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Register a new userSpatial behavior in a Mott insulator near the voltage-driven resistive transition
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We develop a real space theory of the voltage bias driven transition from a Mott insulator to a correlated metal. Within our Keldysh mean field approach the problem reduces to a self-consistency scheme for the charge and spin profiles in this open system. We solve this problem for a two dimensional antiferromagnetic Mott insulator at zero temperature. The charge and spin magnitude is uniform over the system at zero bias, but a bias $V$ leads to spatial modulation over a lengthscale $xi(V)$ near the edges. $xi(V)$ grows rapidly and becomes comparable to system size as $V$ increases towards a threshold scale $V_c$. The linear response conductance of the insulator is zero with the current being exponentially small for $V ll V_c$. The current increases rapidly as $V rightarrow V_c$. Beyond $V_c$, we observe an inhomogeneous low moment antiferromagnetic metal, and at even larger bias a current saturated paramagnetic metal. We suggest an approximate scheme for the spectral features of this nonequilibrium system.
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We use a Langevin dynamics approach to map out the thermal phases of an antiferromagnetic Mott insulator pushed out of equilibrium by a large voltage bias. The Mott insulator is realised in the half-filled Hubbard model in a three dimensional bar geometry with leads at voltage $pm V/2$ connected at the two ends. We decouple the strong Hubbard interaction via the combination of an auxiliary vector field, to capture magnetic fluctuations, and a homogeneous scalar field to maintain half-filling. The magnetic fluctuations are assumed to be slow on electronic timescales. At zero temperature our method reduces to Keldysh mean field theory and yields a voltage driven insulator-metal transition with hysteresis. The Langevin scheme generalises this, allowing us to study the finite temperature nonequilibrium steady state. We find an initially slow and then progressively rapid suppression of the Neel temperature $T_{N}$ and pseudogap temperature $T_{pg}$ with bias, and discover that the bias leads to a finite temperature insulator-metal transition. We explain the thermal results in terms of strong amplitude fluctuation of the local moments in the first order landscape.
We present a new type of colossal magnetoresistance (CMR) arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti-doped Ca$_3$Ru$_2$O$_7$. Such an insulator-metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott-Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin-lattice-charge coupling. This study further provides a model approach to search for CMR systems other than manganites, such as Mott insulators in the vicinity of the boundary between competing phases.
Since the beginnings of the electronic age, a quest for ever faster and smaller switches has been initiated, since this element is ubiquitous and foundational in any electronic circuit to regulate the flow of current. Mott insulators are promising candidates to meet this need as they undergo extremely fast resistive switching under electric field. However the mechanism of this transition is still under debate. Our spatially-resolved {mu}-XRD imaging experiments carried out on the prototypal Mott insulator (V0.95Cr0.05)2O3 show that the resistive switching is associated with the creation of a conducting filamentary path consisting in an isostructural compressed phase without any chemical nor symmetry change. This clearly evidences that the resistive switching mechanism is inherited from the bandwidth-controlled Mott transition. This discovery might hence ease the development of a new branch of electronics dubbed Mottronics.
We point out that fractionalized bosonic charge excitations can explain the recently discovered photo-induced superconducting-like response in $kappatext{-(ET})_2text{Cu}[text{N(CN)}_2]text{Br}$, an organic metal close to the Mott transition. The pump laser exerts a periodic drive on the fractionalized field, creating a non-equilibrium condensate, which gives a Drude peak much narrower than the equilibrium scattering rate, hence superconducting-like response. Our proposal illuminates new possibilities of detecting fractionalization and can be readily tested in spin liquid candidates and in cold atom systems.
I critically examine Goodenoughs explanation for the experimentally observed phase transition in LiVO$_2$ using microscopic calculations based on density functional and dynamical mean field theories. The high-temperature rhombohedral phase exhibits both magnetic and dynamical instabilities. Allowing a magnetic solution for the rhombohedral structure does not open an insulating gap, and an explicit treatment of the on-site Coulomb $U$ interaction is needed to stabilize an insulating rhombohedral phase. The non-spin-polarized phonon dispersions of the rhombohedral phase show two unstable phonon modes at the wave vector $(frac{1}{3},-frac{1}{3},0)$ that corresponds to the experimentally observed trimer forming instability. A full relaxation of the supercell corresponding to this instability yields a nonmagnetic state containing V$_3$ trimers. These results are consistent with Goodenoughs suggestion that the high-temperature phase is in the localized-electron regime and the transition to the low-temperature phase in the itinerant-electron regime is driven by V-V covalency.
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