Thomas Nattermann

Bio: Thomas Nattermann is an academic researcher from University of Cologne. The author has contributed to research in topics: Vortex & Superconductivity. The author has an hindex of 26, co-authored 103 publications receiving 2748 citations. Previous affiliations of Thomas Nattermann include Humboldt State University & Harvard University.

Vortex-glass phases in type-II superconductors

Abstract: A review is given on the theory of vortex-glass phases in impure type-II superconductors in an external field. We begin with a brief discussion of the effects of thermal fluctuations on the spontaneously broken U(1) and translation symmetries, on the global phase diagram and on the critical behaviour. Introducing disorder we restrict ourselves to the experimentally most relevant case of weak uncorrelated randomness which is known to destroy the long-ranged translational order of the Abrikosov lattice in three dimensions. Elucidating possible residual glassy ordered phases, we distinguish between positional and phase-coherent vortex glasses. The study of the behaviour of isolated vortex lines and their generalization directed elastic manifolds in a random potential introduces further important concepts for the characterization of glasses. The discussion of elastic vortex glasses, i.e. topologically ordered dislocation-free positional glasses in two and three dimensions occupy the main part of our review. I...

Scaling approach to pinning: Charge density waves and giant flux creep in superconductors.

Abstract: A general scaling approach to pinning and response in weakly disordered systems is developed that considers pinning at arbitrary high energy barriers. These are a consequence of a disordered T=0 renormalization-group fixed point which characterizes the condensed phase. Application to flux creep in superconductors yields a creep velocity \ensuremath{ u}(j)\ensuremath{\propto}exp-${\mathit{Cj}}^{\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\mu}}}$ where \ensuremath{\mu} is related to the roughness exponents \ensuremath{\zeta} of the flux-line lattice. We argue that \ensuremath{\zeta}=0(log) and \ensuremath{\mu}=(d-2)/2 as for charge-density waves.

Dynamics of Interface Depinning in a Disordered Medium

Abstract: The motion of an interface in a disordered medium driven by a constant force is one of the paradigms of condensed matter physics. Well known examples are domain walls in random magnets1 and interfaces between two immiscible fluids pushed through a porous medium2. Closely related problems include impurity pinning in type-II superconductors3 and in charge-density waves (CDWs)4. Despite the importance of these problems, significant progress has been made only recently by Nattermann et al. for interface motion5 (see also6) and by Narayan and Fisher for CDWs7.

Interface pinning and dynamics in random systems.

Abstract: A detailed low-temperature treatment of the domain wall or interface pinning by imperfections in disordered systems with discrete symmetry of the order parameter is presented. Crossover behavior as well as analogies between pinning mechanisms in different systems is analyzed. Pinning may arise from random bonds, when the disordering agents do not break the local symmetry of the order parameter, or from random fields, when the disordering agents do break this symmetry. The interface roughness and response to an external driving force are discussed. The model is explained for dilute magnetic systems in a uniform field where the magnetic domain walls are pinned by random fields and/or random bonds. The results are, however, more general and apply also to interfaces in other systems, e.g., in fluid-fluid interfaces, (anti)ferroelectrics, solitons in incommensurate systems, etc. The interface roughness and pinning pressure (force per unit area) are estimated for weak and strong pinning and their scaling relations to length scale, temperature, frequency, and disorder strength (concentration) are given. The interface contribution to the static and dynamic susceptibility at low temperatures is evaluated. Because of pinning, the low-temperature dynamical susceptibility of disordered ferromagnets in or out of equilibrium carries a [ln(1/\ensuremath{\omega})${]}^{2/\mathrm{\ensuremath{\theta}}}$ frequency dependence in addition to the Debye relaxation behavior. In particular, \ensuremath{\theta}=(d+1)/3 for random-field systems, and \ensuremath{\theta}(d=2)=1/3 and \ensuremath{\theta}(d=3)\ensuremath{\approxeq}0.83 for random-bond systems.

Pinning and sliding of driven elastic systems: from domain walls to charge density waves

Abstract: This review is devoted to the theory of collective and local pinning effects in various disordered nonlinear driven systems. A common feature of both approaches is the emergence of metastability. Although the emphasis is put on charge and spin density waves and magnetic domain walls, the theory also has applications to flux lines and lattices thereof, dislocation lines, adsorbed monolayers and related systems. In the first part of the article we focus on the theory of collective pinning which includes the equilibrium properties of elastic systems with frozen-in disorder as well as the features close to the dynamic depinning transition enforced by an external driving force. At zero temperature and for adiabatic changes of the force, the dynamic depinning transition is continuous, the correlation length is large, the behaviour is dominated by scaling laws with nontrivial static and dynamical critical indices. The application of functional renormalization group methods allows for the detailed description of both equilibrium as well as non-equilibrium properties. The depinning transition is also characterized by the appearance of new scaling laws. Thermal fluctuations smear out this transition and allow for a creep motion of the elastic objects even at small forces. The application of an ac-driving force also destroys the sharp transition which is replaced by a velocity hysteresis. The second part of the review is devoted to the picture of local pinning and its applications. Local theories apply in the region where correlation effects are less important, i.e. not too close to the depinning transition, at low temperatures, at high enough frequencies or velocities. The inclusion of plastic deformations results in a rich cross-over behaviour of the force–velocity relation as well as of the frequency dependence of the dynamic response. Being easily affected at higher frequencies or velocities, the local pinning becomes an easily accessed source of dispersion, relaxation and dissipation. The picture of the local pinning can be effectively used to explain experimental data: qualitatively and even quantitatively. The advantages come from the explicit treatment of metastable states, their creation and relaxation, and their relation to plasticity and topological defects. The local pinning recovers and exploits new elements of the energy landscape such as termination points of some branches or irreversibility of other ones related to generation of topological defects in the course of sliding. It also provides a clue

Bose-Einstein condensation in a gas of sodium atoms

Abstract: Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Non-equilibrium critical phenomena and phase transitions into absorbing states

Abstract: This review addresses recent developments in non-equilibrium statistical physics. Focusing on phase transitions from fluctuating phases into absorbing states, the universality class of directed percolation is investigated in detail. The survey gives a general introduction to various lattice models of directed percolation and studies their scaling properties, field-theoretic aspects, numerical techniques, as well as possible experimental realizations. In addition, several examples of absorbing-state transitions which do not belong to the directed percolation universality class will be discussed. As a closely related technique, we investigate the concept of damage spreading. It is shown that this technique is ambiguous to some extent, making it impossible to define chaotic and regular phases in stochastic non-equilibrium systems. Finally, we discuss various classes of depinning transitions in models for interface growth which are related to phase transitions into absorbing states.

Nonequilibrium Critical Phenomena and Phase Transitions into Absorbing States

Abstract: This review addresses recent developments in nonequilibrium statistical physics. Focusing on phase transitions from fluctuating phases into absorbing states, the universality class of directed percolation is investigated in detail. The survey gives a general introduction to various lattice models of directed percolation and studies their scaling properties, field-theoretic aspects, numerical techniques, as well as possible experimental realizations. In addition, several examples of absorbing-state transitions which do not belong to the directed percolation universality class will be discussed. As a closely related technique, we investigate the concept of damage spreading. It is shown that this technique is ambiguous to some extent, making it impossible to define chaotic and regular phases in stochastic nonequilibrium systems. Finally, we discuss various classes of depinning transitions in models for interface growth which are related to phase transitions into absorbing states.