7 research outputs found
Magnetic phenomena in holographic superconductivity with Lifshitz scaling
No full textAbstractWe investigate the effects of Lifshitz dynamical critical exponent z on a family of minimal D=4+1 holographic superconducting models, with a particular focus on magnetic phenomena. We see that it is possible to have a consistent Ginzburg–Landau approach to holographic superconductivity in a Lifshitz background. By following this phenomenological approach we are able to compute a wide array of physical quantities. We also calculate the Ginzburg–Landau parameter for different condensates, and conclude that in systems with higher dynamical critical exponent, vortex formation is more strongly unfavored energetically and exhibits a stronger Type I behavior. Finally, following the perturbative approach proposed by Maeda, Natsuume and Okamura, we calculate the critical magnetic field of our models for different values of z
Ads/CFT Correspondence and Superconductivity: Various Approaches and Magnetic Phenomena
No full textThe AdS/CFT correspondence is one of the most important developments in the history of theoretical physics. Using as a binding bridge superstring theory, or, more concretely, some theoretical aspects in the interaction between superstrings and D-branes, the Maldacena conjecture establishes that the physics of a strongly-coupled, perturbatively-inaccessible quantum field theory in d-dimensions can be described equivalently in terms of the dynamics of a dual classical gravitational theory in (d + 1)-dimensional AdS space. Two particular aspects of the duality are of great importance. First, the duality ascertains that the quantum field theory lives in the boundary of the AdS space in which the dual gravitational system exists, and that the two-point functions of the dual field theory are computed in terms boundary-to-bulk propagators. This difference between the dimensions of the theories makes the duality holographic, so giving evidence to the idea that a quantum theory of gravity should be indeed a holographic in nature.
The second important aspect we must mention is that the AdS/CFT co-rrespondence is a strong/weak-coupling duality: it allows one to formulate a strongly-coupled quantum problem in terms of the classical Einstein equations of the dual higher-dimensional gravitational system. Because of this particular nature of the duality, it provides a promising new way of studying quantum gauge theories in the strongly-coupled regime, where the usual perturbative methods fail to apply. The gauge/gravity duality has thus been used to gain insight in a wide variety of physical systems where a satisfactory description in terms of standard methods is lacking, such as the quark-gluon plasma or in condensed matter theory.En aquesta tesi s'ha demostrat que la correspondència AdS/CFT ofereix una nova manera d'estudiar la fase superconductora de les teories large-N al règim fortament acoblat. En discutir els cuprats al final del Capítol 1, veiem algunes de les deficiències que els acostaments usuals basats en teories de camps tenen quan es tracta d'abordar sistemes de molts cossos fortament acoblats. Potser que la més greu d'aquestes deficiències és el col.lapse del concepte de quasi-partícula a causa de les fortes interaccions involucrades. La dualitat gauge/gravity ens permet plantejar problemes gairebé intractables en sistemes quàntics de molts cossos en termes de la dinàmica clàssica d'un sistema dual de gravetat en l'espai AdS. Usant aquest nou punt de vista hologràfic, la condensació de parells de Cooper al costat de la teoria del camps es tradueix en la creació espontània de solucions amb pèl carregat al costat gravitatori de la dualitat. Això dóna lloc a una fase en la teoria del camps dual, on es recuperen els aspectes fenomenològics fonamentals de la superconductivitat. Crida l'atenció que amb només observar al problema des d'un punt de vista hologràfic, es pot demostrar que aquests sistemes completament intractables en el règim d'acoblament fort presenten una fase superconductora. a causa de l'èxit del mètode hologràfic i les dificultats ja esmentades sobre els enfocaments estàndard basats en teories de camps, pot ser que no sigui massa agosarat imaginar que, efectivament, la definició teòrica natural de la superconductivitat en el règim fort acoblament està donada pel sistema dual de gravetat.
Amb aquestes consideracions generals en ment, en aquesta tesi ens hem esforçat a presentar una imatge el més completa possible dels diferents enfocaments seguits en la superconductivitat hologràfica
Superconductors for superstrings on AdS5 × T1,1
No full textWe construct a one-parameter family of five-dimensional N = 2 supergravity Lagrangians with an SU(2, 1)/U(2) hypermultiplet. For certain values of the parameter, these are argued to describe the dynamics of scalar modes of superstrings on AdS5 × T1,1, and therefore to be dual to specific chiral primary operators of Klebanov-Witten superconformal field theory. We demonstrate that, below a critical temperature, the thermodynamics is dominated by charged black holes with hair for the scalars that are dual to the operator of lowest conformal dimension 3/2. The system thus enters into a superconducting phase where 〈Tr[AkBl]〉 condenses.
[[alternative]]Preparation and Application of C60-Cryptand Coated Surface Acoustic Wave Sensor
No full text[[abstract]]Preparation and Application of C60-Cryptand Coated Surface Acoustic Wave Sensor
Abstract
A C60-cryptand [2,2] coated surface acoustic wave (SAW) detection system was prepared and applied as Gas Chromatographic detector for various vapors. The frequency of surface acoustic wave oscillator decrease due to the adsorption of gas molecules on C60-cryptand [2,2] . The C60-cryptand [2,2] coated surface acoustic wave sensor was used to measure various organic moleculesr and CO gas. A software was written to control the interface and data acquisition.
In the stationary system, three coating materials (C60, cryptand [2,2] and C60-cryptand [2,2] ) was tested in organic molecules. The C60-cryptand [2,2] coated SAW dector exhibited more sensitive to polar molecule than Fullerene or cryptand [2,2] coated system respectively. Effect of functional groups, molecular weight, steric hindrance and polarity of organic molecules in both static and flow cell on frequency response of surface acoustic wave sensor had been investigated. The frequency shifts of the C60-cryptand [2,2] coated SAW sensor for various organic molecules and isomer in the order: Alcohols (ROH) > Aldehydes (RCHO) > Ketones (RCOR’); 1-Hexyne>1-Hexene >n-Hexane; Aromatic > cyclo-Alkane > Alkane; 10alcohol > 20alcohol > 30alcohol. The greater frequency shift of a molecule with large molecular weight, less steric hindrance and more polar molecule (especially can form hydrogen bond) was funded. The adsorption of C60-cryptand [2,2] to most organic molecules was found to be physical adsorption(a reversible type) ,which could be desorbed by introducing N2 gas. The detection system also showed the good detection limit of 0.2~3 mg/L for organic molecules.
The frequency response of C60-cytptand[2,2] coated SAW for various organic molecules in the flow system showed quite accordance with that in static system. In the application of Gas Surface acoustic Wave (GC-SAW) in GC, the C60-cryptand[2,2] SAW sensor showed higher selectivity than the TCD for polar organic molecules.
In CO gas study, various metal-ion/C60-cryptand[2,2] adsorbents, e.g. Ti4+/C60-cryptand [2,2]; Co2+/C60-cryptand [2,2]; Al3+/C60-cryptand, were used to adsorb and detect CO gas. The Co2+/C60-cryptand [2,2] coated SAW sensor exhibited more sensitive than another adsorbent for CO gas. It also showed no significant effect for anion group (e.g. SO42-; NO3-; Cl-). The detection limit of the SAW sensor for CO was found to be about 0.13 ppm.
