Collinear and noncollinear spin ground state of wurtzite CoO

We investigate the quantum mechanical origin of resistive phase transitions in solids driven by a constant electric field in the vicinity of a metal-insulator transition. We perform a nonequilibrium mean-field analysis of a driven-dissipative anti-ferromagnet, which we solve analytically for the most part. We find that the insulator-to-metal transition (IMT) and the metal-to-insulator transition (MIT) proceed by two distinct electronic mechanisms: Landau-Zener processes, and the destabilization of metallic state by Joule heating, respectively. However, we show that both regimes can be unified in a common effective thermal description, where the effective temperature T eff depends on the state of the system. This explains recent experimental measurements in which the hot-electron temperature at the IMT was found to match the equilibrium transition temperature. Our analytic approach enables us to formulate testable predictions on the non-analytic behavior of I-V relation near the insulator-to-metal transition. Building on these successes, we propose an effective Ginzburg-Landau theory which paves the way to incorporating spatial fluctuations, and to bringing the theory closer to a realistic description of the resistive switchings in correlated materials.

Section: A Elementary Case: Single-band Metalmentioning

confidence: 99%

Nonequilibrium mean-field theory of resistive phase transitions

Han

Aron

et al. 2018

“…We introduce a dissipative lattice model which consists of tight-binding Hamiltonian coupled to bath systems with open boundary. We solve the problem strictly within the given Hamiltonian according to the Keldysh formalism, and as established previously 13,[28][29][30] , the coupling to infinite degrees of freedom facilitates the infinitetime limit for steady-states under a dc electric field. We use fermion baths to mimic the continuous medium for Ohmic dissipation.…”

Section: A Modelmentioning

confidence: 99%

“…On the other hand, the optical phonons have a large gap ω ph and interact strongly with electrons only through higher-energy processes. It is argued that the dissipation by acoustic phonons is described by considering the exactly soluble fermion-reservoir model 28 . In the regime of small dissipation, this model reproduces successfully the Boltzmann transport theory and gives the correct linear response behavior 13,29 .…”

Section: A Modelmentioning

confidence: 99%

“…To investigate the transport mechanism, we start from a conventional quantum mechanical tight-binding model for graphene lattice with coupling to on-site phonons to simulate the optical phonons. In addition, we implement the dissipation mechanism in the form of fermion baths 28,29 to mimic the dissipation into an infinite medium which is essential to establish a rigorous steadystate nonequilibrium limit within the defined Hamiltonian. We use the Keldysh formalism 13 to obtain the steady-state Green's function (GF) and then transport quantities.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Nonequilibrium excitations and transport of Dirac electrons in electric-field-driven graphene

Han

2018

We investigate nonequilibrium excitations and charge transport in charge-neutral graphene driven with dc electric field by using the nonequilibrium Green's function technique. Due to the vanishing Fermi surface, electrons are subject to non-trivial nonequilibrium excitations such as highly anisotropic momentum distribution of electron-hole pairs, an analog of the Schwinger effect. We show that the electron-hole excitations, initiated by the Landau-Zener tunneling with a superlinear IV relation I ∝ E 3/2 , reaches a steady state dominated by the dissipation due to optical phonons, resulting in a marginally sublinear IV with I ∝ E, in agreement with recent experiments. The linear IV starts to show the sign of current saturation as the graphene is doped away from the Dirac point, and recovers the semi-classical relation for the saturated velocity. We give a detailed discussion on the nonequilibrium charge creation and the relation between the electron-phonon scattering rate and the electric field in the steady-state limit. We explain how the apparent Ohmic IV is recovered near the Dirac point. We propose a mechanism where the peculiar nonequilibrium electron-hole creation can be utilized in an infra-red device.

“…Bloch oscillations can be suppressed by dissipation through coupling the system to a bath. Earlier literature shows that even at a single-particle level, coupling the system to a phonon bath [32] or a fermionic bath [33] results in a finite DC response at any value of the coupling strength; however for the case of coupling to a phonon bath, signatures of the Wannier-Stark ladder are still evident in the spectral function, which are found to diminish with increasing electron-phonon coupling [34]. Recent works have also considered the effect of correlations in dissipative models.…”

Section: Introductionmentioning

confidence: 99%

Keldysh field theory of a driven dissipative Mott insulator: Nonequilibrium response and phase transitions

Sankar

Tripathi

2019

Understanding strongly correlated systems driven out of equilibrium is a challenging task necessitating the simultaneous treatment of quantum mechanics, dynamical constraints and strong interactions. A Mott insulator subjected to a uniform and static electric field is prototypical, raising key questions such as the fate of Bloch oscillations with increasing correlation strength, the approach to a steady state DC transport regime and the role of dissipation in it, and electric field driven phase transitions. Despite tremendous efforts over the last decade employing various numerical and analytical approaches, the manner in which a nonequilibrium steady state gets established has remained an unresolved problem. We develop here an effective large-N Keldysh field theory for studying nonequilibrium transport in a regular one-dimensional dissipative Mott insulator system subjected to a uniform electric field. Upon abruptly turning on the electric field (a quench), a transient oscillatory current response reminiscent of Bloch oscillations is found. In the regime of small tunneling conductance the amplitude of these oscillations, over a large time window, decreases as an inverse square power-law in time, ultimately going over to an exponential decay beyond a large characteristic time τ d that increases with N . Such a relaxation to a steady state DC response is absent in the dissipation free Hubbard chain at half filling. The steady state current at small fields is governed by large distance cotunneling, a process absent in the equilibrium counterpart.The low-field DC current has a Landau-Zener-Schwinger form but qualitatively differs from the expression for pair-production probability for the dissipation free counterpart. The breakdown of perturbation theory in the Mott phase possibly signals a nonequilibrium phase transition to a metallic phase. Our study sheds light on the approach of a driven, dissipative strongly correlated system to a nonequilibrium steady state and also provides a general analytic microscopic framework for understanding other nonequilibrium phenomena in these systems.