Quasiparticle Fermi Surface Research Articles

Friedel oscillation in non-Fermi liquid: lesson from exactly solvable Hatsugai–Kohmoto model

When non-magnetic impurity immerses in Fermi sea, a regular modulation of charge density around impurity will appear and such phenomena is called Friedel oscillation (FO). Although both Luttinger liquid and Landau Fermi liquid show such characteristic oscillation, FO in generic non-Fermi liquid (NFL) phase is still largely unknown. Here, we show that FO indeed exists in NFL state of an exactly solvable model, i.e. the Hatsugai–Kohmoto model which has been intensively explored in recent years. Combining T-matrix approximation and linear-response-theory, an interesting picture emerges, if two interaction-induced quasi-particles bands in NFL are partially occupied, FO in this situation is determined by a novel structure in momentum space, i.e. the ‘average Fermi surface’ (average over two quasi-particle Fermi surface), which highlights the inter-band particle-hole excitation. We hope our study here provides a counterintuitive example in which FO with Fermi surface coexists with NFL quasi-particle, and it may be useful to detect hidden ‘average Fermi surface’ structure in other correlated electron systems.

Truncated mass divergence in a Mott metal

The Mott metal-insulator transition represents one of the most fundamental phenomena in condensed matter physics. Yet, basic tenets of the canonical Brinkman-Rice picture of Mott localization remain to be tested experimentally by quantum oscillation measurements that directly probe the quasiparticle Fermi surface and effective mass. By extending this technique to high pressure, we have examined the metallic state on the threshold of Mott localization in clean, undoped crystals of NiS2. We find that i) on approaching Mott localization, the quasiparticle mass is strongly enhanced, whereas the Fermi surface remains essentially unchanged; ii) the quasiparticle mass closely follows the divergent form predicted theoretically, establishing charge carrier slowdown as the driver for the metal-insulator transition; iii) this mass divergence is truncated by the metal-insulator transition, placing the Mott critical point inside the insulating section of the phase diagram. The inaccessibility of the Mott critical point in NiS2 parallels findings at the threshold of ferromagnetism in clean metallic systems, in which criticality at low temperature is almost universally interrupted by first-order transitions or novel emergent phases such as incommensurate magnetic order or unconventional superconductivity.

Fermionic order by disorder in a van der Waals antiferromagnet

CeTe3 is a unique platform to investigate the itinerant magnetism in a van der Waals (vdW) coupled metal. Despite chemical pressure being a promising route to boost quantum fluctuation in this system, a systematic study on the chemical pressure effect on Ce3+(4f1) states is absent. Here, we report on the successful growth of a series of Se doped single crystals of CeTe3. We found a fluctuation driven exotic magnetic rotation from the usual easy-axis ordering to an unusual hard-axis ordering. Unlike in localized magnetic systems, near-critical magnetism can increase itinerancy hand-in-hand with enhancing fluctuation of magnetism. Thus, seemingly unstable hard-axis ordering emerges through kinetic energy gain, with the self-consistent observation of enhanced magnetic fluctuation (disorder). As far as we recognize, this order-by-disorder process in fermionic system is observed for the first time within vdW materials. Our finding opens a unique experimental platform for direct visualization of the rich quasiparticle Fermi surface deformation associated with the Fermionic order-by-disorder process. Also, the search for emergent exotic phases by further tuning of quantum fluctuation is suggested as a promising future challenge.

Quasiparticle spin relaxation with superconducting velocity-tunable state in GaAs(100) quantum wells in proximity tos-wave superconductor

We present a novel quasiparticle state driven by a supercurrent in GaAs (100) quantum wells in proximity to an $s$-wave superconductor, which can be tuned by the superconducting velocity. Rich features such as the suppressed Cooper pairings, large quasiparticle density and non-monotonically tunable momentum current can be realized by varying the superconducting velocity. In the degenerate regime, the quasiparticle Fermi surface is composed by two arcs, referred to as Fermi arcs, which are contributed by the electron- and hole-like branches. The D'yakonov-Perel' spin relaxation is explored, and intriguing physics is revealed when the Fermi arc emerges. Specifically, when the order parameter tends to zero, it is found that the branch-mixing scattering is forbidden in the quasi-electron band. When the condensation process associated with the annihilation of the quasi-electron and quasi-hole is {\em slow}, this indicates that the electron- and hole-like Fermi arcs in the quasi-electron band are independent. The open structure of the Fermi arc leads to the nonzero angular-average of the effective magnetic field due to the spin-orbit coupling, which acts as an effective Zeeman field. This Zeeman field leads to the spin oscillations even in the strong scattering regime. Moreover, in the strong scattering regime, we show that the open structure of the Fermi arc also leads to the insensitiveness of the spin relaxation to the momentum scattering, in contrast to the conventional motional narrowing situation. Nevertheless, with a {\em finite} order parameter, the branch-mixing scattering can be triggered, opening the inter-branch spin relaxation channel, which is dominant in the strong scattering regime. In contrast to the situation with an extremely small order parameter,....(omitted due to the limit of space)

Anomalies in the Fermi Surface and Band Dispersion of Quasi-One-Dimensional CuO Chains in the High-Temperature SuperconductorYBa2Cu4O8

We have investigated the electronic states in quasi-one-dimensional CuO chains by microprobe angle resolved photoemission spectroscopy. We find that the quasiparticle Fermi surface consists of six disconnected segments, consistent with recent theoretical calculations that predict the formation of narrow, elongated Fermi surface pockets for coupled CuO chains. In addition, we find a strong renormalization effect with a significant kink structure in the band dispersion. The properties of this latter effect [energy scale (∼40 meV), temperature dependence, and behavior with Zn-doping] are identical to those of the bosonic mode observed in CuO2 planes of high-temperature superconductors, indicating they have a common origin.

Bilayer splitting in overdoped high-Tccuprates

Recent angle-resolved photoemission data for overdoped Bi2212 are explained. Of the peak-dip-hump structure, the peak corresponds the $\vec q =0$ component of a hole condensate which appears at $T_c$. The fluctuating part of this same condensate produces the hump. The bilayer splitting is large enough to produce a bonding hole and an electron antibonding quasiparticle Fermi surface. Smaller bilayer splittings observed in some experiments reflect the interaction of the peak structure with quasiparticle states near, but not at, the Fermi surface.

Fermi surface and gap parameter in high- Tc superconductors: the Stripe Quantum Critical Point scenario

We study the single-particle spectral properties of electrons coupled to quasicritical charge and spin fluctuations close to a stripe-phase, which is governed by a Quantum Critical Point near optimum doping. We find that spectral weight is transferred from the quasiparticle peak to incoherent dispersive features. As a consequence, the distribution of low-laying spectral weight is modified with respect to the quasiparticle Fermi surface. The interplay of charge and spin fluctuations reproduces features of the observed Fermi surface, such as the asymmetric suppression of spectral weight near the M points of the Brillouin zone. Within the model, we also analyze the interplay between repulsive spin and attractive charge fluctuations in determining the symmetry and the peculiar momentum dependence of the superconducting gap parameter. When both spin and charge fluctuations are coupled to the electrons, we find d x 2− y 2 -wave gap symmetry in a wide range of parameter. A crossover d- vs. s-wave symmetry of the gap may occur when the strength of charge fluctuations increases with respect to spin fluctuations.

Normal state, superconductivity and quasiparticle Fermi surface of the strongly correlated oxide Sr 2RuO 4

The oxide superconductor Sr 2RuO 4 is emerging as an archetypal strongly correlated electron system. We review the experimental situation, focusing on Fermi surface specific probes. Quantum oscillation measurements have revealed a Fermi surface consisting of three slightly warped cylinders populated by quasiparticles with masses ranging from 3.4 to 14.6 times the bare electron mass. There is strong evidence that Sr 2RuO 4 is a spin-triplet superconductor, and the simplicity of the Fermi surface combined with detailed knowlege of the quasiparticle properties from quantum oscillation and orbital specific NMR measurements means that Sr 2RuO 4 may be a key system for understanding unconventional superconductivity. We compare Sr 2RuO 4 with three-dimensional nearly ferromagnetic 3d-metals, and suggest that quasi-two-dimensional spin-fluctuations may be responsible for the fact that Sr 2RuO 4 is the first nearly ferromagnetic metal to show superconductivity.

Electronic structure of underdoped cuprates

We consider a two-dimensional Fermi-liquid coupled to low-energy commensurate spin fluctuations. At small coupling, the hole Fermi surface is large and centered around Q = ( π, π). We show that as the coupling increases, the shape of the quasiparticle Fermi surface and the spin-fermion vertex undergo a substantial evolution. At strong couplings, g ⪢ ω 0, where ω 0 is the upper cutoff in the spin susceptibility, the hole Fermi surface consists of small pockets centered at ( ± π 2 , ± π 2 ). The full spin-fermion vertex is much smaller than the bare one, and scales nearly linearly with ¦q − Q¦, where q is the momentum of the susceptibility. At intermediate couplings, there exist both, a large hole Fermi surface centered at (π,π), and four hole pockets, but the quasiparticle residue is small everywhere except for the pieces of the pockets which face the origin of the Brillouin zone. The relevance of these results for recent photoemission experiments in YBCO and Bi2212 systems is discussed.

Temperature crossovers in cuprates

We study the temperature crossovers seen in the magnetic and transport properties of cuprates using a nearly antiferromagnetic Fermi-liquid model (NAFLM). We distinguish between underdoped and overdoped systems on the basis of their low-frequency magnetic behaviour and so classify the optimally doped cuprates as a special case of the underdoped cuprates. For the overdoped cuprates, we find, in agreement with earlier work, mean-field z = 2 behaviour of the magnetic variables associated with the fact that the damping rate of their spin fluctuations is essentially independent of temperature, while the resistivity exhibits a crossover from Fermi-liquid behaviour at low temperature to linear-in-T behaviour above a certain temperature . We demonstrate that above the proximity of the quasiparticle Fermi surface to the magnetic Brillouin zone boundary brings about the measured linear-in-T resistivity. For the underdoped cuprates we argue that the sequence of crossovers identified by Barzykin and Pines in the low-frequency magnetic behaviour (from mean-field z = 2 behaviour at high temperatures, , to non-universal z = 1 scaling behaviour at intermediate temperatures, , to pseudogap behaviour below ) reflects the development in the electronic structure of a precursor to a spin-density-wave state. This development begins at with a thermal evolution of the quasiparticle spectral weight which brings about temperature-dependent spin damping and ends at where the Fermi surface has lost pieces near corners of the magnetic Brillouin zone. For the resistivity is linear in T because this change in spectral weight does not affect the resistivity significantly; below vertex corrections act to bring about the measured downturn in and approximately quadratic-in-T resistivity for .

Knight shift and spin-echo decay time of YBa2Cu4O8 and YBa2Cu3O7 in the superconducting state.

We report on calculations of the Knight shift and spin-echo decay time, ${T}_{2G}$, in the superconducting state which are based on a nearly antiferromagnetic Fermi-liquid description of the spin-fluctuation spectrum, in which a single spin component is responsible for the dynamic spin behavior and the magnetic interaction between the planar quasiparticles brings the system close to antiferromagnetic behavior. The dynamic spin susceptibility is described by a random-phase-approximation-like expression, with a restoring force which is unchanged from the normal state, and an irreducible particle-hole susceptibility which reflects the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ symmetry of the gap parameter and a quasiparticle Fermi surface consistent with photoemission experiments. We obtain a quantitative fit to the Knight shift results for Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{8}$ with a ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ strong coupling gap of maximum magnitude $2.8{k}_{B}{T}_{c}$, and show that quantitative agreement with the recent measurements of ${T}_{2G}$ by Corey et al. [Phys. Rev. B 53, 5907 (1996)], may be obtained with this ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ pairing state and a quite substantial antiferromagnetic enhancement (\ensuremath{\sim}140) of the static "band structure" spin susceptibility at wave vectors in the vicinity of $\mathrm{Q}=(\ensuremath{\pi}, \ensuremath{\pi})$. We demonstrate that the experimental results of Corey et al. rule out an anisotropic $s$-wave state. Analogous calculations for the Knight shift of Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ suggest that the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ strong coupling gap possesses a maximum magnitude, $2.6{k}_{B}{T}_{c}$, and on this basis, we predict a reduction in ${T}_{2G}^{\ensuremath{-}1}$ of some 5% for the smaller antiferromagnetic enhancement (\ensuremath{\sim}38) expected for this system.

Observation of heavy fermion quasiparticles in UPt 3 above the metamagnetic transition

Quantum oscillations of the transverse magnetoresistance have been observed in the heavy fermion metal UPt 3 in fields up to 24.5 T applied in the basal plane, providing the first observation of the quasiparticle Fermi surface above the metamagnetic transition. The observed quasiparticle masses remain strongly renormalised in the high field state, ranging from 30 to approximately 100 times the bare electron mass.

Slave-boson approach to the anomalous doping effects of the Hall constants of La 2− xSr xCuO 4

Using the U d = ∞ mean-field slave-boson approach in the three-band CuO 2 model we study the anomalous doping ( δ = x) dependence of the Hall constant R H of the superconducting compound La 2− x Sr x CuO 4; (i) the inversely proportional d dependence R H ∝ δ -1 for low dopings δ ≲ 0.15, and (ii) its deviation for higher dopings and the sign inversion of the R from R H > 0 to R H<0 with increase in δ across some critical concentration δ cr. We show that Cu 2+-fermion quasiparticle states which are formed in the background of Cu 3+ slave bosons under strong correlation in the hole-doped CuO 2 system are responsible for the observed anomalous doping effects of the Hall constant of this compound. The first effect is explained by the bare-particle residues (components) of the quasiparticle states, whose measure is the slave-boson parameter e 2 0 which is roughly proportional to doping δ for low doping concentrations. The second one is due to the effect of the direct oxygen-oxygen hopping t pp on the Cu 2+-fermion quasiparticle Fermi surface. The similar anomalous doping effects observed in the electron-doped compound Nd 2− x Ce x CuO 4− y cannot be explained by the quasiparticle states formed by pairing-type (p-d) hybridization proposed by Newns for more than half-filled Cu d-states.

Is YbAs a heavy fermion system?

Using parameters extracted from a tight binding fit to an ab initio band structure, the specific heat anomaly observed in YbAs around 5 K is computed within the infinite U limit of the degenerate Anderson impurity model. Applying the renormalization procedure derived in variational treatments of the periodic Anderson model, a quasiparticle Fermi surface with strong nesting features and small mass enhancements is obtained. The results suggest that YbAs is not a “classical” heavy Fermion system.

Quasiparticle interactions due to charge and spin fluctuations in the lattice heavy-fermion states

Abstract We investigate quasiparticle interactions, which cause superconducting pairing and antiferromagnetic instability in the heavy-fermion superconductors, using the simple-cubic-lattice SU (N) Coqblin-Schrieffer model. Perturbative treatments of fluctuations from the mean-field Kondo-lattice states lead to both quasiparticle exchange interaction due to the RKKY coupling of conduction spin fluctuations and the boson-mediated renormalized Kondo interaction due to the hybridized density fluctuations. These interactions are calculated at T = 0 as a function of quasiparticle occupation. The renormalized Kondo interaction is strongly repulsive close to the insulating state of the occupied lower band, and becomes less repulsive with a decrease in quasiparticle filling, showing characteristic q dependences, while the exchange interaction has a constant q dependence with an antiferromagnetic RKKY coupling for a nearly half-filled conduction-band situation. An antiferromagnetic SDW-like instability is shown to be possible after the incoherent Kondo states are realized below the Kondo temperature TK but before the coherent Kondo states are attained at T0. It is argued that the SDW instability of heavy-fermion systems may be that of the conduction-band Fermi surface induced in the incoherence temperature range and not that of the quasiparticle Fermi surface obtained in the coherent states. For a heavy-fermion system with a high quasiparticle filling the RKKY-type exchange contribution to the pairing interaction, which does not scale with TK, is more severely restricted due to the small quasiparticle Fermi surface, and the filling-dependent strong boson-mediated interaction becomes dominant.

Current-density-functional theory and the de Haas-van Alphen effect.

The theory of the de Haas--van Alphen effect is developed within the framework of the current-density-functional theory of Vignale and Rasolt. Although the noninteracting kinetic-energy functional generates de Haas--van Alphen oscillations with periods determined by the Kohn-Sham Fermi surface, these oscillations are shown to be exactly canceled by the Vignale-Rasolt exchange-correlation functional, which substitutes in their place the de Haas--van Alphen oscillations determined by the quasiparticle Fermi surface and band structure.

Difference between the quasiparticle and the Kohn-Sham-Fermi surfaces.

The question addressed is whether the Fermi surface calculated from the exact density-functional one-electron eigenvalues coincides with the ``quasiparticle Fermi surface'' calculated from the self-energy \ensuremath{\Sigma}(k,\ensuremath{\mu}), where \ensuremath{\mu} is the chemical potential. For the case of density-functional theory on a lattice this is shown not to be the case.