Onset Of Antiferromagnetic Order Research Articles

Antiferromagnetic metal phase in an electron-doped rare-earth nickelate

Long viewed as passive elements, antiferromagnetic materials have emerged as promising candidates for spintronic devices due to their insensitivity to external fields and potential for high-speed switching. Recent work exploiting spin and orbital effects has identified ways to electrically control and probe the spins in metallic antiferromagnets, especially in non-collinear or non-centrosymmetric spin structures. The rare-earth nickelate NdNiO3 is known to be a non-collinear antiferromagnet in which the onset of antiferromagnetic ordering is concomitant with a transition to an insulating state. Here we find that for low electron doping, the magnetic order on the nickel site is preserved, whereas electronically, a new metallic phase is induced. We show that this metallic phase has a Fermi surface that is mostly gapped by an electronic reconstruction driven by bond disproportionation. Furthermore, we demonstrate the ability to write to and read from the spin structure via a large zero-field planar Hall effect. Our results expand the already rich phase diagram of rare-earth nickelates and may enable spintronics applications in this family of correlated oxides. Films of the correlated oxide NdNiO3 form a metallic antiferromagnetic phase that can be identified using electrical currents, raising the prospect of applications in spintronics.

Intermetallic disordered magnetGd2Pt1.1Ge2.9and its relation to otherAlB2-type compounds

The intermetallic germanide ${\mathrm{Gd}}_{2}{\mathrm{Pt}}_{1.1}{\mathrm{Ge}}_{2.9}$ was synthesized using an arc-melting method. The crystal structure was characterized using powder x-ray diffraction, revealing a disordered ternary ${\mathrm{AlB}}_{2}$-type structure (space group $P6/mmm$, No. 191) with lattice parameters $a=4.2092(1)\phantom{\rule{0.16em}{0ex}}\AA{}$ and $c=4.0546(2)\phantom{\rule{0.16em}{0ex}}\AA{}$. Physical properties were investigated by magnetic susceptibility and heat capacity measurements, which indicated onset of antiferromagnetic order at ${T}_{t}=8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The obtained properties were compared with the ones reported for other members of the ${\mathrm{AlB}}_{2}$-type ${\mathrm{Gd}}_{2}T{\mathrm{Ge}}_{3}$ ($T=\mathrm{Ni}$, Cu, and Pd) family. The magnetic ordering in these compounds was discussed in terms of their crystal structure and the influence of Gd ions.

Connection between magnetic interactions and the spin-wave gap of the insulating phase of NaOsO3

The scenario of a metal-insulator transition driven by the onset of antiferromagnetic order in NaOsO$_3$ calls for a trustworthy derivation of the underlying effective spin Hamiltonian. To determine the latter we rely on {\it ab initio} electronic-structure calculations, linear spin-wave theory, and comparison to experimental data of the corresponding magnon spectrum. We arrive this way to Heisenberg couplings that are $\lesssim$45\% to$\lesssim$63\% smaller than values presently proposed in the literature and Dzyaloshinskii-Moriya interactions in the region of 15\% of the Heisenberg exchange $J$. These couplings together with the symmetric anisotropic exchange interaction and single-ion magnetocrystalline anisotropy successfully reproduce the magnon dispersion obtained by resonant inelastic X-ray scattering measurements. In particular, the spin-wave gap fully agrees with the measured one. We find that the spin-wave gap is defined from a subtle interplay between the single-ion anisotropy, the Dzyaloshinskii-Moriya exchange and the symmetric anisotropic exchange interactions. The results reported here underpin the local-moment description of NaOsO$_3$, when it comes to analyzing the magnetic excitation spectra. Interestingly, this comes about from a microscopic theory that describes the electron system as Bloch states, adjusted to a mean-field solution to Hubbard-like interactions.

Phase coexistence and negative thermal expansion in the triple perovskite iridate Ba3CoIr2O9

The anomalous thermal expansion in a layered $3d\text{\ensuremath{-}}5d$ based triple perovskite iridate ${\mathrm{Ba}}_{3}{\mathrm{CoIr}}_{2}{\mathrm{O}}_{9}$ is investigated using high resolution synchrotron diffraction. Below the magnetostructural transition at 107 K, the onset of antiferromagnetic order is associated with a monoclinic distortion of the hexagonal structure. Deeper within the magnetically ordered state, a part of the monoclinic phase distorts even further, and both these structural phases co-exist down to the lowest measured temperatures. We observe negative thermal expansion in this phase co-existence regime, which appears to be intimately connected to the temperature driven relative fractions of these monoclinic phases. The significant NTE observed in this system could be driven by magnetic exchange striction and is of relevance to a number of systems with pronounced spin orbit interactions.

Effect of Ni doping on vortex pinning in CaK(Fe1−xNix)4As4 single crystals

We study the correlation between chemical composition and vortex dynamics in Ni-doped $\mathrm{CaK}{(\mathrm{F}{\mathrm{e}}_{1\ensuremath{-}x}\mathrm{N}{\mathrm{i}}_{x})}_{4}\mathrm{A}{\mathrm{s}}_{4}$ ($x=0$, 0.015, 0.025, 0.03, and 0.05) single crystals by performing measurements of the critical current densities ${J}_{c}$ and the flux creep rates $S$. The magnetic relaxation of all the crystals is well described by the collective creep theory. The samples display a glassy exponent \ensuremath{\mu} within the predictions for vortex bundles in a weak pinning scenario and relatively small characteristic pinning energy (${U}_{0}l100\phantom{\rule{0.16em}{0ex}}\mathrm{K}$). The undoped crystals display modest ${J}_{c}$ values at low temperatures and high magnetic fields applied along the $c$ axis. ${J}_{c}(T)$ dependences at high fields display an unusual peak. The enhancement in ${J}_{c}(T)$ matches with an increase in ${U}_{0}$ and the appearance of a second peak in the magnetization. As Ni doping increases, whereas there is a monotonic decrease in ${T}_{c}$ there is a nonmonotonic change in ${J}_{c}$. Initially ${J}_{c}$ increases, reaching a maximum value for $x=0.015$, and then ${J}_{c}$ decreases for $x\ensuremath{\ge}0.025$. This change in ${J}_{c}$($x$) is coincident with the onset of antiferromagnetic order. The magnetic field dependence of ${J}_{c}(H)$ also manifests a change in behavior between these $x$ values. The analysis of the vortex dynamics for small and intermediate magnetic fields shows a gradual evolution in the glassy exponent \ensuremath{\mu} with Ni content, $x$. This implies that there is no appreciable change in the mechanism that determines the vortex relaxation.

Crossover from itinerant to localized magnetic excitations through the metal-insulator transition inNaOsO3

NaOsO$_{\text{3}}$ undergoes a metal-insulator transition (MIT) at 410 K, concomitant with the onset of antiferromagnetic order. The excitation spectra have been investigated through the MIT by resonant inelastic x-ray scattering (RIXS) at the Os L$_{\text{3}}$ edge. Low resolution ($\Delta E \sim$ 300 meV) measurements over a wide range of energies reveal that local electronic excitations do not change appreciably through the MIT. This is consistent with a picture in which structural distortions do not drive the MIT. In contrast, high resolution ($\Delta E \sim $ 56 meV) measurements show that the well-defined, low energy magnons in the insulating state weaken and dampen upon approaching the metallic state. Concomitantly, a broad continuum of excitations develops which is well described by the magnetic fluctuations of a nearly antiferromagnetic Fermi liquid. By revealing the continuous evolution of the magnetic quasiparticle spectrum as it changes its character from itinerant to localized, our results provide unprecedented insight into the nature of the MIT in \naoso. In particular, the presence of weak correlations in the paramagnetic phase implies a degree of departure from the ideal Slater limit.

Excitations and relaxation dynamics in multiferroic GeV4S8 studied by terahertz and dielectric spectroscopy

We report on THz time-domain spectroscopy on multiferroic ${\mathrm{GeV}}_{4}{\mathrm{S}}_{8}$, which undergoes orbital ordering at a Jahn-Teller transition at 30.5 K and exhibits antiferromagnetic order below 14.6 K. The THz experiments are complemented by dielectric experiments at audio and radio frequencies. We identify a low-lying excitation close to 0.5 THz, which is only weakly temperature dependent and probably corresponds to a molecular excitation within the electronic level scheme of the ${\mathrm{V}}_{4}$ clusters. In addition, we detect complex temperature-dependent behavior of a low-lying phononic excitation, closely linked to the onset of orbitally driven ferroelectricity. In the high-temperature cubic phase, which is paramagnetic and orbitally disordered, this excitation is of relaxational character becomes an overdamped Lorentzian mode in the orbitally ordered phase below the Jahn-Teller transition, and finally appears as well-defined phonon excitation in the antiferromagnetic state. Abrupt changes in the real and imaginary parts of the complex dielectric permittivity show that orbital ordering appears via a structural phase transition with strong first-order character and that the onset of antiferromagnetic order is accompanied by significant structural changes, which are of first-order character, too. Dielectric spectroscopy documents that at low frequencies, significant dipolar relaxations are present in the orbitally ordered, paramagnetic phase only. In contrast to the closely related ${\mathrm{GaV}}_{4}{\mathrm{S}}_{8}$, this relaxation dynamics that most likely mirrors coupled orbital and polar fluctuations does not seem to be related to the dynamic processes detected in the THz regime.

Optical conductivity in multiferroic GaV4S8 and GeV4S8 : Phonons and electronic transitions

We report on optical spectroscopy on the lacunar spinels GaV$_4$S$_8$ and GeV$_4$S$_8$ in the spectral range from 100 to 23000 cm$^{-1}$ and for temperatures from 5 to 300 K. These multiferroic spinel systems reveal Jahn-Teller driven ferroelectricity and complex magnetic order at low temperatures. We study the infrared-active phonon modes and the low-lying electronic excitations in the cubic high-temperature phase, as well as in the orbitally and in the magnetically ordered low-temperature phases. We compare the phonon modes in these two compounds, which undergo different symmetry-lowering Jahn-Teller transitions into ferroelectric and orbitally ordered phases, and exhibit different magnetic ground states. We follow the splitting of the phonon modes at the structural phase transition and detect additional splittings at the onset of antiferromagnetic order in GeV$_4$S$_8$. We observe electronic transitions within the $d$-derived bands of the V$_4$ clusters and document a significant influence of the structural and magnetic phase transitions on the narrow electronic band gaps.

Low-temperature neutron diffraction and magnetic studies on the magnetoelectric multiferroic Pb(Fe0.534Nb0.4W0.066)O3

We report detailed low-temperature magnetic and neutron diffraction studies on 0.8 Pb(Fe0.5Nb0.5)O3–0.2 Pb(Fe0.67W0.33)O3 which is written as Pb(Fe0.534Nb0.4W0.066)O3 (PFWN) in the general form. Magnetic susceptibility measurement data show that PFN exhibits antiferromagnetic to paramagnetic transition (T N) around 155 K (Matteppanavar et al. in J Mater Sci 50:4980–4993. doi:10.1007/s10853-015-9046-5, 2015). In the present solid solution, the magnetic susceptibility (χ) shows Neel temperature enhanced up to around 187 K. Temperature-dependent neutron diffraction studies well support the tuning up of T N from 155 to 187 K. On decreasing the temperature, for T < T N (T N = 187 K), an extra peak grows at scattering vector Q = 1.35 A−1, which indicates the onset of antiferromagnetic ordering. The observed magnetic structure is G-type antiferromagnetic with the propagation vector, k = [0.25, 0.5, 0.5]. The refined monoclinic lattice parameters (a, b and c), angle (β), unit cell volume, derivative of unit cell volume, magnetic moments and integrated intensity of magnetic peak (111) show anomaly around the T N, which is a manifestation of spin–lattice coupling. Also, the lattice parameters (a, b and c) and unit cell volume exhibit negative thermal expansion below T N and a large thermal expansion above T N.

Multidimensional entropy landscape of quantum criticality

The Third Law of Thermodynamics states that the entropy of any system in equilibrium has to vanish at absolute zero temperature. At nonzero temperatures, on the other hand, matter is expected to accumulate entropy near a quantum critical point (QCP), where it undergoes a continuous transition from one ground state to another. Here, we determine, based on general thermodynamic principles, the spatial-dimensional profile of the entropy S near a QCP and its steepest descent in the corresponding multidimensional stress space. We demonstrate this approach for the canonical quantum critical compound CeCu6-xAux near its onset of antiferromagnetic order. We are able to link the directional stress dependence of S to the previously determined geometry of quantum critical fluctuations. Our demonstration of the multidimensional entropy landscape provides the foundation to understand how quantum criticality nucleates novel phases such as high-temperature superconductivity.

Tiny cause with huge impact: polar instability through strong magneto-electric-elastic coupling in bulk EuTiO3

EuTiO3 exhibits strong magneto-electric coupling at the onset of antiferromagnetic order below TN = 5.7 K. The dielectric permittivity drops at TN by 7% and recovers to normal values with increasing magnetic field. This effect is shown to stem from tiny lattice effects as seen in magnetostriction data which directly affect the soft optic mode and its polarizability coordinate. By combining experimental results with theory we show that marginal changes in the lattice parameter of the order of 0.01% have a more than 1000% effect on the transverse optic soft mode of ETO and thus easily induce a ferroelectric instability.

Evidence for magneto-electric and spin–lattice coupling in PbFe0.5Nb0.5O3 through structural and magneto-electric studies

Neutron diffraction (ND) studies were carried out on polycrystalline single-phase multiferroic Pb(Fe0.5Nb0.5)O3 (PFN) in the temperature range of 290–2 K to understand the structural and magnetic properties as a function of temperature. ND data were refined using the Rietveld refinement method for both crystallographic and magnetic structures. The structure at room temperature was found to be monoclinic, in Cm space group. No structural transition was observed till 2 K. At low temperatures (i.e., from T < T N; T N = 155 K), an additional peak appears at scattering vector, Q = 1.35 A−1, indicating the onset of antiferromagnetic ordering. The magnetic structure was found to be commensurate with the crystallographic structure and could be refined using the propagation vector, k = [0.125, 0.5, and 0.5]. Magnetization, ferroelectric P–E loops, and dielectric measurements on PFN reveal a strong anomaly at the antiferromagnetic transition temperature (T N) indicating the magneto-electric coupling. The refined temperature-dependent structural parameters such as unit cell volume and monoclinic distortion angle (β) reveal pronounced anomalies at the magnetic ordering temperature (T N), which indicates strong spin–lattice coupling. An anomaly in lattice volume was observed with a small negative thermal expansion below and a large thermal expansion above the T N, respectively. It shows the occurrence of isostructural phase transition accompanying the magnetic ordering below T N ~155 K, leading to significant change in ionic polarization, octahedral tilt angle, and lattice strain around T N. We have used refined atomic positional coordinates from the nuclear and magnetic structures, to obtain ionic polarization. These detailed studies confirm the magneto-electric and spin–lattice coupling in PFN across T N.

Low-temperature magnetic properties of GdCoIn5

Abstract A comprehensive experimental and theoretical study of the low temperature properties of GdCoIn 5 was performed. Specific heat, thermal expansion, magnetization and electrical resistivity were measured in good quality single crystals down to 4 He temperatures. All the experiments show a second-order-like phase transition at 30 K probably associated with the onset of antiferromagnetic order. The magnetic susceptibility shows a pronounced anisotropy below T N with an easy magnetic axis perpendicular to the crystallographic ĉ-axis. Total energy GGA+U calculations indicate a ground state with magnetic moments localized at the Gd ions and allowed a determination of the Gd-Gd magnetic interactions. Band structure calculations of the electron and phonon contributions to the specific heat together with Quantum Monte Carlo calculations of the magnetic contributions show a very good agreement with the experimental data. Comparison between experiment and calculations suggests a significant anharmonic contribution to the specific heat at high temperature ( T ≳ 100 K ).

Nernst effect in the electron-doped cuprate superconductorPr2−xCexCuO4: Superconducting fluctuations, upper critical fieldHc2, and the origin of theTcdome

The Nernst effect was measured in the electron-doped cuprate superconductor Pr2-xCexCuO4 (PCCO) at four concentrations, from underdoped (x=0.13) to overdoped (x=0.17), for a wide range of temperatures above the critical temperature Tc. A magnetic field H up to 15 T was used to reliably access the normal-state quasiparticle contribution to the Nernst signal, Nqp, which is subtracted from the total signal, N, to obtain the superconducting contribution, Nsc. As a function of H, Nsc peaks at a field H* whose temperature dependence obeys Hc2* ln(T/Tc), as it does in a conventional superconductor like Nb1-xSix. The doping dependence of the characteristic field scale Hc2* - shown to be closely related to the upper critical field Hc2 - tracks the dome-like dependence of Tc, showing that superconductivity is weakened below the quantum critical point where the Fermi surface is reconstructed, presumably by the onset of antiferromagnetic order. Our data at all dopings are quantitatively consistent with the theory of Gaussian superconducting fluctuations, eliminating the need to invoke unusual vortex-like excitations above Tc, and ruling out phase fluctuations as the mechanism for the fall of Tc with underdoping. We compare the properties of PCCO with those of hole-doped cuprates and conclude that the domes of Tc and Hc2 vs doping in the latter materials are also controlled predominantly by phase competition rather than phase fluctuations.

Tailoring interlayer coupling and coercivity in Co/Mn/Co trilayers by controlling the interface roughness

Epitaxial Co/Mn/Co trilayers with a wedged Mn layer were grown on Cu(001) and studied by magneto-optical Kerr effect measurements. The bottom Co film as well as the Mn film exhibits a layer-by-layer growth mode, which allows to modify both interface roughnesses on the atomic scale by tuning the thicknesses of the films to achieve a certain filling of their topmost atomic layers. The onset of antiferromagnetic order in the Mn layer at room temperature was found at thicknesses of 4.1 (4.8) and 3.4 (4.0) atomic monolayers (ML) for a filled (half-filled) topmost atomic layer of the bottom Co film in Mn/Co bilayers and Co/Mn/Co trilayers, respectively. Magnetization loops with only one step were found for a trilayer with half-filled topmost atomic layer of the bottom Co film, while loops with two separate steps have been observed in trilayers with an integer number of atomic layers in the bottom Co film. The coercivity of the top Co film shows an oscillation with 1 ML period as a function of the Mn thickness above 10 ML, which is interpreted as the influence of the atomic-scale control of the interface roughness on the interface exchange coupling between the antiferromagnetic Mn and the top ferromagnetic (FM) Co layer. The strength of the magnetic interlayer coupling between the top and bottom Co layers through the Mn layer for an integer number of atomic layers in the bottom Co layer, deduced from minor-loop measurements, exhibits an oscillation with a period of 2 ML Mn thickness, indicative of direct exchange coupling through the antiferromagnetic Mn layer. In addition, a long-period interlayer coupling of the two FM layers with antiparallel coupling maxima at Mn thicknesses of 2.5, 8.2, and 13.7 ML is observed and attributed to indirect exchange coupling of the Rudermann-Kittel-Kasuya-Yosida type.

Evolution of antiferromagnetic susceptibility under uniaxial pressure in Ba(Fe1−xCox)2As2

Neutron diffraction measurements are presented measuring the responses of both magnetic and structural order parameters of parent and lightly Co-doped Ba(Fe{1-x}Co{x})2As2 under the application of uniaxial pressure. We find that the uniaxial pressure induces a thermal shift in the onset of antiferromagnetic order that grows as a percentage of T_N as Co-doping is increased and the superconducting phase is approached. Additionally, as uniaxial pressure is increased within parent and lightly-doped Ba(Fe{1-x}Co{x})2As2 on the first order side of the tricritical point, we observe a decoupling between the onsets of the orthorhombic structural distortion and antiferromagnetism. Our findings place needed constraints on models exploring the nematic susceptibility of the bilayer pnictides in the tetragonal, paramagnetic regime.

Large topological Hall effect in the non-collinear phase of an antiferromagnet

Non-trivial spin arrangements in magnetic materials give rise to the topological Hall effect observed in compounds with a non-centrosymmetric cubic structure hosting a skyrmion lattice, in double-exchange ferromagnets and magnetically frustrated systems. The topological Hall effect has been proposed to appear also in presence of non-coplanar spin configurations and thus might occur in an antiferromagnetic material with a highly non-collinear and non-coplanar spin structure. Particularly interesting is a material where the non-collinearity develops not immediately at the onset of antiferromagnetic order but deep in the antiferromagnetic phase. This unusual situation arises in non-cubic antiferromagnetic Mn5Si3. Here we show that a large topological Hall effect develops well below the Néel temperature as soon as the spin arrangement changes from collinear to non-collinear with decreasing temperature. We further demonstrate that the effect is not observed when the material is turned ferromagnetic by carbon doping without changing its crystal structure.

Stretched exponential spin relaxation in organic superconductors

Proton NMR measurements on the organic superconductor \ensuremath{\kappa}-(ET)${}_{2}$Cu[N(CN)${}_{2}$]Br [where ET represents bis(ethylenedithio)tetrathiafulvalene] $\left({T}_{C}=11.6\phantom{\rule{0.28em}{0ex}}\mathrm{K}\right)$ exhibit stretched exponential spin-lattice relaxation below $T\ensuremath{\approx}25\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, suggestive of an inhomogeneous magnetic phase that develops in the normal state and coexists with superconductivity. The onset of this phase coincides approximately with a large normal-state Nernst signal reported previously. By contrast, the closely related superconductor \ensuremath{\kappa}-(ET)${}_{2}$Cu(NCS)${}_{2}$ $\left({T}_{C}=10.5\phantom{\rule{0.28em}{0ex}}\mathrm{K}\right)$ shows single exponential spin-lattice relaxation and a conventional Nernst effect. The temperature range of ${T}_{C}$ $T$ 30 K encompasses several phenomena in the \ensuremath{\kappa}-(ET)${}_{2}X$ conductors, including changes in conduction-electron-spin resonance, electronic phase separation, and the onset of antiferromagnetic order. Analogous behavior in La${}_{2\ensuremath{-}x}$Sr${}_{x}$CuO${}_{4}$ suggests that a spin glass or density wave may develop in \ensuremath{\kappa}-(ET)${}_{2}$Cu[N(CN)${}_{2}$]Br.

Conducting states caused by a surface electric dipole in CrN(001) very thin films

We report a series of electronic-structure calculations for CrN films within the LDA + $U$ method. In the bulk, it was found previously that with the onset of antiferromagnetic order, a gap opens and an insulating state appears. However, for thin films with increasing thickness (4--10 layers), we find that starting with a critical thickness of 10 (cubic symmetry) or 6 layers (orthorhombic) the gap closes and conducting states appear. The appearance of metallic states is connected with a structural relaxation at the surface, where Cr (N) atoms buckle inside (outside), forming an effective dipole moment. With CrN being a low-gap system, the electric dipoles at the surface caused by the Cr atoms displacing inwards shift the bands around the Fermi level significantly enough to drive those thin films metallic. The potential shift due to these surface dipoles is also visible in Cr and O core-level shifts.

Localized moments and the stability of antiferromagnetic order in Yb3Pt4

We present here the results of electrical resistivity $\ensuremath{\rho}$, magnetization $M$, ac susceptibility ${\ensuremath{\chi}}_{ac}^{\ensuremath{'}}$, and specific heat ${C}_{\mathrm{M}}$ measurements that have been carried out on single crystals of ${\mathrm{Yb}}_{3}{\mathrm{Pt}}_{4}$ over a wide range of fields and temperatures. The 2.4-K N\'eel temperature that is found in zero field collapses under field to a first-order transition ${T}_{\mathrm{N}}=0$ at ${B}_{\mathrm{CEP}}=1.85$ T. In the absence of antiferromagnetic order, the specific heat ${C}_{\mathrm{M}}(T,B)$, the magnetization $M(T,B)$, and even the resistivity $\ensuremath{\rho}(T,B)$ all display $B/T$ scaling, indicating that they are dominated by strong paramagnetic fluctuations, where the only characteristic energy scale results from the Zeeman splitting of an energetically isolated, Yb doublet ground state. This paramagnetic scattering disappears with the onset of antiferromagnetic order, revealing Fermi liquid behavior $\ensuremath{\Delta}\ensuremath{\rho}=A{T}^{2}$ that persists up to the antiferromagnetic phase line ${T}_{\mathrm{N}}(B)$, but not beyond. The first-order character of ${T}_{\mathrm{N}}=0$ and the ubiquity of the paramagnetic fluctuations imply that non-Fermi-liquid behaviors are absent in ${\mathrm{Yb}}_{3}{\mathrm{Pt}}_{4}$. In contrast to heavy fermions such as ${\mathrm{YbRh}}_{2}{\mathrm{Si}}_{2}$, ${\mathrm{Yb}}_{3}{\mathrm{Pt}}_{4}$ represents an extremely simple regime of $f$-electron behavior where the Yb moments and conduction electrons are almost decoupled, and where Kondo physics plays little role.