Pub Date : 2024-12-18DOI: 10.1038/s42005-024-01907-z
Yusef Maleki, Alireza Maleki, M. Suhail Zubairy
Hydrogen is the most dominant atom in the universe and is considered the main component of baryonic matter. Thus far, the quantum features of the unbounded hydrogen atoms in the background of the universe and the possibility of emerging unique quantum effects, such as entanglement on the cosmological scale, have not been considered. In this work, we demonstrate that the dynamical expansion of the universe leads to the emergence of natural entanglement in the hyperfine structure of atomic hydrogen. Our findings reveal that there exists a critical age for the universe where hydrogen atoms naturally build up entanglement, resulting from the expansion of the universe. More precisely, when the universe reaches the age of about 2.5 × 1018 seconds (about 80 billion years old), the hyperfine structure entanglement in hydrogen atoms naturally takes off, demonstrating a peculiar quantum phenomenon known as entanglement sudden birth. This expansion-induced entanglement becomes maximum at about 3.6 × 1018 seconds (about 115 billion years), after the Big Bang. By analyzing the fate of seed atoms formed in the early universe, this study underscores the significance of unique quantum mechanical features, such as entanglement, on cosmological scales. The authors investigate quantum entanglement in the hyperfine structure of the neutral hydrogen atom in thermal equilibrium with the cosmological microwave background radiation. They demonstrate that when the universe is around 80 billion years old, neutral hydrogen atoms begin to form entangled states, displaying a phenomenon known as entanglement sudden birth.
{"title":"Cosmic entanglement sudden birth: expansion-induced entanglement in hydrogen atoms","authors":"Yusef Maleki, Alireza Maleki, M. Suhail Zubairy","doi":"10.1038/s42005-024-01907-z","DOIUrl":"10.1038/s42005-024-01907-z","url":null,"abstract":"Hydrogen is the most dominant atom in the universe and is considered the main component of baryonic matter. Thus far, the quantum features of the unbounded hydrogen atoms in the background of the universe and the possibility of emerging unique quantum effects, such as entanglement on the cosmological scale, have not been considered. In this work, we demonstrate that the dynamical expansion of the universe leads to the emergence of natural entanglement in the hyperfine structure of atomic hydrogen. Our findings reveal that there exists a critical age for the universe where hydrogen atoms naturally build up entanglement, resulting from the expansion of the universe. More precisely, when the universe reaches the age of about 2.5 × 1018 seconds (about 80 billion years old), the hyperfine structure entanglement in hydrogen atoms naturally takes off, demonstrating a peculiar quantum phenomenon known as entanglement sudden birth. This expansion-induced entanglement becomes maximum at about 3.6 × 1018 seconds (about 115 billion years), after the Big Bang. By analyzing the fate of seed atoms formed in the early universe, this study underscores the significance of unique quantum mechanical features, such as entanglement, on cosmological scales. The authors investigate quantum entanglement in the hyperfine structure of the neutral hydrogen atom in thermal equilibrium with the cosmological microwave background radiation. They demonstrate that when the universe is around 80 billion years old, neutral hydrogen atoms begin to form entangled states, displaying a phenomenon known as entanglement sudden birth.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-6"},"PeriodicalIF":5.4,"publicationDate":"2024-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01907-z.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142845259","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-16DOI: 10.1038/s42005-024-01898-x
W. Peng, H. Guo, W. Schmidt, A. Piovano, H. Luetkens, C.-T. Chen, Z. Hu, A. C. Komarek
The magnetic excitation spectrum of most high-temperature superconducting (HTSC) cuprates is hour-glass shaped. The observation of hour-glass spectra in the isostructural Sr-doped cobaltates La2−xSrxCoO4 gives rise to a deeper understanding of these spectra. So far, hour-glass spectra have been only observed in those systems that evolve from incommensurate magnetic peaks. Here, we report on the appearance of hour-glass spectra in oxygen-doped cobaltates La2CoO4+δ. The high-energy part of the hour-glass spectrum of oxygen doped cobaltates is extremely anisotropic with a very prominent stripe-like appearance not seen that clearly in purely Sr-doped compounds. A charge stripe scenario is evidenced by (polarized) neutron diffraction measurements and also corroborated by spin wave simulations. Our results indicate that charge stripes are the origin of the anisotropic stripe- or diamond-shaped high-energy part of the hour-glass spectrum. A link between hour-glass spectra and charge stripes could be of relevance for the physics in HTSC cuprates. The hour-glass magnetic excitation spectrum is a universal feature of most cuprate high-temperature superconductors, yet the exact origins are still debated. Here, using inelastic neutron scattering techniques, the authors report hour-glass magnetic spectra in an oxygen-doped cobaltate La2CoO4+δ and discuss the potential link with charge stripes and the “diamond-shaped” high energy part of the hour-glass spectrum of this system.
{"title":"Hour-glass spectra due to oxygen doping in cobaltates","authors":"W. Peng, H. Guo, W. Schmidt, A. Piovano, H. Luetkens, C.-T. Chen, Z. Hu, A. C. Komarek","doi":"10.1038/s42005-024-01898-x","DOIUrl":"10.1038/s42005-024-01898-x","url":null,"abstract":"The magnetic excitation spectrum of most high-temperature superconducting (HTSC) cuprates is hour-glass shaped. The observation of hour-glass spectra in the isostructural Sr-doped cobaltates La2−xSrxCoO4 gives rise to a deeper understanding of these spectra. So far, hour-glass spectra have been only observed in those systems that evolve from incommensurate magnetic peaks. Here, we report on the appearance of hour-glass spectra in oxygen-doped cobaltates La2CoO4+δ. The high-energy part of the hour-glass spectrum of oxygen doped cobaltates is extremely anisotropic with a very prominent stripe-like appearance not seen that clearly in purely Sr-doped compounds. A charge stripe scenario is evidenced by (polarized) neutron diffraction measurements and also corroborated by spin wave simulations. Our results indicate that charge stripes are the origin of the anisotropic stripe- or diamond-shaped high-energy part of the hour-glass spectrum. A link between hour-glass spectra and charge stripes could be of relevance for the physics in HTSC cuprates. The hour-glass magnetic excitation spectrum is a universal feature of most cuprate high-temperature superconductors, yet the exact origins are still debated. Here, using inelastic neutron scattering techniques, the authors report hour-glass magnetic spectra in an oxygen-doped cobaltate La2CoO4+δ and discuss the potential link with charge stripes and the “diamond-shaped” high energy part of the hour-glass spectrum of this system.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-9"},"PeriodicalIF":5.4,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01898-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142826491","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-06DOI: 10.1038/s42005-024-01878-1
Lingzhu Bian, Chen Liu, Zhen Zhang, Yingke Huang, Xinyu Pan, Yi Zhang, Jiaou Wang, Pavel Dudin, Jose Avila, Zhesheng Chen, Yuhui Dong
Unsupervised clustering method has shown strong capabilities in automatically categorizing the ARPES (ARPES: angle-resolved photoemission spectroscopy) spatial mapping dataset. However, there is still room for improvement in distinguishing subtle differences caused by different layers and substrates. Here, we propose a method called Multi-Stage Clustering Algorithm (MSCA). Using the K-means clustering results/metrics for real space in different energy-momentum windows as the input of the second round K-means clustering for momentum space, the energy-momentum windows that exhibit subtle inhomogeneity in real space will be highlighted. It recognizes different types of electronic structures both in real space and momentum space in spatially resolved ARPES dataset. This method can be used to capture the areas of interest, and is especially suitable for samples with complex band dispersions, and can be a practical tool to any high dimensional scientific data analysis. A bottleneck for the analysis of data produced by angle-resolved photoemission spectroscopy (ARPES) is the size of the data related to spatial resolution. Building on earlier work, the authors present a data processing method that adopts unsupervised machine learning-based tools to improve the accuracy and efficiency when analysing data produced by nano-ARPES measurements.
{"title":"Automatic extraction of fine structural information in angle-resolved photoemission spectroscopy by multi-stage clustering algorithm","authors":"Lingzhu Bian, Chen Liu, Zhen Zhang, Yingke Huang, Xinyu Pan, Yi Zhang, Jiaou Wang, Pavel Dudin, Jose Avila, Zhesheng Chen, Yuhui Dong","doi":"10.1038/s42005-024-01878-1","DOIUrl":"10.1038/s42005-024-01878-1","url":null,"abstract":"Unsupervised clustering method has shown strong capabilities in automatically categorizing the ARPES (ARPES: angle-resolved photoemission spectroscopy) spatial mapping dataset. However, there is still room for improvement in distinguishing subtle differences caused by different layers and substrates. Here, we propose a method called Multi-Stage Clustering Algorithm (MSCA). Using the K-means clustering results/metrics for real space in different energy-momentum windows as the input of the second round K-means clustering for momentum space, the energy-momentum windows that exhibit subtle inhomogeneity in real space will be highlighted. It recognizes different types of electronic structures both in real space and momentum space in spatially resolved ARPES dataset. This method can be used to capture the areas of interest, and is especially suitable for samples with complex band dispersions, and can be a practical tool to any high dimensional scientific data analysis. A bottleneck for the analysis of data produced by angle-resolved photoemission spectroscopy (ARPES) is the size of the data related to spatial resolution. Building on earlier work, the authors present a data processing method that adopts unsupervised machine learning-based tools to improve the accuracy and efficiency when analysing data produced by nano-ARPES measurements.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-8"},"PeriodicalIF":5.4,"publicationDate":"2024-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01878-1.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142778670","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-05DOI: 10.1038/s42005-024-01889-y
Hadiseh Safdari, Caterina De Bacco
Anomaly detection is an essential task in the analysis of dynamic networks, offering early warnings of abnormal behavior. We present a principled approach to detect anomalies in dynamic networks that integrates community structure as a foundational model for regular behavior. Our model identifies anomalies as irregular edges while capturing structural changes. Our approach leverages a Markovian framework for temporal transitions and latent variables for community and anomaly detection, inferring hidden parameters to detect unusual interactions. Evaluations on synthetic and real-world datasets show strong anomaly detection across various scenarios. In a case study on professional football player transfers, we detect patterns influenced by club wealth and country, as well as unexpected transactions both within and across community boundaries. This work provides a framework for adaptable anomaly detection, highlighting the value of integrating domain knowledge with data-driven techniques for improved interpretability and robustness in complex networks. The authors propose a method to detect anomalies in dynamic networks by using community structure as a baseline for normal behavior: the model flags anomalies as irregular connections while tracking structural changes. In football player transfers, it reveals patterns tied to club wealth, nationality, and unexpected transactions across communities.
{"title":"Community detection and anomaly prediction in dynamic networks","authors":"Hadiseh Safdari, Caterina De Bacco","doi":"10.1038/s42005-024-01889-y","DOIUrl":"10.1038/s42005-024-01889-y","url":null,"abstract":"Anomaly detection is an essential task in the analysis of dynamic networks, offering early warnings of abnormal behavior. We present a principled approach to detect anomalies in dynamic networks that integrates community structure as a foundational model for regular behavior. Our model identifies anomalies as irregular edges while capturing structural changes. Our approach leverages a Markovian framework for temporal transitions and latent variables for community and anomaly detection, inferring hidden parameters to detect unusual interactions. Evaluations on synthetic and real-world datasets show strong anomaly detection across various scenarios. In a case study on professional football player transfers, we detect patterns influenced by club wealth and country, as well as unexpected transactions both within and across community boundaries. This work provides a framework for adaptable anomaly detection, highlighting the value of integrating domain knowledge with data-driven techniques for improved interpretability and robustness in complex networks. The authors propose a method to detect anomalies in dynamic networks by using community structure as a baseline for normal behavior: the model flags anomalies as irregular connections while tracking structural changes. In football player transfers, it reveals patterns tied to club wealth, nationality, and unexpected transactions across communities.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-10"},"PeriodicalIF":5.4,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01889-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142778626","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-05DOI: 10.1038/s42005-024-01881-6
Xin-Zhi Li, Zhen-Bo Qi, Quansheng Wu, Wen-Yu He
Topological superconductivity has attracted significant attention due to its potential applications in quantum computation, but its experimental realization remains challenging. Recently, monolayer Td−MoTe2 was observed to exhibit gate tunable superconductivity, and its in-plane upper critical field exceeds the Pauli limit. Here, we show that an in-plane magnetic field beyond the Pauli limit can drive the superconducting monolayer Td−MoTe2 into a topological superconductor. The topological superconductivity arises from the interplay between the in-plane Zeeman coupling and the unique Ising plus in-plane spin-orbit coupling (SOC) in the monolayer Td−MoTe2. The Ising plus in-plane SOC plays the essential role to enable the effective px + ipy pairing. As the essential Ising plus in-plane SOC in the monolayer Td−MoTe2 is generated by an in-plane polar field, our proposal demonstrates that applying an in-plane magnetic field to a gate tunable 2D superconductor with an in-plane polar axis is a feasible way to realize topological superconductivity. Topological superconductivity is the holy grail for implementing fault-tolerant quantum computation. Here, the authors show that for a superconducting monolayer Td−MoTe2 characterized by the Ising plus in-plane spin-orbit coupling, applying an in-plane magnetic field can drive it to a topological superconductor.
{"title":"Topological superconductivity in monolayer Td−MoTe2","authors":"Xin-Zhi Li, Zhen-Bo Qi, Quansheng Wu, Wen-Yu He","doi":"10.1038/s42005-024-01881-6","DOIUrl":"10.1038/s42005-024-01881-6","url":null,"abstract":"Topological superconductivity has attracted significant attention due to its potential applications in quantum computation, but its experimental realization remains challenging. Recently, monolayer Td−MoTe2 was observed to exhibit gate tunable superconductivity, and its in-plane upper critical field exceeds the Pauli limit. Here, we show that an in-plane magnetic field beyond the Pauli limit can drive the superconducting monolayer Td−MoTe2 into a topological superconductor. The topological superconductivity arises from the interplay between the in-plane Zeeman coupling and the unique Ising plus in-plane spin-orbit coupling (SOC) in the monolayer Td−MoTe2. The Ising plus in-plane SOC plays the essential role to enable the effective px + ipy pairing. As the essential Ising plus in-plane SOC in the monolayer Td−MoTe2 is generated by an in-plane polar field, our proposal demonstrates that applying an in-plane magnetic field to a gate tunable 2D superconductor with an in-plane polar axis is a feasible way to realize topological superconductivity. Topological superconductivity is the holy grail for implementing fault-tolerant quantum computation. Here, the authors show that for a superconducting monolayer Td−MoTe2 characterized by the Ising plus in-plane spin-orbit coupling, applying an in-plane magnetic field can drive it to a topological superconductor.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-9"},"PeriodicalIF":5.4,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01881-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142778651","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-04DOI: 10.1038/s42005-024-01884-3
Ling Lin, Chaohong Lee
The interplay between crystalline symmetry and band topology gives rise to unprecedented lower-dimensional boundary states in higher-order topological insulators (HOTIs). However, the measurement of the topological invariants of HOTIs remains a significant challenge. Here, we define a multipole winding number (MWN) for chiral-symmetric HOTIs by applying a corner twisted boundary condition. The MWN, arising from both bulk and boundary states, accurately captures the bulk-corner correspondence including boundary-obstructed topological phases. To address the measurement challenge, we leverage the perturbative nature of the corner twisted boundary condition and develop a real-space approach for determining the MWN in both two-dimensional and three-dimensional systems. The real-space formula provides an experimentally viable strategy for directly probing the topology of chiral-symmetric HOTIs through dynamical evolution. Our findings not only highlight the twisted boundary condition as a powerful tool for investigating HOTIs, but also establish a paradigm for exploring real-space formulas for the topological invariants of HOTIs. Topological invariants are critical in characterizing higher-order topological insulators. In this work, the authors show how to define a multipole winding number that can capture the bulk-corner correspondence, including boundary obstructed topological phases. An experimental proposal complements the theoretical one.
{"title":"Probing chiral-symmetric higher-order topological insulators with multipole winding number","authors":"Ling Lin, Chaohong Lee","doi":"10.1038/s42005-024-01884-3","DOIUrl":"10.1038/s42005-024-01884-3","url":null,"abstract":"The interplay between crystalline symmetry and band topology gives rise to unprecedented lower-dimensional boundary states in higher-order topological insulators (HOTIs). However, the measurement of the topological invariants of HOTIs remains a significant challenge. Here, we define a multipole winding number (MWN) for chiral-symmetric HOTIs by applying a corner twisted boundary condition. The MWN, arising from both bulk and boundary states, accurately captures the bulk-corner correspondence including boundary-obstructed topological phases. To address the measurement challenge, we leverage the perturbative nature of the corner twisted boundary condition and develop a real-space approach for determining the MWN in both two-dimensional and three-dimensional systems. The real-space formula provides an experimentally viable strategy for directly probing the topology of chiral-symmetric HOTIs through dynamical evolution. Our findings not only highlight the twisted boundary condition as a powerful tool for investigating HOTIs, but also establish a paradigm for exploring real-space formulas for the topological invariants of HOTIs. Topological invariants are critical in characterizing higher-order topological insulators. In this work, the authors show how to define a multipole winding number that can capture the bulk-corner correspondence, including boundary obstructed topological phases. An experimental proposal complements the theoretical one.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-9"},"PeriodicalIF":5.4,"publicationDate":"2024-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01884-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142762893","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A topological insulator is a quantum material which possesses conducting surfaces and an insulating bulk. Despite extensive researches on the properties of Dirac surface states, the characteristics of bulk states have remained largely unexplored. Here we report the observation of spinor-dominated magnetoresistance anomalies in β-Ag2Se, induced by a magnetic-field-driven band topological phase transition. These anomalies are caused by intrinsic orthogonality in the wave-function spinors of the last Landau bands of the bulk states, in which backscattering is strictly forbidden during a band topological phase transition. This new type of longitudinal magnetoresistance, purely controlled by the wave-function spinors of the last Landau bands, highlights a unique signature of electrical transport around the band topological phase transition. With further reducing the quantum limit and gap size in β-Ag2Se, our results may also suggest possible device applications based on this spinor-dominated mechanism and signify a rare case where topology enters the realm of magnetoresistance control. A defining characteristic of non-trivial topological materials is the bulk-boundary correspondence, and the majority of research activities has tended to centre around the surface states. Here, the authors conduct electrical transport measurements on β-Ag2Se observing anomalies in the magnetoresistance measurements, which they contend has a direct connection to the non-trivial topological nature of β-Ag2Se.
{"title":"Spinor-dominated magnetoresistance in β-Ag2Se","authors":"Cheng-Long Zhang, Yilin Zhao, Yiyuan Chen, Ziquan Lin, Sen Shao, Zhen-Hao Gong, Junfeng Wang, Hai-Zhou Lu, Guoqing Chang, Shuang Jia","doi":"10.1038/s42005-024-01872-7","DOIUrl":"10.1038/s42005-024-01872-7","url":null,"abstract":"A topological insulator is a quantum material which possesses conducting surfaces and an insulating bulk. Despite extensive researches on the properties of Dirac surface states, the characteristics of bulk states have remained largely unexplored. Here we report the observation of spinor-dominated magnetoresistance anomalies in β-Ag2Se, induced by a magnetic-field-driven band topological phase transition. These anomalies are caused by intrinsic orthogonality in the wave-function spinors of the last Landau bands of the bulk states, in which backscattering is strictly forbidden during a band topological phase transition. This new type of longitudinal magnetoresistance, purely controlled by the wave-function spinors of the last Landau bands, highlights a unique signature of electrical transport around the band topological phase transition. With further reducing the quantum limit and gap size in β-Ag2Se, our results may also suggest possible device applications based on this spinor-dominated mechanism and signify a rare case where topology enters the realm of magnetoresistance control. A defining characteristic of non-trivial topological materials is the bulk-boundary correspondence, and the majority of research activities has tended to centre around the surface states. Here, the authors conduct electrical transport measurements on β-Ag2Se observing anomalies in the magnetoresistance measurements, which they contend has a direct connection to the non-trivial topological nature of β-Ag2Se.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-6"},"PeriodicalIF":5.4,"publicationDate":"2024-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01872-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142762924","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-04DOI: 10.1038/s42005-024-01888-z
Giacomo Scalari, Jérôme Faist
It was January 1994, when the first quantum cascade laser (QCL) displayed laser action in Bell Laboratories. During these 30 years the QCL evolved incessantly, from a lab curiosity to the main on-chip source of coherent radiation in the Mid-IR and THz ranges. The journey has seen an impressive development of the QCL in several fields of laser physics and its applications, with a steady growth of research groups and companies worldwide. The 30-years development of quantum cascade lasers has established them as a go-to source of coherent radiation in the Mid-IR and THz ranges. In this comment, the authors guide the reader through the landmark achievements of this technology, from a lab curiosity to a mature technology adopted by research groups and companies.
{"title":"30 years of the quantum cascade laser","authors":"Giacomo Scalari, Jérôme Faist","doi":"10.1038/s42005-024-01888-z","DOIUrl":"10.1038/s42005-024-01888-z","url":null,"abstract":"It was January 1994, when the first quantum cascade laser (QCL) displayed laser action in Bell Laboratories. During these 30 years the QCL evolved incessantly, from a lab curiosity to the main on-chip source of coherent radiation in the Mid-IR and THz ranges. The journey has seen an impressive development of the QCL in several fields of laser physics and its applications, with a steady growth of research groups and companies worldwide. The 30-years development of quantum cascade lasers has established them as a go-to source of coherent radiation in the Mid-IR and THz ranges. In this comment, the authors guide the reader through the landmark achievements of this technology, from a lab curiosity to a mature technology adopted by research groups and companies.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-3"},"PeriodicalIF":5.4,"publicationDate":"2024-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01888-z.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142762909","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-02DOI: 10.1038/s42005-024-01890-5
Jongkyoon Park, Yong Jai Cho, Won Chegal
Spectroscopic ellipsometry (SE), which measures the thickness of thin films in a non-contact way with an accuracy of angstroms, has been widely used for optical metrology. Several types of SE are available both commercially and in research, although they require specific implementations depending on the application. Here, we theoretically and experimentally demonstrate the Frequency Division Multiplexing Spectroscopic Ellipsometry (FDM-SE) technique. With respect to conventional rotating polarizing element ellipsometry, our variant uses discrete-wavelength intensity-modulated laser diodes. This modification enables the measurement of optical properties of materials at multiple wavelengths simultaneously. We further compare the performance of the FDM-SE to a commercial instrument by measuring the thickness of SiO2 films on a Si wafer, obtaining a difference between the measured thicknesses with both methods of less than 5 Å. The proposed FDM-SE technique therefore provides a more efficient alternative to conventional SE with a high accuracy for thickness measurements. Spectroscopic ellipsometry, capable of measuring the thickness of thin films with an accuracy of angstroms, has been widely used both in research and commercially. Here, the authors theoretically and experimentally demonstrate a unique variant of spectroscopic ellipsometry utilizing frequency division multiplexed lasers of different wavelengths.
{"title":"Spectroscopic ellipsometry utilizing frequency division multiplexed lasers","authors":"Jongkyoon Park, Yong Jai Cho, Won Chegal","doi":"10.1038/s42005-024-01890-5","DOIUrl":"10.1038/s42005-024-01890-5","url":null,"abstract":"Spectroscopic ellipsometry (SE), which measures the thickness of thin films in a non-contact way with an accuracy of angstroms, has been widely used for optical metrology. Several types of SE are available both commercially and in research, although they require specific implementations depending on the application. Here, we theoretically and experimentally demonstrate the Frequency Division Multiplexing Spectroscopic Ellipsometry (FDM-SE) technique. With respect to conventional rotating polarizing element ellipsometry, our variant uses discrete-wavelength intensity-modulated laser diodes. This modification enables the measurement of optical properties of materials at multiple wavelengths simultaneously. We further compare the performance of the FDM-SE to a commercial instrument by measuring the thickness of SiO2 films on a Si wafer, obtaining a difference between the measured thicknesses with both methods of less than 5 Å. The proposed FDM-SE technique therefore provides a more efficient alternative to conventional SE with a high accuracy for thickness measurements. Spectroscopic ellipsometry, capable of measuring the thickness of thin films with an accuracy of angstroms, has been widely used both in research and commercially. Here, the authors theoretically and experimentally demonstrate a unique variant of spectroscopic ellipsometry utilizing frequency division multiplexed lasers of different wavelengths.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-8"},"PeriodicalIF":5.4,"publicationDate":"2024-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01890-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142758126","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-01DOI: 10.1038/s42005-024-01887-0
Alex Boschi, Zewdu M. Gebeyehu, Sergey Slizovskiy, Vaidotas Mišeikis, Stiven Forti, Antonio Rossi, Kenji Watanabe, Takashi Taniguchi, Fabio Beltram, Vladimir I. Fal’ko, Camilla Coletti, Sergio Pezzini
Atomically thin materials offer multiple opportunities for layer-by-layer control of their electronic properties. While monolayer graphene (MLG) is a zero-gap system, Bernal-stacked bilayer graphene (BLG) acquires a finite band gap when the symmetry between the layers’ potential energy is broken, usually, via a displacement electric field applied in double-gate devices. Here, we introduce a twistronic stack comprising both MLG and BLG, synthesized via chemical vapor deposition, showing a Bernal gap in the absence of external fields. Although a large (~30°) twist angle decouples the MLG and BLG electronic bands near Fermi level, proximity-induced energy shifts in the outermost layers result in a built-in asymmetry, which requires a displacement field of 0.14 V/nm to be compensated. The latter corresponds to a ~10 meV intrinsic BLG gap, a value confirmed by our thermal-activation measurements. The present results highlight the role of structural asymmetry and encapsulating environment, expanding the engineering toolbox for monolithically-grown graphene multilayers. Atomically thin materials offer unique opportunities for controlling electronic properties layer by layer. This study introduces a monolithically grown twistronic stack of monolayer and bilayer graphene, revealing that structural asymmetry can induce a band gap in bilayer graphene without external fields.
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