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@ARTICLE{Nghiem:808745,
      author       = {Nghiem, Hoa and Kennes, D. M. and Klöckner, C. and Meden,
                      V. and Costi, Theodoulos},
      title        = {{O}hmic two-state system from the perspective of the
                      interacting resonant level model: {T}hermodynamics and
                      transient dynamics},
      journal      = {Physical review / B},
      volume       = {93},
      number       = {16},
      issn         = {2469-9950},
      address      = {College Park, Md.},
      publisher    = {APS},
      reportid     = {FZJ-2016-02366},
      pages        = {165130},
      year         = {2016},
      abstract     = {We investigate the thermodynamics and transient dynamics of
                      the (unbiased) Ohmic two-state system by exploiting the
                      equivalence of this model to the interacting resonant level
                      model. For the thermodynamics, we show, by using the
                      numerical renormalization group (NRG) method, how the
                      universal specific heat and susceptibility curves evolve
                      with increasing dissipation strength α from those of an
                      isolated two-level system at vanishingly small dissipation
                      strength, with the characteristic activatedlike behavior in
                      this limit, to those of the isotropic Kondo model in the
                      limit α→1−. At any finite α>0, and for sufficiently
                      low temperature, the behavior of the thermodynamics is that
                      of a gapless renormalized Fermi liquid. Our results compare
                      well with available Bethe ansatz calculations at rational
                      values of α, but go beyond these, since our NRG
                      calculations, via the interacting resonant level model, can
                      be carried out efficiently and accurately for arbitrary
                      dissipation strengths 0≤α<1−. We verify the dramatic
                      renormalization of the low-energy thermodynamic scale T0
                      with increasing α, finding excellent agreement between NRG
                      and density matrix renormalization group (DMRG) approaches.
                      For the zero-temperature transient dynamics of the two-level
                      system, P(t)=⟨σz(t)⟩, with initial-state preparation
                      P(t≤0)=+1, we apply the time-dependent extension of the
                      NRG (TDNRG) to the interacting resonant level model, and
                      compare the results obtained with those from the
                      noninteracting-blip approximation (NIBA), the functional
                      renormalization group (FRG), and the time-dependent density
                      matrix renormalization group (TD-DMRG). We demonstrate
                      excellent agreement on short to intermediate time scales
                      between TDNRG and TD-DMRG for 0≲α≲0.9 for P(t), and
                      between TDNRG and FRG in the vicinity of α=12. Furthermore,
                      we quantify the error in the NIBA for a range of α, finding
                      significant errors in the latter even for 0.1≤α≤0.4. We
                      also briefly discuss why the long-time errors in the present
                      formulation of the TDNRG prevent an investigation of the
                      crossover between coherent and incoherent dynamics. Our
                      results for P(t) at short to intermediate times could act as
                      useful benchmarks for the development of new techniques to
                      simulate the transient dynamics of spin-boson problems},
      cin          = {IAS-3 / PGI-2 / JARA-HPC},
      ddc          = {530},
      cid          = {I:(DE-Juel1)IAS-3-20090406 / I:(DE-Juel1)PGI-2-20110106 /
                      $I:(DE-82)080012_20140620$},
      pnm          = {142 - Controlling Spin-Based Phenomena (POF3-142) /
                      Thermoelectric properties of molecular quantum dots and
                      time-dependent response of quantum dots $(jiff23_20140501)$},
      pid          = {G:(DE-HGF)POF3-142 / $G:(DE-Juel1)jiff23_20140501$},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000374537600004},
      doi          = {10.1103/PhysRevB.93.165130},
      url          = {https://juser.fz-juelich.de/record/808745},
}