Non-Fermi-liquid behavior and anomalous suppression of Landau damping in layered metals close to ferromagnetism

We analyse the low-energy physics of nearly ferromagnetic metals in two spatial dimensions using the functional renormalization group technique. We find a new low-energy fixed point, at which the fermionic (electron-like) excitations are non-Fermi-liquid ($z_f = 13/10$) and the magnetic fluctuations exhibit an anomalous Landau damping whose rate vanishes as $\Gamma_{\bf q} \sim \vert {\bf q} \vert^{3/5}$ in the low-$\vert {\bf q} \vert$ limit. We discuss this renormalization of the Landau-damping exponent, which is the major novel prediction of our work, and highlight the possible link between that renormalization and neutron-scattering data on UGe$_2$ and related compounds. Implications of our analysis for YFe$_2$Al$_{10}$ are also discussed.Comment: 5 pages, 3 figures; action modified to include spin of fermions, resulting in quantitative changes to exponents but same essential physic

What is the origin of the intermediate-temperature magnetic specific heat capacity in the spin-liquid candidate Ca10_{10}Cr7_7O28_{28}?

We present several approximate calculations of the specific heat capacity of the model for Ca$_{10}$Cr$_7$O$_{28}$ proposed by Balz et al. [Phys. Rev. B 95, 174414 (2017)], using methods including exact diagonalization, Thermal Pure Quantum States, and high-temperature expansions. In none of these cases are we able to reproduce the magnitude of the zero-field specific heat capacity shown in the intermediate-temperature $({\sim}\,5-15\,\rm{K})$ experimental data. We discuss possible reasons for the discrepancy, and what it might tell us about the magnetic Hamiltonian for Ca$_{10}$Cr$_7$O$_{28}$

Thermal versus quantum fluctuations of optical-lattice fermions

We show that, for fermionic atoms in a one-dimensional optical lattice, the fraction of atoms in doubly occupied sites is a highly nonmonotonic function of temperature. We demonstrate that this property persists even in the presence of realistic harmonic confinement, and that it leads to a suppression of entropy at intermediate temperatures that offers a route to adiabatic cooling. Our interpretation of the suppression is that such intermediate temperatures are simultaneously too high for quantum coherence and too low for significant thermal excitation of double occupancy thus offering a clear indicator of the onset of quantum fluctuations.Publisher PDFPeer reviewe

Infinite-redshift localized states of Dirac fermions under Einsteinian gravity

We present a set of localized states for an even number of Dirac fermions under Einsteinian gravity that have an infinite central redshift. Near the center of the localized state the components of the Dirac spinor and the spacetime metric all show simple power-law dependences on the radial distance; further out the fermionic wave function decays to zero and the spacetime becomes asymptotically flat. We show that this "central"solution of the equations of motion can be used to understand much of the structure observed by Finster, Smoller, and Yau [Phys. Rev. D 59, 104020 (1999)] in their numerical solutions of the same problem at finite central redshift.Publisher PDFPeer reviewe

Fisher zeros and persistent temporal oscillations in nonunitary quantum circuits

Funding: UK Engineering and Physical Sciences Research Council (EPSRC) grant EP/R031924/1.We present a quantum circuit with measurements and postselection that exhibits a panoply of space- and/or time-ordered phases from ferromagnetic order to spin-density waves to time crystals. Unlike the time crystals that have been found in unitary models, those that occur here are incommensurate with the drive frequency. The period of the incommensurate time-crystal phase may be tuned by adjusting the circuit parameters. We demonstrate that the phases of our quantum circuit, including the inherently nonequilibrium dynamical ones, correspond to complex-temperature equilibrium phases of the exactly solvable square-lattice anisotropic Ising model.Publisher PDFPeer reviewe

Exploring Scotland's career ecosystem

This report explores career services for young people (up to the age of 25) in Scotland. It describes the overall organisation of career services in the country (what we describe as an ‘ecosystem’), compares it with six other countries and considers options for the development of these services.Skills Development Scotlan

Non-Fermi liquid fixed points and anomalous Landau damping in a quantum critical metal

Funding: CM-CDT under UK Engineering and Physical Sciences Research Council (EPSRC) (UK) Grant No. EP/L015110/1 (M.J.T.); TOPNES programme under EPSRC (UK) Grant No. EP/I031014/1 (C.A.H.).We present a functional renormalization-group calculation of the properties of a quantum critical metal in d=2 spatial dimensions. Our theory describes a general class of Pomeranchuk instabilities with Nb flavors of boson. At small Nb we find a family of fixed points characterized by weakly non-Fermi-liquid behavior of the conduction electrons and z≈2 critical dynamics for the order-parameter fluctuations, in agreement with the scaling observed by Schattner et al. [Phys. Rev. X 6, 031028 (2016)] for the Ising-nematic transition. Contrary to recent suggestions that this represents an intermediate regime en route to the scaling limit, our calculation suggests that this behavior may persist all the way to the critical point. As the number of bosons Nb is increased, the model's fixed-point properties cross over to z≈1 scaling and non-Fermi-liquid behavior similar to that obtained by Fitzpatrick et al. [Phys. Rev. B 88, 125116 (2013)].Publisher PDFPeer reviewe