Insulator-to-Metal Crossover in the Normal State of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>La</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>−</mml:mo><mml:mi mathvariant="italic">x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>Sr</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="italic">x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>CuO</mml:mi></mml:mrow><mml:

Boebinger, G. S.; Ando, Yoichi; Passner, A.; Kimura, T.; Okuya, M.; Shimoyama, Jun–ichi; Kishio, K.; Tamasaku, Kenji; Ichikawa, Noriya; Uchida, S.

doi:10.1103/physrevlett.77.5417

Cited by 515 publications

(491 citation statements)

References 22 publications

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“…1). At x > x opt the ground state becomes metallic and homogeneous, with no evidence for glassiness or other form of nano-scale heterogeneity [9,14,23,25,27,29]. All these results provide strong evidence of a sharp change in ground state properties at x = x opt , and the emergence of vanishing temperature scales as this point is approached -just as one expects at a QCP.…”

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confidence: 92%

“…Simi- lar results have been observed in the "stripe-compound" Nd-LSCO, pure and Y doped Bi-Sr-Ca-Cu-O, pure or Ca doped Y-Ba-Cu-O and more recently Ca-Na-Cu-OCl [8,9,10,11,13,14,21] Spin-charge correlations around the SC dome. To further examine the region where T c > 0, we re-analyzed early measurements in high magnetic fields [23] where bulk superconductivity was suppressed, revealing information about low-T charge transport in the normal phase. A striking similarity is observed between the doping dependence of the spin freezing and the resistivity minima all the way to the overdoped region (Fig.…”

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confidence: 99%

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Self-generated electronic heterogeneity and quantum glassiness in the high-temperature superconductors

Panagopoulos

Dobrosavljević

2005

Phys. Rev. B

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We present a systematic study of the spin and charge dynamics of copper oxide superconductors as a function of carrier concentration x. Our results portray a coherent physical picture, which reveals a quantum critical point at optimum doping (x = xopt), and the formation of an inhomogeneous glassy state at x < xopt. This mechanism is argued to arise as an intrinsic property of doped Mott insulators, and therefore to be largely independent of material quality and level of disorder.Many interesting materials ranging from magnetorestrictive manganite films [1] and field-effect transistors [2,3], to unconventional low dimensional superconductors [4], find themselves close to the metal-insulator transition. In this regime, competition between several distinct ground states [4] produces unusual behavior, displaying striking similarities in a number of different systems. Electronic heterogeneity [1,5] emerges, giving rise to "mesoscopic" coexistence of different ordered phases. Typically, a large number of possible configurations of these local regions have comparable energies, resulting in slow relaxation, aging, and other signatures of glassy systems. Because the stability of such ordering is controlled by doping-dependent quantum fluctuations [6,7] introduced by itinerant carriers, these systems can be regarded as prototypical quantum glasses -a new paradigm of strongly correlated matter.In this Letter we report the emergence and evolution of dynamical heterogeneity and glassy behavior across the phase diagram of the high-transition-temperature (T c ) superconductors (HTS). Based on data of the spin and charge dynamics, we draw a phase diagram (Fig. 1) and propose that self generated glassiness [5] may be a key feature necessary to understand many of the unconventional properties of both the superconducting and the normal state.Glassiness in the pseudo-gap phase. In the archetypal HTS, La 2−x Sr x CuO 4 (LSCO) the parent 2D antiferromagnetic insulator (AFI) La 2 CuO 4 displays a sharp peak in the magnetic susceptibility at the Neel temperature T N = 300K. T N decreases with hole-doping and the transition width broadens (Fig. 2 -upper panel). Concurrently, there is systematic experimental evidence from various techniques and on several HTS that a second freezing transition (T F ) emerges at lower temperatures with the first added holes (Fig. 2) [8,9,10,11,12,13]. At x > 0.02, T N = 0 but the short range order persists [14]: the low-field susceptibility displays a cusp at low temperatures and a thermal hysteresis below, characteristic of a spin glass transition (T g ) (Fig. 2 -upper panel). At T < T g the material displays memory effects like "traditional" spin glasses and is described by an Edwards-Anderson order parameter [15]. Interestingly, it is at this doping range that a pseudogap phase develops [4,16].

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confidence: 92%

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Self-generated electronic heterogeneity and quantum glassiness in the high-temperature superconductors

Panagopoulos

Dobrosavljević

2005

Phys. Rev. B

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“…The MIC happens in the underdoped regime for YBCO around y = 0.5 28,29 , while it occurs near optimal doping for LSCO ( x ∼ 0.16) 27 . If spin excitations are important in determining the charge transport properties of doped copper oxides, they might respond to the changes in the electronic correlations across the MIC.…”

Section: Introductionmentioning

confidence: 99%

“…To understand the microscopic origin of the differences between YBCO and LSCO, we note that although superconductivity in doped copper oxides first appears when the hole-doping level (x in the case of LSCO) exceeds the critical value of 0.055, a fundamental change in the ground state of these materials in the absence of super-conductivity actually takes place at much higher doping levels with a metal-to-insulator (MIC) crossover, where the insulating phase under high magnetic fields shows a log (1/T ) divergence in resistivity 27 . The MIC happens in the underdoped regime for YBCO around y = 0.5 28,29 , while it occurs near optimal doping for LSCO ( x ∼ 0.16) 27 .…”

Section: Introductionmentioning

confidence: 99%

Quantum spin excitations through the metal-to-insulator crossover inYBa2Cu3O6+y

Yamani

Kang

et al. 2008

Phys. Rev. B

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We use inelastic neutron scattering to study the temperature dependence of the spin excitations of a detwinned superconducting YBa2Cu3O6.45 (Tc = 48 K). In contrast to earlier work on YBa2Cu3O6.5 (Tc = 58 K), where the prominent features in the magnetic spectra consist of a sharp collective magnetic excitation termed "resonance" and a large (hω ≈ 15 meV) superconducting spin gap, we find that the spin excitations in YBa2Cu3O6.45 are gapless and have a much broader resonance. Our detailed mapping of magnetic scattering along the a * /b * -axis directions at different energies reveals that spin excitations are unisotropic and consistent with the "hourglass"-like dispersion along the a * -axis direction near the resonance, but they are isotropic at lower energies. Since a fundamental change in the low-temperature normal state of YBa2Cu3O6+y when superconductivity is suppressed takes place at y ∼ 0.5 with a metal-to-insulator crossover (MIC), where the ground state transforms from a metallic to an insulating-like phase, our results suggest a clear connection between the large change in spin excitations and the MIC. The resonance therefore is a fundamental feature of metallic ground state superconductors and a consequence of high-Tc superconductivity.

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“…1 is a metal-insulator transition to a low-doping SDW insulator. We believe this transition is associated with the localization of the small Fermi pockets, and is related to a number of experimental observations [34,33].…”

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Quantum criticality and the phase diagram of the cuprates

Sachdev

2010

Physica C: Superconductivity and its Applications

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I discuss a proposed phase diagram of the cuprate superconductors as a function of temperature, carrier concentration, and a strong magnetic field perpendicular to the layers. I show how the phase diagram gives a unified interpretation of a number of recent experiments. Superconductivity, Tokyo, Sep 7-12, 2009 Keynote talk, 9th International Conference on Materials and Mechanisms of H c2Figure 1: Proposed phase diagram of the cuprates showing the interplay between superconductivity (SC), spin density wave (SDW) order, and Fermi surface configuration as a function of carrier density (x), temperature (T ), and magnetic field (H) perpendicular to the layers. Full lines are thermal or quantum phase transitions, dashed lines are crossovers, and dotted lines are guides to the eye. The phase transitions associated with valence bond solid (VBS) (or "charge") and nematic order are not shown. The superconducting regions are colored pink. We have assumed the absence of interlayer coupling, and so the SDW order is long-ranged only at T = 0: it is present in the regions labeled "SDW" and on the thick orange line for x < x s . In the blue normal regions, the 'pseudogap' is between T c and T * , the 'Strange Metal' has an in-plane resistivity which is measured to be linear in T , and the "Large Fermi surface" has a conventional T 2 resistivity.This brief note contains a summary of the key aspects of the proposed phase diagram of the cuprate superconductors shown in Fig. 1, and the central role played by ideas of quantum criticality. A more detailed discussion can be found in another recent review by the author [1], which also contains more complete citations to the literature. Here, I will focus on the central physical ideas and highlight support from recent experiments.The phase transitions and crossovers in Fig. 1 appear quite intricate. However, they can be understood simply by focusing first on the quantum critical point (QCP) at doping density, x = x m , temperature T = 0, magnetic field H = 0. As indicated in Fig. 1, this quantum critical point is pre-empted by the onset of superconductivity.The QCP at x = x m is a transition between two metallic (hence the subscript m) Fermi liquid phases. At x > x m we have the full symmetry of the square lattice, and a "large" Fermi surface metal consisting of a hole-like Fermi surface enclosing the area 1 + x expected from the Luttinger theorem (this is for hole doping; with electron doping, x, the area enclosed is 1 − x). At x < x m we have the onset of spin density wave (SDW) order, and this breaks apart the large Fermi surface into "small" Fermi pockets. Nevertheless the Luttinger theorem continues to be obeyed, after accounting for the large unit cell created by the SDW order. The ultimate theory of this quantum critical point is not fully understood, despite much theoretical attention [2].Strong evidence for the QCP at x = x m , and its associated T > 0 crossovers comes from recent experiments on Nd-LSCO [3,4]. They detected the crossover between "Strange Metal" and "Fl...

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Insulator-to-Metal Crossover in the Normal State ofLa2−xSrxCuO

Cited by 515 publications

References 22 publications

Self-generated electronic heterogeneity and quantum glassiness in the high-temperature superconductors

Self-generated electronic heterogeneity and quantum glassiness in the high-temperature superconductors

Quantum spin excitations through the metal-to-insulator crossover inYBa2Cu3O6+y

Quantum criticality and the phase diagram of the cuprates

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