Charge density wave in hidden order state of URu2_2Si2_2

We argue that the hidden order state in URu$_2$Si$_2$ will induce a charge density wave. The modulation vector of the charge density wave will be twice that of the hidden order state, $Q_{CDW} = 2Q_{HO}$. To illustrate how the charge density wave arises we use a Ginzburg-Landau theory that contains a coupling of the charge density wave amplitude to the square of the HO order parameter $\Delta_{HO}$. This simple analysis allows us to predict the intensity and temperature dependence of the charge density wave order parameter in terms of the susceptibilities and coupling constants used in the Ginzburg-Landau analysis.Comment: 8 pages, 4 figure

Driving denaturation: Nanoscale thermal transport as a probe of DNA melting

DNA denaturation has long been a subject of intense study due to its relationship to DNA transcription and its fundamental importance as a nonlinear, structural transition. Many aspects of this phenomenon, however, remain poorly understood. Existing models fit quite well with experimental results on the fraction of unbound base pairs versus temperature. Yet, these same models give incorrect results for other essential quantities. For example, the predicted base pair fluctuation timescales - relevant to transcription - are orders of magnitude different from those observed experimentally. Here, we demonstrate that nanoscale thermal transport can serve as a sensitive probe of the underlying microscopic mechanisms responsible for the dynamics of DNA denaturation. Specifically, we show that the heat transport properties of DNA are altered significantly and abruptly as it denaturates, and this alteration encodes detailed information on the dynamics of thermal fluctuations and their interaction along the chain. This finding allows for the unambiguous discrimination between models of DNA denaturation. Measuring the thermal conductance will thus shed new light on the nature of this important molecule.Comment: 7 pages, 2 figures (revised version) Accepted for publication in Physical Review E, Rapid Communication

Crossover behavior of the thermal conductance and Kramers' transition rate theory

Kramers' theory frames chemical reaction rates in solution as reactants overcoming a barrier in the presence of friction and noise. For weak coupling to the solution, the reaction rate is limited by the rate at which the solution can restore equilibrium after a subset of reactants have surmounted the barrier to become products. For strong coupling, there are always sufficiently energetic reactants. However, the solution returns many of the intermediate states back to the reactants before the product fully forms. Here, we demonstrate that the thermal conductance displays an analogous physical response to the friction and noise that drive the heat current through a material or structure. A crossover behavior emerges where the thermal reservoirs dominate the conductance at the extremes and only in the intermediate region are the intrinsic properties of the lattice manifest. Not only does this shed new light on Kramers' classic turnover problem, this result is significant for the design of devices for thermal management and other applications, as well as the proper simulation of transport at the nanoscale.Comment: 8 pages, 5 figures. Supplementary Information available at the journal publication or by request from the author

Topological quantization of energy transport in micro- and nano-mechanical lattices

Topological effects typically discussed in the context of quantum physics are emerging as one of the central paradigms of physics. Here, we demonstrate the role of topology in energy transport through dimerized micro- and nano-mechanical lattices in the classical regime, i.e., essentially "masses and springs". We show that the thermal conductance factorizes into topological and non-topological components. The former takes on three discrete values and arises due to the appearance of edge modes that prevent good contact between the heat reservoirs and the bulk, giving a length-independent reduction of the conductance. In essence, energy input at the boundary mostly stays there, an effect robust against disorder and nonlinearity. These results bridge two seemingly disconnected disciplines of physics, namely topology and thermal transport, and suggest ways to engineer thermal contacts, opening a direction to explore the ramifications of topological properties on nanoscale technology.Comment: 6 pages, 3 figures; Supplemental information included as an ancillary fil

Local Current Distribution and "Hot Spots" in the Integer Quantum Hall Regime

In a recent experiment, the local current distribution of a two-dimensional electron gas in the quantum Hall regime was probed by measuring the variation of the conductance due to local gating. The main experimental finding was the existence of "hot spots", i.e. regions with high degree of sensitivity to local gating, whose density increases as one approaches the quantum Hall transition. However, the direct connection between these "hot spots" and regions of high current flow is not clear. Here, based on a recent model for the quantum Hall transition consisting of a mixture of perfect and quantum links, the relation between the "hot spots" and the current distribution in the sample has been investigated. The model reproduces the observed dependence of the number and sizes of "hot spots" on the filling factor. It is further demonstrated that these "hot spots" are not located in regions where most of the current flows, but rather, in places where the currents flow both when injected from the left or from the right. A quantitative measure, the harmonic mean of these currents is introduced and correlates very well with the "hot spots" positions

Impurity induced bound states and proximity effect in a bilayer exciton condensate

The effect of impurities which induce local interlayer tunneling in bilayer exciton condensates is discussed. We show that a localized single fermion bound state emerges inside the gap for any strength of impurity scattering and calculate the dependence of the impurity state energy and wave function on the potential strength. We show that such an impurity induced single fermion state enhances the interlayer coherence around it, and is similar to the superconducting proximity effect. As a direct consequence of these single impurity states, we predict that a finite concentration of such impurities will increase the critical temperature for exciton condensation.Comment: 4 pages, 2 figure

Pair correlations and the survival of superconductivity in and around a super-conducting impurity

The problem of the survival of superconductivity in a small super-conducting grain placed in a metal substrate is addressed. For this aim the pair correlations and super-conducting gap around and inside a negative-U impurity in one and two dimensions is calculated, in a discrete tight-binding model and a continuous model. Using the Hartree-Fock-Gorkov mean-field decomposition, it is found that pairing inside the gap occurs when the system has a degeneracy between successive number of electron pairs, and is highly sensitive to the chemical potential. For finite pairing in the island, pair correlations in the normal part may either decay exponentially or be long-ranged, depending on the strength of interaction. In addition, it is shown analytically that there is a minimal island size under-which pairing vanishes, and that it scales as a power-law, rather then exponentially as in isolated grains. These results are interpreted in terms of screening of the negative-U impurity by the electron gas.Comment: Accepted for publication in Phys.Rev.

Angular dependence of the magnetic-field driven superconductor-insulator transition in thin films of amorphous indium-oxide

A significant anisotropy of the magnetic-field driven superconductor-insulator transition is observed in thin films of amorphous indium-oxide. The anisotropy is largest for more disordered films which have a lower transition field. At higher magnetic field the anisotropy reduces and even changes sign beyond a sample specific and temperature independent magnetic field value. The data are consistent with the existence of more that one mechanism affecting transport at high magnetic fields.Comment: 4 pages, 5 figure