Nonanalytic Spin Susceptibility of a Fermi Liquid: The Case of Fe-Based Pnictides

Max-Planck-Institut für Physik komplexer Systeme, D-01187 Dresden, Germany.
Physical Review Letters (Impact Factor: 7.51). 07/2009; 102(23):236403. DOI: 10.1103/PhysRevLett.102.236403
Source: PubMed

ABSTRACT We propose an explanation of the peculiar linear temperature dependence of the uniform spin susceptibility chi(T) in ferropnictides. We argue that the linear in T term appears to be due to the nonanalytic temperature dependence of chi(T) in a two-dimensional Fermi liquid. We show that the prefactor of the T term is expressed via the square of the spin-density-wave (SDW) amplitude connecting nested hole and electron pockets. Because of an incipient SDW instability, this amplitude is large, which, along with a small value of the Fermi energy, makes the T dependence of chi(T) strong. We demonstrate that this mechanism is in quantitative agreement with the experiment.

Download full-text


Available from: Dmitri V. Efremov, Sep 25, 2015
1 Follower
16 Reads
  • Source
    • "The former saturates below 50 − 60K, as the nematic order parameter tends to a constant [25]. At the same time the anisotropic part of the transverse susceptibility changes due to non-Fermi liquid effects caused by the enhanced spin fluctuations [28], leading to the observed decrease in ∆K a in the normal state. The issue that remains open from the NMR data is the precise pattern of orbital ordering that is formed. "
    [Show abstract] [Hide abstract]
    ABSTRACT: A very fundamental and unconventional characteristic of superconductivity in iron-based materials is that it occurs in the vicinity of {\it two} other instabilities. Apart from a tendency towards magnetic order, these Fe-based systems have a propensity for nematic ordering: a lowering of the rotational symmetry while time-reversal invariance is preserved. Setting the stage for superconductivity, it is heavily debated whether the nematic symmetry breaking is driven by lattice, orbital or spin degrees of freedom. Here we report a very clear splitting of NMR resonance lines in FeSe at $T_{nem}$ = 91K, far above superconducting $T_c$ of 9.3 K. The splitting occurs for magnetic fields perpendicular to the Fe-planes and has the temperature dependence of a Landau-type order-parameter. Spin-lattice relaxation rates are not affected at $T_{nem}$, which unequivocally establishes orbital degrees of freedom as driving the nematic order. We demonstrate that superconductivity competes with the emerging nematicity.
    Nature Material 02/2015; 14:210. DOI:10.1038/nmat4138 · 36.50 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The work in this thesis falls roughly into three parts, which I characterise loosely as a developmental stage, an exploratory stage, and an attempt to contribute to understanding of the field. In the developmental stage, I have worked to design a variety of methods to create high-quality samples of various Iron Pnictide superconductors, to dope them with various chemicals and to characterise the resulting crystalline samples. I discuss in depth the signature of good quality crystals and the various experiments that they have been used in by myself and my collaborators. These processes are ongoing and will hopefully continue to contribute to my research group’s capabilities. My exploratory work involves a detailed survey of one particular family, Sr(Fe1−xCox)2As2, as the level of Cobalt is varied, and the mapping of the phase diagram for the system. I have also made a comparison to the better-measured Barium analogue, and discuss the reasons for the differences in character between the two, most notably the lack of a splitting of the structural and magnetic transitions in the first species. I also discuss the effect of pressure, which can lead to superconductivity in lightly doped samples for very modest pressures; and annealing, which increases transition temperatures within samples, on a limited quantity of crystals. Finally, I attempt to contribute to the understanding of the field via a series of Resonant Ultrasound Spectroscopic experiments conducted by a collaborator on my crystals and analysed by me. I see distinct first-order transitions in the parent compounds, characterisable above the high-T structural transition within a Ginzburg-Landau pseudoproper ferroelastic scheme for a transition coupling weakly to strain but driven by another order parameter. My observations allow several statements about the symmetry of the order parameter and are suggestive of a non-magnetically driven structural transition. In the case of doped samples a much richer behavior is seen, with a broad transition and simultaneous relaxation of all elastic peaks and a broad temperature range of significant dispersion. The effect of the softening is seen far above TN and lends strong support to the familiy of models predicting such high-T fluctuations.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the Hall resistivity, rho(xy), of polycrystalline SmFeAsO1-xFx for four different fluorine concentrations from the onset of superconductivity through the collapse of the structural phase transition. For the two more highly doped samples, rho(xy) is linear in magnetic field up to 50 T with only weak temperature dependence, reminiscent of a simple Fermi liquid. For the lightly doped samples with x < 0.15, we find a low temperature regime characterized as rho(xy) (H) being both nonlinear in magnetic field and strongly temperature-dependent even though the Hall angle is small. The onset temperature for this nonlinear regime is in the vicinity of the structural phase (SPT)/magnetic ordering (MO) transitions. The temperature dependence of the Hall resistivity is consistent with a thermal activation of carriers across an energy gap. The evolution of the energy gap with doping is reported.
    Journal of Physics Condensed Matter 10/2009; 21(41). DOI:10.1088/0953-8984/21/41/412201 · 2.35 Impact Factor
Show more