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Keywords = kondo insulator

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15 pages, 777 KiB  
Article
Kondo-like Behavior in Lightly Gd-Doped Manganite CaMnO3
by Tomislav Ivek, Matija Čulo, Nikolina Novosel, Maria Čebela, Bojana Laban, Uroš Čakar and Milena Rosić
Nanomaterials 2025, 15(11), 784; https://doi.org/10.3390/nano15110784 - 23 May 2025
Viewed by 524
Abstract
Manganese oxides (manganites) are among the most studied materials in condensed matter physics due to the famous colossal magnetoresistance and very rich phase diagrams characterized by strong competition between ferromagnetic (FM) metallic and antiferromagnetic (AFM) insulating phases. One of the key questions that [...] Read more.
Manganese oxides (manganites) are among the most studied materials in condensed matter physics due to the famous colossal magnetoresistance and very rich phase diagrams characterized by strong competition between ferromagnetic (FM) metallic and antiferromagnetic (AFM) insulating phases. One of the key questions that remains open even after more than thirty years of intensive research is the exact conductivity mechanism in insulating as well as in metallic phases and its relation to the corresponding magnetic structure. In order to shed more light on this problem, here, we report magnetotransport measurements on sintered nanocrystalline samples of the very poorly explored manganites Ca1xGdxMnO3 with x=0.05 and x=0.10, in the temperature range 2–300 K, and in magnetic fields up to 16 T. Our results indicate that both compounds at low temperatures exhibit metallic behavior with a peculiar resistivity upturn and a large negative magnetoresistance. We argue that such behavior is consistent with a Kondo-like scattering on Gd impurities coupled with the percolation of FM metallic regions within insulating AFM matrix. Full article
(This article belongs to the Topic Magnetic Nanoparticles and Thin Films)
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14 pages, 1835 KiB  
Article
Magnetic and Electronic Inhomogeneity in Sm1−xEuxB6
by M. Victoria Ale Crivillero, Priscila F. S. Rosa, Zachary Fisk, Jens Müller, Pedro Schlottmann and Steffen Wirth
Condens. Matter 2024, 9(4), 55; https://doi.org/10.3390/condmat9040055 - 13 Dec 2024
Cited by 1 | Viewed by 1330
Abstract
While SmB6 attracts attention as a possible topological Kondo insulator, EuB6 is known to host magnetic polarons that give rise to large magnetoresistive effects above its ferromagnetic order transition. Here, we investigate single crystals of Sm1−xEuxB6 [...] Read more.
While SmB6 attracts attention as a possible topological Kondo insulator, EuB6 is known to host magnetic polarons that give rise to large magnetoresistive effects above its ferromagnetic order transition. Here, we investigate single crystals of Sm1−xEuxB6 by magnetic and magnetotransport measurements to explore a possible interplay of these two intriguing phenomena, with a focus on the Eu-rich substitutions. Sm0.01Eu0.99B6 exhibits generally similar behavior as EuB6. Interestingly, Sm0.05Eu0.95B6 combines a global antiferromagnetic order with local polaron formation. A pronounced hysteresis is found in the magnetoresistance of Sm0.1Eu0.9B6 at low temperature (T= 1.9 K) and applied magnetic fields between 2.3 and 3.6 T. The latter is in agreement with a phenomenological model that predicts the stabilization of ferromagnetic polarons with an increasing magnetic field within materials with a global antiferromagnetic order. Full article
(This article belongs to the Special Issue Superstripes Physics, 3rd Edition)
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10 pages, 2113 KiB  
Article
Kondo Versus Fano in Superconducting Artificial High-Tc Heterostructures
by Gaetano Campi, Gennady Logvenov, Sergio Caprara, Antonio Valletta and Antonio Bianconi
Condens. Matter 2024, 9(4), 43; https://doi.org/10.3390/condmat9040043 - 31 Oct 2024
Cited by 3 | Viewed by 1491
Abstract
Recently, the quest for high-Tc superconductors has evolved from the trial-and-error methodology to the growth of nanostructured artificial high-Tc superlattices (AHTSs) with tailor-made superconducting functional properties by quantum design. Here, we report the growth by molecular beam epitaxy (MBE) of a superlattice of [...] Read more.
Recently, the quest for high-Tc superconductors has evolved from the trial-and-error methodology to the growth of nanostructured artificial high-Tc superlattices (AHTSs) with tailor-made superconducting functional properties by quantum design. Here, we report the growth by molecular beam epitaxy (MBE) of a superlattice of Mott insulator metal interfaces (MIMIs) made of nanoscale superconducting layers of quantum confined-space charge in the Mott insulator La2CuO4 (LCO), with thickness L intercalated by normal metal La1.55Sr0.45CuO4 (LSCO) with period d. The critical temperature shows the superconducting dome with Tc as a function of the geometrical parameter L/d showing the maximum at the magic ratio L/d = 2/3 where the Fano–Feshbach resonance enhances the superconducting critical temperature. The normal state transport data of the samples at the top of the superconducting dome exhibit Planckian T-linear resistivity. For L/d > 2/3 and L/d < 2/3, the heterostructures show a resistance following Kondo universal scaling predicted by the numerical renormalization group theory for MIMI nanoscale heterostructures. We show that the Kondo temperature, TK, and the Kondo scattering amplitude, R0K, vanish at L/d = 2/3, while TK and R0K increase at both sides of the superconducting dome, indicating that the T-linear resistance regime competes with the Kondo proximity effect in the normal phase of MIMIs. Full article
(This article belongs to the Special Issue Superstripes Physics, 3rd Edition)
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12 pages, 835 KiB  
Article
Band Polarization Effect on the Kondo State in a Zigzag Silicene Nanoribbon
by Ginetom S. Diniz, Edson Vernek and George B. Martins
Nanomaterials 2022, 12(9), 1480; https://doi.org/10.3390/nano12091480 - 27 Apr 2022
Cited by 2 | Viewed by 1934
Abstract
Using the Numerical Renormalization Group method, we study the properties of a quantum impurity coupled to a zigzag silicene nanoribbon (ZSNR) that is subjected to the action of a magnetic field applied in a generic direction. We propose a simulation of what a [...] Read more.
Using the Numerical Renormalization Group method, we study the properties of a quantum impurity coupled to a zigzag silicene nanoribbon (ZSNR) that is subjected to the action of a magnetic field applied in a generic direction. We propose a simulation of what a scanning tunneling microscope will see when investigating the Kondo peak of a magnetic impurity coupled to the metallic edge of this topologically non-trivial nanoribbon. This system is subjected to an external magnetic field that polarizes the host much more strongly than the impurity. Thus, we are indirectly analyzing the ZSNR polarization through the STM analysis of the fate of the Kondo state subjected to the influence of the polarized conduction electron band. Our numerical simulations demonstrate that the spin-orbit-coupling-generated band polarization anisotropy is strong enough to have a qualitative effect on the Kondo peak for magnetic fields applied along different directions, suggesting that this contrast could be experimentally detected. Full article
(This article belongs to the Special Issue Magnetism and Kondo Effect in Graphene)
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23 pages, 3377 KiB  
Article
On Strong f-Electron Localization Effect in a Topological Kondo Insulator
by Udai Prakash Tyagi, Kakoli Bera and Partha Goswami
Symmetry 2021, 13(12), 2245; https://doi.org/10.3390/sym13122245 - 24 Nov 2021
Cited by 3 | Viewed by 1883
Abstract
We study a strong f-electron localization effect on the surface state of a generic topological Kondo insulator (TKI) system by performing a mean-field theoretic (MFT) calculation within the framework of the periodic Anderson model (PAM) using the slave boson technique. The surface [...] Read more.
We study a strong f-electron localization effect on the surface state of a generic topological Kondo insulator (TKI) system by performing a mean-field theoretic (MFT) calculation within the framework of the periodic Anderson model (PAM) using the slave boson technique. The surface metallicity, together with bulk insulation, requires this type of localization. A key distinction between surface states in a conventional insulator and a topological insulator is that, along a course joining two time-reversal invariant momenta (TRIM) in the same BZ, there will be an intersection of these surface states, an even/odd number of times, with the Fermi energy inside the spectral gap. For an even (odd) number of surface state crossings, the surface states are topologically trivial (non-trivial). The symmetry consideration and the pictorial representation of the surface band structure obtained here show an odd number of crossings, leading to the conclusion that, at least within the PAM framework, the generic system is a strong topological insulator. Full article
(This article belongs to the Special Issue Magnetism, Skyrmions and Chirality)
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13 pages, 8431 KiB  
Article
Topological Phase and Strong Correlation in Rare-Earth Hexaborides XB6 (X = La, Ce, Pr, Nd, Pm, Sm, Eu)
by Sheng-Hsiung Hung and Horng-Tay Jeng
Materials 2020, 13(19), 4381; https://doi.org/10.3390/ma13194381 - 1 Oct 2020
Cited by 6 | Viewed by 2845
Abstract
The rare-earth hexaboride SmB6, known as the topological Kondo insulator, has attracted tremendous attention in recent years. It was revealed that the topological phase of SmB6 is insensitive to the value of on-site Coulomb interactions (Hubbard U), indicating that the [...] Read more.
The rare-earth hexaboride SmB6, known as the topological Kondo insulator, has attracted tremendous attention in recent years. It was revealed that the topological phase of SmB6 is insensitive to the value of on-site Coulomb interactions (Hubbard U), indicating that the topological phase in SmB6 is robust against strong correlations. On the contrary, the isostructural YbB6 displays a sensitivity to the Hubbard U value. As U increases, YbB6 transforms from topological Kondo insulator to trivial insulator, showing the weak robustness of the topological phase of YbB6 against U. Consequently, the dependence of the topological phase on Hubbard U is a crucial issue in the rare-earth hexaboride family. In this work, we investigate the structural and electronic properties of rare-earth hexaboride compounds through first-principles calculations based on density functional theory. By taking the strong correlations into consideration using a wide range of on-site U values, we study the evolution of the topological phases in rare-earth hexaboride (XB6, X = La, Ce, Pr, Nd, Pm, Sm, Eu). Unlike YbB6, the topological trends in all the examples of XB6 studied in this work are insensitive to the U values. We conclude that in addition to the well-known SmB6, PmB6, NdB6 and EuB6 are also topologically nontrivial compounds, whereas LaB6, CeB6 and PrB6 are topologically trivial metal. Full article
(This article belongs to the Section Energy Materials)
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13 pages, 5532 KiB  
Article
Crystal Growth by the Floating Zone Method of Ce-Substituted Crystals of the Topological Kondo Insulator SmB6
by Monica Ciomaga Hatnean, Talha Ahmad, Marc Walker, Martin R. Lees and Geetha Balakrishnan
Crystals 2020, 10(9), 827; https://doi.org/10.3390/cryst10090827 - 17 Sep 2020
Cited by 5 | Viewed by 3313
Abstract
SmB6 is a mixed valence topological Kondo insulator. To investigate the effect of substituting Sm with magnetic Ce ions on the physical properties of samarium hexaboride, Ce-substituted SmB6 crystals were grown by the floating zone method for the first time as [...] Read more.
SmB6 is a mixed valence topological Kondo insulator. To investigate the effect of substituting Sm with magnetic Ce ions on the physical properties of samarium hexaboride, Ce-substituted SmB6 crystals were grown by the floating zone method for the first time as large, good quality single crystal boules. The crystal growth conditions are reported. Structural, magnetic and transport properties of single crystals of Sm1xCexB6 (x=0.05, 0.10 and 0.20) were investigated using X-ray diffraction techniques, electrical resistivity and magnetisation measurements. Phase composition analysis of the powder X-ray diffraction data collected on the as-grown boules revealed that the main phase was that of the parent compound, SmB6. Substitution of Sm ions with magnetic Ce ions does not lead to long-range magnetic ordering in the Sm1xCexB6 crystals. The substitution with 5% Ce and above suppresses the cross-over from bulk conductivity at high temperatures to surface-only conductivity at low temperatures. Full article
(This article belongs to the Special Issue Advances in Topological Materials)
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20 pages, 2133 KiB  
Article
Effect of Rashba Impurities on Surface State of a Topological Kondo Insulator
by Partha Goswami
Surfaces 2020, 3(3), 484-504; https://doi.org/10.3390/surfaces3030035 - 10 Sep 2020
Viewed by 2569
Abstract
In this communication, we report surface state, with Rashba impurities, of a generic topological Kondo insulator (TKI) system by performing a mean-field theoretic (MFT) calculation within the framework of slave-boson protocol. The surface metallicity together with bulk insulation is found to require very [...] Read more.
In this communication, we report surface state, with Rashba impurities, of a generic topological Kondo insulator (TKI) system by performing a mean-field theoretic (MFT) calculation within the framework of slave-boson protocol. The surface metallicity together with bulk insulation is found to require very strong f-electron localization. The possibility of intra-band as well as inter-band unconventional plasmons exists for the surface state spectrum. The paramountcy of the bulk metallicity, and, in the presence of the Rashba impurities, the TKI surface comprising of ‘helical liquids’ are the important outcomes of the present communication. The access to the gapless Dirac spectrum leads to spin-plasmons with the usual wave vector dependence q1/2. The Rashba coupling does not impair the Kondo screening and does not affect the quantum critical point (QCP) for the bulk. Full article
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7 pages, 629 KiB  
Article
The Temperature Dependence of the Magnetization Process of the Kondo Insulator YbB12
by Yasuhiro H. Matsuda, Yoshiki Kakita and Fumitoshi Iga
Crystals 2020, 10(1), 26; https://doi.org/10.3390/cryst10010026 - 7 Jan 2020
Cited by 5 | Viewed by 3353
Abstract
The properties of the Kondo insulator in a strong magnetic field are one of the most intriguing subjects in condensed matter physics. The Kondo insulating state is expected to be suppressed by magnetic fields, which results in the dramatic change in the electronic [...] Read more.
The properties of the Kondo insulator in a strong magnetic field are one of the most intriguing subjects in condensed matter physics. The Kondo insulating state is expected to be suppressed by magnetic fields, which results in the dramatic change in the electronic state. We have studied the magnetization process of one of the prototypical Kondo insulators YbB 12 at several temperatures in magnetic fields of up to 80 T. The metamagnetism due to the insulator-metal (IM) transition seen around 50 T was found to become significantly broadened at approximately 30 K. This characteristic temperature T * 30 K in YbB 12 is an order of magnitude lower than the Kondo temperature T K = 240 K. Our results suggest that there is an energy scale smaller than the Kondo temperature that is important to understanding the nature of Kondo insulators. Full article
(This article belongs to the Special Issue Magnetic Field-induced Phase Transition)
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9 pages, 13291 KiB  
Article
Growth Mechanism of SmB6 Nanowires Synthesized by Chemical Vapor Deposition: Catalyst-Assisted and Catalyst-Free
by Yi Chu, Yugui Cui, Shaoyun Huang, Yingjie Xing and Hongqi Xu
Nanomaterials 2019, 9(8), 1062; https://doi.org/10.3390/nano9081062 - 24 Jul 2019
Cited by 6 | Viewed by 3874
Abstract
SmB6 nanowires, as a prototype of nanostructured topological Kondo insulator, have shown rich novel physical phenomena relating to their surface. Catalyst-assisted chemical vapor deposition (CVD) is a common approach to prepare SmB6 nanowires and Ni is the most popular catalyst used [...] Read more.
SmB6 nanowires, as a prototype of nanostructured topological Kondo insulator, have shown rich novel physical phenomena relating to their surface. Catalyst-assisted chemical vapor deposition (CVD) is a common approach to prepare SmB6 nanowires and Ni is the most popular catalyst used to initiate the growth of SmB6 nanowires. Here, we study the effect of growth mechanism on the surface of SmB6 nanowires synthesized by CVD. Two types of SmB6 nanowires are obtained when using Ni as the catalyst. In addition to pure SmB6 nanowires without Ni impurity, a small amount of Ni is detected on the surface of some SmB6 nanowires by element analysis with transmission electron microscopy. In order to eliminate the possible distribution of Ni on nanowire surface, we synthesize single crystalline SmB6 nanowires by CVD without using catalyst. The difference between catalyst-assisted and catalyst-free growth mechanism is discussed. Full article
(This article belongs to the Special Issue Nanotechnologies and Nanomaterials: Selected Papers from CCMR 2019)
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40 pages, 2741 KiB  
Review
Organometallic Routes into the Nanorealms of Binary Fe-Si Phases
by Manoj K. Kolel-Veetil and Teddy M. Keller
Materials 2010, 3(2), 1049-1088; https://doi.org/10.3390/ma3021049 - 9 Feb 2010
Cited by 27 | Viewed by 17850
Abstract
The Fe-Si binary system provides several iron silicides that have varied and exceptional material properties with applications in the electronic industry. The well known Fe-Si binary silicides are Fe3Si, Fe5Si3, FeSi, a-FeSi2 and b-FeSi [...] Read more.
The Fe-Si binary system provides several iron silicides that have varied and exceptional material properties with applications in the electronic industry. The well known Fe-Si binary silicides are Fe3Si, Fe5Si3, FeSi, a-FeSi2 and b-FeSi2. While the iron-rich silicides Fe3Si and Fe5Si3 are known to be room temperature ferromagnets, the stoichiometric FeSi is the only known transition metal Kondo insulator. Furthermore, Fe5Si3 has also been demonstrated to exhibit giant magnetoresistance (GMR). The silicon-rich b-FeSi2 is a direct band gap material usable in light emitting diode (LED) applications. Typically, these silicides are synthesized by traditional solid-state reactions or by ion beam-induced mixing (IBM) of alternating metal and silicon layers. Alternatively, the utilization of organometallic compounds with reactive transition metal (Fe)-carbon bonds has opened various routes for the preparation of these silicides and the silicon-stabilized bcc- and fcc-Fe phases contained in the Fe-Si binary phase diagram. The unique interfacial interactions of carbon with the Fe and Si components have resulted in the preferential formation of nanoscale versions of these materials. This review will discuss such reactions. Full article
(This article belongs to the Special Issue Organometallic Compounds)
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