Resonant magnetic mode in superconducting 2-leg ladders

The spin dynamics of a doped 2-leg spin ladder is investigated by numerical techniques. We show that a hole pair-magnon boundstate evolves at finite hole doping into a sharp magnetic excitation below the two-particle continuum. This is supported by a field theory argument based on a SO(6)-symmetric ladder. Similarities and differences with the resonant mode of the high-T$_c$ cuprates are discussed.Comment: 5 pages, 5 figure

A Technique for In-situ Measurement of Free Spectral Range and Transverse Mode Spacing of Optical Cavities

Length and g-factor are fundamental parameters that characterize optical cavities. We developed a technique to measure these parameters in-situ by determining the frequency spacing between the resonances of fundamental and spatial modes of an optical cavity. Two laser beams are injected into the cavity, and their relative frequency is scanned by a phase-lock loop, while the cavity is locked to either laser. The measurement of the amplitude of their beat note in transmission reveals the resonances of the longitudinal and the transverse modes of the cavity and their spacing. This method proves particularly useful to characterize complex optical systems, including very long and/or coupled optical cavities, as in gravitational wave interferometers. This technique and the results of its application to the coupled cavities of a 40-meter-long gravitational wave interferometer prototype are here presented

Seasonal evolution of Aleutian low pressure systems: Implications for the North Pacific subpolar circulation

The seasonal change in the development of Aleutian low pressure systems from early fall to early winter is analyzed using a combination of meteorological reanalysis fields, satellite sea surface temperature (SST) data, and satellite wind data. The time period of the study is September–December 2002, although results are shown to be representative of the long-term climatology. Characteristics of the storms were documented as they progressed across the North Pacific, including their path, central pressure, deepening rate, and speed of translation. Clear patterns emerged. Storms tended to deepen in two distinct geographical locations—the Gulf of Alaska in early fall and the western North Pacific in late fall. In the Gulf of Alaska, a quasi-permanent “notch” in the SST distribution is argued to be of significance. The signature of the notch is imprinted in the atmosphere, resulting in a region of enhanced cyclonic potential vorticity in the lower troposphere that is conducive for storm development. Later in the season, as winter approaches and the Sea of Okhotsk becomes partially ice covered and cold, the air emanating from the Asian continent leads to enhanced baroclinicity in the region south of Kamchatka. This corresponds to enhanced storm cyclogenesis in that region. Consequently, there is a seasonal westward migration of the dominant lobe of the Aleutian low. The impact of the wind stress curl pattern resulting from these two regions of storm development on the oceanic circulation is investigated using historical hydrography. It is argued that the seasonal bimodal input of cyclonic vorticity from the wind may be partly responsible for the two distinct North Pacific subarctic gyres

Hybrid Monte Carlo algorithm for the Double Exchange Model

The Hybrid Monte Carlo algorithm is adapted to the simulation of a system of classical degrees of freedom coupled to non self-interacting lattices fermions. The diagonalization of the Hamiltonian matrix is avoided by introducing a path-integral formulation of the problem, in $d+1$ Euclidean space-time. A perfect action formulation allows to work on the continuum euclidean time, without need for a Trotter-Suzuki extrapolation. To demonstrate the feasibility of the method we study the Double Exchange Model in three dimensions. The complexity of the algorithm grows only as the system volume, allowing to simulate in lattices as large as $16^3$ on a personal computer. We conclude that the second order paramagnetic-ferromagnetic phase transition of Double Exchange Materials close to half-filling belongs to the Universality Class of the three-dimensional classical Heisenberg model.Comment: 20 pages plus 4 postscript figure

Charge-ordered ferromagnetic phase in manganites

A mechanism for charge-ordered ferromagnetic phase in manganites is proposed. The mechanism is based on the double exchange in the presence of diagonal disorder. It is modeled by a combination of the Ising double-exchange and the Falicov-Kimball model. Within the dynamical mean-field theory the charge and spin correlation function are explicitely calculated. It is shown that the system exhibits two successive phase transitions. The first one is the ferromagnetic phase transition, and the second one is a charge ordering. As a result a charge-ordered ferromagnetic phase is stabilized at low temperature.Comment: To appear in Phys. Rev.

Treatment of cubital tunnel syndrome using the technique of medial partial epicondylectomy of the elbow

OBJECTIVE: The authors made a retrospective analysis of the results of 21 cases of cubital syndrome that were surgically treated with the partial medial epicondylectomy. METHODS: From February 2001 to October 2006, 21 patients with cubital tunnel syndrome were treated with the technique of elbow partial medial epicondylectomy associated to neurolysis of the ulnar nerve. Of these patients, 12 (57.1%) were male. The right side was involved in 15 (71.4%). Mean age of the patients was 51.6 years. According to McGowan classification, six (28.6%) patients were grade I, 11 (52.3%), grade II, and four (19.1%), grade III in the preoperative period. RESULTS: The mean post-operative follow-up time was 25.7 months. In the post-operative period, patients were evaluated according to the Bishop score scale, and nine of them (42.8%) showed excellent results, seven (33.3%) had good results, three (14.2%), regular, and two patients (9.5%) had poor results. The authors did not find in this series any complications represented by residual valgus instability, permanent lesion of the ulnar nerve, recurrent compression, or subluxation of the ulnar nerve. Complications found were the loss of the movement arch in one case (4.7%), superficial infection in one case (4.7%), and residual pain in one case (4.7%). CONCLUSION: The results allow for the conclusion that partial medial epicondylectomy of the elbow associated to neurolysis of the ulnar nerve is effective and safe to treat cubital tunnel syndrome.OBJETIVO: Analisamos retrospectivamente os resultados de 21 casos de síndrome cubital tratados cirurgicamente com a técnica da epicondilectomia parcial medial. MÉTODOS: No período de fevereiro de 2001 a outubro de 2006, 21 pacientes com síndrome do canal cubital foram tratados pela técnica da epicondilectomia parcial medial do cotovelo associada à neurólise do nervo ulnar. Destes, 12 (57,1%) eram do sexo masculino. O lado direito foi o acometido em 15 (71,4%) pacientes. A média da idade dos pacientes foi de 51,6 anos. Pela graduação de McGowan, seis (28,6%) pacientes encontravam-se no grau I, 11 (52,3%), no grau II e quatro (19,1%), no grau III do período pré-operatório. RESULTADOS: O tempo médio de acompanhamento pós-operatório foi de 25,7 meses. No pós-operatório, os pacientes foram avaliados conforme a escala de pontos de Bishop, sendo que nove (42,8%) apresentavam resultados excelentes, sete (33,3%), bons, três (14,2%), regulares e dois (9,5%), ruins. Nesta série, não se encontraram como complicações a instabilidade em valgo residual, a lesão permanente do nervo ulnar, a recidiva da compressão ou a subluxação do nervo ulnar. As complicações encontradas foram perda do arco de movimento em um (4,7%) caso, infecção superficial em um (4,7%) e um (4,7%) com dor residual. CONCLUSÃO: Os resultados apresentados permitem concluir que a epicondilectomia parcial medial do cotovelo associada à neurólise do nervo ulnar é eficiente e segura para o tratamento da síndrome do canal cubital.Universidade Federal de São Paulo (UNIFESP) Escola Paulista de Medicina Departamento de Ortopedia e TraumatologiaUNIFESP, EPM, Depto. de Ortopedia e TraumatologiaSciEL

Magnetic excitations in SrCu2O3: a Raman scattering study

We investigated temperature dependent Raman spectra of the one-dimensional spin-ladder compound SrCu2O3. At low temperatures a two-magnon peak is identified at 3160+/-10 cm^(-1) and its temperature dependence analyzed in terms of a thermal expansion model. We find that the two-magnon peak position must include a cyclic ring exchange of J_cycl/J_perp=0.09-0.25 with a coupling constant along the rungs of J_perp approx. 1215 cm^(-1) (1750 K) in order to be consistent with other experiments and theoretical results.Comment: 4 pages, 3 figure

Inhomogeneously doped two-leg ladder systems

A chemical potential difference between the legs of a two-leg ladder is found to be harmful for Cooper pairing. The instability of superconductivity in such systems is analyzed by compairing results of various analytical and numerical methods. Within a strong coupling approach for the t-J model, supplemented by exact numerical diagonalization, hole binding is found unstable beyond a finite, critical chemical potential difference. The spinon-holon mean field theory for the t-J model shows a clear reduction of the the BCS gaps upon increasing the chemical potential difference leading to a breakdown of superconductivity. Based on a renormalization group approach and Abelian bosonization, the doping dependent phase diagram for the weakly interacting Hubbard model with different chemical potentials was determined.Comment: Revtex4, 11 pages, 7 figure

Thermal/Electronic Transport Properties and Two-Phase Mixtures in La_{5/8-x}Pr_{x}Ca_{3/8}MnO_{3}

We measured thermal conductivity, k, thermoelectric power, S, and dc electric conductivity, sigma, of La_{5/8-x}Pr_{x}Ca_{3/8}MnO_{3}, showing an intricate interplay between metallic ferromagnetism (FM) and charge ordering (CO) instability. The change of k, S and sigma with temperature (T) and x agrees well with the effective medium theories for binary metal-insulator mixtures. This agreement clearly demonstrates that with the variation of T as well as x, the relative volumes of FM and CO phases drastically change and percolative metal-insulator transition occurs in the mixture of FM and CO domains.Comment: 8 pages, 4 eps figures included, to appear in Phys. Rev. Let

Phase Diagram of Coupled Ladders

The 2-leg t-J ladder forms a spin liquid at half-filling which evolves to a Luther-Emery liquid upon doping. Our aim is to obtain a complete phase diagram for isotropic coupling (i.e. rungs and legs equal) as a function of electron density n and the ratio J/t (>0). Two known limiting cases are: n<1/2 which is a single band Luttinger liquid and small hole doping for J/t close to 0 which is a Nagaoka ferromagnet. Using Lanczos techniques we examine the region between the Nagaoka and Luther-Emery phases for 1>n>1/2. We find evidences for gapless behavior in both spin and charge channels for J/t<0.3 consistent with Luttinger liquids in both bonding and anti-bonding bands (i.e., C2S2). This proposal is based on the behavior of spin and charge correlation functions. For example the hole-hole correlation function which displays hole pairing at larger J/t, shows hole-hole repulsion in this region. As a further test, we examined the dependence of the energy on a relative phase shift between bonding and antibonding bands. For J/t < 0.3 this is very weak, indicating a lack of pairing between these channels.Comment: 21 pages, 18 figure