Fermi Surface Volume Research Articles

Decrease of the coherence temperature with low Rh doping in [formula omitted

Comparative study of U ( Ru 1 - x Rh x ) 2 Si 2 ( x = 0 and 4%) through resistivity, magnetic susceptibility, and Hall coefficient measurements reveals that the coherence temperature, T coh , of the Rh 4% doped sample clearly decreases by about 10–20% as compared with that of undoped one located around 50 K. Furthermore, T * , a characteristic temperature below which the resistivity shows the T 2 dependence, is also found to decrease by almost the same factor. These findings suggest that the low Rh doping sensitively destroys the itinerant band gap due to the hidden order (HO) through the reduction of the Fermi surface volume in the quasi-particle band.

Electronic Structure and Fermi Surface of NpGe3

Fermi surface topology of transuranium compound NpGe 3 is investigated from an itinerant 5 f picture with a relativistic band calculation in a local-density approximation (LDA), thereby analyzing the frequency branches observed by the de Haas–van Alphen (dHvA) effect. The Fermi surface volume of NpGe 3 is sensitive to the lattice constant because of its special shape. A LDA equilibrium lattice constant of NpGe 3 is determined from total-energy minimization as a function of lattice constant under the AuCu 3 -type crystal structure. The Fermi surface obtained at the LDA equilibrium can explain precisely the origin of all the dHvA frequency branches like the familiar Fermi surface of Cu. This suggests that the fermiology of Np compounds should progress on the 5 f band scheme, though Np-5 f electrons are more localized than those of a lighter actinide atom.

Sum rules and Ward identities in the Kondo lattice

We derive a generalized Luttinger-Ward expression for the Free energy of a many body system involving a constrained Hilbert space. In the large $N$ limit, we are able to explicity write the entropy as a functional of the Green's functions. Using this method we obtain a Luttinger sum rule for the Kondo lattice. One of the fascinating aspects of the sum rule, is that it contains two components, one describing the heavy electron Fermi surface, the other, a sea of oppositely charged, spinless fermions. In the heavy electron state, this sea of spinless fermions is completely filled and the electron Fermi surface expands by one electron per unit cell to compensate the positively charged background, forming a ``large'' Fermi surface. Arbitrarily weak magnetism causes the spinless Fermi sea to annihilate with part of the Fermi sea of the conduction electrons, leading to a small Fermi surface. Our results thus enable us to show that the Fermi surface volume contracts from a large, to a small volume at a quantum critical point. However, the sum rules also permit the possible formation of a new phase, sandwiched between the antiferromagnet and the heavy electron phase, where the charged spinless fermions develop a true Fermi surface.

Hall-effect evolution across a heavy-fermion quantum critical point

A quantum critical point (QCP) develops in a material at absolute zero when a new form of order smoothly emerges in its ground state. QCPs are of great current interest because of their singular ability to influence the finite temperature properties of materials. Recently, heavy-fermion metals have played a key role in the study of antiferromagnetic QCPs. To accommodate the heavy electrons, the Fermi surface of the heavy-fermion paramagnet is larger than that of an antiferromagnet. An important unsolved question is whether the Fermi surface transformation at the QCP develops gradually, as expected if the magnetism is of spin-density-wave (SDW) type, or suddenly, as expected if the heavy electrons are abruptly localized by magnetism. Here we report measurements of the low-temperature Hall coefficient (R(H))--a measure of the Fermi surface volume--in the heavy-fermion metal YbRh2Si2 upon field-tuning it from an antiferromagnetic to a paramagnetic state. R(H) undergoes an increasingly rapid change near the QCP as the temperature is lowered, extrapolating to a sudden jump in the zero temperature limit. We interpret these results in terms of a collapse of the large Fermi surface and of the heavy-fermion state itself precisely at the QCP.

Anisotropy and carrier distribution in HgBa 2Ca n−1 Cu nO 2 n+2 ( n=3,4)

The electronic structure of HgBa 2Ca n−1 Cu n O 2 n+2 ( n=3,4, Hg12( n−1) n) is investigated by using the scalar-relativistic full-potential linearized augmented-plane-wave method. We calculated Fermi velocities v F and Fermi surface volume, and found that the anisotropy defined by the ratio v F x / v F z is similar to that in TlBa 2Ca 2Cu 3O 9. This anisotropy is also in good agreement with the experimental value. Each of the large Fermi surfaces contains 0.93–1.11 holes in Hg1223 and 0.90–1.14 holes in Hg1234. These values are similar to that in CuBa 2Ca 3Cu 4O 9F, which are designed to have an optimum set of the Fermi surface for superconductivity.

Multiple first-order metamagnetic transitions and quantum oscillations in ultrapure Sr3Ru2O7.

We present measurements on ultraclean single crystals of the bilayered ruthenate metal Sr3Ru2O7, which has a magnetic-field-tuned quantum critical point. Quantum oscillations of differing frequencies can be seen in the resistivity both below and above its metamagnetic transition. This frequency shift corresponds to a small change in the Fermi surface volume that is qualitatively consistent with the small moment change in the magnetization across the metamagnetic transition. Very near the metamagnetic field, unusual behavior is seen. There is a strong enhancement of the resistivity in a narrow field window, with a minimum in the resistivity as a function of temperature below 1 K that becomes more pronounced as the disorder level decreases. The region of anomalous behavior is bounded at low temperatures by two first-order phase transitions. The implications of the results are discussed.

Weak magnetism and non-Fermi liquids near heavy-fermion critical points

This paper is concerned with the weak-moment magnetism in heavy-fermion materials and its relation to the non-Fermi liquid physics observed near the transition to the Fermi liquid. We explore the hypothesis that the primary fluctuations responsible for the non-Fermi liquid physics are those associated with the destruction of the large Fermi surface of the Fermi liquid. Magnetism is suggested to be a low-energy instability of the resulting small Fermi surface state. A concrete realization of this picture is provided by a fractionalized Fermi liquid state which has a small Fermi surface of conduction electrons, but also has other exotic excitations with interactions described by a gauge theory in its deconfined phase. Of particular interest is a three-dimensional fractionalized Fermi liquid with a spinon Fermi surface and a U(1) gauge structure. A direct second-order transition from this state to the conventional Fermi liquid is possible and involves a jump in the electron Fermi surface volume. The critical point displays non-Fermi liquid behavior. A magnetic phase may develop from a spin density wave instability of the spinon Fermi surface. This exotic magnetic metal may have a weak ordered moment although the local moments do not participate in the Fermi surface. Experimental signatures of this phase and implications for heavy-fermion systems are discussed.

Instabilities of interacting electrons on the triangular lattice

Motivated by the recent finding of superconductivity in layered CoO_2 compounds, we investigate superconducting and magnetic instabilities of interacting electrons on the two-dimensional triangular lattice. Using a one-loop renormalization group scheme for weak to moderate coupling strengths, we find that for purely local interactions U>0 and small Fermi surfaces the renormalization group flow remains bounded down to very low scales and no superconducting or other instabilities can be detected. Antiferromagnetic exchange interactions J generate a wide density region with a d_{x^2-y^2}+id_{xy}-wave superconducting instability similar to recent proposals for the strongly correlated t-J model. For larger Fermi surface volumes the interactions flow to strong coupling also for purely local interactions U>0. We find a singlet pairing instability in the vicinity of strong magnetic ordering tendencies at three wavevectors for the van Hove filling.

Exotic heavy-fermion state in the filled skutteruditePrFe4P12uncovered by the de Haas–van Alphen effect

We report the de Haas-van Alphen (dHvA) experiment on the filled skutterudite PrFe$_4$P$_{12}$ exhibiting apparent Kondo-like behaviors in the transport and thermal properties. We have found enormously enhanced cyclotron effective mass $m^{\rm \ast}_{\rm c}=81 m_{\rm 0}$ in the high field phase (HFP), which indicates that PrFe$_4$P$_{12}$ is the first Pr-compound in which really heavy mass has been unambiguously confirmed. Also in the low field non-magnetic ordered phase (LOP), we observed the dHvA branch with $m^{\rm \ast}_{\rm c}=10 m_{0}$ that is quite heavy taking into account its small Fermi surface volume (0.15% of the Brillouin zone size). The insensitivity of mass in LOP against the magnetic field suggests that the quadrupolar interaction plays a main role both in the mass renormalization and the LOP formation.

Doping dependence of an n-type cuprate superconductor investigated by angle-resolved photoemission spectroscopy.

We present an angle-resolved photoemission doping dependence study of the n-type cuprate superconductor Nd(2-x)Ce(x)CuO(4+/-delta), from the half-filled Mott insulator to the T(c) = 24 K superconductor. In Nd2CuO4, we reveal the charge-transfer band for the first time. As electrons are doped into the system, this feature's intensity decreases with the concomitant formation of near- E(F) spectral weight. At low doping, the Fermi surface is an electron-pocket (with volume approximately x) centered at (pi,0). Further doping leads to the creation of a new holelike Fermi surface (volume approximately 1+x) centered at (pi,pi). These findings shed light on the Mott gap, its doping evolution, as well as the anomalous transport properties of the n-type cuprates.

High-resolution photoemission study of strongly correlated f electron systems

Abstract The importance and powerfulness of high-resolution photoemission spectroscopy in studying the strongly correlated f electron systems are demonstrated by presenting recent results on some Ce and U compounds. Using angle-resolved photoemission spectroscopy (ARPES), we observed a clear change in the Fermi-surface volume accompanied by the magnetic phase transition in CeSb, showing an important role of temperature-dependent p–f mixing in dominating the electronic and magnetic properties. It was also found by ARPES that USb, which is isostructural to CeSb but has 5f electrons instead of 4f electrons in the outermost shell, has a Fermi-surface topology totally different from that of CeSb, indicating the different nature between 4f and 5f electrons. The ARPES result has elucidated the dual (itinerant and localized) character of 5f electrons in USb. We found a temperature-dependent energy pseudogap at E F in CeRhSb and CeRhAs at low temperature, which is ascribed to the ‘Kondo-insulator gap’ formed through the hybridization between f and conduction electrons.

Three-Dimensional Reconstruction of the Fermi Surface of LaB<sub>6</sub>

The 2-dimensional angular correlations of the positron annihilation radiation (2D-ACAR) on a single crystal of LaB6 was measured for three projections. The 2D-ACAR spectra were subjected to the Van Citter-Gerhard deconvolution alghorithm. From the experimental spectra we produced the 3D k-space density rho(k) via three different methods: i) we reconstructed the 3D electron-positron momentum density rho(p) via the Cormack method. rho(k) was then obtained by applying the 3D LCW transformation to rho(p). ii) The same steps of point i) were repeated adopting a modified Fourier-transform-based algorithm. iii) The 3d k-space occupancy rho(k) was obtained directly by parameterising the Fermi surface volume with prolate ellipsoids whose axes were determined by a least-square fit to the 2D LCW transformations applied to two high symmetry projections. The ellipsoids diameters along high symmetry directions of the cubic Brillouin zone (BZ), as a fraction of the BZ size, were 0.64 (dir. X-M) and 0.82 (dir. Gamma-X). The resulting Fermi volume, as a fraction of the BZ volume, was 0.55. These results agree within 1% with those obtained via the de Haas van Alphen experiments.

The Kondo effect to heavy fermions studied using the de Haas–van Alphen effect

In this paper, we briefly review some recent de Haas–van Alphen experiments on two contrasting types of heavy fermion/Kondo systems for varying concentrations x of the impurity ion, Ce or U. In both systems the Fermi surface is observed to vary continuously with x: in Ce x La 1− x B 6, the Ce ions behave as Kondo impurities while in U x Th 1− x Be 13 they do not. In both systems, the f electrons are also found to contribute only partially to the Fermi surface volume, therefore raising questions concerning the applicability of Fermi liquid theory.

Doping-dependent electronic structure of cuprates studied using angle-scanned photoemission

Full kk-maps of the electronic structure near the Fermi level of dierently doped cuprates measured with angle-scanned photoelectron spectroscopy are presented. The valence band maximum of the antiferromagnetic insulator Sr2CuO2Cl2, which is taken as a representative of an undoped cuprate, and the Fermi surfaces of overdoped, optimally doped and underdoped Bi2Sr2CaCu2O8+ high-temperature superconductors are mapped in the normal state. The results conrm the existence of large Luttinger Fermi surfaces at high doping with a Fermi surface volume proportional to (1 +x), where x is the hole concentration. At very low doping, however, we nd that this assumption based on Luttinger's theorem is not fullled. This implies a change in the topology of the Fermi surface. Furthermore the intensity of the shadow bands observed on the Fermi surface of Bi2Sr2CaCu2O8+ as a function of the doping is discussed. PACS. 79.60.-i Photoemission and photoelectron spectra { 74.25.Jb Electronic structure { 71.18.+y Fermi surface: calculations and measurements; eective mass, g factor

Anomalous low-doping phase of the Hubbard model

We present results of a systematic quantum Monte Carlo study for the single-band Hubbard model. Thereby we evaluated single-particle spectra (PES and IPES), two-particle spectra (spin and density correlation functions), and the dynamical correlation function of suitably defined diagnostic operators, all as a function of temperature and hole doping. The results allow us to identify different physical regimes. Near half-filling we find an anomalous ``Hubbard-I phase,'' where the band structure is, up to some minor modifications, consistent with the Hubbard-I predictions. At lower temperatures, where the spin response becomes sharp, additional dispersionless ``bands'' emerge due to the dressing of electrons/holes with spin excitations. We present a simple phenomenological fit that reproduces the band structure of the insulator quantitatively. The Fermi surface volume in the low-doping phase, as derived from the single-particle spectral function, is not consistent with the Luttinger theorem, but qualitatively in agreement with the predictions of the Hubbard-I approximation. The anomalous phase extends up to a hole concentration of $\ensuremath{\approx}15%,$ i.e., the underdoped region in the phase diagram of high-${T}_{c}$ superconductors. We also investigate the nature of the magnetic ordering transition in the single-particle spectra. We show that the transition to a spin-density wave-like band structure is not accomplished by the formation of any resolvable ``precursor bands,'' but rather by a (spectroscopically invisible) band of spin-3/2 quasiparticles. We discuss implications for the ``remnant Fermi surface'' in insulating cuprate compounds and the shadow bands in the doped materials.

Fermiology of a one-dimensional heavy-electron metal

We present a Quantum Monte Carlo (QMC) study of the 1D Kondo lattice at non-integer filling, i.e. a one-dimensional version of a heavy electron metal. For this special system the minus-sign problem turns out to be strongly reduced, which allows QMC simulations for temperatures as low as 1% of the conduction electron bandwidth. The single particle Green's function shows and intricate network of low-energy bands at low temperature, with a Fermi surface volume that comprises both c and f-electrons. As temperature increases the system evolves through two distinct crossover temperatures into a very simple band structure with one free c-electron band and a disconnected upper and lower Hubbard band for f-electrons. The f-electrons thus `drop out' of the Fermi surface volume as temperature increases.

Many-body band structure and Fermi surface of the Kondo lattice

We present a theory for the single-particle excitations and Fermi surface of the Kondo lattice. Thereby we construct an effective Hamiltonian describing the creation and propagation of single-particle-like charge fluctuations on a ``resonating-valence-bond background'' of local singlets. The theory may be viewed as a Fermionic version of linear spin-wave theory and is of comparable simplicity so that the calculations for the strong-coupling limit can be performed analytically. We calculate the single-particle spectral function for the ``pure'' Kondo lattice as well as for several extended versions: with a Coulomb repulsion between conduction and $f$ electrons, Coulomb repulsion between conduction electrons, and a ``breathing'' $f$ orbital. In all cases we study the evolution of the spectrum in going from the Kondo insulator to the heavy electron metal. We compare our results to exact diagonalization of small clusters and find remarkable agreement in nearly all cases studied. In the metallic case the $f$ electrons participate in the Fermi surface volume even when they are replaced by localized Kondo spins and the number of bands, their dispersion and spectral character, and the nontrivial (i.e., nonrigid bandlike) doping dependence including a pronounced transfer of spectral weight are reproduced at least semiquantitatively by the theory.

Puzzles on Fermi Surfaces in CeRu2Si2: Bonding Kondo State

Mechanism of the unusual continuous transition in CeRu 2 Si 2 from valence fluctuation regime to Kondo regime, in which the Fermi surface volume changes exactly by one electron, is studied in detail. The transition occurs due to the singlet bonding Kondo band, which becomes sharper and more dispersionless as it approaches the Fermi energy with weakening quasiparticle character and crosses the Fermi energy at the transition. Various anomalous properties are related also with the mixed valence character in the valence fluctuation regime, disappearing in the Kondo regime. An unusual behavior of Hall effect with a large and sharp peak at low temperature, which has been misunderstood as the anomalous Hall effect, is explained from the mechanism that there are two kinds of Fermi surfaces, the first group formed from small holes with weak c - f mixing, showing a little change at the transition, and the second group of large Fermi surfaces with strong c - f mixing changing nearly discontinuously at the transition...

Theory for dynamical short-range order and Fermi surface volume in strongly correlated systems.

Using the fluctuation exchange approximation of the one band Hubbard model, we discuss the origin of the changing Fermi surface volume in underdoped cuprate systems due to the transfer of occupied states from the Fermi surface to its shadow, resulting from the strong dynamical antiferromagnetic short range correlations. The momentum and temperature dependence of the quasi particle scattering rate shows unusual deviations from the conventional Fermi liquid like behavior. Their consequences for the changing Fermi surface volume are discussed. Here, we investigate in detail which scattering processes might be responsible for a violation of the Luttinger theorem. Finally, we discuss the formation of hole pockets near half filling.

The electronic band structure of Pb1-xSnxTe alloys. I. Cubic and rhombohedral phase at 4.2K

The Fermi surfaces of Pb1-xSnxTe in the cubic and rhombohedrally distorted phases for both normal and inverted band structures have been investigated using the Shubnikov-de Haas effect. Comparison of the observed Fermi-surface cross-sectional areas with the band structures of Dimmock (1981), for the cubic phase, and of Bangert (1981), for the rhombohedral phase, yield parameters which are in agreement with values established previously for the cubic phase. The complex character of the Fermi surfaces at the points T and L in the rhomobohedral Brillouin zone is found to agree with the predicted splitting of the ellipsoids of the cubic phase into the 'skin' and 'core' of an apple-like composite surface, originating in the lifting of the inversion symmetry of the structure in the structural phase transition. Clear evidence is obtained for the presence of structural domains in the rhombohedral phase. The carrier concentrations deduced from the Fermi-surface volumes are found to agree with those measured from the weak-field Hall coefficients, when account is taken of the anisotropy of the multiple carrier valleys in the band structure.