Three axis vector magnet set-up for cryogenic scanning probe microscopy.

We describe a three axis vector magnet system for cryogenic scanning probe microscopy measurements. We discuss the magnet support system and the power supply, consisting of a compact three way 100 A current source. We obtain tilted magnetic fields in all directions with maximum value of 5T along z-axis and of 1.2T for XY-plane magnetic fields. We describe a scanning tunneling microscopy-spectroscopy (STM-STS) set-up, operating in a dilution refrigerator, which includes a new high voltage ultralow noise piezodrive electronics and discuss the noise level due to vibrations. STM images and STS maps show atomic resolution and the tilted vortex lattice at 150 mK in the superconductor ß-Bi2Pd. We observe a strongly elongated hexagonal lattice, which corresponds to the projection of the tilted hexagonal vortex lattice on the surface. We also discuss Magnetic Force Microscopy images in a variable temperature insert.

Quasiparticle mass enhancement close to the quantum critical point in BaFe2(As(1-x)P(x))2.

We report a combined study of the specific heat and de Haas-van Alphen effect in the iron-pnictide superconductor BaFe2(As(1-x)P(x))2. Our data when combined with results for the magnetic penetration depth give compelling evidence for the existence of a quantum critical point close to x=0.30 which affects the majority of the Fermi surface by enhancing the quasiparticle mass. The results show that the sharp peak in the inverse superfluid density seen in this system results from a strong increase in the quasiparticle mass at the quantum critical point.

Magnetic field-induced dissipation-free state in superconducting nanostructures.

A superconductor in a magnetic field acquires a finite electrical resistance caused by vortex motion. A quest to immobilize vortices and recover zero resistance at high fields made intense studies of vortex pinning one of the mainstreams of superconducting research. Yet, the decades of efforts resulted in a realization that even promising nanostructures, utilizing vortex matching, cannot withstand high vortex density at large magnetic fields. Here, we report a giant reentrance of vortex pinning induced by increasing magnetic field in a W-based nanowire and a TiN-perforated film densely populated with vortices. We find an extended range of zero resistance with vortex motion arrested by self-induced collective traps. The latter emerge due to order parameter suppression by vortices confined in narrow constrictions by surface superconductivity. Our findings show that geometric restrictions can radically change magnetic properties of superconductors and reverse detrimental effects of magnetic field.

de Haas-van Alphen study of the Fermi surfaces of superconducting LiFeP and LiFeAs.

We report a de Haas-van Alphen oscillation study of the 111 iron pnictide superconductors LiFeAs with T(c) ≈ 18 K and LiFeP with T(c) ≈ 5 K. We find that for both compounds the Fermi surface topology is in good agreement with density functional band-structure calculations and has almost nested electron and hole bands. The effective masses generally show significant enhancement, up to ~3 for LiFeP and ~5 for LiFeAs. However, one hole Fermi surface in LiFeP shows a very small enhancement, as compared with its other sheets. This difference probably results from k-dependent coupling to spin fluctuations and may be the origin of the different nodal and nodeless superconducting gap structures in LiFeP and LiFeAs, respectively.

Scanning tunneling spectroscopy under large current flow through the sample.

We describe a method to make scanning tunneling microscopy/spectroscopy imaging at very low temperatures while driving a constant electric current up to some tens of mA through the sample. It gives a new local probe, which we term current driven scanning tunneling microscopy/spectroscopy. We show spectroscopic and topographic measurements under the application of a current in superconducting Al and NbSe(2) at 100 mK. Perspective of applications of this local imaging method includes local vortex motion experiments, and Doppler shift local density of states studies.

Compact very low temperature scanning tunneling microscope with mechanically driven horizontal linear positioning stage.

We describe a scanning tunneling microscope for operation in a dilution refrigerator with a sample stage which can be moved macroscopically in a range up to a cm and with an accuracy down to the tens of nm. The position of the tip over the sample as set at room temperature does not change more than a few micrometers when cooling down. This feature is particularly interesting for work on micrometer sized samples. Nanostructures can be also localized and studied, provided they are repeated over micrometer sized areas. The same stage can be used to approach a hard single crystalline sample to a knife and cleave it, or break it, in situ. In situ positioning is demonstrated with measurements at 0.1 K in nanofabricated samples. Atomic resolution down to 0.1 K and in magnetic fields of 8 T is demonstrated in NbSe(2). No heat dissipation nor an increase in mechanical noise has been observed at 0.1 K when operating the slider.

Direct observation of stress accumulation and relaxation in small bundles of superconducting vortices in tungsten thin films.

We study the behavior of bundles of superconducting vortices when increasing the magnetic field using scanning tunneling microscopy and spectroscopy at 100 mK. Pinning centers are given by features on the surface corrugation. We find strong net vortex motion in a bundle towards a well-defined direction. We observe continuous changes of the vortex arrangements, and identify small displacements, which stress and deform the vortex bundle, separated by larger rearrangements or avalanches, which release accumulated stress.

Superconducting density of states and vortex cores of 2H-NbS2.

Scanning tunneling microscopy and spectroscopy measurements in the superconducting dichalcogenide 2H-NbS2 show a peculiar superconducting density of states with two well-defined features at 0.97 and 0.53 meV, located, respectively, above and below the value for the superconducting gap expected from the single band s-wave BCS model (Delta=1.76k_(B)T_(c)=0.9 meV). Both features have a continuous temperature evolution and disappear at T_(c)=5.7 K. Moreover, we observe the hexagonal vortex lattice with radially symmetric vortices and a well-developed localized state at the vortex cores. The sixfold star shape characteristic of the vortex lattice of the compound 2H-NbSe2 is, together with the charge density wave order, absent in 2H-NbS2.

[Spanish adaptation of the disease-specific questionnaire MSQOL-54 in multiple sclerosis patients]. / Adaptación al español del cuestionario específico MSQOL-54 para pacientes con esclerosis múltiple.

INTRODUCTION: The Multiple Sclerosis Quality of Life 54 (MSQOL-54) is a health-related quality of life specific questionnaire for multiple sclerosis (MS) patients. The objective of this study was to develop the Spanish version of the MSQOL-54 and to obtain a conceptually equivalent version to the original one for its use in patients with MS in the first phase of the project. METHODS: A transcultural adaptation procedure was designed according to the following phases: a) two independent translations made by bilingual native Spanish speaking translators (forward translation); b) a revision of the items by an expert panel; c) a back translation by a bilingual native English speaking person; d) comparison with the original version (expert panel and advise by the original authors), and e) cognitive debriefing (interviews with subjects with MS) to test the comprehension and feasibility of the instrument. RESULTS: Ten interviews were carried out with 5 men and 5 women with MS, aged 21 to 54 years, with different education levels and EDSS scores ranging from 1,0 to 8,0. Most of the patients found the questionnaire easy to fill out and the understanding favorable. Only one item (item 51) was modified after the cognitive debriefing to improve its comprehension. Finally, a final pretest version was obtained. CONCLUSIONS: The procedure carried out maximizes the conceptual equivalence between the original MSQOL-54 and the translated version and shows that the Spanish pre-test version is comprehensible and its administration feasible in patients with MS. The psychometric properties must be evaluated in the next phase of the project.

Adaptación al español del cuestionario específico MSQOL-54 para pacientes con esclerosis múltiple / Spanish adaptation of the disease-specific questionnaire MSQOL-54 in multiple sclerosis patients

Introducción. El Multiple Sclerosis Quality of Life 54 (MSQOL-54) es un cuestionario de calidad de vida relacionada con la salud especifico para esclerosis múltiple (EM). El objetivo de este estudio fue desarrollar la versión española del MSQOL-54 y obtener en una primera fase una versión conceptualmente equivalente a la original para su uso en pacientes con EM. Métodos. Se diseñó un proceso de adaptación transcultural con las siguientes etapas: a) traducción independiente por dos traductores bilingües de lengua materna española; b) revisión de los ítems por un panel de expertos; e) traducción inversa por una persona bilingüe de lengua materna inglesa; d) comparación eon la versión original (panel de expertos y asesoramiento de los autores originales), y e) entrevistas individuales a pacientes con EM para valorar la comprensión y factibilidad del instrumento (cognitive debriefing). Resultados. Se realizaron 10 entrevistas a 5 hombres y 5 mujeres con EM, de 21 a 54 años, con diferentes niveles educativos y diversos grados de discapacidad física (Expanded Disability Status Scale, 1.0-8.0). A la mayoría de pacientes les pareció sencilla la cumplimentación y fácil la comprensión. Sólo uno de los ítems (item 51) fue modificado después de la prueba para mejorar su comprensión. Finalmente se obtuvo la versión final pretest. Conclusiones. El proceso seguido maximiza la equivalencia conceptual con el MSQOL-54 original y muestra que la versión pretest española es comprensible y su administración factible en los pacientes con EM. Las propiedades métricas serán evaluadas en la siguiente fase del proyecto

Introduction: The Multiple Sclerosis Quality of Life 54 (MSQOL-54) is a health-related quality of life specific questionnaire for multiple sclerosis (MS) patients. The objective of this study was to develop the Spanish version of the MSQOL-54 and to obtain a conceptually equivalent version to the original one for its use in patients with MS in the first phase of the project. Methods: A transcultural adaptation procedure was designed according to the following phases: a) two independent translations made by bilingual native Spanish speaking translators (forward translation); b) a revision of the items by an expert panel; c) a back translation by a bilingual native English speaking person; d) comparison with the original version (expert panel and advise by the original authors), and e) cognitive debriefing (interviews with subjects with MS) to test the comprehension and feasibility of the instrument. Results: Ten interviews were carried out with 5 men and 5 women with MS, aged 21 to 54 years, with different education levels and EDSS scores ranging from 1,0 to 8,0. Most of the patients found the questionnaire easy to fill out and the understanding favorable. Only one item (item 51) was modified after the cognitive debriefing to improve its comprehension. Finally, a final pretest version was obtained. Conclusions: The procedure carried out maximizes the conceptual equivalence between the original MSQOL-54 and the translated version and shows that the Spanish pre-test version is comprehensible and its administration feasible in patients with MS. The psychometric properties must be evaluated in the next phase of the project

[Cross-cultural adaptation of the Spanish version of the Child Health and Illness Profile, Child Edition (CHIP-CE)]. / Adaptación de la versión española del Perfil de Salud Infantil (Child Health and Illness Profile-Child Edition, CHIP-CE).

OBJECTIVES: To obtain a Spanish version of the CHIP-CE semantically and culturally equivalent to the original version. METHOD: The methodology used was based on the forward-backward method. Two translations into Spanish were performed. After the first reconciled version, 44 cognitive interviews were carried out with children aged 6-11 years old, selected from two schools in Barcelona. The interviews were recorded and transcribed. A qualitative content analysis of the textual data was carried out. A panel of experts developed the second reconciled version taking into account the children's comments. A back-translation into English was carried out and was compared with the original version. RESULTS: Of a total of 45 items induced in the first reconciled version, 21 were considered equivalent, 23 required changes and 1 was considered not equivalent. Comprehension of abstract concepts differed according to age. Older children differentiated among concepts and gave different examples of experiences related to these concepts, while younger children (6 to 7-year olds) provided similar examples for different concepts. The children's comments were used in the reformulation of the items. An illustrative figure reinforced understanding. Children aged 7 or more started to use an adequate recall period and used the response options correctly. CONCLUSIONS: The Spanish version of the CHIP-CE seems appropriate for children aged 6-11 in Spain. The present study shows that children from the age of 6 years onwards are able to describe the health concepts included in the CHIP-CE.

Adaptación de la versión española del Perfil de Salud Infantil (Child Health and Illness Profile-Child Edition, CHIP-CE) / Cross-cultural adaptation of the Spanish version of the child health and illness profile, child edition (CHIP-CE)

Objetivos: Obtener una versión española del Perfil de Salud Infantil (Child Health and Illness Profile-Child Edition, CHIP-CE), semántica y culturalmente equivalente a la versión original. Método: Se ha seguido la metodología de traducción directa e inversa. Se obtuvieron dos traducciones iniciales al español. Tras la primera versión consensuada se realizaron 44 entrevistas cognitivas a niños/as de 6 a 11 años de dos colegios de Barcelona. Las entrevistas fueron grabadas y transcritas. Se realizó un análisis cualitativo de contenido temático de los datos textuales. Con los comentarios de los niños, y tras un panel de expertos, se obtuvo la segunda versión consensuada. Se realizó la retrotraducción al inglés y se comparó con la versión original. Resultados: De los 45 ítems de la primera versión consensuada, 21 se consideraron equivalentes, 23 requirieron modificaciones y uno fue considerado no equivalente. Se observó una diferencia según la edad en la comprensión de los conceptos abstractos. Los niños/as de más edad diferenciaban los conceptos y daban ejemplos distintos de experiencias relacionadas con ellos, los de menor edad (6-7 años) describieron ejemplos similares para conceptos diferentes. Los comentarios de los niños/as ayudaron a la reformulación de las preguntas. La figura representó un refuerzo para la comprensión. A partir de los 7 años enmarcaron sus respuestas en un período recordatorio adecuado, y utilizaron correctamente las opciones de respuesta. Conclusiones: La versión española del CHIP-CE parece adecuada para los niños de 6-11 años de edad en nuestro medio. El presente estudio ha mostrado que los niños/as son capaces de describir los aspectos de su salud que se incluyen en el CHIP-CE (AU)