ORAL SESSION 2E3: Stripe Phase

Tuesday, Feb. 22, 3:30 p.m. – 6:00 p.m., Room 301D (GRB)

Chairs: R. Greene (U of Maryland), C. Castellani (U Rome)

2E3.1 Stripes and High Temperature Superconductivity

S.A. Kivelson, University of California, Los Angeles, Los Angeles, CA 90095, and V.J. Emery, Brookhaven National Laboratory, Upton, NY 11973-5000

Presenting Author: S.A. Kivelson

The origin, character, and consequences of "stripe" order in doped antiferromagnets are discussed. The nature and stability of the "electronic liquid crystalline" states that derive from stripe physics is summarized. The implications of these ideas for the phase diagram of the high temperature superconductors are explored, with particular emphasis on the relation between stripes and the mechanism of high temperature superconductivity.

2E3.2 Stripes and Superconductivity in La_2-xSr_xCuO₄

John M. Tranquada, Physics Dept., Brookhaven National Laboratory, Upton, NY 11973

Presenting Author: J.M. Tranquada

The strongest evidence for spatial segregation of holes doped into antiferromagnetic CuO₂ planes has come from studies of La_2-xSr_xCuO₄. Neutron and x-ray diffraction experiments on Nd-doped single crystals have demonstrated the existence of a charge-stripe ordered state consisting of narrow antiphase antiferromagnetic domains separated by periodically spaced, hole-rich domain walls. Such studies have now been extended over a wide range of Sr concentrations, allowing verification of the speculation that the magnetic and charge ordering temperatures reach their maxima at x = 1/8. In-plane resistivity measurements by Ichikawa on La_1.5Nd_0.4Sr_0.10CuO₄ indicate that the ordered stripes are intrinsically metallic, while Noda, Eisaki, and Uchida have performed Hall effect measurements on related samples and have obtained direct evidence for the one-dimensional conduction expected for pinned stripes. A signature in the resistivity has been identified which correlates with the onset of charge order indicated by the nuclear-quadrupole-resonance studies by Imai's group. The gradual deviation of the resistivity from a linear temperature dependence is consistent with a glass-like ordering of pre-existing stripes. These experiments and their connection with other work will be discussed.

Work at Brookhaven is supported by Contract No. DE-AC02-98CH10886, Division of Materials Sciences, U.S. Department of Energy.

2E3.3 Transport properties in the striped phase in underdoped cuprates*

N.P. Ong 1, Z.A. Xu 1, and S. Uchida 2. 1 Joseph Henry Laboratories of Physics, Princeton University, Princeton, NJ 08544. 2 School of Frontier Sciences, University of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Tokyo 113-8656, Japan.

Presenting Author: N.P. Ong

While several neutron scattering experiments on the striped phase in underdoped cuprates have been reported, there are fewer studies of their transport properties. In the LTT phase of (La,Nd)SrCuO, in which static stripes are observed, the Hall resistivity is strongly suppressed (Nakamura and Uchida 1992). We have searched for comparable signatures in underdoped LaSrCuO where the stripes are assumed to be dynamic. Hall measurements reveal the gradual growth of one-dimensional states below an onset temperature T_H that matches well with the onset of the wipe-out effect recently observed in the NQR experiment of Hunt et al. We discuss why this may have been missed in many previous Hall studies. In addition, the in-plane magnetoresistance 'signatures' of stripe formation will be discussed.

*Supported by US National Science Foundation through the DMR-MRSEC program.

2E3.4 The physics of the Stripe-Quantum-Critical-Point in the superconducting cuprates

Claudio Castellani, Carlo Di Castro, and Marco Grilli, Dipartimento di Fisica, Universita di Roma ``La Sapienza'', 00185 Roma, Italy.

Presenting Author: C. Di Castro

The stripe phase realizes the compromise between the local tendency of strongly correlated systems towards phase separation and the electrostatic cost to segregate charged carriers. This phase connects the high-doping regime, where charge fluctuations play a major role and enslave spin fluctuations, with the low-doping region of the phase diagram dominated by the spin degrees of freedom. The onset of the stripe phase is governed by a quantum critical point (QCP), which, as confirmed by several experimental findings, is placed by the Rome group around optimum doping. According to this scenario, in the proximity of the QCP, critical fluctuations provide both a strong pairing mechanism and a source of non-Fermi liquid behavior.

In the context of the above Stripe-QCP scenario, we elaborate on several observable consequences. In particular as far as single-particle spectral properties are concerned, we show that the strong k-dependent scattering of the quasiparticles with the quasi-critical charge and spin fluctuations reproduces the main features of the low-energy spectral weights and of the observed Fermi surfaces (including the absence of bilayer splitting in cuprates with two CuO₂ planes per cell).

In the underdoped cuprates the attractive k-dependent charge scattering drives the formation of the pseudogap at the M points below the crossover temperature T*. In this framework we discuss a two-gap model, which provides a unified description of the superconducting fluctuations both in the overdoped cuprates, where BCS pairing is observed, and in the underdoped regime, where tightly bound pairs coexist with fermionic quasiparticles at T*>T>T_c. The experimental consequences for the pair-fluctuation stiffness and the pseudogap behavior are investigated.

2E3.5 Neutron Scattering Study of Incommensurate Magnetic Order in Superconducting La₂CuO_4+y

Young S. Lee 1, Robert J. Birgeneau 2, Yasuo Endoh 3, Ross W. Erwin 1, Marc A. Kastner 2, Seung-Hun Lee 1, Gen Shirane 4, Shuichi Wakimoto 2, Kazuyoshi Yamada 5. 1 NIST Center for Neutron Research, Gaithersburg, MD 20899. 2 Department of Physics, MIT, Cambridge, MA 02139. 3 Department of Physics, Tohoku University, Aramaki Aoba, Sendai 980-77, Japan. 4 Department of Physics, Brookhaven National Laboratory, Upton, NY 11973, 5 Institute for Chemical Research, Kyoto University, Gokasho, Uji 610-0011, Japan.

Presenting Author: Y.S. Lee

We have investigated the microscopic magnetism and the structural phases of excess-oxygen doped La₂CuO_4+y superconducting single crystals using neutron scattering. We directly observe that the interstitial oxygen dopants are ordered in three dimensions. A relationship is found which links the ordered arrangement of dopants with higher superconducting transition temperatures. For crystals with an optimal T_c of 42 K, a transition to a magnetically ordered phase occurs coincident with the superconductivity. The transition does not appear to be glassy, and the magnetic phase is characterized by static, long-range spin correlations within the CuO₂ planes with an incommensurate modulation. Our data provide clear constraints regarding possible stripe models for the magnetism in orthorhombic La₂CuO₄-based superconductors.

2E3.6 Stripes, superconductivity and T_c amplification

Antonio Bianconi, Department of Physics, University of Rome La Sapienza, 00185 Rome, Italy

Presenting Author: A. Bianconi

The instantaneous mesoscopic structure of cuprate superconductors is investigated by x-ray scattering and absorption. Charge and lattice stripes are detected by fast experimental probes in cuprate superconductors. A systematic x-ray scattering study at a third generation synchrotron source, Elettra on oxygen doped La₂CuO₄ (T_c=40K) allows us to distinguish 2D ordering of dopants from 1D

charge charge ordering. 1D charge ordering show strong contribution of higher harmonics indicating stripes. The superlattice of 1D stripes arises from charge odering of polarons below a characteristic temperature T* as determined by EXAFS data.

A superlattice of quantum stripes appears with two characteristic lengths: the stripe width L of the order of the Fermi wavelength and the stripe period of the order of the Pippard coherence length. Under these conditions the superconducting critical temperature is amplified at optimum doping by tuning the chemical potential at the shape resonance.

2E3.7 Optical Responses of the Stripe Phase in High-T_c Cuprates

S. Tajima 1, N.L. Wang 1, T. Noda 2, H. Eisaki 2, and S. Uchida 2. 1 Superconductivity Research Laboratory, ISTEC, Tokyo 135-0062, Japan. 2 Dept. of Superconductivity, The University of Tokyo, Tokyo 113-8656, Japan.

Presenting Author: S. Tajima

Temperature dependencies of optical spectra of (La,Nd,Sr)₀CuO₄ cystals have been investigated for both in-plane and out-of-plane directions. A big difference of electonic response between the stripe phases of high-T_c cuprates and the other stripe materials is a charge dynamics. In the cuprates, even in the spin/charge ordered state, the system is highly conducive, showing no gap-like feature in the spectrum. In contrast to this weak stripe effect on the plane conductivity, the out-of-plane optical response is dramatically changed by the stripe ordering. The static stripe ordering below the orthohombic to tetragonal transition temperature radically weakens the Josephson coupling between the CuO_x-planes, creating a lot of unpaired carriers in the out-of-plane conductivity spectrum. This provides rather negative evidence for a role of stripes in high-T_c superconductivity. This work was partially supported by the NEDO.