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Costs and benefits of phytoplankton motility
Authors:
Peyman Fahimi,
Andrew J. Irwin,
Michael Lynch
Abstract:
The motility skills of phytoplankton have evolved and persisted over millions of years, primarily in response to factors such as nutrient and light availability, temperature and viscosity gradients, turbulence, and predation pressure. Phytoplankton motility is broadly categorized into swimming and buoyancy regulation. Despite studies in the literature exploring the motility costs and benefits of p…
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The motility skills of phytoplankton have evolved and persisted over millions of years, primarily in response to factors such as nutrient and light availability, temperature and viscosity gradients, turbulence, and predation pressure. Phytoplankton motility is broadly categorized into swimming and buoyancy regulation. Despite studies in the literature exploring the motility costs and benefits of phytoplankton, there remains a gap in our integrative understanding of direct and indirect energy expenditures, starting from when an organism initiates movement due to any biophysical motive, to when the organism encounters intracellular and environmental challenges. Here we gather available pieces of this puzzle from literature in biology, physics, and oceanography to paint an overarching picture of our current knowledge. The characterization of sinking and rising behavior as passive motility has resulted in the concept of sinking and rising internal efficiency being overlooked. We define this efficiency based on any energy dissipation associated with processes of mass density adjustment, as exemplified in structures like vacuoles, gas vesicles, and frustules. We propose that sinking and rising are active motility processes involving non-visible mechanisms, as species demonstrate active and rapid strategies in response to turbulence, predation risk, and gradients of nutrients, light, temperature, and viscosity. In swimmers, internal and external motility efficiencies have been extensively explored in theoretical studies, yet they are largely neglected in energetic estimates within marine and freshwater sciences. Identifying the dissipative processes associated with swimming and buoyancy-regulating machinery offers deeper insight into motility costs relative to an organism's total metabolic rate.
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Submitted 11 August, 2026; v1 submitted 18 March, 2025;
originally announced March 2025.
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Low-Voltage Magnetoelectric Coupling in Membrane Heterostructures
Authors:
S. Lindemann,
J. Irwin,
G. -Y. Kim,
B. Wang,
K. Eom,
J. J. Wang,
J. M. Hu,
L. Q. Chen,
S. Y. Choi,
C. B. Eom,
M. S. Rzchowski
Abstract:
Strain-mediated magnetoelectric (ME) coupling in ferroelectric (FE) / ferromagnetic (FM) heterostructures offers a unique opportunity for both fundamental scientific research and low power multifunctional devices. Relaxor-ferroelectrics, like (1-x)Pb(Mg1/3Nb2/3)O3-(x)PbTiO3 (PMN-xPT), are ideal FE layer candidates due to their giant piezoelectricity. But thin films of PMN-PT suffer from substrate…
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Strain-mediated magnetoelectric (ME) coupling in ferroelectric (FE) / ferromagnetic (FM) heterostructures offers a unique opportunity for both fundamental scientific research and low power multifunctional devices. Relaxor-ferroelectrics, like (1-x)Pb(Mg1/3Nb2/3)O3-(x)PbTiO3 (PMN-xPT), are ideal FE layer candidates due to their giant piezoelectricity. But thin films of PMN-PT suffer from substrate clamping which substantially reduces piezoelectric in-plane strains. Here we present the first demonstration of low voltage ME coupling in an all-thin-film heterostructure which utilizes the anisotropic strains induced by the (011) orientation of PMN-PT. We completely remove PMN-PT films from their substrate and couple with FM Ni overlayers to create membrane PMN-PT/Ni heterostructures showing 90 degree Ni magnetization rotation with 3V PMN-PT bias, much less than the bulk PMNPT ~100V requirement. Scanning transmission electron microscopy and phase-field simulations clarify the membrane response. These results provide a crucial step towards understanding the microstructural behavior of PMN-PT thin films for use in piezo-driven magnetoelectric heterostructures.
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Submitted 11 October, 2021;
originally announced October 2021.
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Strain-Driven Disproportionation at a Correlated Oxide Metal-Insulator Transition
Authors:
T. H. Kim,
T. R. Paudel,
R. J. Green,
K. Song,
H. -S. Lee,
S. -Y. Choi,
J. Irwin,
B. Noesges,
L. J. Brillson,
M. S. Rzchowski,
G. A. Sawatzky,
E. Y. Tsymbal,
C. B. Eom
Abstract:
Metal-to-insulator phase transitions in complex oxide thin films are exciting phenomena which may be useful for device applications, but in many cases the physical mechanism responsible for the transition is not fully understood. Here we demonstrate that epitaxial strain generates local disproportionation of the NiO6 octahedra, driven through changes in the oxygen stoichiometry, and that this dire…
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Metal-to-insulator phase transitions in complex oxide thin films are exciting phenomena which may be useful for device applications, but in many cases the physical mechanism responsible for the transition is not fully understood. Here we demonstrate that epitaxial strain generates local disproportionation of the NiO6 octahedra, driven through changes in the oxygen stoichiometry, and that this directly modifies the metal-to-insulator phase transition in epitaxial (001) NdNiO3 thin films. Theoretically, we predict that the Ni-O-Ni bond angle decreases, while octahedral tilt and local disproportionation of the NiO6 octahedra increases resulting in a small band gap in otherwise metallic system. This is driven by an increase in oxygen vacancy concentration in the rare-earth nickelates with increasing in-plane biaxial tensile strain. Experimentally, we find an increase in pseudocubic unit-cell volume and resistivity with increasing biaxial tensile strain, corroborating our theoretical predictions. With electron energy loss spectroscopy and x-ray absorption, we find a reduction of the Ni valence with increasing tensile strain. These results indicate that epitaxial strain modifies the oxygen stoichiometry of rare-earth perovskite thin films and through this mechanism affect the metal-to-insulator phase transition in these compounds.
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Submitted 29 December, 2019;
originally announced December 2019.
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Controlling spin current polarization through non-collinear antiferromagnetism
Authors:
T. Nan,
C. X. Quintela,
J. Irwin,
G. Gurung,
D. F. Shao,
J. Gibbons,
N. Campbell,
K. Song,
S. Y. Choi,
L. Guo,
R. D. Johnson,
P. Manuel,
R. V. Chopdekar,
I. Hallsteinsen,
T. Tybell,
P. J. Ryan,
J. W. Kim,
Y. S. Choi,
P. G. Radaelli,
D. C. Ralph,
E. Y. Tsymba,
M. S. Rzchowski,
C. B. Eom
Abstract:
The spin-Hall effect describes the interconversion of charge currents and spin currents, enabling highly efficient manipulation of magnetization for spintronics. Symmetry conditions generally restrict polarizations of these spin currents to be orthogonal to both the charge and spin flows. Spin polarizations can deviate from such direction in nonmagnetic materials only when the crystalline symmetry…
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The spin-Hall effect describes the interconversion of charge currents and spin currents, enabling highly efficient manipulation of magnetization for spintronics. Symmetry conditions generally restrict polarizations of these spin currents to be orthogonal to both the charge and spin flows. Spin polarizations can deviate from such direction in nonmagnetic materials only when the crystalline symmetry is reduced11. Here we experimentally show control of the spin polarization direction by using a non-collinear antiferromagnet Mn$_{3}$GaN, in which the triangular spin structure creates a low magnetic symmetry state while maintaining a high crystalline symmetry. We demonstrate that epitaxial Mn3GaN/Permalloy heterostructures can generate unique types of spinHall torques at room temperature corresponding to unconventional spin polarizations collinear to spin currents or charge currents which are forbidden in any sample with two-fold rotational symmetry. Our results demonstrate an approach based on spin-structure design for controlling spinorbit torque, paving the way for further progress in the emergent field of antiferromagnetic spintronics.
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Submitted 29 December, 2019;
originally announced December 2019.
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Magnetoelectric Coupling by Giant Piezoelectric Tensor Design
Authors:
J. Irwin,
S. Lindemann,
W. Maeng,
J. J. Wang,
V. Vaithyanathan,
J. M. Hu,
L. Q. Chen,
D. G. Schlom,
C. B. Eom,
M. S. Rzchowski
Abstract:
Strain-coupled magnetoelectric (ME) phenomena in piezoelectric / ferromagnetic thin-film bilayers are a promising paradigm for sensors and information storage devices, where strain is utilized to manipulate the magnetization of the ferromagnetic film. In-plane magnetization rotation with an electric field across the film thickness has been challenging due to the virtual elimination of in-plane pie…
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Strain-coupled magnetoelectric (ME) phenomena in piezoelectric / ferromagnetic thin-film bilayers are a promising paradigm for sensors and information storage devices, where strain is utilized to manipulate the magnetization of the ferromagnetic film. In-plane magnetization rotation with an electric field across the film thickness has been challenging due to the virtual elimination of in-plane piezoelectric strain by substrate clamping, and to the requirement of anisotropic in-plane strain in two-terminal devices. We have overcome both of these limitations by fabricating lithographically patterned devices with a piezoelectric membrane on a soft substrate platform, in which in-plane strain is freely generated, and a patterned edge constraint that transforms the nominally isotropic piezoelectric strain into the required uniaxial strain. We fabricated 500 nm thick, (001) oriented [Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$]$_{0.7}$-[PbTiO$_3$]$_{0.3}$ (PMN-PT) unclamped piezoelectric membranes with ferromagnetic Ni overlayers. Guided by analytical and numerical continuum elastic calculations, we designed and fabricated two-terminal devices exhibiting Ni magnetization rotation in response to an electric field across the PMN-PT. Similar membrane heterostructures could be used to apply designed strain patterns to many other materials systems to control properties such as superconductivity, band topology, conductivity, and optical response.
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Submitted 8 January, 2019;
originally announced January 2019.
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Observation of magnetic vortex pairs at room temperature in a planar α-Fe2O3/Co heterostructure
Authors:
F. P. Chmiel,
N. Waterfield Price,
R. D. Johnson,
A. D. Lamirand,
J. Schad,
G. van der Laan,
D. T. Harris,
J. Irwin,
M. S. Rzchowski,
C. -B. Eom,
P. G. Radaelli
Abstract:
Vortices are among the simplest topological structures, and occur whenever a flow field `whirls' around a one-dimensional core. They are ubiquitous to many branches of physics, from fluid dynamics to superconductivity and superfluidity, and are even predicted by some unified theories of particle interactions, where they might explain some of the largest-scale structures seen in today's Universe. I…
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Vortices are among the simplest topological structures, and occur whenever a flow field `whirls' around a one-dimensional core. They are ubiquitous to many branches of physics, from fluid dynamics to superconductivity and superfluidity, and are even predicted by some unified theories of particle interactions, where they might explain some of the largest-scale structures seen in today's Universe. In the crystalline state, vortex formation is rare, since it is generally hampered by long-range interactions: in ferroic materials (ferromagnetic and ferroelectric), vortices are only observed when the effects of the dipole-dipole interaction is modified by confinement at the nanoscale, or when the parameter associated with the vorticity does not couple directly with strain. Here, we present the discovery of a novel form of vortices in antiferromagnetic (AFM) hematite ($α$-Fe$_2$O$_3$) epitaxial films, in which the primary whirling parameter is the staggered magnetisation. Remarkably, ferromagnetic (FM) topological objects with the same vorticity and winding number of the $α$-Fe$_2$O$_3$ vortices are imprinted onto an ultra-thin Co ferromagnetic over-layer by interfacial exchange. Our data suggest that the ferromagnetic vortices may be merons (half-skyrmions, carrying an out-of-plane core magnetisation), and indicate that the vortex/meron pairs can be manipulated by the application of an in-plane magnetic field, H$_{\parallel}$, giving rise to large-scale vortex-antivortex annihilation.
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Submitted 29 March, 2018; v1 submitted 8 January, 2018;
originally announced January 2018.
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Hole concentration and phonon renormalization in Ca-doped YBa_2Cu_3O_y (6.76 < y < 7.00)
Authors:
K. C. Hewitt,
X. K. Chen,
C. Roch,
J. Chrzanowski,
J. C. Irwin,
E. H. Altendorf,
R. Liang,
D. Bonn,
W. N. Hardy
Abstract:
In order to access the overdoped regime of the YBa_2Cu_3O_y phase diagram, 2% Ca is substituted for Y in YBa_2Cu_3O_y (y = 7.00,6.93,6.88,6.76). Raman scattering studies have been carried out on these four single crystals. Measurements of the superconductivity-induced renormalization in frequency (Delta ω) and linewidth (Δ2γ) of the 340 cm^{-1} B_{1g} phonon demonstrate that the magnitude of the…
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In order to access the overdoped regime of the YBa_2Cu_3O_y phase diagram, 2% Ca is substituted for Y in YBa_2Cu_3O_y (y = 7.00,6.93,6.88,6.76). Raman scattering studies have been carried out on these four single crystals. Measurements of the superconductivity-induced renormalization in frequency (Delta ω) and linewidth (Δ2γ) of the 340 cm^{-1} B_{1g} phonon demonstrate that the magnitude of the renormalization is directly related to the hole concentration (p), and not simply the oxygen content. The changes in Δωwith p imply that the superconducting gap (Δ_{max}) decreases monotonically with increasing hole concentration in the overdoped regime, and Δωfalls to zero in the underdoped regime. The linewidth renormalization Δ2γis negative in the underdoped regime, crossing over at optimal doping to a positive value in the overdoped state.
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Submitted 6 November, 2002;
originally announced November 2002.
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Evidence for Two Superconducting Gaps in $MgB_2$
Authors:
X. K. Chen,
M. J. Konstantinovic,
J. C. Irwin,
D. D. Lawrie,
J. P. Franck
Abstract:
We have measured the Raman spectra of polycrystalline MgB$_{2}$ from 25 {\cm} to 1200 {\cm}. When the temperature was decreased below the superconducting transition temperature $T_c$, we observed a superconductivity-induced redistribution in the electronic Raman continuum. Two pair-breaking peaks appear in the spectra, suggesting the presence of two superconducting gaps. Furthermore, we have ana…
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We have measured the Raman spectra of polycrystalline MgB$_{2}$ from 25 {\cm} to 1200 {\cm}. When the temperature was decreased below the superconducting transition temperature $T_c$, we observed a superconductivity-induced redistribution in the electronic Raman continuum. Two pair-breaking peaks appear in the spectra, suggesting the presence of two superconducting gaps. Furthermore, we have analyzed the measured spectra using a quasi two-dimensional model in which two s-wave superconducting gaps open on two sheets of Fermi surface. For the gap values we have obtained $Δ_1 = 22 cm^{-1}$ (2.7 meV) and $Δ_2 = 50 cm^{-1}$ (6.2 meV). Our results suggest that a conventional phonon-mediated pairing mechanism occurs in the planar boron $σ$ bands and is responsible for the superconductivity of MgB$_{2}$.
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Submitted 24 July, 2001; v1 submitted 31 March, 2001;
originally announced April 2001.
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Low-energy excitations in NaV2O5
Authors:
M. J. Konstantinovic,
J. C. Irwin,
M. Isobe,
Y. Ueda
Abstract:
In the (ab) polarized Raman scattering spectra of NaV2O5 single crystals, measured with 647.1 nm laser line at T < Tc, we found two modes at 86, and 126 cm-1 not previously reported. These two modes, together with 66, and 106 cm-1 modes, make an array of four low-energy equidistant modes below the energy onset of the continuum at about 132 cm-1. All four modes are strongly suppressed by increasi…
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In the (ab) polarized Raman scattering spectra of NaV2O5 single crystals, measured with 647.1 nm laser line at T < Tc, we found two modes at 86, and 126 cm-1 not previously reported. These two modes, together with 66, and 106 cm-1 modes, make an array of four low-energy equidistant modes below the energy onset of the continuum at about 132 cm-1. All four modes are strongly suppressed by increasing Na deficiency, indicating their nonvibrational origin and the existence of a quantum phase transition at critical Na deficiency between 3 and 4%. These results question current understanding of NaV2O5 as quasi one-dimensional Heisenberg antiferromagnet.
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Submitted 21 March, 2001;
originally announced March 2001.
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Doping dependence of the superconducting gap in Bi2Sr2CaCu2O{8 + delta}
Authors:
K. C. Hewitt,
J. C. Irwin
Abstract:
Bi2Sr2CaCu2O{8 + δ} crystals with varying hole concentrations (0.12 < p < 0.23) were studied to investigate the effects of doping on the symmetry and magnitude of the superconducting gap. Electronic Raman scattering experiments that sample regions of the Fermi surface near the diagonal (B_{2g}) and principal axes (B_{1g}) of the Brillouin Zone have been utilized. The frequency dependence of the…
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Bi2Sr2CaCu2O{8 + δ} crystals with varying hole concentrations (0.12 < p < 0.23) were studied to investigate the effects of doping on the symmetry and magnitude of the superconducting gap. Electronic Raman scattering experiments that sample regions of the Fermi surface near the diagonal (B_{2g}) and principal axes (B_{1g}) of the Brillouin Zone have been utilized. The frequency dependence of the Raman response function at low energies is found to be linear for B_{2g} and cubic for B_{1g} (T< T_c). The latter observations have led us to conclude that the doping dependence of the superconducting gap is consistent with d_{x^2-y^2} symmetry, for slightly underdoped and overdoped crystals. Studies of the pair-breaking peak found in the B_{1g} spectra demonstrate that the magnitude of the maximum gap decreases monotonically with increasing hole doping, for p > 0.12. Based on the magnitude of the B_{1g} renormalization, it is found that the number of quasiparticles participating in pairing increases monotonically with increased doping. On the other hand, the B_{2g} spectra show a weak "pair-breaking peak" that follows a parabolic-like dependence on hole concentration, for 0.12 < p < 0.23.
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Submitted 6 November, 2002; v1 submitted 21 December, 2000;
originally announced December 2000.
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Charge-ordering and optical transitions of LiV2O5 and NaV2O5
Authors:
M. J. Konstantinovic,
J. Dong,
M. E. Ziaei,
B. P. Clayman,
J. C. Irwin,
K. Yakushi,
M. Isobe,
Y. Ueda
Abstract:
We present the measurements of the polarized optical spectra of NaV2O5 and LiV2O5. In an energy range from 0.5 to 5.5 eV we observe similar peaks in the E parallel a spectra of LiV2O5 and NaV2O5, which suggests similar electronic structure along the a axis in both materials. On the other hand, we find an almost complete suppression of the peaks in sigma_b of LiV2O5 around 1 and 5 eV. We attribut…
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We present the measurements of the polarized optical spectra of NaV2O5 and LiV2O5. In an energy range from 0.5 to 5.5 eV we observe similar peaks in the E parallel a spectra of LiV2O5 and NaV2O5, which suggests similar electronic structure along the a axis in both materials. On the other hand, we find an almost complete suppression of the peaks in sigma_b of LiV2O5 around 1 and 5 eV. We attribute this suppression to the charge localization originating from the existence of double-chain charge-ordering patterin in LiV2O5.
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Submitted 31 January, 2001; v1 submitted 20 October, 2000;
originally announced October 2000.
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The Pseudogap in La(2-x)Sr(x)CuO(4): A Raman Viewpoint
Authors:
J. G. Naeini,
J. C. Irwin,
T. Sasagawa,
Y. Togawa,
K. Kishio
Abstract:
We report the results of Raman scattering experiments on single crystals of La(2-x)Sr(x)CuO(4) [La214] as a function of temperature and doping. In underdoped compounds low-energy B1g spectral weight is depleted in association with the opening of a pseudogap on regions of the Fermi surface located near (pi, 0) and (0, pi). The magnitude of the depletion increases with decreasing doping, and in th…
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We report the results of Raman scattering experiments on single crystals of La(2-x)Sr(x)CuO(4) [La214] as a function of temperature and doping. In underdoped compounds low-energy B1g spectral weight is depleted in association with the opening of a pseudogap on regions of the Fermi surface located near (pi, 0) and (0, pi). The magnitude of the depletion increases with decreasing doping, and in the most underdoped samples, with decreasing temperature. The spectral weight that is lost at low-energies (omega < 800 cm-1) is transferred to the higher energy region normally occupied by multi-magnon scattering. From the normal state B2g spectra we have determined the scattering rate Gamma(omega, T) of qausiparticles located near the diagonal directions in k-space, (pi/2, pi/2) regions. In underdoped compounds, Gamma(omega, T) is suppressed at low temperatures for energies less than Eg(x) ~ 800 cm-1. The observed doping dependence of the two-magnon scattering and the scattering rate suppression thus suggest that the pseudogap is characterized by an energy scale Eg ~ J, where J is the antiferromagnetic super-exchange energy. Comparison with the results from other techniques provides a consistent picture of the pseudogap in La214.
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Submitted 14 February, 2000; v1 submitted 23 September, 1999;
originally announced September 1999.
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On the 590cm-1 B1g feature in underdoped Bi2Sr2CaCu2O8+delta
Authors:
Kevin C. Hewitt,
N. L. Wang,
J. C. Irwin,
D. M. Pooke,
A. E. Pantoja,
H. J. Trodahl
Abstract:
Raman scattering studies have been performed on underdoped Bi2Sr2CaCu2O8+delta. In single crystals underdoped by oxygen removal, a 590 cm-1 peak is observed in the B1g spectrum. The feature is observed to soften in frequency by 3.8% with isotopic exchange for 16-O by 18-O. In contrast, the 590cm-1 peak is not observed in crystals underdoped by Y substitution which suggests that it correspond to…
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Raman scattering studies have been performed on underdoped Bi2Sr2CaCu2O8+delta. In single crystals underdoped by oxygen removal, a 590 cm-1 peak is observed in the B1g spectrum. The feature is observed to soften in frequency by 3.8% with isotopic exchange for 16-O by 18-O. In contrast, the 590cm-1 peak is not observed in crystals underdoped by Y substitution which suggests that it correspond to a disorder induced vibrational mode. We have also found that underdoping leads to a depletion of low energy spectral weight from regions of the Fermi surface located near the Brillouin zone axes.
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Submitted 1 April, 1999;
originally announced April 1999.
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Doping Dependence of the Pseudogap in La(2-x)Sr(x)CuO(4)
Authors:
J. G. Naeini,
X. K. Chen,
J. C. Irwin,
M. Okuya,
T. Kimura,
K. Kishio
Abstract:
We report the results of Raman scattering experiments on single crystals of La(2-x)Sr(x)CuO(4) that span the range from underdoped (x = 0.10) to overdoped (x =0.22). The spectra are consistent with the existence of a strong anisotropic quasiparticle interaction that results in a normal state depletion of spectral weight from regions of the Fermi surface located near the zone axes. The strength o…
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We report the results of Raman scattering experiments on single crystals of La(2-x)Sr(x)CuO(4) that span the range from underdoped (x = 0.10) to overdoped (x =0.22). The spectra are consistent with the existence of a strong anisotropic quasiparticle interaction that results in a normal state depletion of spectral weight from regions of the Fermi surface located near the zone axes. The strength of the interaction decreases rapidly with increasing hole concentration and the spectral evidence for the pseudogap vanishes when the optimum doping level is reached. The results suggest that the pseudogap and superconducting gap arise from different mechanisms.
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Submitted 11 January, 1999; v1 submitted 23 April, 1998;
originally announced April 1998.
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Evidence for Magnetic Pseudoscaling in Overdoped La(2-x)Sr(x)CuO(4)
Authors:
J. G. Naeini,
X. K. Chen,
K. C. Hewitt,
J. C. Irwin,
T. P. Devereaux,
M. Okuya,
T. Kimura,
K. Kishio
Abstract:
We report the results of electronic Raman scattering experiments on an overdoped La(1.78)Sr(0.22)CuO(4) single crystal as a function of temperature. The scattering rate Gamma(w->0,T) has been determined from the normal state B(1g) spectra in the range 50 K < T < 300 K. Gamma(T) decreases linearly from 300 K to about 175 K and then undergoes a reduction with respect to the expected mean-field beh…
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We report the results of electronic Raman scattering experiments on an overdoped La(1.78)Sr(0.22)CuO(4) single crystal as a function of temperature. The scattering rate Gamma(w->0,T) has been determined from the normal state B(1g) spectra in the range 50 K < T < 300 K. Gamma(T) decreases linearly from 300 K to about 175 K and then undergoes a reduction with respect to the expected mean-field behavior. This trend suggests a crossover to pseudoscaling regime at about T(cr)=160 K. The results are in good agreement with the prediction of the nearly antiferromagnetic Fermi liquid model. There is no evidence of a pseudogap in the spectra obtained from this overdoped sample.
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Submitted 11 May, 1998; v1 submitted 25 November, 1997;
originally announced November 1997.
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Comment on "Superconducting gap anisotropy vs. doping level in high-T_c cuprates" by C. Kendziora et al, PRL 77, 727 (1996)
Authors:
K. Hewitt,
T. Devereaux,
X. K. Chen,
X. -Z. Wang,
J. Naeini,
J. C. Irwin
Abstract:
In a recent paper Kendziora et al concluded that the superconducting gap in overdoped Bi-2212 is isotropic. From data obtained from electronic Raman scattering measurements, their conclusion was based on the observation that pair breaking peaks occured at approximately the same frequency in different scattering geometries and that the normalized scattering intensity at low energies was strongly…
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In a recent paper Kendziora et al concluded that the superconducting gap in overdoped Bi-2212 is isotropic. From data obtained from electronic Raman scattering measurements, their conclusion was based on the observation that pair breaking peaks occured at approximately the same frequency in different scattering geometries and that the normalized scattering intensity at low energies was strongly depleted. We discuss a different interpretation of the raw data and present new data which is consistent with a strongly anisotropic gap with nodes. The spectra can be successfully described by a model for Raman scattering in a d_{x^{2}-y^{2}} superconductor with spin fluctuations and impurity scattering included.
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Submitted 23 January, 1997;
originally announced January 1997.