We consider the Fermi surface inside the antiferromagnetic ordered region of a Kondo lattice system in an arbitrary dimension higher than one. We establish the existence of ${\rm AF_S}$, an antiferromagnetic phase whose Fermi surface is ``small,'' in the sense that the local moments do not participate in the Fermi-surface formation. This is in contrast to the ``large'' Fermi surface that is typically assumed for heavy fermion metals. We extend our earlier work to the case that the Fermi surface of the conduction electrons intersects the antiferromagnetic Brillouin zone boundary. Our results provide a new perspective on local quantum criticality. In addition, our results imply that, for the ${\rm AF_S}$ phase, it is important to keep track of the dynamical screening processes; we suggest that this effect is not captured in a recent variational Monte-Carlo study of the Kondo lattice.
We present a one dimensional model of electrons coupled to localized moments of spin $S\ge 1$ in which magnetism and superconductivity interplay in a nontrivial manner. This model has a non-Fermi liquid ground state of the chiral spin liquid type. A non-conventional odd-frequency pairing is shown to be the dominant instability of the system, together with antiferromagnetism of the local moments. We argue that this model captures the physics of the Kondo-Heisenberg spin S=1 chain, in the limit of strong Kondo coupling. Finally, we discuss briefly the effect of interchain coupling.
The one dimensional dilute Kondo lattice model is investigated by means of bosonization for different dilution patterns of the array of impurity spins. The physical picture is very different if a commensurate or incommensurate doping of the impurity spins is considered. For the commensurate case, the obtained phase diagram is verified using a non-Abelian density-matrix renormalization-group algorithm. The paramagnetic phase widens at the expense of the ferromagnetic phase as the $f$-spins are diluted. For the incommensurate case, antiferromagnetism is found at low doping, which distinguishes t…
A review is given of the experimental situation and theoretical predictions concerning unconventional magnetic ordering in dense Kondo 4f- and 5f-systems, including recently investigated on cerium, ytterbium, and actinide based ternary systems. This unconventional ordering is characterized by a small magnetic moment and exhibits features typical of both localized-spin and itinerant-electron magnets. Particular attention is paid to ferromagnetic systems and the competition among different types of magnetic ordering. The perturbation theory method, renormalization group approach, and auxiliary p…
A scaling theory of the Kondo lattices with frustrated exchange interactions is developed, criterium of antiferromagnetic ordering and quantum-disordered state being investigated. The calculations taking into account magnon and incoherent spin dynamics are performed. Depending on the bare model parameters, one or two quantum phase transitions into non-magnetic spin-liquid and Kondo Fermi-liquid ground states can occur with increasing the bare coupling constant. Whereas the renormalization of the magnetic moment in the ordered phase can reach orders of magnitude, spin fluctuation frequency and …
The unusual electronic and magnetic properties of the systems Ce$_3$Pd$_{20}$T$_6$ (T = Ge, Si) with two non-equivalent Ce positions are discussed. The logarithmic growth of resistance for both the systems confirms the presence of the Kondo effect in the two respective temperature ranges. The two-scale behavior is explained by consecutive splitting of Ce ion levels in the crystal field. The effects of the frustration caused by the coexistence of the different positions of cerium are treated, which may also significantly enhance the observed values of specific heat. A model of "molecular magnet…
Kondo-based semimetals and semiconductors are of extensive current interest as a viable platform for strongly correlated states. It is thus important to understand the routes towards such dilute-carrier correlated states. One established pathway is through Kondo effect in metallic non-magnetic analogues. Here we advance a new mechanism, through which Kondo-based semimetals develop out of conduction electrons with a low carrier-density in the presence of an even number of rare-earth sites. We demonstrate this effect by studying the Kondo material Yb3Ir4Ge13 along with its closed-f-shell counter…
Topological Kondo insulators are a rare example of an interaction-enabled topological phase of matter in three-dimensional crystals - making them an intriguing but also hard case for theoretical studies. Here, we aim to advance their theoretical understanding by solving the paradigmatic two-band model for topological Kondo-insulators using a fully spin-rotation invariant slave-boson treatment. Within a mean-field approximation, we map out the magnetic phase diagram and characterize both antiferromagnetic and paramagnetic phases by their topological properties. Among others, we identify an anti…
We find evidence that superconductivity intrudes into the paramagnetic-to-magnetic transition of the Kondo lattice model if magnetic frustration is added. Specifically, we study by variational method the model on a square lattice in the presence of both nearest- ($t$) and next-nearest-neighbor ($t^\prime$) hopping of the conduction electrons. We find that when $t^\prime/t$ is finite a $d$-wave superconducting dome emerges between the magnetic and paramagnetic metal phases and close to the compensated regime, i.e., the number of conduction electrons equal to the number of localized spin-1/2 mom…
We report on the physical properties of the series Ce_(1-x)La_xIr_2B_2 (x D 0-0.9), obtained by means of magnetization, heat capacity and electrical resistivity measurements as a function of temperature (down to 0.7 K for the latter two measurements). The Curie temperature of CeIr2B2 (?5 K) is lowered due to La substitution, as expected. However, no quantum critical point or 'non-Fermi liquid' behavior was observed even in the dilute limit of x D 0:9. Interestingly, ferromagnetic ordering persists even for Ce0:1La0:9Ir2B2, below 0.8 K. Among the Ce systems, CeIr2B2 is one of the compounds in w…
The nature of magnetic order and transport properties near surfaces is a topic of great current interest. Here we model metal-insulator interfaces with a multi-layer system governed by a tight-binding Hamiltonian in which the interaction is non-zero on one set of adjacent planes and zero on another. As the interface hybridization is tuned, magnetic and metallic properties undergo an evolution that reflects the competition between anti-ferromagnetism and (Kondo) singlet formation in a scenario similar to that occurring in heavy-fermion materials. For a few-layer system at intermediate hybridiza…
The cooperative behavior of quantum impurities on 2D materials, such as graphene and bilayer graphene, is characterized by a non-trivial competition between screening (Kondo effect), and Ruderman-Kittel-Kasuya-Yosida (RKKY) magnetism. In addition, due to the small density of states at the Fermi level, impurities may not couple to the conduction electrons at all, behaving as free moments. Employing a recently developed {\em{exact}} numerical method to study multi-impurity lattice systems, we obtain non-perturbative results that dramatically depart from expectations based on the conventional RKK…
We analyze antiferromagnetism in $f$ electron superlattices. We show that the competition between the Kondo effect and the RKKY interaction in $f$ electron materials is modified by the superlattice structure. Thus, the quantum critical point which separates the magnetic phase and the Fermi liquid phase depends on the structure of the $f$ electron superlattice. The competition between the Kondo effect and the RKKY interaction is also reflected in the magnetic interlayer coupling between different $f$ electron layers. We demonstrate that in the case of weak Kondo effect the magnetic interlayer c…
Muon spin relaxation experiments have been performed in the pyrochlore iridate Pr_2Ir_2O_7 for temperatures in the range 0.025-250 K. Kubo-Toyabe relaxation functions are observed up to > 200 K, indicating static magnetism over this temperature range. The T -> 0 static muon spin relaxation rate Delta(0) ~ 8 mus^-1 implies a weak quasistatic moment (~0.1 mu_B). The temperature dependence of Delta is highly non-mean-field-like, decreasing smoothly by orders of magnitude but remaining nonzero below ~150 K. The data rule out ordering of the full Pr^3+ CEF ground-state moment (3.0 mu_B) down to 0.0…
A magnetic Bragg reflection corresponding to the wave vector k13 = (2pi/a)[1/2,1/2,1/2] of the antiferro-quadrupolar ordering is found in CeB6 in zero magnetic field below the Neel temperature TN. Its intensity is two orders of magnitude weaker than those due to the basic magnetic structure [O. Zaharko et al., Phys. Rev. B 68, 214401 (2003)]. The peak has a width of the other Bragg reflections below TN, but widens abruptly at T = TN with simultaneous increase of intensity. Correlation length just above TN is of the order of 70 A. The peak intensity decreases to zero at T = 7 K with no visible …
Formation of magnetically ordered state in the Kondo lattices is treated within the degenerate $s-f$ exchange and Coqblin-Schrieffer models. The Kondo renormalizations of the effective coupling parameter, magnetic moment and spin excitation frequencies are calculated within perturbation theory. The results of one-loop scaling consideration of the magnetic state in Kondo lattices are analyzed. The dependence of the critical values of the bare model parameters on the type of the magnetic phase and space dimensionality is investigated. Renormalization of the effective Kondo temperature by the int…
Recently, there has been a resurgence of intense experimental and theoretical interest on the Kondo physics of nanoscopic and mesoscopic systems due to the possibility of making experiments in extremely small samples. We have carried out exact diagonalization calculations to study the effect of energy spacing $Δ$ in the conduction band states, hybridization, number of electrons, and disorder on the ground-state and thermal properties of strongly-correlated electron nanoclusters. For the ordered systems, the calculations reveal for the first time that $Δ$ tunes the interplay between the {\it lo…
The interplay between Kondo effect, indirect magnetic interaction and geometrical frustration is studied in the Kondo lattice on the one-dimensional zigzag ladder. Using the density-matrix renormalization group (DMRG), the ground state and various short- and long-range spin- and density-correlation functions are calculated for the model at half-filling as a function of the antiferromagnetic Kondo interaction down to $J=0.3t$ where $t$ is the nearest-neighbor hopping on the zigzag ladder. Geometrical frustration is shown to lead to at least two critical points: Starting from the strong-$J$ limi…
We study the Kondo lattice model of band electrons coupled to classical spins, in three dimensions, using a combination of variational calculation and Monte Carlo. We use the weak coupling `RKKY' window and the strong coupling regime as benchmarks, but focus on the physically relevant intermediate coupling regime. Even for modest electron-spin coupling the phase boundaries move away from the RKKY results, the non interacting Fermi surface no longer dictates magnetic order, and weak coupling `spiral' phases give way to collinear order. We use these results to revisit the classic problem of 4f m…
We derive, by means of an extended Gutzwiller wavefunction and within the Gutzwiller approximation, the phase diagram of the Kondo lattice model. We find that generically, namely in the absence of nesting, the model displays an $f$-electron Mott localization accompanied by a discontinuous change of the conduction electron Fermi surface as well as by magnetism. When the non interacting Fermi surface is close to nesting, the Mott localization disentangles from the onset of magnetism. First the paramagnetic heavy fermion metal turns continuously into an itinerant magnet - the Fermi surface evolve…
Intricacies of Frustrated Magnetism in the Kondo Metal YbAgGe
PSI Center for Neutron and Muon Sciences（保罗谢勒研究所中子与μ子科学中心）；Department of Physics and Astronomy, Iowa State University（爱荷华州立大学物理与天文系）；Ames National Laboratory（艾姆斯国家实验室）；Neutron Scattering Division, Oak Ridge National Laboratory（橡树岭国家实验室中子散射部）；Dresden High Magnetic Field Laboratory (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf（德累斯顿强磁场实验室（HLD-EMFL），赫尔霍兹德累斯顿-罗斯多夫中心）；ISIS Facility, STFC Rutherford Appleton Laboratory（STFC卢瑟福阿普尔顿实验室ISIS设施）；Institut Laue-Langevin（朗之万研究所）
We present a theory of magnetic and magneto-transport phenomena at LaAlO$_3$/SrTiO$_3$ interfaces, which as a central ingredient includes coupling between the conduction bands and local magnetic moments originating from charge traps at the interface. Tuning the itinerant electron density in the model drives transitions between a heavy Fermi liquid phase with screened moments and various magnetic states. The dependence of the magnetic phenomena on the electron density or gate voltage stems from competing magnetic interactions between the local moments and the different conduction bands. At low …
Building on the results of Ref. \cite{faye2018phase}, which identified an antiferromagnetic and Kondo singlet phases on the Kondo-Hubbard square lattice, we use the variational cluster approximation (VCA) to investigate the competition between these phases on a two-dimensional triangular lattice with $120^{o}$ spin orientation. In addition to the antiferromagnetic exchange interaction $J_{\perp}$ between the localized (impurity) and conduction (itinerant) electrons, our model includes the local repulsion $U$ of the conduction electrons and the Heisenberg interaction $J_H$ between the impuritie…
We present an extensive numerical study of a new type of frustrated itinerant magnetism on the pyrochlore lattice. In this theory, the pyrochlore magnet can be viewed as a cross-linking network of Kondo or double-exchange chains. Contrary to models based on Mott insulators, this itinerant magnetism approach provides a natural explanation for several spin and orbital superstructures observed on the pyrochlore lattice. Through extensive Monte Carlo simulations, we obtain the phase diagrams at two representative electron filling fractions $n = 1/2$ and 2/3. In particular, we show that an intrigui…
We theoretically study the magnetic phase diagram of a three-dimensional topological Kondo insulator by means of real-space dynamical mean field theory. We find that ferromagnetically ordered states become stable upon hole doping. Besides a wide ferromagnetic phase, we observe surface magnetism close to half-filling, which corresponds to an A-type antiferromagnetic state. We further study the impact of the magnetism on the symmetry protected surface states and find that depending on the surface and the magnetization direction, surface states are still protected by reflection symmetry present i…
Motivated by the observation of light surface states in SmB6, we examine the effects of surface Kondo breakdown in topological Kondo insulators. We present both numerical and analytic results which show that the decoupling of the localized moments at the surface disturbs the compensation between light and heavy electrons and dopes the Dirac cone. Dispersion of these uncompensated surface states are dominated by inter-site hopping, which leads to a much lighter quasiparticles. These surface states are also highly durable against the effects of surface magnetism and decreasing thickness of the s…
Chiral Magnetism and Quantum Anomalous Hall Effect in a Low-energy Kondo Model on the Triangular Lattice
University of California Santa Barbara（加州大学圣塔芭芭拉分校）；Kavli Institute for Theoretical Physics, University of California, Santa Barbara（加州大学圣塔芭芭拉分校卡弗里理论物理研究所）；French American Center for Theoretical Science, CNRS, KITP, Santa Barbara, California（法国美国理论科学中心）；Canadian Institute for Advanced Research（加拿大高级研究院）
Despite intense research in the field of strongly correlated electron behavior for the past few decades, there has been very little effort to understand this phenomenon in nano particles of the Kondo lattices. In this article, we review the results of our investigation on the fine particles (less than 1 micron) of some of the alloys obtained by high-energy ball-milling to bring out that this synthetic method paves a way to study strong electron correlations in nanocrystals of such alloys. We primarily focus on the alloys of the series, CeRu(2-x)Rh(x)Si2, lying at different positions in Doniach…
The quantum critical point (QCP) in the archetypical heavy-fermion compound CeCu$_6$ doped by Au is described, accounting for the localized $4f$-electron of Ce, using realistic electronic structure calculations combined with dynamical mean-field theory (DMFT). Magnetism trends in Ce(Cu$_{1-ε}$Au$_ε$)$_6$ are compared with those in Co-doped CeCu$_{5}$, which resides on the non-ferromagnetic side of the composition space of one of the earliest rare-earth permanent magnet compounds, Ce(Co,Cu)$_5$. The construction of a realistic Doniach phase diagram shows that the system crosses over a magnetic …
A theory of Kondo lattices is applied to the crossover between local-moment magnetism and itinerant-electron magnetism in the t-J model on a quasi-two dimensional lattice. The Kondo temperature T_K is defined as a characteristic temperature or energy scale of local quantum spin fluctuations. Magnetism with T_N >> T_K, where T_N is the N\eel temperature, is characterized as local-moment one, while magnetism with T_N << T_K is characterized as itinerant-electron one. The Kondo temperature, which also gives a measure of the strength of the quenching of magnetic moments, is renormalized by the Foc…
We consider the potential for novel forms of magnetism arising from the subtle interplay between electrons and spins in the under-screened kagome Kondo lattice model. At weak coupling, we show that incommensurate non-coplanar multi-wave vector magnetic orders arise at nearly all fillings and that this results from Fermi surface effects that introduces competing interactions between the spins. At strong coupling, we find that such complex order survives near half filling despite the presence of ferromagnetism at all other fillings. We show this arises due to state selection among a massive dege…
A detailed $^{31}$P (I=1/2) and $^{75}$As (I=3/2) NMR study on polycrystalline CeFeAs$_{1-x}$P$_{x}$O alloys is presented. The magnetism of CeFeAsO changes drastically upon P substitution on the As site. CeFePO is a heavy fermion system without long range order whereas CeFeAsO exhibits a Fe-3$d$ SDW type of ordering accompanied by a structural transition from tetragonal ($TT$) to orthorhombic ($OT$) structure. Furthermore Ce-4$f^{1}$ orders antiferromagnetically (AFM) at low temperature. At the critical concentration where the Fe-magnetism is diminished the Ce-Ce interaction changes to a ferro…
The quantum phase transition between paramagnetic and antiferromagnetic phases of the Kondo lattice model with Ising anisotropy in the intersite exchange is studied within the framework of extended dynamical mean-field theory. Nonperturbative numerical solutions at zero temperature point to a continuous transition for both two- and three-dimensional magnetism. In the former case, the transition is associated with critical local physics, characterized by a vanishing Kondo scale and by an anomalous exponent in the dynamics close in value to that measured in heavy-fermion CeCu_{5.9}Au_{0.1}.
We show within the slave boson technique, that the Anderson lattice model exhibits a Kondo breakdown quantum critical point (KB-QCP) where the hybridization goes to zero at zero temper- ature. At this fixed point, the f-electrons experience as well a selective Mott transition separating a local-moment phase from a Kondo-screened phase. The presence of a multi-scale QCP in the An- derson lattice in the absence of magnetism is discussed in the context of heavy fermion compounds. This study is the first evidence for a selective Mott transition in the Anderson lattice.
A renormalization group treatment of the Kondo model with logarithmic Van Hove singularity in the electron density of states is performed within next-leading order scaling, different magnetic phases being considered. The effective coupling constant remains small, renormalized magnetic moment and spin-fluctuation frequency decreasing by several orders of magnitude. Thus wide non-Fermi-liquid behavior regions are found from the scaling trajectories in a broad interval of the bare coupling parameter. Applications to itinerant magnetism theory are discussed.
We study the competition between Kondo screening and frustrated magnetism on the non-symmorphic Shastry-Sutherland Kondo lattice at a filling of two conduction electrons per unit cell. A previous analysis of this model identified a set of gapless partially Kondo screened phases intermediate between the Kondo-destroyed paramagnet and the heavy Fermi liquid. Based on crystal symmetries, we argue that (i)~both the paramagnet and the heavy Fermi liquid are {\it semimetals} protected by a glide symmetry; and (ii)~partial Kondo screening breaks the symmetry, removing this protection and allowing the…
We study the phase diagram of the Kondo-lattice model with nearest-neighbor hopping in the square lattice by means of the variational Monte Carlo technique. Specifically, we analyze a wide class of variational wave functions that allow magnetic and superconducting order parameters, so to assess the possibility that superconductivity might emerge close to the magnetic instability, as often observed in heavy fermion systems. Indeed, we do find evidence of d-wave superconductivity in the paramagnetic sector, i.e., when magnetic order is not allowed in the variational wave function. However, when …
Revealing altermagnetic Fermi surfaces with two Kondo impurities
New Cornerstone Science Laboratory, Department of Physics, School of Science, Westlake University（西湖大学理学院物理系新 cornerstone 科学实验室）；Institute for Theoretical Solid State Physics, IFW Dresden（德累斯顿工业大学IFW理论固体物理研究所）；Würzburg-Dresden Cluster of Excellence ctd.qmat（维尔茨堡-德累斯顿卓越集群ctd.qmat）；Institut für Theoretische Physik und Astrophysik, Universität Würzburg（维尔茨堡大学理论与天体物理研究所）；Institute for Theoretical Sciences, Westlake University（西湖大学理论科学研究院）；Key Laboratory for Quantum Materials of Zhejiang Province, School of Science, Westlake University（西湖大学理学院浙江省量子材料重点实验室）；Institute of Natural Sciences, Westlake Institute for Advanced Study（西湖高等研究院自然科学研究院）
The magnetic phase diagram of the ferromagnetic Kondo lattice model is determined at T=0 in 1D, 2D, and 3D for various magnitudes of the quantum mechanical localized spins ranging from S=1/2 to classical spins. We consider the ferromagnetic phase, the paramagnetic phase, and the ferromagnetic/antiferromagnetic phase separated regime. There is no significant influence of the spin quantum number on the phase boundaries except for the case S=1/2, where the model exhibits an instability of the ferromagnetic phase with respect to spin disorder. Our results give support, at least as far as the low t…
Strongly correlated electron systems at the border of magnetism are of active current interest, particularly because the accompanying quantum criticality provides a route towards both strange-metal non-Fermi liquid behavior and unconventional superconductivity. Among the many important questions is whether the magnetism acts simply as a source of fluctuations in the textbook Landau framework, or instead serves as a proxy for some unexpected new physics. We put into this general context the recent developments on quantum phase transitions in antiferromagnetic heavy fermion metals. Among these a…
The frustrated magnetism on the Kondo lattice system motivates intriguing Kondo-breakdown beyond the traditional Doniach scenario. Among them, the fractionalized Fermi liquid (FL*) has drawn a particular interest by virtue of its fractionalized nature. Here, we study the phase diagram of $J_{1}$-$J_{2}$ Kondo-Heisenberg model on a honeycomb lattice at a quarter filling. Employing the slave-fermion mean-field theory with $d \pm id$ spin liquid ansatz and exact diagonalization, we discuss the emergence of partial Kondo screening in the frustrated regime with comparable $J_{1}$ and $J_{2}$, and t…
We report on the muon Knight shift measurement in single crystals of LiV2O4. Contrary to what is anticipated for the heavy-fermion state based on the Kondo mechanism, the presence of inhomogeneous local magnetic moments is demonstrated by the broad distribution of the Knight shift at temperatures well below the presumed "Kondo temperature" ($T^*\simeq 30$ K). Moreover, a significant fraction ($\simeq10$ %) of the specimen gives rise to a second component which is virtually non-magnetic. These observations strongly suggest that the anomalous properties of LiV2O4 originates from frustration of l…
We investigate in detail antiferromagnetic (AF) and superconducting (SC) phases as well as their coexistence in the two-dimensional Kondo lattice model on a square lattice, which is a paradigmatic model for heavy fermion materials. The results presented are mainly obtained using the variational cluster approximation (VCA) and are complemented by analytical findings for the equations of motion of pairing susceptibilities. A particularly interesting aspect is the possibility to have s-wave SC near half filling as reported by Bodensiek \textit{et al.} [Phys. Rev. Lett. \textbf{110}, 146406 (2013)…
Heavy fermion metals typically exhibit unconventional quantum critical point or quantum critical phase at zero temperature due to competition of Kondo effect and magnetism. Previous theories were often based on certain local type of assumptions and a fully consistent explanation of experiments has not been achieved. Here we develop an efficient algorithm for the Schwinger boson approach to explore the effect of spatial correlations on the Kondo lattice and introduce the concept of nonlocal Kondo effect in the quantum critical region with deconfined spinons. We predict a global phase diagram co…
Recently, the MnBi$_2$Te$_4$ material has been proposed as the first intrinsic antiferromagnetic topological insulator (AFMTI), where the interplay between magnetism and topology induces several fascinating topological phases, such as the quantum anomalous Hall effect, Majorana fermions, and axion electrodynamics. However, an exactly solvable model being capable to capture the essential physics of the interplay between magnetism and topology is still absent. Here, inspired by the the Ising-like nature [B. Li \textit{et al.} Phys. Rev. Lett. \textbf{124}, 167204 (2020)] and the topological prop…
Heavy fermions represent an archetypal example of strongly correlated electron systems which, due to entanglement among different interactions, often exhibit exotic and fascinating physics involving Kondo screening, magnetism and unconventional superconductivity. Here we report a comprehensive study on the transport and thermodynamic properties of a cerium-based heavy fermion compound CeBi$_2$ which undergoes an anti-ferromagnetic transition at $T_N$ $\sim$ 3.3 K. Its high temperature paramagnetic state is characterized by an enhanced heat capacity with Sommerfeld coefficient $γ$ over 200 mJ/m…
We study the quasiparticle spectrum in an underscreened Kondo-lattice (KL) model that involves a single spin degenerate conduction band and two crystalline-electric-field (CEF) split Kramers doublets coupled by both orbital-diagonal and non-diagonal exchange interactions. We find the three quasiparticle bands of the model using a constrained fermionic mean field approach. While two bands are similar to the one-orbital model a new genuinely heavy band inside the main hybridization gap appears in the quasiquartet model. Its dispersion is due to effective hybridization with conduction states but …
The filled-skutterudite compound CePt4Ge12 is situated close to the border between intermediate-valence of Ce and heavy-fermion behavior. Substitution of Ge by Sb drives the system into a strongly correlated and ultimately upon further increasing the Sb concentration into an antiferromagnetically ordered state. Our experiments evidence a delicate interplay of emerging Kondo physics and the formation of a local 4f moment. An extended non-Fermi-liquid region, which can be understood in the framework of a Kondo-disorder model, is observed. Band-structure calculations support the conclusion that t…
Muon spin relaxation experiments have been carried out in the Kondo compound PrInAg_2. The zero-field muon relaxation rate is found to be independent of temperature between 0.1 and 10 K, which rules out a magnetic origin (spin freezing or a conventional Kondo effect) for the previously-observed specific heat anomaly at \sim0.5 K. The low-temperature muon relaxation is quantitatively consistent with nuclear magnetism including hyperfine enhancement of the ^{141}Pr nuclear moment. This is strong evidence against a Pr^{3+} electronic magnetic moment, and for the Γ_3 crystalline-electric-field-spl…
We present the results of a systematic investigation of the magnetic properties of the three-dimensional Kondo topological insulator SmB6 using magnetization and muon-spin relaxation/rotation (muSR) measurements. The muSR measurements exhibit magnetic field fluctuations in SmB6 below 15 K due to electronic moments present in the system. However, no evidence for magnetic ordering is found down to 19 mK. The observed magnetism in SmB6 is homogeneous in nature throughout the full volume of the sample. Bulk magnetization measurements on the same sample show consistent behavior. The agreement betwe…
These lecture notes give a brief introduction to heavy fermion physics, emphasizing aspects of particular modern interest. Following an introduction to the Kondo effect and the phenomenology of heavy fermions, the article introduces Kondo insulators, the simplest heavy fermions; the large N expansion for the Kondo lattice; heavy fermion superconductivity including the symplectic N approach; topological Kondo insulators and finally a discussion of the challenge of understanding the co-existence of magnetism and the Kondo effect.
It is demonstrated that itinerant-localized transition of heavy electrons occurs inside the magnetically ordered phase of the Kondo-Heisenberg lattice. The phase diagram and electronic structure are derived by means of the continuous-time quantum Monte Carlo combined with the dynamical mean-field theory. Around the itinerant-localized transition, nearly flat bands appear on the Fermi surface with almost vanishing quasi-particle renormalization factor. At the same time, there emerges a strong local magnetic fluctuation with a minute energy scale. Considering both antiferromagnetic and ferromagn…
