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Sudip Chakravarty - One of the best experts on this subject based on the ideXlab platform.
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quantum oscillations in electron doped High Temperature Superconductors
Physical Review B, 2010Co-Authors: Jonghyoun Eun, Xun Jia, Sudip ChakravartyAbstract:Quantum oscillations in hole-doped High-Temperature Superconductors are difficult to understand within the prevailing views. An emerging idea is that of a putative normal ground state, which appears to be a Fermi liquid with a reconstructed Fermi surface. The oscillations are due to formation of Landau levels. Recently the same oscillations were found in the electron-doped cuprate, ${\text{Nd}}_{2\ensuremath{-}x}{\text{Ce}}_{x}{\text{CuO}}_{4}$, in the optimal to overdoped regime. Although these electron-doped nonstoichiometric materials are naturally more disordered, they strikingly complement the hole-doped cuprates. Here we provide an explanation of these observations from the perspective of density waves using a powerful transfer matrix method to compute the conductance as a function of the magnetic field.
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competing order fermi surface reconstruction and quantum oscillations in underdoped High Temperature Superconductors
Physical Review B, 2008Co-Authors: Ivailo Dimov, Xun Jia, Pallab Goswami, Sudip ChakravartyAbstract:We consider incommensurate $d$-density wave order in underdoped High Temperature Superconductors. We find that Fermi surface reconstruction can correctly capture the phenomenology of the recent quantum oscillation experiments that suggest incommensurate order. The predicted frequencies are a frequency around 530 T arising from the electron pocket, a hole frequency at around 1650 T, and a new low frequency from a smaller hole pocket at 250 T for which there are some indications that require further investigation. The oscillation corresponding to the electron pocket will be further split due to bilayer coupling but the splitting is sufficiently small to require more refined measurements. The truly incommensurate $d$-density wave breaks both time reversal and inversion but the product of these two symmetry operations is preserved. There is some similarity of our results with the spiral spin density wave order, which, as pointed out by Overhauser, also breaks time reversal and inversion. Calculations corresponding to Higher order commensuration produces results similar to anti-phase spin stripes, but appear to us to be an unlikely explanation of the experiments. The analysis of the Gorkov equation in the mixed state shows that the oscillation frequencies are unshifted from the putative normal state and the additional Dingle factor arising from the presence of the mixed state can provide a subtle distinction between the spiral spin density wave and the $d$-density wave.
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fermi pockets and quantum oscillations of the hall coefficient in High Temperature Superconductors
Proceedings of the National Academy of Sciences of the United States of America, 2008Co-Authors: Sudip Chakravarty, Haeyoung KeeAbstract:Recent quantum oscillation measurements in High-Temperature Superconductors in High magnetic fields and low Temperatures have ushered in a new era. These experiments explore the normal state from which superconductivity arises and provide evidence of a reconstructed Fermi surface consisting of electron and hole pockets in a regime in which such a possibility was previously considered to be remote. More specifically, the Hall coefficient has been found to oscillate according to the Onsager quantization condition, involving only fundamental constants and the areas of the pockets, but with a sign that is negative. Here, we explain the observations with the theory that the alleged normal state exhibits a hidden order, the d-density wave, which breaks symmetries signifying time reversal, translation by a lattice spacing, and a rotation by an angle π/2, while the product of any two symmetry operations is preserved. The success of our analysis underscores the importance of spontaneous breaking of symmetries, Fermi surface reconstruction, and conventional quasiparticles. We primarily focus on the version of the order that is commensurate with the underlying crystalline lattice, but we also touch on the consequences if the order were to incommensurate. It is shown that whereas commensurate order results in two independent oscillation frequencies as a function of the inverse of the applied magnetic field, incommensurate order leads to three independent frequencies. The oscillation amplitudes, however, are determined by the mobilities of the charge carriers comprising the Fermi pockets.
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interlayer tunneling and gap anisotropy in High Temperature Superconductors
Science, 1993Co-Authors: Sudip Chakravarty, Asle Sudbo, Philip W Anderson, S P StrongAbstract:A quantitative analysis of a recent model of High-Temperature Superconductors based on an interlayer tunneling mechanism is presented. This model can account well for the observed magnitudes of the High transition Temperatures in these materials and implies a gap that does not change sign, can be substantially anisotropic, and has the same symmetry as the crystal. The experimental consequences explored so far are consistent with the observations.
Hong Ding - One of the best experts on this subject based on the ideXlab platform.
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local antiferromagnetic exchange and collaborative fermi surface as key ingredients of High Temperature Superconductors
Scientific Reports, 2012Co-Authors: Hong DingAbstract:Cuprates, ferropnictides and ferrochalcogenides are three classes of unconventional High Temperature Superconductors, who share similar phase diagrams in which superconductivity develops after a magnetic order is suppressed, suggesting a strong interplay between superconductivity and magnetism, although the exact picture of this interplay remains elusive. Here we show that there is a direct bridge connecting antiferromagnetic exchange interactions determined in the parent compounds of these materials to the superconducting gap functions observed in the corresponding superconducting materials: in all High Temperature Superconductors, the Fermi surface topology matches the form factor of the pairing symmetry favored by local magnetic exchange interactions. We suggest that this match offers a principle guide to search for new High Temperature Superconductors.
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Local antiferromagnetic exchange and collaborative Fermi surface as key ingredients of High Temperature Superconductors
Scientific Reports, 2012Co-Authors: Jiangping Hu, Hong DingAbstract:Cuprates, ferropnictides and ferrochalcogenides are three classes of unconventional High-Temperature Superconductors, who share similar phase diagrams in which superconductivity develops after a magnetic order is suppressed, suggesting a strong interplay between superconductivity and magnetism, although the exact picture of this interplay remains elusive. Here we show that there is a direct bridge connecting antiferromagnetic exchange interactions determined in the parent compounds of these materials to the superconducting gap functions observed in the corresponding superconducting materials. High superconducting transition Temperature is achieved when the Fermi surface topology matches the form factor of the pairing symmetry favored by local magnetic exchange interactions. Our result offers a principle guide to search for new High Temperature Superconductors.
A I Larkin - One of the best experts on this subject based on the ideXlab platform.
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giant flux creep through surface barriers and the irreversibility line in High Temperature Superconductors
Physical Review B, 1994Co-Authors: L Burlachkov, A I Larkin, A E Koshelev, V B Geshkenbein, V M VinokurAbstract:Magnetic and transport phenomena in High-Temperature Superconductors due to magnetic flux relaxation and transport over the surface barrier are investigated. Vortex dynamics controlled by the penetration both of pancake vortices and vortex lines is discussed. The penetration field ${\mathit{H}}_{\mathit{p}}$ for pancakes decays exponentially with Temperature. The size of the magnetization loop is determined by the decay of ${\mathit{H}}_{\mathit{p}}$ during the process of relaxation, but its shape remains unchanged. The irreversibility line associated with the pancake penetration is given by ${\mathit{H}}_{\mathrm{irr}}$ \ensuremath{\propto}exp(-2T/${\mathit{T}}_{0}$) and may lie both above and below the melting line.
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giant flux creep through surface barriers and the irreversibility line in High Temperature Superconductors
Physical Review B, 1994Co-Authors: L Burlachkov, A I Larkin, A E Koshelev, V B Geshkenbein, V M VinokurAbstract:Magnetic and transport phenomena in High-Temperature Superconductors due to magnetic flux relaxation and transport over the surface barrier are investigated. Vortex dynamics controlled by the penetration both of pancake vortices and vortex lines is discussed. The penetration field [ital H][sub [ital p]] for pancakes decays exponentially with Temperature. The size of the magnetization loop is determined by the decay of [ital H][sub [ital p]] during the process of relaxation, but its shape remains unchanged. The irreversibility line associated with the pancake penetration is given by [ital H][sub irr] [proportional to]exp([minus]2[ital T]/[ital T][sub 0]) and may lie both above and below the melting line.
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vortices in High Temperature Superconductors
Reviews of Modern Physics, 1994Co-Authors: G Blatter, A I Larkin, V B Geshkenbein, M V Feigelman, V M VinokurAbstract:With the High-Temperature Superconductors a qualitatively new regime in the phenomenology of type-II superconductivity can be accessed. The key elements governing the statistical mechanics and the dynamics of the vortex system are (dynamic) thermal and quantum fluctuations and (static) quenched disorder. The importance of these three sources of disorder can be quantified by the Ginzburg number $Gi=\frac{{(\frac{{T}_{c}}{{H}_{c}^{2}}\ensuremath{\varepsilon}{\ensuremath{\xi}}^{3})}^{2}}{2}$, the quantum resistance $Qu=(\frac{{e}^{2}}{\ensuremath{\hbar}})(\frac{{\ensuremath{\rho}}_{n}}{\ensuremath{\varepsilon}\ensuremath{\xi}})$, and the critical current-density ratio $\frac{{j}_{c}}{{j}_{o}}$, with ${j}_{c}$ and ${j}_{o}$ denoting the depinning and depairing current densities, respectively (${\ensuremath{\rho}}_{n}$ is the normal-state resistivity and ${\ensuremath{\varepsilon}}^{2}=\frac{m}{M}l1$ denotes the anisotropy parameter). The material parameters of the oxides conspire to produce a large Ginzburg number $\mathrm{Gi}\ensuremath{\sim}{10}^{\ensuremath{-}2}$ and a large quantum resistance $\mathrm{Qu}\ensuremath{\sim}{10}^{\ensuremath{-}1}$, values which are by orders of magnitude larger than in conventional Superconductors, leading to interesting effects such as the melting of the vortex lattice, the creation of new vortex-liquid phases, and the appearance of macroscopic quantum phenomena. Introducing quenched disorder into the system turns the Abrikosov lattice into a vortex glass, whereas the vortex liquid remains a liquid. The terms "glass" and "liquid" are defined in a dynamic sense, with a sublinear response $\ensuremath{\rho}={\frac{\ensuremath{\partial}E}{\ensuremath{\partial}j}|}_{j\ensuremath{\rightarrow}0}$ characterizing the truly superconducting vortex glass and a finite resistivity $\ensuremath{\rho}(j\ensuremath{\rightarrow}0)g0$ being the signature of the liquid phase. The smallness of $\frac{{j}_{c}}{{j}_{o}}$ allows one to discuss the influence of quenched disorder in terms of the weak collective pinning theory. Supplementing the traditional theory of weak collective pinning to take into account thermal and quantum fluctuations, as well as the new scaling concepts for elastic media subject to a random potential, this modern version of the weak collective pinning theory consistently accounts for a large number of novel phenomena, such as the broad resistive transition, thermally assisted flux flow, giant and quantum creep, and the glassiness of the solid state. The strong layering of the oxides introduces additional new features into the thermodynamic phase diagram, such as a layer decoupling transition, and modifies the mechanism of pinning and creep in various ways. The presence of strong (correlated) disorder in the form of twin boundaries or columnar defects not only is technologically relevant but also provides the framework for the physical realization of novel thermodynamic phases such as the Bose glass. On a macroscopic scale the vortex system exhibits self-organized criticality, with both the spatial and the temporal scale accessible to experimental investigations.
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geometrical barriers in High Temperature Superconductors
Physical Review Letters, 1994Co-Authors: Eli Zeldov, A I Larkin, V B Geshkenbein, V M Vinokur, M Konczykowski, D Majer, Boris Khaykovich, Hadas ShtrikmanAbstract:A theoretical description of vortex dynamics in thin flat samples is derived and is found to compare favorably with experimental results. In perpendicular applied magnetic field the vortex penetration is delayed significantly due to the presence of a potential barrier of geometrical origin. This novel geometrical barrier effect results in hysteretic magnetization and in the existence of an irreversibility line in the absence of bulk pinning. Among the unique characteristics of the barrier are a vortex concentration in the center of the sample and a zero-field peak in the magnetization loops.
Elbio Dagotto - One of the best experts on this subject based on the ideXlab platform.
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one particle spectral function and local density of states in a phenomenological mixed phase model for High Temperature Superconductors
Physical Review B, 2006Co-Authors: M Mayr, Elbio Dagotto, Gonzalo Alvarez, Adriana MoreoAbstract:The dynamical properties of a recently introduced phenomenological model for High-Temperature Superconductors are investigated. In the clean limit, it was observed that none of the homogeneous or striped states that are induced by the model at low Temperatures can reproduce the recent angle-resolved photoemission results for La2�xSrxCuO4 Yoshida et al., Phys. Rev. Lett. 91, 027001 2003, which show a signal with two branches in the underdoped regime. On the other hand, upon including quenched disorder in the model and breaking the homogeneous state into “patches” that are locally either superconducting or antiferromagnetic, the two-branch spectra can be reproduced. In this picture, the nodal regions are caused by d-wave superconducting clusters. Studying the density of states DOS, a pseudogap is observed, caused by the mixture of the gapped antiferromagnetic state and a d-wave superconductor. The local DOS can be interpreted using a mixed-phase picture, similar to what is observed in tunneling experiments. It is concluded that a simple phenomenological model for cuprates can capture several of the one-particle features observed in the underdoped regime of these materials.
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correlated electrons in High Temperature Superconductors
Reviews of Modern Physics, 1994Co-Authors: Elbio DagottoAbstract:Theoretical ideas and experimental results concerning High-Temperature Superconductors are reviewed. Special emphasis is given to calculations performed with the help of computers applied to models of strongly correlated electrons proposed to describe the two-dimensional Cu${\mathrm{O}}_{2}$ planes. The review also includes results using several analytical techniques. The one- and three-band Hubbard models and the $t\ensuremath{-}J$ model are discussed, and their behavior compared against experiments when available. The author found, among the conclusions of the review, that some experimentally observed unusual properties of the cuprates have a natural explanation through Hubbard-like models. In particular, abnormal features like the mid-infrared band of the optical conductivity $\ensuremath{\sigma}(\ensuremath{\omega})$, the new states observed in the gap in photoemission experiments, the behavior of the spin correlations with doping, and the presence of phase separation in the copper oxide Superconductors may be explained, at least in part, by these models. Finally, the existence of superconductivity in Hubbard-like models is analyzed. Some aspects of the recently proposed ideas to describe the cuprates as having a ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ superconducting condensate at low Temperatures are discussed. Numerical results favor this scenario over others. It is concluded that computational techniques provide a useful, unbiased tool for studying the difficult regime where electrons are strongly interacting, and that considerable progress can be achieved by comparing numerical results against analytical predictions for the properties of these models. Future directions of the active field of computational studies of correlated electrons are briefly discussed.
V M Vinokur - One of the best experts on this subject based on the ideXlab platform.
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giant flux creep through surface barriers and the irreversibility line in High Temperature Superconductors
Physical Review B, 1994Co-Authors: L Burlachkov, A I Larkin, A E Koshelev, V B Geshkenbein, V M VinokurAbstract:Magnetic and transport phenomena in High-Temperature Superconductors due to magnetic flux relaxation and transport over the surface barrier are investigated. Vortex dynamics controlled by the penetration both of pancake vortices and vortex lines is discussed. The penetration field ${\mathit{H}}_{\mathit{p}}$ for pancakes decays exponentially with Temperature. The size of the magnetization loop is determined by the decay of ${\mathit{H}}_{\mathit{p}}$ during the process of relaxation, but its shape remains unchanged. The irreversibility line associated with the pancake penetration is given by ${\mathit{H}}_{\mathrm{irr}}$ \ensuremath{\propto}exp(-2T/${\mathit{T}}_{0}$) and may lie both above and below the melting line.
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giant flux creep through surface barriers and the irreversibility line in High Temperature Superconductors
Physical Review B, 1994Co-Authors: L Burlachkov, A I Larkin, A E Koshelev, V B Geshkenbein, V M VinokurAbstract:Magnetic and transport phenomena in High-Temperature Superconductors due to magnetic flux relaxation and transport over the surface barrier are investigated. Vortex dynamics controlled by the penetration both of pancake vortices and vortex lines is discussed. The penetration field [ital H][sub [ital p]] for pancakes decays exponentially with Temperature. The size of the magnetization loop is determined by the decay of [ital H][sub [ital p]] during the process of relaxation, but its shape remains unchanged. The irreversibility line associated with the pancake penetration is given by [ital H][sub irr] [proportional to]exp([minus]2[ital T]/[ital T][sub 0]) and may lie both above and below the melting line.
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vortices in High Temperature Superconductors
Reviews of Modern Physics, 1994Co-Authors: G Blatter, A I Larkin, V B Geshkenbein, M V Feigelman, V M VinokurAbstract:With the High-Temperature Superconductors a qualitatively new regime in the phenomenology of type-II superconductivity can be accessed. The key elements governing the statistical mechanics and the dynamics of the vortex system are (dynamic) thermal and quantum fluctuations and (static) quenched disorder. The importance of these three sources of disorder can be quantified by the Ginzburg number $Gi=\frac{{(\frac{{T}_{c}}{{H}_{c}^{2}}\ensuremath{\varepsilon}{\ensuremath{\xi}}^{3})}^{2}}{2}$, the quantum resistance $Qu=(\frac{{e}^{2}}{\ensuremath{\hbar}})(\frac{{\ensuremath{\rho}}_{n}}{\ensuremath{\varepsilon}\ensuremath{\xi}})$, and the critical current-density ratio $\frac{{j}_{c}}{{j}_{o}}$, with ${j}_{c}$ and ${j}_{o}$ denoting the depinning and depairing current densities, respectively (${\ensuremath{\rho}}_{n}$ is the normal-state resistivity and ${\ensuremath{\varepsilon}}^{2}=\frac{m}{M}l1$ denotes the anisotropy parameter). The material parameters of the oxides conspire to produce a large Ginzburg number $\mathrm{Gi}\ensuremath{\sim}{10}^{\ensuremath{-}2}$ and a large quantum resistance $\mathrm{Qu}\ensuremath{\sim}{10}^{\ensuremath{-}1}$, values which are by orders of magnitude larger than in conventional Superconductors, leading to interesting effects such as the melting of the vortex lattice, the creation of new vortex-liquid phases, and the appearance of macroscopic quantum phenomena. Introducing quenched disorder into the system turns the Abrikosov lattice into a vortex glass, whereas the vortex liquid remains a liquid. The terms "glass" and "liquid" are defined in a dynamic sense, with a sublinear response $\ensuremath{\rho}={\frac{\ensuremath{\partial}E}{\ensuremath{\partial}j}|}_{j\ensuremath{\rightarrow}0}$ characterizing the truly superconducting vortex glass and a finite resistivity $\ensuremath{\rho}(j\ensuremath{\rightarrow}0)g0$ being the signature of the liquid phase. The smallness of $\frac{{j}_{c}}{{j}_{o}}$ allows one to discuss the influence of quenched disorder in terms of the weak collective pinning theory. Supplementing the traditional theory of weak collective pinning to take into account thermal and quantum fluctuations, as well as the new scaling concepts for elastic media subject to a random potential, this modern version of the weak collective pinning theory consistently accounts for a large number of novel phenomena, such as the broad resistive transition, thermally assisted flux flow, giant and quantum creep, and the glassiness of the solid state. The strong layering of the oxides introduces additional new features into the thermodynamic phase diagram, such as a layer decoupling transition, and modifies the mechanism of pinning and creep in various ways. The presence of strong (correlated) disorder in the form of twin boundaries or columnar defects not only is technologically relevant but also provides the framework for the physical realization of novel thermodynamic phases such as the Bose glass. On a macroscopic scale the vortex system exhibits self-organized criticality, with both the spatial and the temporal scale accessible to experimental investigations.
-
geometrical barriers in High Temperature Superconductors
Physical Review Letters, 1994Co-Authors: Eli Zeldov, A I Larkin, V B Geshkenbein, V M Vinokur, M Konczykowski, D Majer, Boris Khaykovich, Hadas ShtrikmanAbstract:A theoretical description of vortex dynamics in thin flat samples is derived and is found to compare favorably with experimental results. In perpendicular applied magnetic field the vortex penetration is delayed significantly due to the presence of a potential barrier of geometrical origin. This novel geometrical barrier effect results in hysteretic magnetization and in the existence of an irreversibility line in the absence of bulk pinning. Among the unique characteristics of the barrier are a vortex concentration in the center of the sample and a zero-field peak in the magnetization loops.