 Problems 87 3 Mirrors and Resonators for Diode Lasers 91 3.1 Introduction 91 3.2 Scattering Theory 92 3.3 S and T Matrices for Some Common Elements 95 3.3.1 The Dielectric Interface 96 3.3.2 Transmission Line with No Discontinuities 98 3.3.3 Dielectric Segment and the Fabry–Perot Etalon 100 3.3.4 S-Parameter Computation Using Mason’s Rule 104 3.3.5 Fabry–Perot Laser 105 3.4 Three- and Four-Mirror Laser Cavities 107 3.4.1 Three-Mirror Lasers 107 3.4.2 Four-Mirror Lasers 111 3.5 Gratings 113 3.5.1 Introduction 113 3.5.2 Transmission Matrix Theory of Gratings 115 3.5.3 Effective Mirror Model for Gratings 121 3.6 Lasers Based on DBR Mirrors 123 3.6.1 Introduction 123 3.6.2 Threshold Gain and Power Out 124 3.6.3 Mode Selection in DBR-Based Lasers 127 3.6.4 VCSEL Design 128 3.6.5 In-Plane DBR Lasers and Tunability 135 3.6.6 Mode Suppression Ratio in DBR Laser 139 3.7 DFB Lasers 141 3.7.1 Introduction 141 3.7.2 Calculation of the Threshold Gains and Wavelengths 143 3.7.3 On Mode Suppression in DFB Lasers 149 References 151 Reading List 151 Problems 151 4 Gain and Current Relations 157 4.1 Introduction 157 4.2 Radiative Transitions 158 4.2.1 Basic Definitions and Fundamental Relationships 158 4.2.2 Fundamental Description of the Radiative Transition Rate 162 4.2.3 Transition Matrix Element 165 4.2.4 Reduced Density of States 170 4.2.5 Correspondence with Einstein’s Stimulated Rate Constant 174 4.3 Optical Gain 174 4.3.1 General Expression for Gain 174 4.3.2 Lineshape Broadening 181 4.3.3 General Features of the Gain Spectrum 185 4.3.4 Many-Body Effects 187 4.3.5 Polarization and Piezoelectricity 190 4.4 Spontaneous Emission 192 4.4.1 Single-Mode Spontaneous Emission Rate 192 4.4.2 Total Spontaneous Emission Rate 193 4.4.3 Spontaneous Emission Factor 198 4.4.4 Purcell Effect 198 4.5 Nonradiative Transitions 199 4.5.1 Defect and Impurity Recombination 199 4.5.2 Surface and Interface Recombination 202 4.5.3 Auger Recombination 211 4.6 Active Materials and Their Characteristics 218 4.6.1 Strained Materials and Doped Materials 218 4.6.2 Gain Spectra of Common Active Materials 220 4.6.3 Gain versus Carrier Density 223 4.6.4 Spontaneous Emission Spectra and Current versus Carrier Density 227 4.6.5 Gain versus Current Density 229 4.6.6 Experimental Gain Curves 233 4.6.7 Dependence on Well Width, Doping, and Temperature 234 References 238 Reading List 240 Problems 240 5 Dynamic Effects 247 5.1 Introduction 247 5.2 Review of Chapter 2 248 5.2.1 The Rate Equations 249 5.2.2 Steady-State Solutions 250 Case (i): Well Below Threshold 251 Case (ii): Above Threshold 252 Case (iii): Below and Above Threshold 253 5.2.3 Steady-State Multimode Solutions 255 5.3 Differential Analysis of the Rate Equations 257 5.3.1 Small-Signal Frequency Response 261 5.3.2 Small-Signal Transient Response 266 5.3.3 Small-Signal FM Response or Frequency Chirping 270 5.4 Large-Signal Analysis 276 5.4.1 Large-Signal Modulation: Numerical Analysis of the Multimode Rate Equations 277 5.4.2 Mode Locking 279 5.4.3 Turn-On Delay 283 5.4.4 Large-Signal Frequency Chirping 286 5.5 Relative Intensity Noise and Linewidth 288 5.5.1 General Definition of RIN and the Spectral Density Function 288 5.5.2 The Schawlow–Townes Linewidth 292 5.5.3 The Langevin Approach 294 5.5.4 Langevin Noise Spectral Densities and RIN 295 5.5.5 Frequency Noise 301 5.5.6 Linewidth 303 5.6 Carrier Transport Effects 308 5.7 Feedback Effects and Injection Locking 311 5.7.1 Optical Feedback Effects—Static Characteristics 311 5.7.2 Injection Locking—Static Characteristics 317 5.7.3 Injection and Feedback Dynamic Characteristics and Stability 320 5.7.4 Feedback Effects on Laser Linewidth 321 References 328 Reading List 329 Problems 329 6 Perturbation, Coupled-Mode Theory, Modal Excitations, and Applications 335 6.1 Introduction 335 6.2 Guided-Mode Power and Effective Width 336 6.3 Perturbation Theory 339 6.4 Coupled-Mode Theory: Two-Mode Coupling 342 6.4.1 Contradirectional Coupling: Gratings 342 6.4.2 DFB Lasers 353 6.4.3 Codirectional Coupling: Directional Couplers 356 6.4.4 Codirectional Coupler Filters and Electro-optic Switches 370 6.5 Modal Excitation 376 6.6 Two Mode Interference and Multimode Interference 378 6.7 Star Couplers 381 6.8 Photonic Multiplexers, Demultiplexers and Routers 382 6.8.1 Arrayed Waveguide Grating De/Multiplexers and Routers 383 6.8.2 Echelle Grating based De/Multiplexers and Routers 389 6.9 Conclusions 390 References 390 Reading List 391 Problems 391 7 Dielectric Waveguides 395 7.1 Introduction 395 7.2 Plane Waves Incident on a Planar Dielectric Boundary 396 7.3 Dielectric Waveguide Analysis Techniques 400 7.3.1 Standing Wave Technique 400 7.3.2 Transverse Resonance 403 7.3.3 WKB Method for Arbitrary Waveguide Profiles 410 7.3.4 2-D Effective Index Technique for Buried Rib Waveguides 418 7.3.5 Analysis of Curved Optical Waveguides using Conformal Mapping 421 7.3.6 Numerical Mode Solving Methods for Arbitrary Waveguide Profiles 424 7.4 Numerical Techniques for Analyzing PICs 427 7.4.1 Introduction 427 7.4.2 Implicit Finite-Difference Beam-Propagation Method 429 7.4.3 Calculation of Propagation Constants in a z–invariant Waveguide from a Beam Propagation Solution 432 7.4.4 Calculation of Eigenmode Profile from a Beam Propagation Solution 434 7.5 Goos–Hanchen Effect and Total Internal Reflection Components 434 7.5.1 Total Internal Reflection Mirrors 435 7.6 Losses in Dielectric Waveguides 437 7.6.1 Absorption Losses in Dielectric Waveguides 437 7.6.2 Scattering Losses in Dielectric Waveguides 438 7.6.3 Radiation Losses for Nominally Guided Modes 438 References 445 Reading List 446 Problems 446 8 Photonic Integrated Circuits 451 8.1 Introduction 451 8.2 Tunable, Widely Tunable, and Externally Modulated Lasers 452 8.2.1 Two- and Three-Section In-plane DBR Lasers 452 8.2.2 Widely Tunable Diode Lasers 458 8.2.3 Other Extended Tuning Range Diode Laser Implementations 463 8.2.4 Externally Modulated Lasers 474 8.2.5 Semiconductor Optical Amplifiers 481 8.2.6 Transmitter Arrays 484 8.3 Advanced PICs 484 8.3.1 Waveguide Photodetectors 485 8.3.2 Transceivers/Wavelength Converters and Triplexers 488 8.4 PICs for Coherent Optical Communications 491 8.4.1 Coherent Optical Communications Primer 492 8.4.2 Coherent Detection 495 8.4.3 Coherent Receiver Implementations 495 8.4.4 Vector Transmitters 498 References 499 Reading List 503 Problems 503 Appendices 1 Review of Elementary Solid-State Physics 509 A1.1 A Quantum Mechanics Primer 509 A1.1.1 Introduction 509 A1.1.2 Potential Wells and Bound Electrons 511 A1.2 Elements of Solid-State Physics 516 A1.2.1 Electrons in Crystals and Energy Bands 516 A1.2.2 Effective Mass 520 A1.2.3 Density of States Using a Free-Electron (Effective Mass) Theory 522 References 527 Reading List 527 2 Relationships between Fermi Energy and Carrier Density and Leakage 529 A2.1 General Relationships 529 A2.2 Approximations for Bulk Materials 532 A2.3 Carrier Leakage Over Heterobarriers 537 A2.4 Internal Quantum Efficiency 542 References 544 Reading List 544 3 Introduction to Optical Waveguiding in Simple Double-Heterostructures 545 A3.1 Introduction 545 A3.2 Three-Layer Slab Dielectric Waveguide 546 A3.2.1 Symmetric Slab Case 547 A3.2.2 General Asymmetric Slab Case 548 A3.2.3 Transverse Confinement Factor, Γx 550 A3.3 Effective Index Technique for Two-Dimensional Waveguides 551 A3.4 Far Fields 555 References 557 Reading List 557 4 Density of Optical Modes, Blackbody Radiation, and Spontaneous Emission Factor 559 A4.1 Optical Cavity Modes 559 A4.2 Blackbody Radiation 561 A4.3 Spontaneous Emission Factor, βsp 562 Reading List 563 5 Modal Gain, Modal Loss, and Confinement Factors 565 A5.1 Introduction 565 A5.2 Classical Definition of Modal Gain 566 A5.3 Modal Gain and Confinement Factors 568 A5.4 Internal Modal Loss 570 A5.5 More Exact Analysis of the Active/Passive Section Cavity 571 A5.5.1 Axial Confinement Factor 572 A5.5.2 Threshold Condition and Differential Efficiency 573 A5.6 Effects of Dispersion on Modal Gain 576 6 Einstein’s Approach to Gain and Spontaneous Emission 579 A6.1 Introduction 579 A6.2 Einstein A and B Coefficients 582 A6.3 Thermal Equilibrium 584 A6.4 Calculation of Gain 585 A6.5 Calculation of Spontaneous Emission Rate 589 Reading List 592 7 Periodic Structures and the Transmission Matrix 593 A7.1 Introduction 593 A7.2 Eigenvalues and Eigenvectors 593 A7.3 Application to Dielectric Stacks at the Bragg Condition 595 A7.4 Application to Dielectric Stacks Away from the Bragg Condition 597 A7.5 Correspondence with Approximate Techniques 600 A7.5.1 Fourier Limit 601 A7.5.2 Coupled-Mode Limit 602 A7.6 Generalized Reflectivity at the Bragg Condition 603 Reading List 605 Problems 605 8 Electronic States in Semiconductors 609 A8.1 Introduction 609 A8.2 General Description of Electronic States 609 A8.3 Bloch Functions and the Momentum Matrix Element 611 A8.4 Band Structure in Quantum Wells 615 A8.4.1 Conduction Band 615 A8.4.2 Valence Band 616 A8.4.3 Strained Quantum Wells 623 References 627 Reading List 628 9 Fermi’s Golden Rule 629 A9.1 Introduction 629 A9.2 Semiclassical Derivation of the Transition Rate 630 A9.2.1 Case I: The Matrix Element-Density of Final States Product is a Constant 632 A9.2.2 Case II: The Matrix Element-Density of Final States Product is a Delta Function 635 A9.2.3 Case III: The Matrix Element-Density of Final States Product is a Lorentzian 636 Reading List 637 Problems 638 10 Transition Matrix Element 639 A10.1 General Derivation 639 A10.2 Polarization-Dependent Effects 641 A10.3 Inclusion of Envelope Functions in Quantum Wells 645 Reading List 646 11 Strained Bandgaps 647 A11.1 General Definitions of Stress and Strain 647 A11.2 Relationship Between Strain and Bandgap 650 A11.3 Relationship Between Strain and Band Structure 655 References 656 12 Threshold Energy for Auger Processes 657 A12.1 CCCH Process 657 A12.2 CHHS and CHHL Processes 659 13 Langevin Noise 661 A13.1 Properties of Langevin Noise Sources 661 A13.1.1 Correlation Functions and Spectral Densities 661 A13.1.2 Evaluation of Langevin Noise Correlation Strengths 664 A13.2 Specific Langevin Noise Correlations 665 A13.2.1 Photon Density and Carrier Density Langevin Noise Correlations 665 A13.2.2 Photon Density and Output Power Langevin Noise Correlations 666 A13.2.3 Photon Density and Phase Langevin Noise Correlations 667 A13.3 Evaluation of Noise Spectral Densities 669 A13.3.1 Photon Noise Spectral Density 669 A13.3.2 Output Power Noise Spectral Density 670 A13.3.3 Carrier Noise Spectral Density 671 References 672 Problems 672 14 Derivation Details for Perturbation Formulas 675 Reading List 676 15 Multimode Interference 677 A15.1 Multimode Interference-Based Couplers 677 A15.2 Guided-Mode Propagation Analysis 678 A15.2.1 General Interference 679 A15.2.2 Restricted Multimode Interference 681 A15.3 MMI Physical Properties 682 A15.3.1 Fabrication 682 A15.3.2 Imaging Quality 682 A15.3.3 Inherent Loss and Optical Bandwidth 682 A15.3.4 Polarization Dependence 683 A15.3.5 Reflection Properties 683 Reference 683 16 The Electro-Optic Effect 685 References 692 Reading List 692 17 Solution of Finite Difference Problems 693 A17.1 Matrix Formalism 693 A17.2 One-Dimensional Dielectric Slab Example 695 Reading List 696 Index 697 Read the full article

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materialsscienceandengineering · 10 days ago

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Researchers unveil pressure-tuned superconductivity in natural bulk heterostructure 6R-TaS₂

By combining comprehensive high-pressure measurements and first-principles calculations, a research group has discovered the pressure-induced unusual evolution of superconductivity (SC) and exotic interplay between SC and charge-density-wave (CDW) order in a natural bulk van der Waals heterostructure. Their research results are published in Physical Review Letters. Engineering van der Waals heterostructures (vdWHs) via pressure in a continuous manner not only allows for generation of new states of matter, but also provides a distinctive platform to study the interplay between competing electronic orders in separated layers. Natural bulk vdWHs 6R-TaS2 incorporates CDW order and SC in distinct 1T- and 1H-TaS2 monolayers and is equivalent to a stack of superconductor-insulator-superconductor Josephson junctions.