David R. Reichman

Heinrich-Heine-Universität Düsseldorf, Düsseldorf, North Rhine-Westphalia, Germany

Are you David R. Reichman?

Claim your profile

Publications (162)864.43 Total impact

  • Hsing-Ta Chen · Guy Cohen · Andrew J. Millis · David R. Reichman
    [Show abstract] [Hide abstract]
    ABSTRACT: The dynamical interplay between electron--electron interactions and electron--phonon coupling is investigated within the Anderson--Holstein model, a minimal model for open quantum systems that embody these effects. The influence of phonons on spectral and transport properties is explored in equilibrium, for non-equilibrium steady state and for transient dynamics after a quench. Both the particle--hole symmetric and the more generic particle--hole asymmetric cases are studied. The treatment is based on two complementary non-crossing approximations, the first of which is constructed around the weak-coupling limit and the second around the polaron limit. In general, the two methods disagree in nontrivial ways, indicating that more reliable approaches to the problem are needed. The frameworks used here can form the starting point for numerically exact methods based on bold-line continuous-time quantum Monte Carlo algorithms capable of treating open systems simultaneously coupled to multiple fermionic and bosonic baths.
    No preview · Article · Jan 2016
  • Hsing-Ta Chen · David R. Reichman
    [Show abstract] [Hide abstract]
    ABSTRACT: We perform extensive benchmark comparisons of surface hopping dynamics with numerically exact calculations for the spin-boson model over a wide range of energetic and coupling parameters as well as temperature. We find that deviations from golden-rule scaling in the Marcus regime are generally small and depend sensitively on the energetic bias between electronic states. Fewest switched surface hopping (FSSH) is found to be surprisingly accurate over a large swath of parameter space. The inclusion of decoherence corrections via the augmented FSSH (A-FSSH) algorithm improves the accuracy of dynamical behavior compared to exact simulations, but the effects are generally not dramatic, at least for the case of an environment modeled with the commonly used Debye spectral density.
    No preview · Article · Jan 2016
  • Liesbeth M. C. Janssen · Peter Mayer · David R. Reichman
    [Show abstract] [Hide abstract]
    ABSTRACT: We present an extensive treatment of the generalized mode-coupling theory (GMCT) of the glass transition, which seeks to describe the dynamics of glass-forming liquids using only static structural information as input. This theory amounts to an infinite hierarchy of coupled equations for multi-point density correlations, the lowest-order closure of which is equivalent to standard mode-coupling theory. Here we focus on simplified schematic GMCT hierarchies, which lack any explicit wavevector-dependence and therefore allow for greater analytical and numerical tractability. For one particular schematic model, we derive the unique analytic solution of the infinite hierarchy, and demonstrate that closing the hierarchy at finite order leads to uniform convergence as the closure level increases. We also show numerically that a similarly robust convergence pattern emerges for more generic schematic GMCT models, suggesting that the GMCT framework is generally convergent, even though no small parameter exists in the theory. Finally, we discuss how different effective weights on the high-order contributions ultimately control whether the transition is continuous, discontinuous, or strictly avoided, providing new means to relate structure to dynamics in glass-forming systems.
    No preview · Article · Oct 2015
  • Guy Cohen · Emanuel Gull · David. R. Reichman · Andrew J. Millis
    [Show abstract] [Hide abstract]
    ABSTRACT: Current nonequilibrium Monte Carlo methods suffer from a dynamical sign problem that makes simulating real-time dynamics for long times exponentially hard. We propose a new `Inchworm Algorithm', based on iteratively reusing information obtained in previous steps to extend the propagation to longer times. The algorithm largely overcomes the dynamical sign problem, changing the scaling from exponential to quadratic. We use the method to solve the Anderson impurity model in the Kondo and mixed valence regimes, obtaining results both for quenches and for spin dynamics in the presence of an oscillatory magnetic field.
    No preview · Article · Oct 2015 · Physical Review Letters
  • Source
    R. Härtle · G. Cohen · D. R. Reichman · A. J. Millis
    [Show abstract] [Hide abstract]
    ABSTRACT: We give a detailed comparison of the hierarchical quantum master equation (HQME) method to a continuous-time quantum Monte Carlo (CT-QMC) approach, assessing the usability of these numerically exact schemes as impurity solvers in practical nonequilibrium calculations. We review the main characteristics of the methods and discuss the scaling of the associated numerical effort. We substantiate our discussion with explicit numerical results for the nonequilibrium transport properties of a single-site Anderson impurity. The numerical effort of the HQME scheme scales linearly with the simulation time but increases (at worst exponentially) with decreasing temperature. In contrast, CT-QMC is less restricted by temperature at short times, but in general the cost of going to longer times is also exponential. After establishing the numerical exactness of the HQME scheme, we use it to elucidate the influence of the applied bias voltage on the initial dynamics, discuss the phenomenon of coherent current oscillations, known as current ringing, and explain the non-monotonic temperature dependence of the steady-state magnetization as a result of broadening.
    Full-text · Article · Aug 2015 · Physical Review B
  • Source
    Yevgeny Bar Lev · David R. Reichman
    [Show abstract] [Hide abstract]
    ABSTRACT: We study the real-time dynamics of a two-dimensional Anderson--Hubbard model using nonequilibrium self-consistent perturbation theory within the second-Born approximation. When compared with exact diagonalization performed on small clusters, we demonstrate that for strong disorder this technique approaches the exact result on all available timescales, while for intermediate disorder, in the vicinity of the many-body localization transition, it produces quantitatively accurate results up to nontrivial times. Our method allows for the treatment of system sizes inaccessible by any numerically exact method and for the complete elimination of finite size effects for the largest times considered. We show that for a sufficiently strong disorder the system becomes nonergodic, while for intermediate disorder strengths and for all accessible time scales transport in the system is strictly subdiffusive. We argue that these results are incompatible with a simple percolation picture. Our results are consistent with the heuristic random resistor network model where subdiffusion may be observed for long times until a crossover to diffusion occurs. The prediction of a broad subdiffusive regime in a two-dimensional interacting and disordered system can be directly verified in future cold atoms experiments.
    Preview · Article · Aug 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Ground state diffusion Monte Carlo is used to investigate the binding energies and carrier probability distributions of excitons, trions, and biexcitons in a variety of two-dimensional transition metal dichalcogenide materials. We compare these results to approximate variational calculations, as well as to analogous Monte Carlo calculations performed with simplified carrier interaction potentials. Our results highlight the successes and failures of approximate approaches as well as the physical features that determine the stability of small carrier complexes in monolayer transition metal dichalcogenide materials. Lastly, we discuss points of agreement and disagreement with recent experiments.
    Preview · Article · Aug 2015 · Physical Review B
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a new, computationally inexpensive method for the calculation of reduced density matrix dynamics for systems with a potentially large number of subsystem degrees of freedom coupled to a generic bath. The approach consists of propagation of weak-coupling Redfield-like equations for the high frequency bath degrees of freedom only, while the low frequency bath modes are dynamically arrested but statistically sampled. We examine the improvements afforded by this approximation by comparing with exact results for the spin-boson model over a wide range of parameter space. The results from the method are found to dramatically improve Redfield dynamics in highly non--Markovian regimes, at a similar computational cost. Relaxation of the mode-freezing approximation via classical (Ehrenfest) evolution of the low frequency modes results in a dynamical hybrid method. We find that this Redfield-based dynamical hybrid approach, which is computationally more expensive than bare Redfield dynamics, yields only a marginal improvement over the simpler approximation of complete mode arrest.
    Preview · Article · Jul 2015 · The Journal of Chemical Physics
  • Source
    Liesbeth M. C. Janssen · David R. Reichman
    [Show abstract] [Hide abstract]
    ABSTRACT: Glasses are solid materials whose constituent atoms are arranged in a disordered manner. The transition from a liquid to a glass remains one of the most poorly understood phenomena in condensed matter physics, and still no fully microscopic theory exists that can describe the dynamics of supercooled liquids in a quantitative manner over all relevant time scales. Here we present such a theoretical framework that yields near-quantitative accuracy for the time-dependent correlation functions of a supercooled system over a broad density range. Our approach requires only simple static structural information as input and is based entirely based on first principles. Owing to this first-principles nature, the framework offers a unique platform to study the relation between structure and dynamics in glass-forming matter, and paves the way towards a systematically correctable and ultimately fully quantitative theory of microscopic glassy dynamics.
    Preview · Article · Jul 2015 · Physical Review Letters
  • Source
    Timothy C. Berkelbach · Mark S. Hybertsen · David R. Reichman
    [Show abstract] [Hide abstract]
    ABSTRACT: We discuss the linear and two-photon spectroscopic selection rules for spin-singlet excitons in monolayer transition metal dichalcogenides. Our microscopic formalism combines a fully $k$-dependent few-orbital band structure with a many-body Bethe-Salpeter equation treatment of the electron-hole interaction, using a model dielectric function. We show analytically and numerically that the single-particle, valley-dependent selection rules are preserved in the presence of excitonic effects. Furthermore, we definitively demonstrate that the bright (one-photon allowed) excitons have $s$-type azimuthal symmetry and that dark $p$-type excitons can be probed via two-photon spectroscopy. The screened Coulomb interaction in these materials substantially deviates from the $1/\varepsilon_0 r$ form; this breaks the "accidental" angular momentum degeneracy in the exciton spectrum, such that the 2$p$ exciton has a lower energy than the 2$s$ exciton by at least 50 meV. We compare our calculated two-photon absorption spectra to recent experimental measurements.
    Preview · Article · May 2015 · Physical Review B
  • [Show abstract] [Hide abstract]
    ABSTRACT: Transition metal dichalcogenide (TMDC) crystals exhibit new emergent properties at monolayer thickness, notably strong many-body effects mediated by Coulomb interactions. A manifestation of these many-body interactions is the formation of excitons, bound electron-hole pairs, but higher-order excitonic states are also possible. Here we demonstrate the existence of four-body, biexciton states in monolayer WSe 2. The biexciton is identified as a sharply defined state in photoluminescence at high exciton density. Its binding energy of 52 meV is more than an order of magnitude greater than that found in conventional quantum-well structures. A variational calculation of the biexciton state reveals that the high binding energy arises not only from strong carrier confinement, but also from reduced and non-local dielectric screening. These results open the way for the creation of new correlated excitonic states linking the degenerate valleys in TMDC crystals, as well as more complex many-body states such as exciton condensates or the recently reported dropletons.
    No preview · Article · May 2015 · Nature Physics
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have identified excited exciton states in monolayers of MoS2 and WS2 supported on fused silica by means of photoluminescence excitation spectroscopy. In monolayer WS2, the positions of the excited A exciton states imply an exciton binding energy of 0.32 eV. In monolayer MoS2, excited exciton transitions are observed at energies of 2.24 and 2.34 eV. Assigning these states to the B exciton Rydberg series yields an exciton binding energy of 0.44 eV.Keywords: Transition metal dichalcogenides; molybdenum disulfide; tungsten disulfide; 2D materials; binding energy; excitons
    No preview · Article · Mar 2015 · Nano Letters
  • Source
    Glen M Hocky · Ludovic Berthier · David R. Reichman
    [Show abstract] [Hide abstract]
    ABSTRACT: Ultrastable glasses have risen to prominence due to their potentially useful material properties and the tantalizing possibility of a general method of preparation via vapor deposition. Despite the importance of this novel class of amorphous materials, numerical studies have been scarce because achieving ultrastability in atomistic simulations is an enormous challenge. Here, we bypass this difficulty and establish that randomly pinning the position of a small fraction of particles inside an equilibrated supercooled liquid generates ultrastable configurations at essentially no numerical cost, while avoiding undesired structural changes due to the preparation protocol. Building on the analogy with vapor-deposited ultrastable glasses, we study the melting kinetics of these configurations following a sudden temperature jump into the liquid phase. In homogeneous geometries, we find that enhanced kinetic stability is accompanied by large scale dynamic heterogeneity, while a competition between homogeneous and heterogeneous melting is observed when a liquid boundary invades the glass at constant velocity. Our work demonstrates the feasibility of large-scale, atomistically resolved, and experimentally relevant simulations of the kinetics of ultrastable glasses.
    Preview · Article · Sep 2014 · The Journal of Chemical Physics
  • Source
    Timothy C Berkelbach · Mark S Hybertsen · David R Reichman
    [Show abstract] [Hide abstract]
    ABSTRACT: We extend our previous work on singlet exciton fission in isolated dimers to the case of crystalline materials, focusing on pentacene as a canonical and concrete example. We discuss the proper interpretation of the character of low-lying excited states of relevance to singlet fission. In particular, we consider a variety of metrics for measuring charge-transfer character, conclusively demonstrating significant charge-transfer character in the low-lying excited states. The impact of this electronic structure on the subsequent singlet fission dynamics is assessed by performing real-time master-equation calculations involving hundreds of quantum states. We make direct comparisons with experimental absorption spectra and singlet fission rates, finding good quantitative agreement in both cases, and we discuss the mechanistic distinctions that exist between small isolated aggregates and bulk systems.
    Preview · Article · Aug 2014 · The Journal of Chemical Physics
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have experimentally determined the energies of the ground and first four excited excitonic states of the fundamental optical transition in monolayer WS_{2}, a model system for the growing class of atomically thin two-dimensional semiconductor crystals. From the spectra, we establish a large exciton binding energy of 0.32 eV and a pronounced deviation from the usual hydrogenic Rydberg series of energy levels of the excitonic states. We explain both of these results using a microscopic theory in which the nonlocal nature of the effective dielectric screening modifies the functional form of the Coulomb interaction. These strong but unconventional electron-hole interactions are expected to be ubiquitous in atomically thin materials.
    No preview · Article · Aug 2014 · Physical Review Letters
  • Source
    Yevgeny Bar Lev · Guy Cohen · David R. Reichman
    [Show abstract] [Hide abstract]
    ABSTRACT: We study the infinite temperature dynamics of a prototypical one-dimensional system expected to exhibit many-body localization. Using numerically exact methods, we establish the dynamical phase diagram of this system based on the statistics of its eigenvalues and its dynamical behavior. We show that the non-ergodic phase is re-entrant as a function of the interaction strength, illustrating that localization can be reinforced by sufficiently strong interactions even at infinite temperature. Surprisingly, within the accessible time range, the ergodic phase shows sub-diffusive behavior, suggesting that the diffusion coefficient vanishes throughout much of the phase diagram in the thermodynamic limit. Our findings strongly suggest that Wigner-Dyson statistics of eigenvalue spacings may appear in a class of ergodic but sub-diffusive systems.
    Full-text · Article · Jul 2014 · Physical Review Letters
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have measured the single-molecule conductance of a family of oligothiophenes comprising one to six thiophene moieties terminated with methyl-sulfide linkers using the scanning tunneling microscope based break-junction technique. We find an anomalous behavior: the peak of the conductance histogram distribution does not follow a clear exponential decay with increasing number of thiophene units in the chain. The electronic properties of the materials were characterized by optical spectroscopy and electrochemistry to gain an understanding of the factors affecting the conductance of these molecules. We postulate that different conformers in the junction are a contributing factor to the anomalous trend in the observed conductance as a function of molecule length.
    No preview · Article · Jul 2014 · Journal of the American Chemical Society
  • [Show abstract] [Hide abstract]
    ABSTRACT: Singlet fission, the conversion of a singlet excitation into two triplet excitations, is a viable route to improved solar-cell efficiency. Despite active efforts to understand the singlet fission mechanism, which would aid in the rational design of new materials, a comprehensive understanding of mechanistic principles is still lacking. Here, we present the first study of singlet fission in crystalline hexacene which, together with tetracene and pentacene, enables the elucidation of mechanistic trends. We characterize the static and transient optical absorption and combine our findings with a theoretical analysis of the relevant electronic couplings and rates. We find a singlet fission time scale of 530 fs, which is orders of magnitude faster than tetracene (10–100 ps) but significantly slower than pentacene (80–110 fs). We interpret this increased time scale as a multiphonon relaxation effect originating from a large exothermicity and present a microscopic theory that quantitatively reproduces the rates in the acene family.
    No preview · Article · Jul 2014 · Journal of the American Chemical Society
  • [Show abstract] [Hide abstract]
    ABSTRACT: Molybdenum disulfide bilayers with well-defined interlayer twist angle were constructed by stacking single-crystal monolayers. Varying interlayer twist angle results in strong tuning of the indirect optical transition energy and second-harmonic generation and weak tuning of direct optical transition energies and Raman mode frequencies. Electronic structure calculations show the interlayer separation changes with twist due to repulsion between sulfur atoms, resulting in shifts of the indirect optical transition energies. These results show that interlayer alignment is a crucial variable in tailoring the properties of two-dimensional heterostructures.
    No preview · Article · Jun 2014 · Nano Letters
  • [Show abstract] [Hide abstract]
    ABSTRACT: Excitons are studied experimentally and theoretically in atomically thin WS2 layers. We find a binding energy of 0.32eV as well as non-hydrogenic behavior of the exciton states due to the non-uniformity of the dielectric environment.
    No preview · Conference Paper · Jun 2014

Publication Stats

6k Citations
864.43 Total Impact Points

Institutions

  • 2015
    • Heinrich-Heine-Universität Düsseldorf
      • Institute for Theoretical Physics II.
      Düsseldorf, North Rhine-Westphalia, Germany
  • 2005-2015
    • Columbia University
      • Department of Chemistry
      New York, New York, United States
  • 2009
    • Boston University
      Boston, Massachusetts, United States
  • 2001-2007
    • Harvard University
      • Department of Chemistry and Chemical Biology
      Cambridge, Massachusetts, United States
  • 2000
    • University of Utah
      • Department of Chemistry
      Salt Lake City, Utah, United States
  • 1996-1997
    • Massachusetts Institute of Technology
      • • Department of Materials Science and Engineering
      • • Department of Chemistry
      Cambridge, MA, United States