Non-Fermi liquid at the FFLO quantum critical point (original) (raw)
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arXiv (Cornell University), 2015
Increasing the spin imbalance in superconductors can spatially modulate the gap by forming Cooper pairs with finite momentum. For large imbalances compared to the Fermi energy, the inhomogeneous FFLO superconductor ultimately becomes a normal metal. There is mounting experimental evidence for this scenario in 2D organic superconductors in large in-plane magnetic fields; this is complemented by ongoing efforts to realize this scenario in coupled tubes of atomic Fermi gases with spin imbalance. Yet, a theory for the phase transition from a metal to an FFLO superconductor has not been developed so far and the universality class has remained unknown. Here we propose and analyze a spin imbalance driven quantum critical point between a 2D metal and an FFLO phase in anisotropic electron systems. We derive the effective action for electrons and bosonic FFLO pairs at this quantum phase transition. Using this action, we predict non-Fermi liquid behavior and the absence of quasi-particles at a discrete set of hot spots on the Fermi surfaces. This results in strange power-laws in thermodynamics and response functions, which are testable with existing experimental setups on 2D organic superconductors and may also serve as signatures of the elusive FFLO phase itself. The proposed universality class is distinct from previously known quantum critical metals and, because its critical fluctuations appear already in the pairing channel, a promising candidate for naked metallic quantum criticality over extended temperature ranges.
Fermi Liquid Near a Quantum Critical Point
Journal of Low Temperature Physics, 2007
We investigate the approach to the quantum critical point of a Pomeranchuk instability from the symmetric, disordered side of the phase diagram. In the low-temperature limit, a Fermi liquid description of the metal is possible and becomes exact for T → 0. We discuss in detail which features of the approach to quantum criticality can be captured within Fermi liquid theory and which are outside of its scope.
Annals of Physics, 2015
The quantum phase transition in iron-based superconductors with 'half-Dirac' node at the electron Fermi surface as a T = 0 structural phase transition described in terms of nematic order is discussed. An effective low energy theory that describes half-Dirac nodal Fermions and their coupling to Ising nematic order that describes the phase transition is derived and analyzed using renormalization group (RG) study of the large-N f version of the theory. The inherent absence of Lorentz invariance of the theory leads to RG flow structure where the velocities vF and v∆ at the paired half-Dirac nodes (11 and 22) in general flow differently under RG, implying that the nodal electron gap is deformed and the C4 symmetry is broken, explaining the structural (orthogonal to orthorhombic) phase transition at the quantum critical point (QCP). The theory is found to have Gaussian fixed point λ * = 0, (v∆/vF) * = 0 with stable flow lines toward it, suggesting a second order nematic phase transition. Interpreting the fermion-Ising nematic boson interaction as a decay process of nematic Ising order parameter scalar field fluctuations into half-Dirac nodal fermions, I find that the theory surprisingly behaves as systems with dynamical critical exponent z = 1, reflecting undamped quantum critical dynamics and emergent fully relativistic field theory arising from the non(fully)relativistic field theory and is direct consequence of (v∆/vF) * = 0 fixed point. The nematic critical fluctuations lead to remarkable change to the spectral function peak where at a critical point λc, directly related to nematic QCP, the central spectral peak collapses and splits into satellite spectral peaks around nodal point. The vanishing of the zero modes density of states leads to the undamped z = 1 quantum critical dynamics.
Three-Dimensional Non-Fermi-Liquid Behavior from One-Dimensional Quantum Critical Local Moments
Physical review letters, 2018
We study the temperature dependence of the electrical resistivity in a system composed of critical spin chains interacting with three-dimensional conduction electrons and driven to criticality via an external magnetic field. The relevant experimental system is Yb_{2}Pt_{2}Pb, a metal where itinerant electrons coexist with localized moments of Yb ions which can be described in terms of effective S=1/2 spins with a dominantly one-dimensional exchange interaction. The spin subsystem becomes critical in a relatively weak magnetic field, where it behaves like a Luttinger liquid. We theoretically examine a Kondo lattice with different effective space dimensionalities of the two interacting subsystems. We characterize the corresponding non-Fermi liquid behavior due to the spin criticality by calculating the electronic relaxation rate and the dc resistivity and establish its quasilinear temperature dependence.
3D non-Fermi liquid behavior from 1D quantum critical local moments
arXiv: Strongly Correlated Electrons, 2018
We study the temperature dependence of the electrical resistivity in a system composed of critical spin chains interacting with three dimensional conduction electrons and driven to criticality via an external magnetic field. The relevant experimental system is Yb$_2$Pt$_2$Pb, a metal where itinerant electrons coexist with localized moments of Yb-ions which can be described in terms of effective S = 1/2 spins with dominantly one-dimensional exchange interaction. The spin subsystem becomes critical in a relatively weak magnetic field, where it behaves like a Luttinger liquid. We theoretically examine a Kondo lattice with different effective space dimensionalities of the two interacting subsystems. We characterize the corresponding non-Fermi liquid behavior due to the spin criticality by calculating the electronic relaxation rate and the dc resistivity and establish its quasi linear temperature dependence.
Weak magnetism and non-Fermi liquids near heavy-fermion critical points
Physical Review B, 2004
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.
Non-Fermi liquid in a truncated two-dimensional Fermi surface
Physical Review B, 2003
Using perturbation theory and the field theoretical renormalization group approach we consider a two-dimensional anisotropic truncated Fermi Surface(F S) with both flat and curved sectors which approximately simulates the "cold" and "hot" spots in the cuprate superconductors. We calculate the one-particle two-loop irreducible functions Γ (2) and Γ (4) as well as the spin, the charge and pairing response functions up to one-loop order. We find non-trivial infrared stable fixed points and we show that there are important effects produced by the mixing of the existing scattering channels in higher order of perturbation theory. Our results indicate that the "cold " spots are turned into a non-Fermi liquid with divergents ∂Σ0/∂p0 and ∂Σ0/∂p, a vanishing Z and a finite Fermi velocity at F S when the effects produced by the flat portions are taken into account.
Scaling behaviour and superconducting instability in anisotropic non-Fermi liquids
Annals of Physics, 2017
We study the scaling behaviour of the optical conductivity (σ), free energy density (F) and shear viscosity of the quantum critical point associated with spin density wave phase transition for a two-dimensional metallic system with C 2 symmetry. A non-Fermi liquid behaviour emerges at two pairs of isolated points on the Fermi surface due to the coupling of a bosonic order parameter to fermionic excitations at those so-called "hot-spots". We find that near the hot-spots, σ and F obey the scalings expected for such an anisotropic system, and the direction-dependent viscosity to entropy density ratio is not a universal number due to the anisotropy. Lastly, we also estimate the effect of the fermion-boson coupling at the hot-spots on superconducting instabilities.
Physical Review B, 2016
All superconductors known so far exhibit pairing of electrons into a state with vanishing total momentum. In the presence of a finite difference in the population of electrons with opposite spin it is possible, however, that pairs with finite momentum condense in the ground state. The associated periodic modulation of the superconducting order parameter has not been observed to date; but there is indirect experimental evidence for such an exotic type of pairing in 2D organic superconductors. Here, we show that the normal state above a 2D superconductor with finite momentum pairs exhibits a new strange metal phase at low temperatures. It has no proper electronic quasiparticles over parts of the Fermi surface and leads to anomalies both in thermodynamics and response functions. In particular, the specific heat and NMR-relaxation rate exhibit nontrivial power laws at low temperature, consistent with experimental data on 2D organic superconductors.