It was named for italian physicist enrico fermi, who along with english physicist p. We focus on an extended patch of the fermi surface, and expand in momenta about the point k 0 on the fermi surface. Probing the reconstructed fermi surface of antiferromagnetic bafe2as2 in one domain. The detachment can be repaired by a transformation to the first brillouin zone. A crucial knowledge in this regard is the degree to which the nematic order influences the electronic structure of these materials. To quantify the shift and broadening of the leading edge, we have approximated the spectra with a lorentzian plus a constant background, multiplied by a fermi dirac function and convoluted with a gaussian representing the experimental energy resolution. Lowenergy tunable excitation photons have allowed the first observation of a saddlepoint singularity at the z point, as well as the gamma point. The existence of a fermi surface is a direct consequence of the pauli exclusion principle, which allows a. The fermi surface nesting is asking how well the fermi surface meets itself under translation by v. We observe that fe and ru orbitals hybridize to form a coherent electronic structure and that ru does not induce doping. Our analysis suggests that the cone is slightly anisotropic and its apex is located very near the fermi level, leading to tiny fermi surface pockets. In a metal, the fermi surface is the locus of low energy excitations in momentum space.
This yields a theory of ddimensional fermions in 7, with dispersion 14. Atomicorbital analysis on multiorbital fermi surfaces of. This filled region is known as an electron pocket and the fermi surface here is known as an electron orbit. Fermi surfaces for free electrons are constructed by a procedure credited to harrison. Fe pnictides with tc values up to 55 k, the febased superconductors have attracted considerable recent attention. Orbitaldependent modifications of electronic structure. Atomicorbital analysis on multiorbital fermi surfaces of bafe 2 as 2 masaru takizawa1, hidetoshi namba2, toshiaki ohta3, kenya ohgushi4, fumihiko matsui5, and hiroshi daimon5. While so far there are no experimental reports on the lowenergy electronic dispersions of kfecoas 2. The fermi surface pockets we observe are consistently larger than those in srfe 2as 2, but the effective masses are smaller, keeping the orbitally average velocities about the same. Signature of excitonic effect in bafe2as2 revealed by.
In this effect, the magnetization, normalized by the applied field, of a sample of bismuth was found to oscillate with h1. The procedure is known as mapping the fermi surface in the reduced zone scheme. Here, we considered the nonmagnetic, checkerboard, stripe, and sdw. Its microscopic origin and in particular its importance for the mechanism of hightemperature superconductivity itself are highly debated. The displacement between the edges of these cuts is called the nesting vector. Periodic table of the fermi surfaces of elemental solids. It can be seen that the small inner fermi surface or the hole pocket near the. Fermisurface reconstruction involving two van hove bafe. Physics department, drexel university, philadelphia, pennsylvania 19104, usa dated. Small and large fermi surfaces in metals with local moments.
Threedimensional fermisurface mapping of bafe2as2 using. Fermisurface calculation of the anomalous hall conductivity. Fermi surface reconstruction has occurred in this compound. We have performed a systematic angleresolved photoemission study on some of the parent compounds, mostly on srfe 2 as 2 and bafe 2 as 2, to investigate their electronic structure and fermi surface. For a freeelectron gas, the fermi surface is a sphere. If we turn on a weak lattice potential, the sharp corners of the fermi surfaces will be rounded up and one can prove that when the fermi surface crosses with a zone boundary, the fermi surface must be perpendicular to the boundary. Interactioninduced singular fermi surface in a hightemperature.
Fermi surface definition of fermi surface by merriamwebster. Written by his students, colleagues and friends, it is devoted to the theme of electrons at the fermi surface. Allan mackintosh came a year later and he was an idea guy more than a nuts and bolts guy. Electronic structure of the bafe2as2 family of iron. Our highresolution measurements of samples detwinned by the application of a mechanical strain reveal a highly anisotropic 3d fermi surface in the lowtemperature antiferromagnetic phase. The homepage of the database contains a periodic table that links to the fermi surface pages of individual elements. Febased superconductors exhibit a diverse interplay between charge, orbital, and magnetic ordering14. For each of the solids, the fermi surface of a band that crosses the fermi level is contained in one of the 167 vrml 1. F bounded by fermi surfacethat is, the volume per unit cell in quasimomentum spaceis determined by the density n of conduction electrons in a metal. Bafe2as2 has a rich and flexible materials chemistry that makes it an ideal model platform.
Observation of fermisurface dependent nodeless superconducting gaps in ba0. Unexpected fermisurface nesting in the pnictide parent. With antiferromagnetic ordering, both of these two van hove singularities come down below the fermi energy, leading to a topological change in the innermost fermi surface around the kz axis from cylindrical to tearshaped, as expected from firstprinciples calculation. Yates,2,3 and ivo souza2,3 1department of physics and astronomy, rutgers university, piscataway, new jersey 088548019, usa. The topology of the pockets has been concluded from the dispersion of. Our high quality data reveals that although the fermi surface is strongly threedimensional, it does indeed have long parallel segments along the k z direction that can lead to the emergence of. The fermi surface consists of two electron pockets and two pairs of hole pockets along the xgammax direction.
The number of holes and electrons, deduced from the area of the fermi surface pockets, are both about twice larger than in bafe2as2. Effects of spin structures on fermi surface topologies in. Variations in atomic geometry affect electron hopping between fe atoms5,6 and the fermi surface topology, influencing magnetic frustration and the pairing mechanism through changes of orbital overlap and occupancies711. Arrows represent the orientation of magnetic moments on the. Our analysis indicates that bafe2as2 is a strongly correlated compound with strongly doping and temperaturedependent properties. Thermoelectric power of bafe1xrux2as2 and bafe1xcox2as2. Fermisurface reconstruction involving two van hove. We report an angleresolved photoemission study of bafe2as2, a parent compound of ironbased superconductors. In bafe2as2, the lattice couples strongly to the magnetic and electronic degrees of freedom, providing a way to control them. We found that these van hove singularities are not only involved in threedimensional fermisurface reconstruction with antiferromagnetic ordering but also renormalized and predominant at low energies.
Hence, the fermi surface instability due to these singularities would also underlie the associated superconductors. Ultrafast transient generation of spindensitywave order. Our results suggest that the fermi surfaces of bafe2as2 are largely reconstructed due to collinear antiferromagnetic order. Ultrafast modulation of the chemical potential in bafe2as2. Electronic band structure of ferropnictide superconductors from. Fermi surface definition is a theoretical geometric surface that consists of points representing the wavelength and direction of propagation of electrons with energies at the fermi level in an atom of a solid material, that reflects the materials electronic structure, and that is used to characterize or predict the materials physical properties. Recent citations superconductivity induced at a point contact on the topological semimetal tungsten. The effects of spin structures on the fermi surface topologies of bafe2as2 were calculated using the firstprinciples approach. Fermisurface reconstruction involving two van hove singularities. Our consideration will be based on a semiclassical model. An important aspect of the surface states is the formation of the surface dipole, which directly affect the electron affinity of the semiconductor.
Electron dynamics and fermi surfaces electron dynamics the next important subject we address is electron dynamics in metals. Quantum oscillations in the parent pnictide bafe2as2. Moreover, the arpes measurements on bafe2as2 in the literature were never fully reconciled with the fermi surface determined by quantum oscillations. In some sense, it is exactly opposite to the case 6b. Direct characterization of photoinduced lattice dynamics. Pdf uniaxial nematiclike electronic structure and fermi. Alternative low energy formulation of fermi liquid theory. Pressure dependence of the bafe2as2 fermi surface within the. In addition, they may well provide insight into exotic superconductivity that extends beyond.
Electronic structure studies of bafe2as2 by angleresolved photoemission spectroscopy. Bafe2as2 is structurally simple, available as highquality large crystals, can be both hole and electron doped, and is amenable to firstprinciples electronic structure calculations. The key structural element appears to be a square planar arrangement of fe ions, tetrahedrally coordinated by a pnictogen or chalcogen, as exemplified by bafe2as2. Introduction the pauli exclusion principleis the source of electron degeneracy. Ferropnictides electronic band structure fermi surface.
We have made measurements of the extremal crosssectional areas of the open hole surface of the fermi surface of platinum for the previously unobserved, heavy mass orbits centered on. Dirac developed the statistical theory of electrons. By knowing the fermi surface of different materials one could predict their properties and aim to develop materials with desired functionality. We found that these van hove singularities are not only involved in threedimensional fermi surface reconstruction with antiferromagnetic ordering but also renormalized and predominant at low energies. Fermi surface calculation of the anomalous hall conductivity xinjie wang, 1david vanderbilt, jonathan r. What is an intuitive explanation of fermi surfaces.
A drastic transformation in fermi surface fs shape across tn is observed, as expected by firstprinciples band calculations. In condensed matter physics, the fermi surface is the surface in reciprocal space which separates occupied from unoccupied electron states at zero temperature. Every metal is characterized by its own fermi surface, so that the shapes of the surfaces vary. To the extent that the old fermi surface happens to land right by the edge of a band, the electronic energy is lowered. Lowtemperature fermi surface maps before and after the application of strain. When combined with previous measurements, the necessary data associated with all classes of orbits on all three sheets of. Using experimentally derived structural data, we show that the electronic structure evolves similarly in both cases. Click here to download the pdf version for printing. Given a solid, i believe i have some feeling for the fermi level. Fermi surface article about fermi surface by the free. The recently discovered feasbased superconductors are a new, promising set of materials for technological and basic research. Hence, the fermisurface instability due to these singularities would also underlie the associated superconductors. Observation of dirac cone electronic dispersion in bafe as. Abstract we use angleresolved photoemission spectroscopy to study the band structure of bafe 2 as 2 and cafe 2 as 2, two of the parent compounds of the iron arsenic hightemperature superconductors.
Significant reduction of electronic correlations upon. Upon increase of temperature from 40k, the hole pockets gradually sink below the chemical potential. First published in 1980, this is a festschrift to honour professor david schoenberg, frs, on the occasion of his retirement from the cavendish laboratory, cambridge, in 1978. Mar 05, 2009 photon energies between 30 and 175 ev and polarizations parallel and perpendicular to the scattering plane have been used. The term semiclassical comes from the fact that within this. Thus it is important to understand the undoped parent compounds that also have a puzzling collinear antiferromagnetic ground state. It separates occupied states inside the fermi sea from unoccupied states outside the fermi sea. Satellites and large doping and temperature dependence of. Perhaps because the net surface charge is the only relevant parameter for the determination of surface fermi level, the surface pinning concept is clear and straightforward. The fermi surface of pnictides is composed of electron and hole pockets centred around the x and. Nematicity plays an important role in the physics of ironbased superconductors ibs. Direct characterization of photoinduced lattice dynamics in.
These results suggest that modification of the fermi surface by structural distortions is more important than charge doping for inducing superconductivity in bafe2as2. The bands forming the cone show an anisotropic leading edge gap. Figure 2 shows the temperature dependence of the 118 t lattice bragg peak in tetragonal notation near the structural t s and the antiferromagnetic phase transition t n during slow cooling from a nominal temperature of t140 to 7 k. With antiferromagnetic ordering, both of these two van hove singularities come down below the fermi energy, leading to a topological change.
Study of band structure and fermi surface of srfe2as2 and. Pressure dependence of the bafe2as2 fermi surface within. Here, we experimentally demonstrate a systematic approach to realize. Additional electrons to a certain volume cause the already existing electrons to increase their energy.
Jul 16, 2019 reconstructed fermi surface in the afm phase. They offer transition temperatures as high as 55 k as well as essentially isotropic, and extremely large, upper, superconducting critical fields, in excess of 40 t at 20 k. Measurements of the fermi surface of afe 2as 2 a ba,ca,and sr by surface conductivity and magnetization have shown small orbits from the remaining fermi surface, where each orbit is less than 2% of the. Electronic structure and doping in bafe 2 as 2 and lifeas. Laser angleresolved photoemission spectroscopy arpes is employed to investigate the temperature t dependence of the electronic structure in bafe2as2 across the magnetostructural transition at tn 140 k. Fermi surface, in condensedmatter physics, abstract interface that defines the allowable energies of electrons in a solid. Electronic structure studies of bafe2as2 by angleresolved. Fermi surface is an abstract geometrical representation of the all available electronic states in various metals which are responsible for the electrical, thermal and magnetic properties.
Directional pointcontact andreevreflection spectroscopy of. Much of the discussion has focused on understanding things that happen as a result of features of the fermi surface topology. Thus the fermi surface is a constant energy surface surfaces in kspace. The shape of the fermi surface is derived from the periodicity and symmetry of the crystalline lattice and from the occupation of electronic energy bands. Uniaxial nematiclike electronic structure and fermi surface of untwinned cafe2as2. Jan 19, 2010 bafe2as2 is the parent compound of a family of unconventional superconductors with critical temperatures approaching 40 k. Magnetism and charge dynamics in iron pnictides nature. Our highresolution measurements of samples detwinned by the application of a mechanical strain reveal a highly anisotropic 3d fermi surface in. Fermi surfaces university of oxford department of physics. There is also another way to represent the fermi surface in the reduced and periodic zone scheme. Band structure, fermi surface, and superconducting gap in feasbased superconductors revealed by angleresolved photoemission spectroscopy. Strong electron pairing at the iron 3dxz,yz orbitals in holedoped bafe2as2 superconductors revealed by angleresolved photoemission. Probing the reconstructed fermi surface of antiferromagnetic. Pdf band structure, fermi surface, and superconducting.
Fermisurface reconstruction involving two van hove bafe as. Here, we revisit the electronic structure of bafe2as2 using angleresolved photoemission spectroscopy arpes. Pdf thermoelectric power of bafe1xrux2as2 and bafe1. Probing the reconstructed fermi surface of antiferromagnetic bafe. Decoupling of critical temperature and superconducting gaps in irradiated films of a febased superconductor dario daghero, mauro tortello, giovanni a ummarino et al. We have measured quantum oscillations in the magnetically ordered ground state of bafe2as2, a parent compound of the superconducting ternary pnictides. Role of the fermi surface for the pressuretuned nematic. Like bafe2as2, wte2 has clear and substantial changes in its fermi surface driven by modest changes in temperature.