Instabilities and insulator-metal transitions in half-doped manganites induced by magnetic-field and doping

Cepas, Olivier; Krishnamurthy, H. R.; Ramakrishnan, T. V.

doi:10.1103/physrevb.73.035218

Cited by 20 publications

(17 citation statements)

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“…Away from the "orbital liquid regime," the ᐉ-b model can be extended in a straightforward way to include charge and orbital order particularly near x = 0.5. 29,30 The work cited above did not address the issue of electronic inhomogeneities. In fact, an effective homogeneous state was assumed in the dynamical mean-field solution.…”

Section: A Summary Of the ഞB Modelmentioning

confidence: 97%

Long-range Coulomb interactions and nanoscale electronic inhomogeneities in correlated oxides

et al. 2009

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Electronic, magnetic, or structural inhomogeneities ranging in size from nanoscopic to mesoscopic scales seem endemic and are possibly generic to colossal magnetoresistance manganites and other transition metal oxides. They are hence of great current interest and understanding them is of fundamental importance. We show here that an extension, to include long-range Coulomb interactions, of a quantum two-fluid ᐉ-b model proposed recently for manganites ͓Phys. Rev. Lett. 92, 157203 ͑2004͔͒ leads to an excellent description of such inhomogeneities. In the ᐉ-b model two very different kinds of electronic states, one localized and polaronic ͑ᐉ͒ and the other extended or broad band ͑b͒ coexist. For model parameters appropriate to manganites and even within a simple dynamical mean-field theory ͑DMFT͒ framework, it describes many of the unusual phenomena seen in manganites, including colossal magnetoresistance ͑CMR͒, qualitatively and quantitatively. However, in the absence of long-ranged Coulomb interaction, a system described by such a model would actually phase separate, into macroscopic regions of l and b electrons, respectively. As we show in this paper, in the presence of Coulomb interactions, the macroscopic phase separation gets suppressed and instead nanometer scale regions of polarons interspersed with band electron puddles appear, constituting a kind of quantum Coulomb glass. We characterize the size scales and distribution of the inhomogeneity using computer simulations. For realistic values of the long-range Coulomb interaction parameter V 0 , our results for the thresholds for occupancy of the b states are in agreement with, and hence support, the earlier approach mentioned above based on a configuration averaged DMFT treatment which neglects V 0 ; but the present work has features that cannot be addressed in the DMFT framework. Our work points to an interplay of strong correlations, long-range Coulomb interaction, and dopant ion disorder, all inevitably present in transition metal oxides as the origin of nanoscale inhomogeneities rather than disorder frustrated phase competition as is generally believed. As regards manganites, it argues against explanations for CMR based on disorder frustrated phase separation and for an intrinsic origin of CMR. Based on this, we argue that the observed micrometer ͑meso͒ scale inhomogeneities owe their existence to extrinsic causes, e.g., strain due to cracks and defects. We suggest possible experiments to validate our speculation.

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Section: A Summary Of the ഞB Modelmentioning

confidence: 97%

Long-range Coulomb interactions and nanoscale electronic inhomogeneities in correlated oxides

et al. 2009

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“…0.5 eV). Competition between these different interactions, leading to a variety of states very close in energy, is responsible for the complex phase diagram of manganites with many electronic orders, and their extreme sensitivity to external perturbations such as temperature, magnetic field and strain (Sarma et al 1995;Satpathy et al 1996;Millis 1998;Ramakrishnan et al 2003;Cepas et al 2006). Owing to the difficulties of dealing with all the degrees of freedom and competing interactions mentioned above, much of the early work aimed at understanding colossal responses and electronic inhomogeneities in manganites has been based on simplified models which neglect one or more of them.…”

Section: Theoretical Approachesmentioning

confidence: 99%

Electronic phase separation and other novel phenomena and properties exhibited by mixed-valent rare-earth manganites and related materials

Shenoy

Rao

2007

Phil. Trans. R. Soc. A.

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Transition metal oxides, such as the mixed-valent rare-earth manganites Ln (1Kx) A x MnO 3 (Ln, rare-earth ion, and A, alkaline-earth ion), show a variety of electronic orders with spatially correlated charge, spin and orbital arrangements, which in turn give rise to many fascinating phenomena and properties. These materials are also electronically inhomogeneous, i.e. they contain disjoint spatial regions with different electronic orders. Not only do we observe signatures of such electronic phase separation in a variety of properties, but we can also observe the different 'phases' visually through different types of imaging. We discuss various experiments pertaining to electronic orders and electronic inhomogeneities in the manganites and present a discussion of theoretical approaches to their understanding. It is noteworthy that the mixed-valent rare-earth cobaltates of the type Ln (1Kx) A x CoO 3 also exhibit electronic inhomogeneities just as the manganites.

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“…There have been some attempts at a theory of field induced melting in CO manganites [49][50][51][52] .…”

Section: Status Of Theorymentioning

confidence: 99%

“…(iii) Finally, a two orbital model was studied, with a large family of variational states in a recent work 51 . This established that the smallness of the (thermodynamic) melting field is due to the closeness in energy of the CE-CO-I and the FM-M phases.…”

Section: Status Of Theorymentioning

confidence: 99%

A real space description of magnetic field induced melting in the charge ordered manganites: I. The clean limit

Mukherjee

Majumdar

2014

Eur. Phys. J. B

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We study the melting of charge order in the half doped manganites using a model that incorporates double exchange, antiferromagnetic superexchange, and Jahn-Teller coupling between electrons and phonons. We primarily use a real space Monte Carlo technique to study the phase diagram in terms of applied field (h) and temperature (T ), exploring the melting of charge order with increasing h and its recovery on decreasing h. We observe hysteresis in this response, and discover that the 'field melted' high conductance state can be spatially inhomogeneous even without extrinsic disorder. The hysteretic response plays out in the background of field driven equilibrium phase separation. Our results, exploring h, T , and the electronic parameter space, are backed up by analysis of simpler limiting cases and a Landau framework for the field response. This paper focuses on our results in the 'clean' systems, a companion paper studies the effect of cation disorder on the melting phenomena. c , discussed later) is small. The associated energy scale gµ B h c k B T CO , where T CO is the zero field melting temperature (g is the gyromagnetic ratio and µ B the Bohr magneton). The smallness of h c is attributed to the small energy difference between the CE-CO-I and FM-M states. (ii) The field induced transition is seen to be first order and is accompanied by hysteresis since there are competing metastable minima, particularly for materials close to the CE-CO-I -FM-M phase boundary. (iii) The field induced FM-M is believed to be homogeneous, and is arXiv:0811.3563v4 [cond-mat.str-el]

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Instabilities and insulator-metal transitions in half-doped manganites induced by magnetic-field and doping

Cited by 20 publications

References 60 publications

Long-range Coulomb interactions and nanoscale electronic inhomogeneities in correlated oxides

Long-range Coulomb interactions and nanoscale electronic inhomogeneities in correlated oxides

Electronic phase separation and other novel phenomena and properties exhibited by mixed-valent rare-earth manganites and related materials

A real space description of magnetic field induced melting in the charge ordered manganites: I. The clean limit

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