3D-XY critical fluctuations of the thermal expansivity in detwinned YBa2Cu3O7-d single crystals near optimal doping

The strong coupling of superconductivity to the orthorhombic distortion in YBa2Cu3O7-d makes possible an analysis of the superconducting fluctuations without the necessity of subtracting any background. The present high-resolution capacitance dilatometry data unambiguously demonstrate the existence of critical, instead of Gaussian, fluctuations over a wide temperature region (+/- 10 K) around Tc. The values of the amplitude ratio A+/A-=0.9-1.1 and the leading scaling exponent |alpha|<0.018, determined via a least-squares fit of the data, are consistent with the 3D-XY universality class. Small deviations from pure 3D-XY behavior are discussed.Comment: 11 pages including three figure

Multiband Superconductivity in KFe2As2: Evidence for one Isotropic and several Liliputian Energy Gaps

We report a detailed low-temperature thermodynamic investigation (heat capacity and magnetization) of the superconducting state of KFe2As2 for H || c axis. Our measurements reveal that the properties of KFe2As2 are dominated by a relatively large nodeless energy gap (Delta?0 = 1.9 kBTc) which excludes dx2-y2 symmetry. We prove the existence of several additional extremely small gaps (?Delta0 < 1.0 kBTc) that have a profound impact on the low-temperature and low-field behavior, similar to MgB2, CeCoIn5 and PrOs4Sb12. The zero-field heat capacity is analyzed in a realistic self-consistent 4-band BCS model which qualitatively reproduces the recent laser ARPES results of Okazaki et al. (Science 337 (2012) 1314). Our results show that extremely low-temperature measurements, i.e. T < 0.1 K, will be required in order to resolve the question of the existence of line nodes in this compound.Comment: 7 pages, 6 figure

Interplay of stripe and double-Q magnetism with superconductivity in Ba1−xKxFe2As2\mathrm{Ba}_{1-x}\mathrm{K}_{x}\mathrm{Fe}_{2}\mathrm{As}_{2} under the influence of magnetic fields

At $x\approx0.25$ $\mathrm{Ba}_{1-x}\mathrm{K}_{x}\mathrm{Fe}_{2}\mathrm{As}_{2}$ undergoes a novel first-order transition from a four-fold symmetric double-Q magnetic phase to a two-fold symmetric single-Q phase, which was argued to occur simultaneously with the onset of superconductivity (B\"ohmer et al., Nat. Comm. 6, 7911 (2015)). Here, by applying magnetic fields up to 10T, we investigate in more detail the interplay of superconductivity with this magneto-structural transition using a combination of high-resolution thermal-expansion and heat-capacity measurements. We find that a magnetic field suppresses the reentrance of the single-Q orthorhombic phase more strongly than the superconducting transition, resulting in a splitting of the zero-field first-order transition. The suppression rate of the orthorhombic reentrance transition is stronger for out-of-plane than for in-plane fields and scales with the anisotropy of the superconducting state. These effects are captured within a phenomenological Ginzburg-Landau model, strongly suggesting that the suppression of the reentrant orthorhombic single-Q phase is primarily linked to the field-induced weakening of the superconducting order. Not captured by this model is however a strong reduction of the orthorhombic distortion for out-of-plane fields, which deserves further theoretical attention

Resultados funcionales de la estapedotomía en pacientes con otosclerosis. Hospital de Clínicas

Introducción: La otosclerosis es una enfermedad que produce remodelación anormal de hueso maduro y fijación de la platina del estribo a la ventana oval, produciendo hipoacusia conductiva. La estapedotomía es la técnica quirúrgica más utilizada. Tiene como objetivo aliviar la fijación de la cadena oscicular mediante una estapedotomía e inserción de una prótesis, con buenos resultados en manos expertas. Objetivo: Evaluar la variación audiométrica en pacientes operados de estapedotomía por otosclerosis. Metodología: Estudio observacional, descriptivo, de corte transversal retrospectivo, de serie de casos de pacientes con diagnóstico de Otosclerosis sometidos a estapedotomías en Hospital de Clínicas, desde el 2012 a 2016. Resultados: Se analizó un total de 14 fichas correspondientes a 11 pacientes operados en el periodo de enero 2012 a julio 2016. El 72% fue de sexo femenino. La media de edades fue de 38,35±15 años. Todos los pacientes presentaban hipoacusia. El 50% de las estapedotomías fue del lado derecho; 3 pacientes (27 %) fueron operados bilateralmente en dos tiempos. El 85,7 % presentaba afectación bilateral en la audiometría pre quirúrgica. La impedanciometría informó que el 71 % presentó curva As bilateral; 14 % curva As del oído derecho y 14% curva A en ambos oídos y reflejo estapedial negativo bilateral en el 57 %. En audiometría postquirúrgica se encontró una mejoría del 64 %, y una evolución de la enfermedad con empeoramiento de la hipoacusia en 21,4 %. Solo 2 pacientes presentaron complicaciones post quirúrgicas (1 fístula perilinfática y 1 desinserción de prótesis de yunque). Discusión: Acorde a la literatura la mayoría fue del sexo femenino, el rango etario coincide con estudios similares en la región, constatamos mejoría conductiva en la audiometría, pero un empeoramiento neurosensorial por la evolución de la enfermedad. La estapedotomía en nuestro estudio resultó una cirugía con buenos resultados y pocas complicaciones

Thermal expansion and Gr\"uneisen parameters of Ba(Fe1-xCox)2As2 - a thermodynamic quest for quantum criticality

Thermal expansion data are used to study the uniaxial pressure dependence of the electronic/magnetic entropy of Ba(Fe1-xCox)2As2. Uniaxial pressure is found to be proportional to doping and, thus, also an appropriate tuning parameter in this system. Many of the features predicted to occur for a pressure-tuned quantum critical system, in which superconductivity is an emergent phase hiding the critical point, are observed. The electronic/magnetic Gr\"uneisen parameters associated with the spin-density wave and superconducting transitions further demonstrate an intimate connection between both ordering phenomena.Comment: 13 pages, 4 figure