A Holographic model of Striped Superconductors

One of the most prominent distinguishing features in strongly correlated electron systems, such as the high Tc (critical temperature) cuprates and the most recent iron pnictides, is the presence of competing orders that are related to the breaking of the lattice symmetries. Does the ubiquitous presence of such inhomogeneous orders in strongly correlated superconductors have a deep connection to superconductivity? The answer to this question is crucial for identifying the mechanism of superconductivity, at least in the cuprates. Amidst serious difficulties within conventional theoretical framework to deal with strongly interacting degrees of freedom at finite density, AdS/CFT correspondence or gauge/gravity duality sheds new light into the origin of high Tc superconductivity by mapping the original system into an appropriate weakly coupled one. An example of the ``Holographic principle , according to which, a quantum theory with gravity must be describable by a boundary theory, AdS/CFT duality provides guidelines to model a d dimensional strongly coupled condensed matter system in terms of a suitable gravity theory (as low energy limit of String theory) on a d+1 dimensional anti de-Sitter (AdS) space. In this thesis I will develop a phenomenological holographic model of strongly coupled ``striped superconductors in two spatial dimensions and study the interplay between charge density waves and superconductivity. It will be shown that charge density waves with large modulation compete with superconducting order, causing the critical temperature to fall off with increasing modulation in various ways depending on free parameters of the theory. For small modulation, the effects of fluctuations dominate, causing an enhancement of critical temperature upon turning on modulation. The highest critical temperature is obtained at an intermediate modulation. Moreover, there exists a region in parameter space of the theory within which the modulation vs Tc phase structures show striking resemblance to doping phase structure of cuprates

Superconducting Dome from Holography

We find a regime in which a strongly coupled striped superconductor features a superconducting dome. This regime is signified by i) a modulating chemical potential that averages to zero, and ii) a superconducting order parameter that has a scaling dimension larger than 3/2 but less than or equal to 3. We also find that in this regime, the order parameter exhibits a mild dependence on the modulation wavelength of the stripe.Comment: 5 pages, 4 figure

Enhancement of Critical Temperature of a Striped Holographic Superconductor

We study the interplay between the stripe order and the superconducting order in a strongly coupled striped superconductor using gauge/gravity duality. In particular, we study the effects of inhomogeneity introduced by the stripe order on the superconducting transition temperature beyond the mean field level by including the effects of backreaction onto the spacetime geometry in the dual gravitational picture. We find that inhomogeneity \emph{enhances} the critical temperature relative to its value for the uniform system.Comment: 8 pages, 7 figure

Antiferromagnetism, spin splitting, and spin-orbit interaction in MnTe

Hexagonal MnTe emerges as a critical component in designing magnetic quantum heterostructures, calling for a detailed study. After finding a suitable combination of exchange-correlation functional and corrections, our study within {\em ab initio} density functional theory uncovers an insulating state with a preferred antiferromagnetic order. We compute the exchange interaction strengths to estimate the antiferromagnetic ordering temperature via Monte Carlo calculations. Our calculations and symmetry analysis reveal a large spin splitting in the system due to the antiferromagnetic order without considering spin-orbit interaction, except in the $k_x$-$k_y$ plane. Critically examining the band dispersion and spin textures obtained from our calculations and comparing them with an insightful symmetry analysis and analytical model, we confirm a combined Rashba-Dresselhaus interaction in the $k_x$-$k_y$ plane, around the K point of the system. Finally, we find ferroelectricity in the system for a higher energy magnetic configuration. Our results and insights would help design heterostructures of MnTe for technological applications.Comment: 10 pages, 6 figure

Strongly coupled striped superconductor with large modulation

A bstract Using gauge/gravity duality, we analytically calculate properties of a strongly coupled striped superconductor, with the charge density wave sourced by a modulated chemical potential, in the large modulation wavenumber Q limit. In the absence of a homogeneous term in the chemical potential, we show that the critical temperature scales as a negative power of Q for scaling dimensions \Delta \u3c \frac{3}{2} , whereas for \Delta \u3e \frac{3}{2} , there is no phase transition above a certain critical value of Q . The condensate is found to scale as a positive power of Q such that the gap is proportional to Q . We discuss how these results change if a homogeneous term is added to the chemical potential. We compare our analytic results with numerical calculations whenever the latter are available and find good agreement

The CMS Outer Hadron Calorimeter

The CMS hadron calorimeter is a sampling calorimeter with brass absorber and plastic scintillator tiles with wavelength shifting fibres for carrying the light to the readout device. The barrel hadron calorimeter is complemented with a outer calorimeter to ensure high energy shower containment in CMS and thus working as a tail catcher. Fabrication, testing and calibrations of the outer hadron calorimeter are carried out keeping in mind its importance in the energy measurement of jets in view of linearity and resolution. It will provide a net improvement in missing \et measurements at LHC energies. The outer hadron calorimeter has a very good signal to background ratio even for a minimum ionising particle and can hence be used in coincidence with the Resistive Plate Chambers of the CMS detector for the muon trigger

Design, Performance, and Calibration of the CMS Hadron-Outer Calorimeter

The CMS hadron calorimeter is a sampling calorimeter with brass absorber and plastic scintillator tiles with wavelength shifting fibres for carrying the light to the readout device. The barrel hadron calorimeter is complemented with an outer calorimeter to ensure high energy shower containment in the calorimeter. Fabrication, testing and calibration of the outer hadron calorimeter are carried out keeping in mind its importance in the energy measurement of jets in view of linearity and resolution. It will provide a net improvement in missing \et measurements at LHC energies. The outer hadron calorimeter will also be used for the muon trigger in coincidence with other muon chambers in CMS