Pub Date : 2022-10-07DOI: 10.3389/femat.2022.1020076
Wei Wang, Shahar Kvatinsky, Heidemarie Schmidt, Nan Du
Biologically-inspired neuromorphic computing paradigms are computational platforms that imitate synaptic and neuronal activities in the human brain to process big data flows in an efficient and cognitive manner. In the past decades, neuromorphic computing has been widely investigated in various application fields such as language translation, image recognition, modeling of phase, and speech recognition, especially in neural networks (NNs) by utilizing emerging nanotechnologies; due to their inherent miniaturization with low power cost, they can alleviate the technical barriers of neuromorphic computing by exploiting traditional silicon technology in practical applications. In this work, we review recent advances in the development of brain-inspired computing (BIC) systems with respect to the perspective of a system designer, from the device technology level and circuit level up to the architecture and system levels. In particular, we sort out the NN architecture determined by the data structures centered on big data flows in application scenarios. Finally, the interactions between the system level with the architecture level and circuit/device level are discussed. Consequently, this review can serve the future development and opportunities of the BIC system design.
{"title":"Review on data-centric brain-inspired computing paradigms exploiting emerging memory devices","authors":"Wei Wang, Shahar Kvatinsky, Heidemarie Schmidt, Nan Du","doi":"10.3389/femat.2022.1020076","DOIUrl":"https://doi.org/10.3389/femat.2022.1020076","url":null,"abstract":"Biologically-inspired neuromorphic computing paradigms are computational platforms that imitate synaptic and neuronal activities in the human brain to process big data flows in an efficient and cognitive manner. In the past decades, neuromorphic computing has been widely investigated in various application fields such as language translation, image recognition, modeling of phase, and speech recognition, especially in neural networks (NNs) by utilizing emerging nanotechnologies; due to their inherent miniaturization with low power cost, they can alleviate the technical barriers of neuromorphic computing by exploiting traditional silicon technology in practical applications. In this work, we review recent advances in the development of brain-inspired computing (BIC) systems with respect to the perspective of a system designer, from the device technology level and circuit level up to the architecture and system levels. In particular, we sort out the NN architecture determined by the data structures centered on big data flows in application scenarios. Finally, the interactions between the system level with the architecture level and circuit/device level are discussed. Consequently, this review can serve the future development and opportunities of the BIC system design.","PeriodicalId":119676,"journal":{"name":"Frontiers in Electronic Materials","volume":"60 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134183625","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-10-04DOI: 10.3389/femat.2022.988785
Ziang Chen, Guofu Zhang, Hao Cai, C. Bengel, Feng Liu, Xianyue Zhao, Shahar Kvatinsky, Heidemarie Schmidt, R. Waser, S. Menzel, Nan Du
The high demand for performance and energy efficiency poses significant challenges for computing systems in recent years. The memristor-based crossbar array architecture is enthusiastically regarded as a potential competitor to traditional solutions due to its low power consumption and fast switching speed. Especially by leveraging self-rectifying memristive devices, passive crossbar arrays potentially enable high memory densities. Nonetheless, due to the lack of a switching control per cell, these passive, self-rectifying memristive crossbar arrays (srMCA) suffer from sneak path current issues that limit the range of accurate operation of the crossbar array. In this work, the sneak path current issues in the passive srMCAs based on self-rectifying bipolar and complementary switching memristive devices are comparatively analyzed. Under consideration of the worst-case scenario, three reading schemes are investigated: one wordline pull-up (OneWLPU), all wordline pull-up (AllWLPU), and floating (FL) reading schemes. As a conclusion, despite different switching dynamics, both types of self-rectifying memristive devices can efficiently suppress sneak path current in the srMCAs. In the FL reading scheme, the sneak path current flowing through the unselected reversely biased memristive cells in the srMCA can be considered as an accurate estimation for the practical sneak path current in the srMCA. By analyzing the sneak path current in the srMCAs with a size up to 64 × 64, it is demonstrated that the leakage current plays a crucial role for suppressing the sneak path current, and the sneak path current via an individual cell exhibits a continuous decrease while the accumulated total sneak path current in the unselected reverse biased region is increasing with expanding the crossbar size. The comparative study on the bipolar and complementary memristive devices based srMCAs under diverse reading schemes reveals the influence of the switching dynamics on the sneak path current effect in the srMCAs, and provides a beneficial reference and feasible solutions for the future optimization of the crossbar topology with the intention of mitigating sneak path effects.
{"title":"Study on sneak path effect in self-rectifying crossbar arrays based on emerging memristive devices","authors":"Ziang Chen, Guofu Zhang, Hao Cai, C. Bengel, Feng Liu, Xianyue Zhao, Shahar Kvatinsky, Heidemarie Schmidt, R. Waser, S. Menzel, Nan Du","doi":"10.3389/femat.2022.988785","DOIUrl":"https://doi.org/10.3389/femat.2022.988785","url":null,"abstract":"The high demand for performance and energy efficiency poses significant challenges for computing systems in recent years. The memristor-based crossbar array architecture is enthusiastically regarded as a potential competitor to traditional solutions due to its low power consumption and fast switching speed. Especially by leveraging self-rectifying memristive devices, passive crossbar arrays potentially enable high memory densities. Nonetheless, due to the lack of a switching control per cell, these passive, self-rectifying memristive crossbar arrays (srMCA) suffer from sneak path current issues that limit the range of accurate operation of the crossbar array. In this work, the sneak path current issues in the passive srMCAs based on self-rectifying bipolar and complementary switching memristive devices are comparatively analyzed. Under consideration of the worst-case scenario, three reading schemes are investigated: one wordline pull-up (OneWLPU), all wordline pull-up (AllWLPU), and floating (FL) reading schemes. As a conclusion, despite different switching dynamics, both types of self-rectifying memristive devices can efficiently suppress sneak path current in the srMCAs. In the FL reading scheme, the sneak path current flowing through the unselected reversely biased memristive cells in the srMCA can be considered as an accurate estimation for the practical sneak path current in the srMCA. By analyzing the sneak path current in the srMCAs with a size up to 64 × 64, it is demonstrated that the leakage current plays a crucial role for suppressing the sneak path current, and the sneak path current via an individual cell exhibits a continuous decrease while the accumulated total sneak path current in the unselected reverse biased region is increasing with expanding the crossbar size. The comparative study on the bipolar and complementary memristive devices based srMCAs under diverse reading schemes reveals the influence of the switching dynamics on the sneak path current effect in the srMCAs, and provides a beneficial reference and feasible solutions for the future optimization of the crossbar topology with the intention of mitigating sneak path effects.","PeriodicalId":119676,"journal":{"name":"Frontiers in Electronic Materials","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126306440","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-21DOI: 10.3389/femat.2022.977164
S. S. Yu, H. Zhao, W. Xu, H. Zhang, H. Duan
The properties can be switched between different states and can be used in sensors, displays, and memory devices. In this study, two multi-functional switchable materials [C5-Pmim][Ni(mnt)2] (1) and [C6-Hmim][Ni(mnt)2] (2) (where mnt2- = maleonitriledithiolate, C5-Pmim = 1-pentyl-3-methylimidazolium, and C6-Hmim = 1-hexyl-3-methylimidazolium) have been designed and synthesized, which has segregated cation and anion stacks in the crystal structure. 1 shows two-step switchable dielectric transition with a thermal hysteresis loop accompanying structure phase transition. Dielectric transition of 1 can be attributed to the reorientation of the polar cations and crystal to mesophase transition. Switchable conductivity properties of 1 and 2 were realized by the crystal to mesophase structure transition. The conductivity of the mesophase for 1 and 2 is higher than the corresponding crystal phase. Furthermore, magnetic phase transition with the non-common hysteresis loop for 2 is observed being triggered by the structure and dielectric transition. To the best of our knowledge, this study might be the rare multi-functional switchable examples with dielectric, conductivity, and magnetic transition.
{"title":"Switchable magnetic, dielectric, conductivity, and phase transition properties of charge-transfer crystals","authors":"S. S. Yu, H. Zhao, W. Xu, H. Zhang, H. Duan","doi":"10.3389/femat.2022.977164","DOIUrl":"https://doi.org/10.3389/femat.2022.977164","url":null,"abstract":"The properties can be switched between different states and can be used in sensors, displays, and memory devices. In this study, two multi-functional switchable materials [C5-Pmim][Ni(mnt)2] (1) and [C6-Hmim][Ni(mnt)2] (2) (where mnt2- = maleonitriledithiolate, C5-Pmim = 1-pentyl-3-methylimidazolium, and C6-Hmim = 1-hexyl-3-methylimidazolium) have been designed and synthesized, which has segregated cation and anion stacks in the crystal structure. 1 shows two-step switchable dielectric transition with a thermal hysteresis loop accompanying structure phase transition. Dielectric transition of 1 can be attributed to the reorientation of the polar cations and crystal to mesophase transition. Switchable conductivity properties of 1 and 2 were realized by the crystal to mesophase structure transition. The conductivity of the mesophase for 1 and 2 is higher than the corresponding crystal phase. Furthermore, magnetic phase transition with the non-common hysteresis loop for 2 is observed being triggered by the structure and dielectric transition. To the best of our knowledge, this study might be the rare multi-functional switchable examples with dielectric, conductivity, and magnetic transition.","PeriodicalId":119676,"journal":{"name":"Frontiers in Electronic Materials","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127067011","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-08-29DOI: 10.3389/femat.2022.991754
N. Pouse, Y. Deng, S. Ran, D. Graf, Y. Lai, J. Singleton, F. Balakirev, R. Baumbach, M. Maple
The correlated f-electron compound URu2Si2 exhibits superconductivity (SC) with a critical temperature T c = 1.5 K that coexists with the “hidden order” (HO) phase that forms below a characteristic temperature T 0 = 17.5 K. The SC of URu2Si2 appears to be spin singlet chiral SC with d-wave order parameter symmetry, and the pairing of SCing electrons may involve spin excitations of the HO phase. Electrical resistance R measurements were performed on single crystal specimens of URu2−x Fe x Si2 with increasing x throughout the transition from the HO phase to the large moment antiferromagnetic LMAFM phase in high magnetic fields H oriented at various angles θ with respect to the tetragonal c-axis. Measurements of R(θ) at H = 20, 33, 40, and 45 T were conducted in the temperature range 0.33 ≤ T ≤ 20 K and showed θ-dependent behavior in the various phase transitions of URu2−x Fe x Si2 (HO, LMAFM, spin density wave, Fermi surface reconstruction, etc.). These phase transitions, as functions of T, H, and θ are plotted in a phase diagram of T vs. H//c = Hcosθ for multiple values of x and show that H//c, not θ is a tuning parameter of the URu2−x Fe x Si2 system throughout all Fe concentrations, as previously found by Scheereret al. for the URu2Si2 parent compound.
相关的f电子化合物URu2Si2表现出超导性(SC)，临界温度T c = 1.5 K，与特征温度T 0 = 17.5 K以下形成的“隐序”相(HO)共存。URu2Si2的SC表现为具有d波序参量对称的自旋单重态手性SC, SCing电子的配对可能涉及到HO相的自旋激发。对URu2 - x Fe x Si2的单晶试样进行了电阻R测量，在高磁场中，从HO相到大矩反铁磁LMAFM相的转变过程中，电阻R随磁场的增大而增大。在0.33≤T≤20 K的温度范围内，对H = 20、33、40和45 T下的R(θ)进行了测量，并在URu2−x Fe x Si2的各种相变(HO、LMAFM、自旋密度波、费米表面重构等)中表现出θ依赖行为。这些相变，作为T, H和θ的函数，在x的多个值下绘制在T vs. H//c = hcost θ的相图中，并表明H//c，而不是θ，是URu2 - x Fe x Si2体系在所有Fe浓度下的调谐参数，正如Scheereret等人在URu2Si2母化合物中发现的那样。
{"title":"Anisotropy of the T vs. H phase diagram and the HO/LMAFM phase boundary in URu2−x Fe x Si2","authors":"N. Pouse, Y. Deng, S. Ran, D. Graf, Y. Lai, J. Singleton, F. Balakirev, R. Baumbach, M. Maple","doi":"10.3389/femat.2022.991754","DOIUrl":"https://doi.org/10.3389/femat.2022.991754","url":null,"abstract":"The correlated f-electron compound URu2Si2 exhibits superconductivity (SC) with a critical temperature T c = 1.5 K that coexists with the “hidden order” (HO) phase that forms below a characteristic temperature T 0 = 17.5 K. The SC of URu2Si2 appears to be spin singlet chiral SC with d-wave order parameter symmetry, and the pairing of SCing electrons may involve spin excitations of the HO phase. Electrical resistance R measurements were performed on single crystal specimens of URu2−x Fe x Si2 with increasing x throughout the transition from the HO phase to the large moment antiferromagnetic LMAFM phase in high magnetic fields H oriented at various angles θ with respect to the tetragonal c-axis. Measurements of R(θ) at H = 20, 33, 40, and 45 T were conducted in the temperature range 0.33 ≤ T ≤ 20 K and showed θ-dependent behavior in the various phase transitions of URu2−x Fe x Si2 (HO, LMAFM, spin density wave, Fermi surface reconstruction, etc.). These phase transitions, as functions of T, H, and θ are plotted in a phase diagram of T vs. H//c = Hcosθ for multiple values of x and show that H//c, not θ is a tuning parameter of the URu2−x Fe x Si2 system throughout all Fe concentrations, as previously found by Scheereret al. for the URu2Si2 parent compound.","PeriodicalId":119676,"journal":{"name":"Frontiers in Electronic Materials","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129689485","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-08-08DOI: 10.3389/femat.2022.950487
L. Rahimifard, Ahish Shylendra , Shamma Nasrin , Stephanie E. Liu , Vinod K. Sangwan , Mark C. Hersam , A. Trivedi
The increasing complexity of deep learning systems has pushed conventional computing technologies to their limits. While the memristor is one of the prevailing technologies for deep learning acceleration, it is only suited for classical learning layers where only two operands, namely weights and inputs, are processed simultaneously. Meanwhile, to improve the computational efficiency of deep learning for emerging applications, a variety of non-traditional layers requiring concurrent processing of many operands are becoming popular. For example, hypernetworks improve their predictive robustness by simultaneously processing weights and inputs against the application context. Two-electrode memristor grids cannot directly map emerging layers’ higher-order multiplicative neural interactions. Addressing this unmet need, we present crossbar processing using dual-gated memtransistors based on two-dimensional semiconductor MoS2. Unlike the memristor, the resistance states of memtransistors can be persistently programmed and can be actively controlled by multiple gate electrodes. Thus, the discussed memtransistor crossbar enables several advanced inference architectures beyond a conventional passive crossbar. For example, we show that sneak paths can be effectively suppressed in memtransistor crossbars, whereas they limit size scalability in a passive memristor crossbar. Similarly, exploiting gate terminals to suppress crossbar weights dynamically reduces biasing power by ∼20% in memtransistor crossbars for a fully connected layer of AlexNet. On emerging layers such as hypernetworks, collocating multiple operations within the same crossbar cells reduces operating power by ∼ 15 × on the considered network cases.
{"title":"Higher order neural processing with input-adaptive dynamic weights on MoS2 memtransistor crossbars","authors":"L. Rahimifard, Ahish Shylendra , Shamma Nasrin , Stephanie E. Liu , Vinod K. Sangwan , Mark C. Hersam , A. Trivedi","doi":"10.3389/femat.2022.950487","DOIUrl":"https://doi.org/10.3389/femat.2022.950487","url":null,"abstract":"The increasing complexity of deep learning systems has pushed conventional computing technologies to their limits. While the memristor is one of the prevailing technologies for deep learning acceleration, it is only suited for classical learning layers where only two operands, namely weights and inputs, are processed simultaneously. Meanwhile, to improve the computational efficiency of deep learning for emerging applications, a variety of non-traditional layers requiring concurrent processing of many operands are becoming popular. For example, hypernetworks improve their predictive robustness by simultaneously processing weights and inputs against the application context. Two-electrode memristor grids cannot directly map emerging layers’ higher-order multiplicative neural interactions. Addressing this unmet need, we present crossbar processing using dual-gated memtransistors based on two-dimensional semiconductor MoS2. Unlike the memristor, the resistance states of memtransistors can be persistently programmed and can be actively controlled by multiple gate electrodes. Thus, the discussed memtransistor crossbar enables several advanced inference architectures beyond a conventional passive crossbar. For example, we show that sneak paths can be effectively suppressed in memtransistor crossbars, whereas they limit size scalability in a passive memristor crossbar. Similarly, exploiting gate terminals to suppress crossbar weights dynamically reduces biasing power by ∼20% in memtransistor crossbars for a fully connected layer of AlexNet. On emerging layers such as hypernetworks, collocating multiple operations within the same crossbar cells reduces operating power by ∼ 15 × on the considered network cases.","PeriodicalId":119676,"journal":{"name":"Frontiers in Electronic Materials","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128593089","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-06-16DOI: 10.3389/femat.2022.895959
Z. Cao, Sorcha Hulme, T. Veal, M. Ashwin, I. Sandall
The viability of incorporating Bi and N into GaSb layers to realise photodetectors operating in the mid-infrared has been investigated. The effects of Bi and N on the cut-off wavelength of GaSb metal-semiconductor-metal photodetectors has been evaluated. The spectral responsivity measurements indicate a clear wavelength extension, to 1950 nm (Bi, 2.9%), 1990 nm (Bi, 3.8%), 2080 nm (Bi, 4.5%) and 2190 nm (N, 1.5%) from a reference GaSb device at 1720 nm, with only a relatively modest reduction in the external quantum efficiency (EQE). Comparisons of spectral response characteristics indicate that Bi incorporation reduces the carrier extraction and the impact of this on future device design is considered.
{"title":"GaSbBi Metal Semiconductor Metal Detectors for Mid-Infrared Sensing","authors":"Z. Cao, Sorcha Hulme, T. Veal, M. Ashwin, I. Sandall","doi":"10.3389/femat.2022.895959","DOIUrl":"https://doi.org/10.3389/femat.2022.895959","url":null,"abstract":"The viability of incorporating Bi and N into GaSb layers to realise photodetectors operating in the mid-infrared has been investigated. The effects of Bi and N on the cut-off wavelength of GaSb metal-semiconductor-metal photodetectors has been evaluated. The spectral responsivity measurements indicate a clear wavelength extension, to 1950 nm (Bi, 2.9%), 1990 nm (Bi, 3.8%), 2080 nm (Bi, 4.5%) and 2190 nm (N, 1.5%) from a reference GaSb device at 1720 nm, with only a relatively modest reduction in the external quantum efficiency (EQE). Comparisons of spectral response characteristics indicate that Bi incorporation reduces the carrier extraction and the impact of this on future device design is considered.","PeriodicalId":119676,"journal":{"name":"Frontiers in Electronic Materials","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128946468","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-06-08DOI: 10.3389/femat.2022.892496
Jing Guo, Cheng Huang, S. Long, Yazhou Zhou, Shu Cai, Xiaodong Li, Yanchun Li, Ke Yang, Aiguo Li, Jian-gang Guo, Qi Wu, Liling Sun
A new class of van der Waals-type layered materials, ASn2 Pn 2 (A= Li, Na, Sr, Eu; Pn= As, P, Sb), has attracted much attention in the field of condensed matter physics because they have interesting physical properties and various ground states, as well as potential applications. Here, we are the first to report the close connection among the superconducting transition temperature T c , crystal structure and Hall coefficient in pressurized NaSn2As2 single crystal. We found that the superconducting NaSn2As2 displays two pressure-induced crystal structure phase transitions, first from an ambient-pressure rhombohedral (R) phase to a monoclinic (M) phase starting at ∼ 12 GPa (P C1 ), and then to a simple cubic (C) phase starting at ∼ 33 GPa (P C2 ). In these phases, the T c value and carrier concentration change correspondingly. Our results suggest that the observed three superconducting states are related to the change of structural phase and the variation of carrier concentrations.
{"title":"Coevolution of Superconductivity With Structure and Hall Coefficient in Pressurized NaSn2As2","authors":"Jing Guo, Cheng Huang, S. Long, Yazhou Zhou, Shu Cai, Xiaodong Li, Yanchun Li, Ke Yang, Aiguo Li, Jian-gang Guo, Qi Wu, Liling Sun","doi":"10.3389/femat.2022.892496","DOIUrl":"https://doi.org/10.3389/femat.2022.892496","url":null,"abstract":"A new class of van der Waals-type layered materials, ASn2 Pn 2 (A= Li, Na, Sr, Eu; Pn= As, P, Sb), has attracted much attention in the field of condensed matter physics because they have interesting physical properties and various ground states, as well as potential applications. Here, we are the first to report the close connection among the superconducting transition temperature T c , crystal structure and Hall coefficient in pressurized NaSn2As2 single crystal. We found that the superconducting NaSn2As2 displays two pressure-induced crystal structure phase transitions, first from an ambient-pressure rhombohedral (R) phase to a monoclinic (M) phase starting at ∼ 12 GPa (P C1 ), and then to a simple cubic (C) phase starting at ∼ 33 GPa (P C2 ). In these phases, the T c value and carrier concentration change correspondingly. Our results suggest that the observed three superconducting states are related to the change of structural phase and the variation of carrier concentrations.","PeriodicalId":119676,"journal":{"name":"Frontiers in Electronic Materials","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134178221","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-05-26DOI: 10.3389/femat.2022.934691
Xinwei Li, J. Kono, Q. Si, S. Paschen
Strange metal behavior appears across a variety of condensed matter settings and beyond, and achieving a universal understanding is an exciting prospect. The beyond-Landau quantum criticality of Kondo destruction has had considerable success in describing the behavior of strange metal heavy fermion compounds, and there is some evidence that the associated partial localization-delocalization nature can be generalized to diverse materials classes. Other potential overarching principles at play are also being explored. An intriguing proposal is that Planckian scattering, with a rate of k B T/ℏ, leads to the linear temperature dependence of the (dc) electrical resistivity, which is a hallmark of strange metal behavior. Here we extend a previously introduced analysis scheme based on the Drude description of the dc resistivity to optical conductivity data. When they are well described by a simple (ac) Drude model, the scattering rate can be directly extracted. This avoids the need to determine the ratio of charge carrier concentration to effective mass, which has complicated previous analyses based on the dc resistivity. However, we point out that strange metals typically exhibit strong deviations from Drude behavior, as exemplified by the “extreme” strange metal YbRh2Si2. This calls for alternative approaches, and we point to the power of strange metal dynamical (energy-over-temperature) scaling analyses for the inelastic part of the optical conductivity. If such scaling extends to the low-frequency limit, a strange metal relaxation rate can be estimated, and may ultimately be used to test whether strange metals relax in a Planckian manner.
奇怪的金属行为出现在各种凝聚态设置和超越，实现普遍的理解是一个令人兴奋的前景。近藤破坏的超朗道量子临界在描述奇异金属重费米子化合物的行为方面取得了相当大的成功，并且有一些证据表明，相关的部分局域-非局域性质可以推广到不同的材料类别。其他潜在的总体原则也在探索中。一个有趣的建议是，普朗克散射，速率为k B T/ h，导致(直流)电阻率的线性温度依赖，这是奇怪金属行为的标志。在这里，我们将先前介绍的基于直流电阻率的原始描述的分析方案扩展到光学电导率数据。当它们被简单的(ac) Drude模型很好地描述时，可以直接提取散射率。这避免了确定载流子浓度与有效质量之比的需要，这使以前基于直流电阻率的分析变得复杂。然而，我们指出，奇怪的金属通常表现出强烈的偏离德鲁德行为，例如“极端”奇怪的金属YbRh2Si2。这需要替代方法，我们指出了奇异金属动力学(能量-超温)标度分析对光学导电性非弹性部分的作用。如果这种标度扩展到低频极限，就可以估计出奇怪金属的弛豫率，并可能最终用于测试奇怪金属是否以普朗克方式弛豫。
{"title":"Is the optical conductivity of heavy fermion strange metals Planckian?","authors":"Xinwei Li, J. Kono, Q. Si, S. Paschen","doi":"10.3389/femat.2022.934691","DOIUrl":"https://doi.org/10.3389/femat.2022.934691","url":null,"abstract":"Strange metal behavior appears across a variety of condensed matter settings and beyond, and achieving a universal understanding is an exciting prospect. The beyond-Landau quantum criticality of Kondo destruction has had considerable success in describing the behavior of strange metal heavy fermion compounds, and there is some evidence that the associated partial localization-delocalization nature can be generalized to diverse materials classes. Other potential overarching principles at play are also being explored. An intriguing proposal is that Planckian scattering, with a rate of k B T/ℏ, leads to the linear temperature dependence of the (dc) electrical resistivity, which is a hallmark of strange metal behavior. Here we extend a previously introduced analysis scheme based on the Drude description of the dc resistivity to optical conductivity data. When they are well described by a simple (ac) Drude model, the scattering rate can be directly extracted. This avoids the need to determine the ratio of charge carrier concentration to effective mass, which has complicated previous analyses based on the dc resistivity. However, we point out that strange metals typically exhibit strong deviations from Drude behavior, as exemplified by the “extreme” strange metal YbRh2Si2. This calls for alternative approaches, and we point to the power of strange metal dynamical (energy-over-temperature) scaling analyses for the inelastic part of the optical conductivity. If such scaling extends to the low-frequency limit, a strange metal relaxation rate can be estimated, and may ultimately be used to test whether strange metals relax in a Planckian manner.","PeriodicalId":119676,"journal":{"name":"Frontiers in Electronic Materials","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125342969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-05-25DOI: 10.3389/femat.2022.906213
Jianning Guo, Su Chen, Wuhao Chen, Xiaoli Huang, T. Cui
Room-temperature superconductors have long been the ultimate goal of scientists. Pressure-stabilized hydrides are a new rapidly growing class of high-temperature superconductors and are believed to be a new superconducting system, undoubtedly leading to a surge in the discovery of new hydrogen-rich materials. They are the forefront of physics and material science. Lanthanide polyhydrides formed under pressure are promising conventional superconductors. Especially, both the theoretical and experimental reports on lanthanum superhydrides under pressure, exhibiting superconductivity at temperatures as high as 250 K, have further stimulated an intense search for room-temperature superconductors in hydrides. This review focuses on the recent advances of crystal structures, stabilities, and superconductivity of lanthanide polyhydrides at high pressures, including the experimental results from our group. By using in situ four-probe electrical measurements and the synchrotron X-ray diffraction technique, we have identified several high-temperature superconducting phases: a lanthanum superhydride and two cerium superhydrides. The present work indicates that superconductivity declines along the La–Ce–Pr–Nd series, while magnetism becomes more and more pronounced. These discoveries have enriched the binary system of clathrate superhydrides and provided more hints for studying the role of rare earth metal elements having high-temperature superconductivity.
{"title":"Advances in the Synthesis and Superconductivity of Lanthanide Polyhydrides Under High Pressure","authors":"Jianning Guo, Su Chen, Wuhao Chen, Xiaoli Huang, T. Cui","doi":"10.3389/femat.2022.906213","DOIUrl":"https://doi.org/10.3389/femat.2022.906213","url":null,"abstract":"Room-temperature superconductors have long been the ultimate goal of scientists. Pressure-stabilized hydrides are a new rapidly growing class of high-temperature superconductors and are believed to be a new superconducting system, undoubtedly leading to a surge in the discovery of new hydrogen-rich materials. They are the forefront of physics and material science. Lanthanide polyhydrides formed under pressure are promising conventional superconductors. Especially, both the theoretical and experimental reports on lanthanum superhydrides under pressure, exhibiting superconductivity at temperatures as high as 250 K, have further stimulated an intense search for room-temperature superconductors in hydrides. This review focuses on the recent advances of crystal structures, stabilities, and superconductivity of lanthanide polyhydrides at high pressures, including the experimental results from our group. By using in situ four-probe electrical measurements and the synchrotron X-ray diffraction technique, we have identified several high-temperature superconducting phases: a lanthanum superhydride and two cerium superhydrides. The present work indicates that superconductivity declines along the La–Ce–Pr–Nd series, while magnetism becomes more and more pronounced. These discoveries have enriched the binary system of clathrate superhydrides and provided more hints for studying the role of rare earth metal elements having high-temperature superconductivity.","PeriodicalId":119676,"journal":{"name":"Frontiers in Electronic Materials","volume":"43 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114658270","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-05-25DOI: 10.3389/femat.2022.904405
Min-Ki Ji, D. Min, Qingzhou Wu, Rui Mi, Wenfeng Liu, Shengtao Li, Shaorui Qin, Shenglong Zhu
Polymer dielectrics with high breakdown strength are very competitively used in the dielectric capacitor, which is widely applied in pulsed power devices and power systems due to their ultra-high power density. The polypropylene (PP) film is the most popularly used polymer for the dielectric capacitor in the market. However, its low energy density cannot meet the emerging demand for miniaturized, compact, and high-energy performance dielectrics. Therefore, it is urgent to raise the energy storage density of the polypropylene film. Here, this study described the improved energy storage density of polypropylene nanocomposites via macroscopic and mesoscopic structure designs. The ABA-structured, BAB-structured, and single-layered nanocomposites were prepared by melting blending and hot-pressing methods, where “A” and “B” films refer to PP/MgO and PP/BaTO3 nanocomposite dielectrics, respectively. Then, the microstructure, dielectric, breakdown, and energy storage properties of these nanocomposite dielectrics were tested. According to the test results, for the sandwich-structured dielectrics, the B layer and the interface between adjacent layers can increase the polarization, and the A layer and the barrier at the interface can reduce the charge mobility. In addition, the sandwich structures can redistribute the electric field. Correspondingly, the breakdown strength and permittivity of PP dielectrics are improved synergistically. Compared to the PP nanocomposite dielectrics with the BAB structure, the dielectric with the ABA structure exhibits more excellent energy storage performance. The largest energy storage density of ABA films with a BaTO3 content of 45 wt% in the B layer is 3.10 J/cm3, which is 67% higher than that of pure PP. The study provides a new concept for improving the energy storage performance of polymer nanocomposite dielectrics from the perspective of macroscopic and mesoscopic structure designs.
{"title":"Significantly Improved Energy Storage Density of Polypropylene Nanocomposites via Macroscopic and Mesoscopic Structure Designs","authors":"Min-Ki Ji, D. Min, Qingzhou Wu, Rui Mi, Wenfeng Liu, Shengtao Li, Shaorui Qin, Shenglong Zhu","doi":"10.3389/femat.2022.904405","DOIUrl":"https://doi.org/10.3389/femat.2022.904405","url":null,"abstract":"Polymer dielectrics with high breakdown strength are very competitively used in the dielectric capacitor, which is widely applied in pulsed power devices and power systems due to their ultra-high power density. The polypropylene (PP) film is the most popularly used polymer for the dielectric capacitor in the market. However, its low energy density cannot meet the emerging demand for miniaturized, compact, and high-energy performance dielectrics. Therefore, it is urgent to raise the energy storage density of the polypropylene film. Here, this study described the improved energy storage density of polypropylene nanocomposites via macroscopic and mesoscopic structure designs. The ABA-structured, BAB-structured, and single-layered nanocomposites were prepared by melting blending and hot-pressing methods, where “A” and “B” films refer to PP/MgO and PP/BaTO3 nanocomposite dielectrics, respectively. Then, the microstructure, dielectric, breakdown, and energy storage properties of these nanocomposite dielectrics were tested. According to the test results, for the sandwich-structured dielectrics, the B layer and the interface between adjacent layers can increase the polarization, and the A layer and the barrier at the interface can reduce the charge mobility. In addition, the sandwich structures can redistribute the electric field. Correspondingly, the breakdown strength and permittivity of PP dielectrics are improved synergistically. Compared to the PP nanocomposite dielectrics with the BAB structure, the dielectric with the ABA structure exhibits more excellent energy storage performance. The largest energy storage density of ABA films with a BaTO3 content of 45 wt% in the B layer is 3.10 J/cm3, which is 67% higher than that of pure PP. The study provides a new concept for improving the energy storage performance of polymer nanocomposite dielectrics from the perspective of macroscopic and mesoscopic structure designs.","PeriodicalId":119676,"journal":{"name":"Frontiers in Electronic Materials","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128805601","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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