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D. N. Basov

Publications and source records attributed to D. N. Basov.

At least 127 records · Page 7Linked to original sources
arXiv2011

Nanoscale imaging of the electronic and structural transitions in vanadium dioxide

We investigate the electronic and structural changes at the nanoscale in vanadium dioxide (VO2) in the vicinity of its thermally driven phase transition. Both electronic and structural changes exhibit phase coexistence leading to percolation. In addition, we observe a dichotomy between the local electronic and structural transitions. Nanoscale x-ray diffraction reveals local, non-monotonic switching of the lattice structure, a phenomenon that is not seen in the electronic insulator-to-metal transition mapped by near-field infrared microscopy.

cond-mat.str-el↗
arXiv2011

An infrared probe of the insulator-to-metal transition in GaMnAs and GaBeAs

We report infrared studies of the insulator-to-metal transition (IMT) in GaAs doped with either magnetic (Mn) or non-magnetic acceptors (Be). We observe a resonance with a natural assignment to impurity states in the insulating regime of Ga$_{1-x}$Mn$_x$As, which persists across the IMT to the highest doping (16%). Beyond the IMT boundary, behavior combining insulating and metallic trends also persists to the highest Mn doping. Be doped samples however, display conventional metallicity just above the critical IMT concentration, with features indicative of transport within the host valence band.

cond-mat.mtrl-sci↗
arXiv2011

Reconfigurable Gradient Index using VO2 Memory Metamaterials

We demonstrate tuning of a metamaterial device that incorporates a form of spatial gradient control. Electrical tuning of the metamaterial is achieved through a vanadium dioxide layer which interacts with an array of split ring resonators. We achieved a spatial gradient in the magnitude of permittivity, writeable using a single transient electrical pulse. This induced gradient in our device is observed on spatial sc ales on the order of one wavelength at 1 THz. Thus, we show the viability of elements for use in future devices with potential applications in beamforming and communications

cond-mat.mes-hall↗
arXiv2011

Phonon splitting and anomalous enhancement of infrared-active modes in BaFe$_2$As$_2$

We present a comprehensive infrared spectroscopic study of lattice dynamics in the pnictide parent compound BaFe$_2$As$_2$. In the tetragonal structural phase, we observe the two degenerate symmetry-allowed in-plane infrared active phonon modes. Following the structural transition from the tetragonal to orthorhombic phase, we observe splitting into four non-degenerate phonon modes and a significant phonon strength enhancement. These detailed data allow us to provide a physical explanation for the anomalous phonon strength enhancement as the result of anisotropic conductivity due to Hund's coupling.

cond-mat.supr-con↗
arXiv2011

Electronic correlations and unconventional spectral weight transfer in BaFe$_{2-x}$Co$_{x}$As$_{2}$

We report an infrared optical study of the pnictide high-temperature superconductor BaFe$_{1.84}$Co$_{0.16}$As$_{2}$ and its parent compound BaFe$_{2}$As$_{2}$. We demonstrate that electronic correlations are moderately strong and do not change across the spin-density wave transition or with doping. By examining the energy scale and direction of spectral weight transfer, we argue that Hund's coupling \emph{J} is the primary mechanism that gives rise to correlations.

cond-mat.str-el↗
arXiv2011

Breakdown of the universal Josephson relation in spin ordered cuprate superconductors

We present \emph{c} axis infrared optical data on a number of Ba, Sr and Nd-doped cuprates of the La$_{2}$CuO$_{4}$ (La214) series in which we observe significant deviations from the universal Josephson relation linking the normal state transport (DC conductivity $σ_{DC}$ measured at $T_{c}$) with the superfluid density ($ρ_{s}$): $ρ_{s}\proptoσ_{DC}(T_{c})$. We find the violation of Josephson scaling is associated with striking enhancement of the anisotropy in the superfluid density. The data allows us to link the breakdown of Josephson interlayer physics with the development of magnetic order in the CuO$_2$ planes.

cond-mat.supr-con↗
arXiv2011

Manifesto for a higher Tc -- lessons from pnictides and cuprates

We explore energy scales, features in the normal state transport, relevant interactions and constraints for the pairing mechanisms in the high-Tc cuprates and Fe-pnictides. Based on this analysis we attempt to identify a number of attributes of superconductors with a higher T_c. Expanded version of the article published in Nature Physics, 7, 271 (2011).

cond-mat.supr-con↗
arXiv2011

Chaotic memristor

We suggest and experimentally demonstrate a chaotic memory resistor (memristor). The core of our approach is to use a resistive system whose equations of motion for its internal state variables are similar to those describing a particle in a multi-well potential. Using a memristor emulator, the chaotic memristor is realized and its chaotic properties are measured. A Poincaré plot showing chaos is presented for a simple nonautonomous circuit involving only a voltage source directly connected in series to a memristor and a standard resistor. We also explore theoretically some details of this system, plotting the attractor and calculating Lyapunov exponents. The multi-well potential used resembles that of many nanoscale memristive devices, suggesting the possibility of chaotic dynamics in other existing memristive systems.

cond-mat.mes-hall↗
arXiv2010

Interplane charge dynamics in a valence-bond dynamical mean-field theory of cuprate superconductors

We present calculations of the interplane charge dynamics in the normal state of cuprate superconductors within the valence-bond dynamical mean-field theory. We show that by varying the hole doping, the c-axis optical conductivity and resistivity dramatically change character, going from metallic-like at large doping to insulating-like at low-doping. We establish a clear connection between the behavior of the c-axis optical and transport properties and the destruction of coherent quasiparticles as the pseudogap opens in the antinodal region of the Brillouin zone at low doping. We show that our results are in good agreement with spectroscopic and optical experiments.

cond-mat.str-el↗
arXiv2010

Evidence of precursor superconductivity as high as 180 K from infrared spectroscopy

We show that a multilayer analysis of the infrared c-axis response of RBa2Cu3O7-d (R=Y, Gd, Eu) provides important new information about the anomalous normal state properties of underdoped cuprate high temperature superconductors. Besides competing correlations which give rise to a pseudogap that depletes the low-energy electronic states below T*>>Tc, it enables us to identify the onset of a precursor superconducting state below Tons>Tc. We map out the doping phase diagram of Tons which reaches a maximum of ~180 K at strong underdoping and present magnetic field dependent data which confirm our conclusions.

cond-mat.supr-con↗
arXiv2010

Optical characterization of Bi$_2$Se$_3$ in a magnetic field: infrared evidence for magnetoelectric coupling in a topological insulator material

We present an infrared magneto-optical study of the highly thermoelectric narrow-gap semiconductor Bi$_2$Se$_3$. Far-infrared and mid-infrared (IR) reflectance and transmission measurements have been performed in magnetic fields oriented both parallel and perpendicular to the trigonal $c$ axis of this layered material, and supplemented with UV-visible ellipsometry to obtain the optical conductivity $σ_1(ω)$. With lowering of temperature we observe narrowing of the Drude conductivity due to reduced quasiparticle scattering, as well as the increase in the absorption edge due to direct electronic transitions. Magnetic fields $H \parallel c$ dramatically renormalize and asymmetrically broaden the strongest far-IR optical phonon, indicating interaction of the phonon with the continuum free-carrier spectrum and significant magnetoelectric coupling. For the perpendicular field orientation, electronic absorption is enhanced, and the plasma edge is slightly shifted to higher energies. In both cases the direct transition energy is softened in magnetic field.

cond-mat.str-el↗
arXiv2010

Optical probe of strong correlations in LaNiO$_{3} $ thin films

The optical properties of LaNiO$_3$ thin films are investigated over a wide energy and temperature range. Thin films of varying thickness were epitaxially grown by pulsed laser deposition on LaAlO$_3$ and SrTiO$_3$ substrates. The optical conductivity data of the films reveal a number of interband transitions above 1 eV which are in good agreement with band structure calculations. No well defined Drude peak is observed however, in stark contrast with LDA theory predicting a finite density of states at the Fermi energy. This experimental finding of a vanishing Drude spectral weight, compared to a finite electron kinetic energy obtained from band structure calculations, highlights the importance of strong electronic correlations in LaNiO$_3$.

cond-mat.str-el↗
arXiv2010

Towards a two-dimensional superconducting state of La$_{2-x}$Sr$_{x}$CuO$_{2}$ in a moderate external magnetic field

We report a novel aspect of the competition and coexistence between magnetism and superconductivity in the high-$T_{c}$ cuprate La$_{2-x}$Sr$_{x}$CuO$_{4}$ (La214). With a modest magnetic field applied $H \parallel c$-axis, we monitored the infrared signature of pair tunneling between the CuO$_2$ planes and discovered the complete suppression of interlayer coupling in a series of underdoped La214 single crystals. We find that the in-plane superconducting properties remain intact, in spite of enhanced magnetism in the planes.

cond-mat.supr-con↗
arXiv2010

Reconsidering the interpretation of quantum oscillation experiments on underdoped YBa(2)Cu(3)O(6+x)

On the basis of negative transport coefficients, it has been argued that the quantum oscillations observed in underdoped YBa(2)Cu(3)O(6+x) in high magnetic fields must be due to antinodal electron pockets. We point out a counter example in which electron-like transport in a hole-doped cuprate is associated with Fermi-arc states. We also present evidence that the antinodal gap in YBa(2)Cu(3)O(6+x) is robust to modest applied magnetic fields. We suggest that these observations should be taken into account when interpreting the results of the quantum oscillation experiments.

cond-mat.supr-con↗
arXiv2009

Electronic correlations in the iron pnictides

In correlated metals derived from Mott insulators, the motion of an electron is impeded by Coulomb repulsion due to other electrons. This phenomenon causes a substantial reduction in the electron's kinetic energy leading to remarkable experimental manifestations in optical spectroscopy. The high-Tc superconducting cuprates are perhaps the most studied examples of such correlated metals. The occurrence of high-Tc superconductivity in the iron pnictides puts a spotlight on the relevance of correlation effects in these materials. Here we present an infrared and optical study on single crystals of the iron pnictide superconductor LaFePO. We find clear evidence of electronic correlations in metallic LaFePO with the kinetic energy of the electrons reduced to half of that predicted by band theory of nearly free electrons. Hallmarks of strong electronic many-body effects reported here are important because the iron pnictides expose a new pathway towards a correlated electron state that does not explicitly involve the Mott transition.

cond-mat.str-el↗
arXiv2009

Infrared spectroscopy and nano-imaging of the insulator-to-metal transition in vanadium dioxide

We present a detailed infrared study of the insulator-to-metal transition (IMT) in vanadium dioxide (VO2) thin films. Conventional infrared spectroscopy was employed to investigate the IMT in the far-field. Scanning near-field infrared microscopy directly revealed the percolative IMT with increasing temperature. We confirmed that the phase transition is also percolative with cooling across the IMT. We present extensive near-field infrared images of phase coexistence in the IMT regime in VO2. We find that the coexisting insulating and metallic regions at a fixed temperature are static on the time scale of our measurements. A novel approach for analyzing the far-field and near-field infrared data within the Bruggeman effective medium theory was employed to extract the optical constants of the incipient metallic puddles at the onset of the IMT. We found divergent effective carrier mass in the metallic puddles that demonstrates the importance of electronic correlations to the IMT in VO2. We employ the extended dipole model for a quantitative analysis of the observed near-field infrared amplitude contrast and compare the results with those obtained with the basic dipole model.

cond-mat.str-el↗
arXiv2009

Phase-transition driven memristive system

Memristors are passive circuit elements which behave as resistors with memory. The recent experimental realization of a memristor has triggered interest in this concept and its possible applications. Here, we demonstrate memristive response in a thin film of Vanadium Dioxide. This behavior is driven by the insulator-to-metal phase transition typical of this oxide. We discuss several potential applications of our device, including high density information storage. Most importantly, our results demonstrate the potential for a new realization of memristive systems based on phase transition phenomena.

cond-mat.str-el↗