Fermi surface reconstruction by dynamic magnetic fluctuations

We demonstrate that nearly critical quantum magnetic fluctuations in strongly correlated electron systems can change the Fermi surface topology and also lead to spin charge separation in two dimensions. To demonstrate these effects, we consider a small number of holes injected into the bilayer antiferromagnet. The system has a quantum critical point (QCP) which separates magnetically ordered and disordered phases. We demonstrate that in the physically interesting regime, there is a magnetically driven Lifshitz point (LP) inside the magnetically disordered phase. At the LP, the topology of the hole Fermi surface is changed. We also demonstrate that in this regime, the hole spin and charge necessarily separate when approaching the QCP. The considered model sheds light on generic problems concerning the physics of the cuprates.     

Fermi surface spectroscopy: a magnetic resonance approach

We describe recently-developed GHz magneto-optical techniques which measure the Fermi-surface topologies and superconducting order parameter symmetry in organic molecular metals.     

Study on the electronic structure and Fermi surface of 3d-transition-metal disilisides CoSi2

We have investigated the electronic structure, the momentum density distribution ρ(p), and the Fermi surface FS of single crystals of the Pyrite-type 3d-transition-metal disilisides CoSi₂. The band structure calculations, the density of states DOS, and the FS, in vicinity of Fermi level, have been carried out using the full-potential linearized augmented plane wave FP-LAPW method within generalized gradient approximation GGA for exchange and correlation potential. The measurements have been performed via the 2D angular correlation of annihilation radiation ACAR experiments. ρ(p) has been reconstructed by using the Fourier transformation technique. The FS has been reconstructed within the first Brillion zone BZ through the Locks, Crisp, and West LCW folding procedures. The analysis confirmed that Si 3sp states hybrid with both Co 3d–t _2g and Co 3d–e _g states around Γ and X points, respectively. The dimensions of the FS of CoSi₂ have been compared to the present calculations as well as to the earlier results.     

Antiferroquadrupolar and antiferromagnetic structures in TmGa3

Magnetization processes and magnetic phase diagrams have been studied in magnetic fields applied along the three main crystallographic directions of the cubic cell in TmGa₃. Large magnetization jumps occur at well-defined critical fields. Each of the corresponding magnetic phases has been characterized by means of neutron diffraction on monocrystalline samples. They are shown to be stabilized by antiferroquadrupolar pair interactions within the trigonal symmetry which favours multiaxial spin arrangements: in the spontaneous triple q-structure, the spins point along the four threefold axes. A comparison with the magnetic properties of dysprosium intermetallic compounds within the CsCl-type structure is given. The difficulties of studying antiferroquadrupolar interactions and orderings in rare earth intermetallics are then underlined.     

Fermi surface measurements on UPd3

The Fermi surface of the DO24 compound UPd₃ has been investigated by the de Haas-van Alphen effect in magnetic fields up to 46 Tesla. Two sheets are detected, one with a high frequency, about 4 10³ Tesla, and one having low frequencies, about 4 10² Tesla. Values of the effectives mass obtained are in accordance with a non-f character of the electron wave function on the orbits investigated.     

Fermi surface,magnetic, and superconducting properties in actinide compounds

The de Haas–van Alphen effect, which is a powerful method to explore Fermi surface properties, has been observed in cerium, uranium, and nowadays even in neptunium and plutonium compounds. Here, we present the results of several studies concerning the Fermi surface properties of the heavy fermion superconductors UPt₃ and NpPd₅Al₂, and of the ferromagnetic pressure-induced superconductor UGe₂, together with those of some related compounds for which fascinating anisotropic superconductivity, magnetism, and heavy fermion behavior has been observed.     

Electronic structure and the Fermi surface of PuCoGa5 and NpCoGa5

Using a relativistic linear augmented-plane-wave method, we clarify energy band structures and Fermi surfaces of recently discovered plutonium-based superconductor PuCoGa5 and the isostructural material NpCoGa5. For PuCoGa5, we find several cylindrical sheets of Fermi surfaces with large volume, similar to CeMIn5, while for NpCoGa5, the Fermi surfaces are found to be similar to those of UMGa5. These similarities are discussed based on the j-j coupling scheme, suggesting some hints for the superconducting mechanism in HoCoGa5-type f-electron compounds.     

Fermi surface of LaAg

Electronic structure, especially the Fermi surface, is calculated for the intermetallic rare-earth compound LaAg, known to show the structural phase transition when In is substituted for Ag, by a self-consistent fully-relativistic APW method with the exchange-correlation potential in a local-density approximation. The Fermi surface is found to consist of large hole and electron sheets as well as small hole and electron sheets. This result confirms well the theoretical prediction by Niksch et al. (1987). These Fermi surface sheets are found to explain the experimental results for the de Haas-van Alphen effect by Niksch et al. (1987) and Motoki et al. (1995) reasonably well. But, the frequency branches originating from the large hole sheet have been observed only partially. Local curvature of the large hole sheet is investigated as a possible origin of the disappearance of these frequency branches.     

Reconstruction of the Fermi surface of HTSC cuprates in a high magnetic field

The effect of a high magnetic field on the electronic structure of HTSC cuprates is considered. The study is performed in the t-t′-t″-J* model, and the high magnetic field effect is taken into account not only as the Zeeman splitting of the one-electron levels, but also in the occupation numbers of the states with different spin projections and in the formation of the spin correlation functions. The field is assumed to be high enough to align all of the spins along the field. As a result, the Fermi surface reconstruction is obtained from four hole pockets about the nodal point (π/2, π/2) in the paramagnetic phase to a large hole pocket about the point (π, π) in the ferromagnetic phase. As the magnetic field strength decreases, a number of quantum phase transitions are revealed; they are manifested in the changed Fermi surface topology. The Fermi surface reconstruction with a decreasing field is qualitatively the same as that with an increasing doping degree in the absence of a magnetic field.     

Fermi surface of sodium and potassium

The deviations of the Fermi surface from sphericity and the Fermi energy of Na and K are calculated using a local model-pseudopotential determined from the measured phonon dispersion curves.     

Fermi surface of doped lithium

The Korringa-Kohn-Rostoker method with Green’s function averaged over the atomic configurations in a complex Ising lattice and a muffin-tin potential was used to calculate the electronic-band structure in lithium containing vacancies and s, p, and d impurities. It is shown that substantial changes in the profile of the Fermi surface do not lead to necking, as was postulated previously, but cause splitting of the electronic states at the face of the Brillouin zone. This is attributed to the reduced symmetry of the crystal lattice with impurity excitation of the electronic-subsystem. Fiz. Tverd. Tela (St. Petersburg) 40, 1185–1186 (July 1998)     

Fermi surface of NaxCoO2

Doping evolution of the Fermi surface topology of Na(x)CoO(2) is studied systematically. Both local density approximation (LDA) and local spin density approximation (LSDA) predict a large Fermi surface as well as small hole pockets for doping levels x approximately 0.5. In contrast, the hole pockets are completely absent for all doping levels within LSDA+U. More importantly, we find no violation of Luttinger's rule in this system. The measured Fermi surface of Na(0.7)CoO(2) can be explained by its half-metallic behavior and agrees with our LSDA+U calculations.     

Fermi surface effect on intrinsic Lorenz number of Fermi liquids

We investigate a Fermi surface effect on the ideal Lorenz ratio of an anisotropic Fermi liquid caused by the onset of Umklapp scatterings. After discussing simple models by way of illustration, we present numerical results for transition metals, and indicate a material with a simple Fermi surface like sodium cobaltite as a possible candidate to observe the effect.     

Electronic band structure and Fermi surface of CaB6 studied by angle-resolved photoemission spectroscopy

We report high-resolution angle-resolved photoemission spectroscopy (ARPES) on CaB6. The band structure determined by ARPES shows a 1 eV energy gap at the X point between the valence and the conduction bands. We found a small electron pocket at the X point, whose carrier number is estimated to be (4-5) x 10(19) cm(-3), in good agreement with the Hall resistivity measurement with the same crystal. The experimental results are discussed in comparison with band structure calculations and theoretical models for the high-temperature ferromagnetism.